POSITION STATEMENT
It is the position of the Academy of Nutrition and Dietetics that dietary fat for the healthy adult population should provide 20% to 35% of energy, with an increased consumption of n-3 polyunsaturated fatty acids and limited intake of saturated and trans fats. The Academy recommends a food-based approach through a diet that includes regular consumption of fatty fish, nuts and seeds, lean meats and poultry, low-fat dairy products, vegetables, fruits, whole grains, and legumes
OBJECTIVE
To provide information on specific fatty acids including
structure, current and recommended intakes, function, and impact on health
TARGET POPULATION
- Healthy Adult
- Not for: children,
pregnant women, or specific disease states
INTRODUCTION
- Fatty acids are the major form of dietary fat and
primarily exist in foods in the triglyceride form.
- Although fatty acids are often categorized by their
saturation status (eg, monounsaturated, saturated), understanding the role of
individual fatty acids on health, rather than as a group, is important.
- Because of this, fatty acids will be presented
individually in the following order: polyunsaturated, monounsaturated, saturated,
and trans.
- In addition, fatty acids are consumed as a part of foods
that contain other nutrients and dietary compounds; these have both additive
and synergistic effects on health and interact in complex ways that are
difficult to delineate.
- Therefore, the roles of individual fatty acids within the
broader context of food and dietary patterns will be discussed.
FATTY ACID
CLASSIFICATION SYSTEM
- Fatty acid structures vary considerably by both hydrocarbon chain length and saturation status
- Although carbon chain length can vary from 2 to 40
carbons, most dietary fatty acids contain 12 to 22 carbons
- Fatty acids are often categorized into short chain (up to
6 carbons), medium chain (8 to 12 carbons), or long chain (>12 carbons).
- Although hydrocarbon chain length is an important
determinant of function, fatty acids are often classified based on whether or
not the fatty acid carbon chain contains no double bonds (SFA), one double bond
(MUFA), or more than one double bond (PUFA), as well as the configuration of
the double bonds (cis or trans).
- In addition, PUFAs are often further classified based on
the position of the first double bond from the fatty acid methyl terminus,
creating n-3 and n-6 fatty acids.
- In n-3s, the first double bond occurs at the third carbon
of the fatty acid chain from the methyl (or omega) end, and in n-6s, the first
double bond occurs at the sixth carbon in the fatty acid chain
- Figure 1 presents
nomenclature and common food sources of dietary fatty acids. It is the differences
in chain length and saturation status that dictate their performance in food
and cooking, as well as their role in the body and impact on human health and
disease risk.
TOTAL FAT VS INDIVIDUAL FATTY ACIDS
- Total fat intake of 20%
to 35% of energy is recommended by the Institute of Medicine and the Food
and Agriculture Organization of the United Nations (FAO) and is supported by
the
2010 Dietary Guidelines for Americans (DGA) [Note: Similar
recommendation for 2015 DGA]
- The American Heart Association (AHA) and National
Cholesterol Education Program recommend 25% to 35% of daily calories from fat
- These total fat intake recommendations are based on
evidence that indicates consumption outside of these ranges is associated with
a greater intake of energy and SFA (fat
intake >35%) or greater intake in
carbohydrate (fat intake <20%); higher
intake of carbohydrate leads to increases in plasma triglyceride and reductions in high-density lipoprotein (HDL) cholesterol levels.
- It is important
to note that individuals often eat more than their energy needs, and examining
total fat intake as a percentage of calories might well reflect more fat in the diet than is recommended and
necessary.
- Achieving intake of total fat within the recommended range
(20% to 35%) is an important goal, but the quality
of fat in the diet is equally important.
- Altering fat
consumption, for example, the unsaturated/saturated fat balance, instead of reducing total fat might be more advantageous to health
and chronic disease risk reduction.
- In tissues, an increase in concentration of one fatty acid
corresponds to the reduction of the same magnitude of another fatty acid.
- The displacement or replacement of the quality of fatty
acid is important to consider.
- Recent recognition that individual fatty acids have
differing effects on health, even within the conventional fat categories, has
brought examination of these fatty acids into the forefront.
- Although this reductionist viewpoint allows for
understanding specific fatty acid functions and is important in determining
which fatty acids are best for health, examination of the foods containing these fatty acids is also important.
- Knowledge of the individual fatty acids in foods provides
a foundation for the RDN to make whole food recommendations to their clients.
- The variety of fatty acids in common fats and oils is
provided in Table 1.
- Additional information on individual fatty acids in foods
can be found at the US Department of Agriculture’s Nutrient Database
(http://ndb.nal.usda.gov)
DIFFERING,
WIDE-RANGING IMPACTS ON HEALTH
- The impact of
specific fatty acids on disease incidence is difficult to elucidate, as
chronic disease develops over many years and is the culmination of many genetic
and lifestyle factors.
- This complexity makes randomized controlled trials of
dietary interventions largely impractical, but these trials, coupled with
observational, epidemiologic, and mechanistic studies, provide valuable
evidence on the health effects of dietary fat and specific fatty acids.
- Modulation of known
and emerging risk factors, such as chronic low-grade inflammation, through dietary fatty acid intake can beneficially
impact development of common diseases, such as cardiovascular disease,
diabetes, and depression, as well as emerging diseases, such as Alzheimer’s and
dementia.
- For example, evidence from randomized clinical trials and
observational studies provide convincing argument that inadequate intake of
long-chain n-3 fatty acids is associated with an increased risk of sudden
cardiac death.
- Targeting multiple
risk factors through modulation of diet, specifically fatty acids, holds promise
for promoting public health and attaining meaningful reductions in disease risk
in healthy individuals.
NEED FOR KNOWLEDGE
- Fatty acids can no
longer be viewed in general categories, such as saturated and unsaturated,
because individual fatty acids within these categories have different
influences on health status and disease risk.
- For example, both stearic acid (18:0) and palmitic acid
(16:0) are saturated fats, differing only in chain length by two carbons, but they
appear to have different effects on circulating LDL cholesterol.
- Another example is the difference between the locations of
the first double bond on the fatty acid carbon chain. Whether the double bond
is located on carbon number 3 or 6 (as in n-3 and n-6 PUFA) makes a remarkable
difference in biological function (eg, vasoconstriction vs vasodilation).
- Therefore, understanding the breadth of information while delineating
specifics about individual dietary fatty acids is essential.
- RDNs have the opportunity and responsibility to translate
research into practice for the population at large.
- National organizations specializing in evidence-based
dietary recommendations are valuable resources
- Table 2 summarizes
intake recommendations for dietary fatty acids
1) PUFAs
Specific Fatty
Acids and Food Sources
- PUFAs are triglycerides that contain fatty acids with two
or more (poly) double bonds.
- PUFAs are liquid at
room temperature and, because they are not solid fats, they are often
referred to as oils.
- In recent decades, researchers have discovered that the
function of PUFAs in human nutrition differ based on the fatty acid structure.
- The most common
PUFAs are n-3 and n-6, and because humans cannot synthesize them, they are
considered essential dietary
nutrients.
- Dietary fatty acids
are oxidized as fuel; incorporated in plasma phospholipids, lipoprotein
particles, and cell membranes; or stored as triglycerides.
- The most abundant
PUFAs in the diet are α-linolenic acid (ALA; 18:3n-3) and linoleic acid (LA;
18:2n-6); both of these fatty acid hydrochains are 18 carbons in length and are
considered the parent fatty acids for n-3 and n-6, respectively.
- In the n-3
family, ALA and stearidonic
acid (SDA; 18:4n-3) are considered
the shorter chain n-3s, while eicosapentaenoic acid (EPA; 20:5n-3), docosapentaenoic acid (DPA; 22:5n-3), and
docosahexaenoic acid (DHA; 22:6n-3)
are the longer-chain n-3s.
- ALA occurs in plant foods such as nuts,
particularly walnuts and flax, chia and hemp seeds, and vegetable oils, such as canola
and soybean oils.
- SDA is not typically found in food; very small amounts occur in fish and uncommon
plant sources (eg, echium, black currant). In the United States, the
soybean has been genetically modified to produce oil containing SDA n-3; the
SDA-rich soybean oil has Generally Recognized as Safe approval in the United
States.
- EPA, DPA, and DHA
occur in fatty fish and seafood, and
the best sources are salmon, sardines, tuna, herring, and trout.
- An abundance of foods fortified
with EPA and/or DHA from either marine or algal sources are now available; called
functional foods, examples include
soy milks and juices, cooking oils, spreads, snack foods and even fish sticks,
where fortification is in the breading.
- Most of the research on long-chain n-3s has used EPA and
DHA.
- DPA is a lesser known n-3; it occurs in fatty fish along with EPA and DHA
but is particularly rich in seal meat, a traditional food of Eskimos and other
cultures.
- Interest in new or unique health contributions from DPA is
growing.
- The predominant and best understood n-3 fatty acids are
ALA from plants and EPA and DHA from fish and seafood.
- In the n-6
family, LA and γ-linolenic acid (GLA; 18:3n-6) are shorter-chain fatty
acids, and arachidonic acid (ARA; 20:4n-6)
is a longer chain.
- Longer chain n-3 and n-6 fatty acids (≥20 carbons) carbons are
sometimes called highly unsaturated fatty acids.
- LA occurs in plant foods; the richest sources are soybean,
corn, and safflower oils.
- GLA is not
found to any great extent in foods and is available through dietary supplements from borage and evening primrose
oil.
- The best sources of ARA
are meat, poultry, and eggs.
- Conjugated linoleic acid (CLA) is an 18-carbon n-6 PUFA that occurs in small amounts in the milk
(about 0.3% to 0.6% total dairy fat) and
meat of ruminants.
- A conjugated fatty acid is one in which the double bonds
occur on adjacent carbons.
- The two major CLA
forms are cis-9, trans-11 18:2
(c9, t11 18:2) and the trans-10, cis-12
18:2 (t10,c12 18:2).
- There is usually more
c9, t11 18:2 in food, while supplements
typically contain an equal mixture of both forms.
- For the purpose of food
labeling, CLA is classified as
an n-6 fatty acid and not a TFA.
- One pilot study reported intake of CLA from foods at 94.9
mg/day in healthy adults in North America
Contributions of n-3 and n-6 to human nutrition
- Within the n-3 and n-6 families, the shorter-chain and
longer-chain fatty acids make different contributions to human nutrition.
- ALA n-3 is predominantly used as a fuel source for β-oxidation
and only a small portion is converted to longer-chain fatty acids.
- Desaturase and
elongase enzymes are required for the conversion
of shorter-chain to longer-chain fatty
acids.
- It was originally believed that the shorter-chain fatty
acids readily converted to the longer chains, but contemporary research
indicates that n-3 conversion from short
chain to long chain in humans is very limited;
- ALA converts to EPA at a rate of 5% to 15%, and <1% of
ALA reliably converts to DHA.
- Rate of conversion
of these essential fatty acids is determined
by the presence of and competition
for the desaturase and elongase enzymes and is further influenced by other factors, including sex, diet, health status, and genetics.
- This explains the interest in genetically engineered SDA;
more SDA than ALA is converted to EPA because with SDA, the rate-limiting conversion
step requiring delta-6 desaturase is bypassed.
- Conversion, however, is limited; two published human
trials reported that about 17% of
SDA converts to EPA and there is no conversion from SDA to
DHA.
- As a result, SDA is best considered an EPA-only precursor
- Individuals who follow a vegetarian or vegan diet and include no marine foods in their diet will consume ALA (n-3) because of its wide distribution
in plant-sourced foods. Through conversion, ALA will provide some EPA but little,
if any, DHA.
- Emerging science suggests there is individual variation in
conversion rate of fatty acids, influenced by genetics and dietary habits,
including the presence of other fatty acids in the diet.
- Those who follow a vegetarian diet might be more efficient
at n-3 conversion, but this has not been confirmed
Physiological function of PUFAs
- As 20-carbon PUFAs, EPA
n-3 and ARA n-6 function as eicosanoids.
- Eicosanoids are bioactive
mediators and precursors for prostaglandins, thromboxanes, and leukotrienes.
- Eicosanoids are considered hormone-like substances because they are produced when stimulated,
rapidly utilized and metabolized, and not stored in cells.
- Prostaglandins,
thromboxanes, and leukotrienes are involved
with a myriad of physiological and
homeostatic activities, including inflammation modulation, platelet
aggregation, cell growth and proliferation, smooth muscle contraction, and
vasoconstriction and vasodilatation. EPA, ARA, and DHA are also involved with
gene expression, cytokine activity, cell signaling, and immune modulation.
- The eicosanoids
produced from EPA and ARA differ from each other in structure, and they
function in complementary metabolic pathways.
- Eicosanoids produced from
ARA have high biological activity
and are considered more potent than
EPA-derived eicosanoids.
- For example, prostaglandins
produced from ARA promote inflammation, serve as vasoconstrictors, and
stimulate platelet aggregation, while prostaglandins
produced from EPA function as vasodilators and anti-aggregators.
- Eicosanoids derived from ARA are mostly pro-inflammatory but
have some anti-inflammatory effects.
- A balance of
eicosanoid synthesis in tissues is optimal.
- Resolvins and neuroprotectins, derived from EPA and
DHA, respectively, are a new class of
modulators that appear to have
anti-inflammatory and neuroprotective activity.
- Finally, DHA is a structural
component of red blood cell membranes and exists in higher concentrations in
retina tissue, neuronal cells, liver, and testes.
PUFAs from
Supplements
- n-3 supplements are widespread in the marketplace.
- The most common supplement forms of ALA are flax and chia seed oils.
- SDA supplements from algae are being synthesized.
- EPA and DHA supplements
are made from fish oil (typically
anchovy, menhaden, and salmon oils), cod
liver oil, krill oil, and squid (calamari) oil.
- Generally Regarded as Safe status of up to 3 g/day of EPA and DHA from fish oil in healthy people was
obtained in 1997.
- Vegetarian sources of EPA and DHA are available from algal
sources, and genetically engineered supplements are under development.
- GLA n-6
supplements are most often sourced from borage
and evening primrose oils.
- CLA, the
conjugated n-6 supplement, is synthesized from vegetable oils.
Current Intake of
PUFAs
- NHANES reported mean daily intake of ALA among males was
1.77 g and 1.38 g among females
- Mean daily intake of EPA among men was 40 mg and 30 mg for
women.
- Mean daily intake of DHA was 80 mg for men and 60 mg for
women.
- There is little difference between mean intakes by sex,
race/ethnicity, and income.
Dietary
Recommendations for PUFA
- The 2005 Daily Reference Intakes recommend 5% to 10% energy from n-6 and 0.6% to 1.2% of energy from n-3, but it did not set a
Recommended Dietary Allowance (RDA) or Estimated Average Requirement for
either.
- The Adequate Intake (AI) for n-6 is 17g/day and 12 g/day
for men and women 19 to 50 years, respectively; the AI for ALA is 1.6 g/day and
1.1 g/day for men and women age 19 to older than 70 years, respectively.
- These intakes are equivalent to 5% to 6% energy from LA
and 0.5% energy from ALA.
- Recognizing that differences in metabolic function among
n-3s existed, the Daily Reference Intake report noted that EPA and DHA could
provide up to 10% of ALA intake.
- It is important to recall that AI recommendations are observed
median intakes for the US population, not
an RDA or an intake of fatty acids shown to confer lower risk of disease.
- The DGA
2010 recommend
that adults consume 8 oz or more of seafood per week, or about 20% of the
recommended intake of protein foods from a variety of seafood (fish and shellfish).
- For primary
prevention of coronary heart disease (CHD), the AHA, the National Heart
Foundation of Australia, and the United Kingdom Scientific Advisory Committee,
all recommend at least two servings of fish
per week, preferably fatty fish, providing an average daily intake of 450
to 500 mg EPA and DHA.
- American Psychiatric Association also suggest two or more servings per week for
support of mental health.
- An increased intake of nuts and seeds is also recommended.
Because these foods have greater caloric density, they should replace servings
of meat and poultry and/or be consumed in small portions
- The World Health Organization/Food and Agricultural
Organization (WHO/FAO) established an upper Acceptable Macronutrient Distribution
Range (AMDR) for total PUFAs at 11% energy.
- They recommend total n-3
intake of 0.5% to 2% energy, with a minimum requirement of >0.5% energy
from ALA to prevent deficiency, and 250
mg EPA and DHA/day for men and nonpregnant women
- For LA n-6,
they recommend an estimated average requirement of 2% energy, an AI of 2% to 3% energy, and an AMDR of 2.5% to 9% The lower levels in the range are to prevent
deficiency, and the upper level is suggested
as part of healthy diet for long-term cardiovascular health.
- The European Food Safety Authority recommends an AI
of 0.5% energy for ALA and an AI of 250 mg EPA and DHA for primary prevention
in healthy adults; for n-6, recommended AI is 4% energy for LA; they do not
give a Dietary Reference Value for ARA.
- The International Society for the Study of Fatty Acids
and Lipids recommends a healthy intake of ALA n-3 as 0.7% energy and for
cardiovascular health, a minimum of 500
mg/day of EPA and DHA n-3. They also recommended an AI of LA
n-6 at 2% energy
In 2004, the Food and Drug Administration (FDA)
approved a Qualified Health Claim for n-3 fatty acids and heart disease,
stating: “Supportive but not conclusive research shows that consumption of EPA
and DHA n-3 fatty acids may reduce the risk of CHD.
- One serving of [name of food] provides [x] grams of EPA
and DHA n-3 fatty acids.”
- The FDA also approved a Qualified Health Claim for nuts
and heart disease as well as walnuts and heart disease, stating: “Scientific
evidence suggests but does not prove that eating 1.5 ounces per day of most
nuts [such as name of specific nut] as part of a diet low in saturated fat and
cholesterol may reduce the risk of heart disease.”
- The FDA made the same statement for walnuts
- Based on recent literature, increasing consumption of PUFAs with a particular focus on increasing n-3 intake (ie, striving to consume two or
more servings of fatty fish per week to provide at least 500 mg EPA and DHA per day, and aiming toward an intake of at
least 0.5% to 2% energy as n-3 fatty acids and 5% to 10% energy as n-6 fatty
acids per day) is desirable.
PUFAs and Health
i) n-3 Fatty Acids
- The role of n-3 fatty acids in heart health is one of the
most studied areas of nutrition science.
- Observations specific to long-chain n-3 fatty acids were
first made in the 1960s when epidemiologists observed that Greenland Eskimos
and native Alaskans had a low incidence of CHD, although they consumed large
amounts of fat.
- In the 1970s, death rates from heart disease among males
aged 45 to 64 years were 40% in the United States and nearly 35% in Denmark,
yet only 5% in Greenland
- Compared to the
Danes, Greenland Eskimos had higher blood levels of saturated fat and lower
levels of PUFAs, cholesterol, and triglycerides, even though both groups ate
about the same amount of total fat (Danes 40%; Eskimos 37%).
- The Greenland Eskimos also had considerably higher blood levels
(up to 16%) of the n-3 fatty acid EPA.
- The researchers noted more
of a qualitative than quantitative difference with respect to fatty acid
composition in the diets.
Fish: EPA and DHA
- Based on these findings, as well as observations in
countries that consume large amounts of fish such as Japan, associations
between fish consumption and overall cardiovascular mortality and sudden
cardiac death have been noted
- According to a 2011, meta-analysis, observational and
randomized clinical trial evidence suggests that fish or fish oil consumption can also reduce inflammation, improve
endothelial function, normalize heart rate variability, improve myocardial
relaxation and efficiency, and, at
higher doses, limit platelet aggregation (Mozaffarian et al. Circulation.
2011;123(24): 2870-2891)
- In addition, inverse relationships between blood levels of
n-3 and risk for sudden cardiac death have been observed
- Habitual fish consumption is associated with lower risk of
CHD and ischemic stroke and, among the general healthy population, those who
consume a modest amount of fish or fish oil providing ≥250 mg EPA and DHA/day have a 36% lower risk of
fatal heart disease.
- These benefits have not been shown among those who eat
commercially fried fish or fish sandwiches; this might be a reflection of the
type of fish commonly fried, as it tends to be lower in EPA and DHA content.
- Nonetheless, researchers have shown that consumption of non-fried fish is associated
with higher EPA and DHA blood levels.
- In addition to providing long-chain n-3s, fish provides
lean protein, vitamins, and minerals.
- Due to the concern of potential methylmercury contamination
in fish, in 2004 the US Department of Agriculture recommended pregnant women and children under 5 years
old limit fish consumption and avoid
the following types of fish: shark,
swordfish, king mackerel, and tilefish.
- Since then, an extensive risk-to-benefit analysis concluded
that, with the exception of select fish
(shark, swordfish, king mackerel, and tilefish), the health benefits of fish consumption outweigh potential risks.
- At this time, however, the US Department of Agriculture
advisory remains in effect.
- Although fish oil supplements have been shown to be equally
effective as fish at increasing tissue levels of EPA and DHA, it is unclear whether benefits observed in those
with habitual fish consumption can be fully reproduced with refined fish oil
supplements.
- Clinical research has shown that supplementing with refined
fish oil can help reduce triglycerides and improve blood pressure and heart
rate levels.
Health benefits of ALA
- The benefits of ALA
independent of EPA and DHA are not well documented; but, because it is
plant sourced, ALA is more readily available in the diet and is a particularly
important source of PUFAs for vegetarians.
- Studies investigating cardiovascular benefits of ALA in the
healthy population have shown mixed or inconsistent
results
- Diets rich in ALA have been reported to lower lipid
levels, reduce vascular inflammation, and reduce blood pressure in those with
elevated cholesterol levels.
- Interestingly, an 11-country study in Europe reported
reductions in CHD in countries that consumed ALA-rich canola oil compared to
countries that consumed primarily sunflower oil, which contains no ALA.
- Walnuts are a particularly rich source of ALA and several
studies have reported benefits from ALA by including walnuts and a variety of
nuts in the diet.
- Plant-sources of n-3s have also been shown to have a
protective effect on bone metabolism.
- However, a cardioprotective
blood level of long-chain n-3s (EPA and DHA) cannot be achieved by consuming
ALA alone.
Health benefits of SDA
- Health benefits of SDA independent of EPA and DHA are
unclear.
- Although little is known about the biological effects of
SDA, incorporating genetically engineered SDA into the food supply is motivated
by barriers to fish consumption and global concerns for sustainability.
- Modulating lipid levels with EPA and DHA require
relatively high doses; preliminary studies indicate that consuming SDA at a
bioequivalent dose of EPA (approximately 4 g SDA=approximately 1 g EPA) has
little impact on circulating lipids
Depression and n-3
fatty acids
- Depression is an increasingly common mental health
disorder.
- It can be chronic or recurrent, and the impact on individuals,
families, caregivers, communities, and the work force is significant.
- It is the leading cause of disability worldwide and is
predicted to be among the top three leading causes of burden of disease by
2030.
- An association between fish consumption and incidence of
major depression was first reported in 1998.
- Since then, a link between low levels of long-chain n-3
fatty acids and depression has been observed in a number of trials.
- The recommendation by the American Psychiatric Association
to consume fatty fish at least twice a week reflects these findings
Cognitive decline and
EPA/DHA
- Some level of cognitive decline is considered normal with
aging and lower levels of DHA have been observed in individuals with cognitive decline
and Alzheimer’s disease.
- The results of studies examining the relationship between
long-chain n-3s on cognitive decline have been mixed.
- The Academy’s Evidence Analysis Library recently examined
this question (see Figure 2);
- 6 of
the 14 studies analyzed reported positive associations between EPA, DHA, or
fish consumption and decreased risk of cognitive decline.
- Results varied based on amount and source of EPA and DHA consumed
and, perhaps more importantly, the state of cognitive health at the outset of
the study.
- A study evaluating healthy middle-aged adults showed that
DHA but not ALA or EPA was associated with better performance on cognitive
tests, such as nonverbal reasoning, mental flexibility, memory, and vocabulary
Other potential health
benefits
- Essential fatty acids are potentially potent anti-inflammatory agents and, as such, clinical evidence has
shown a role for EPA and DHA in reducing
symptoms of rheumatoid arthritis.
- Currently, there is interest in the role of fatty acids in
immune health, in part because
long-chain fatty acids appear to influence proteins directly involved with
immune cell activation.
- Despite promising results from animal models and cultured
tumor cell lines, no clear relationship between dietary intake of EPA and DHA
and risk for cancer have been
demonstrated
ii) n-6 Fatty Acids
- LA is the most highly consumed PUFA in the Western diet and
is found in virtually all commonly consumed foods.
- LA is the metabolic precursor of ARA and there is concern that
LA consumption can enrich tissues with ARA and contribute to overproduction of
bioactive eicosanoids, thereby increasing inflammatory markers and/or chronic
disease risk.
- However, a 2011 review reported that decreasing dietary LA
up to 90% did not significantly correlate with change in ARA tissue levels and,
similarly, increasing dietary LA levels did not increase ARA levels
substantially.
- A 2012 systematic review of randomized controlled trials
that assessed the impact of LA on biologic markers of chronic inflammation
among healthy adults also reported no
evidence that LA increased inflammatory markers.
- Nevertheless, emerging
evidence indicates significant racial differences in conversion rate of LA to
ARA, particularly between those of European and African descent, making
this an important area for further learning.
- With regard to GLA,
a linear relationship between dietary GLA and increases in plasma and serum phospholipid
ARA levels has been measured
- An AHA advisory published in 2009 summarized evidence on
n-6 consumption, particularly LA and CHD risk.
- It reported that consuming 5% to 10% of energy from n-6
PUFAs reduced the risk of CHD relative to lower intakes.
- A more recent meta-analysis, however, challenges this
conclusion.
- Evidence from animal studies suggests a beneficial role
for CLA for weight loss. However,
results from supplementation trials using intake levels of CLA unattainable
from food (1.8 to 4.5 g/day) have been mixed.
- The Academy’s Evidence Analysis Library recently reviewed
this question (see Figure 2).
- Impaired insulin sensitivity has been reported in some but
not all studies using CLA supplementation in those with obesity and metabolic syndrome.
2) MUFAs
Specific Fatty Acids
and Their Food Sources
- By definition, MUFAs contain one double bond; this double bond varies in location but is
frequently located at carbon nine from the methyl end of the fatty acid
hydrocarbon chain.
- MUFAs also differ based on chain length, and although
these fatty acids can exist from 10 to 32 carbons, the majority exist as an 18-carbon
fatty acid in the form of oleic acid.
Oleic Acid
- Oleic acid
contains one double bond at carbon nine, with the double bond existing in the
cis position (18:1 c-9).
- One of the most abundant fatty acids found in foods, oleic
acid is present in high amounts in olive and canola oils (Table 1) as well as in avocados and almonds (9.8 g/avocado half and
8.8 g/1 oz almonds, respectively).
- As a result, oleic
acid is the most abundantly consumed fatty acid in the American diet at 12%
energy intake
Erucic Acid
- Several other MUFAs exist but are present in foods in low
quantities.
- One MUFA that naturally exists in lower quantities in
foods is erucic acid, a 22-carbon
fatty acid that contains one double bond at carbon 9 (22:1, c-9).
- Food sources of erucic acid include rapeseed and other
plants from the Brassicaceae family, including kale and broccoli.
- Canola oil is produced from rapeseed, but removal of
erucic acid through genetic modification has essentially eliminated the erucic
acid content in canola oil and subsequently from the diet
Palmitoleic acid
- In addition to n-9 MUFAs, an n-7 MUFA with a purported
health benefit is palmitoleic acid, containing 16 carbons with one double bond
at carbon 7 from the methyl end (16:1, c-7).
- Palmitoleic acid is not commonly found in foods, but is a product of palmitic acid (16:0) metabolism in the body.
- Foods that naturally contain palmitoleic acid include
certain blue-green algae, macadamia nuts (3.7 g/oz; 17% of fat content), and
sea buckthorn oil.
- Although the fatty acids mentioned have one double bond
that exists in the cis formation,
MUFAs can exist in
the trans conformation as a result of industrial hydrogenation; most often
these TFA exist as 18:1, t-9. TFAs will be discussed in the trans-fat section
of this article.
- Although additional MUFAs exist, the quantities consumed
through diet are negligible and therefore will not be discussed.
MUFAs from
Supplements
- Supplementation with MUFA is not common practice and is not
supported by authoritative bodies.
- However, MUFAs are available in supplement form,
- Despite its abundance in various foods and oils, oleic
acid from olive oil is marketed as a dietary supplement.
- Given the quantity of oleic acid in common food oils (9.6
g per Tbsp olive oil; 8.3 g per Tbsp canola oil; 3 g per Tbsp soybean oil),
supplementing with olive oil does not provide appreciable quantities compared
to the common daily diet.
- Oleic acid from olive oil can also be found in supplements
containing the combination of n-3, n-6, and n-9 fatty acids; given the abundant supply of both n-6 (18:2)
and n-9 (oleic acid; 18:1) in the diet, the supplemental use of this combination is not supported.
- In addition to oleic acid, palmitoleic acid is currently being marketed as an n-7 fatty acid supplement with claims of preventing or reducing
heart disease.
Current Dietary
Intake of MUFAs
- NHANES 2009-2010 reports the dietary intake of MUFA for both men and women was 12% of total energy.
- This rivals SFA intake (11%) and is nearly double that of
PUFA intake (7%).
- Of all the fatty acid categories, MUFAs are consumed the
most, comprising 36% of total fat intake.
- The majority (93%) of MUFA consumption is oleic acid at pproximately
27 g/day; second to this is palmitoleic acid at 1.2 g/day.
- MUFA intake has remained relatively stable with an average
daily intake of 30.9 g in 2001-2002 vs 28.7 g in 2009-2010.
- No differences in MUFA intake currently exist between sex,
race, and income.
- Global consumption
of MUFA is variable but approximates
intake in the United States
MUFA Recommendations
- MUFA intake recommendations by authoritative bodies exist
as general guidelines.
- There is no AMDR
for MUFAs.
- Although the DGA do not recommend a specific amount of
MUFA to consume each day, they do recommend replacing solid fats with oils rich
in PUFAs and MUFAs, possibly through adopting a Mediterranean dietary pattern.
- Similarly, the AHA’s 2006 Diet and Lifestyle
Recommendations for cardiovascular disease (CVD) risk reduction in the general
population stated PUFAs and MUFAs should replace animal fats in the diet, with
a total fat intake of 25% to 35% of energy intake.
- To date, the most specific recommendation for MUFAs has been
the Adult Treatment Panel III (2004) recommendation, which states up to 20% of
energy intake as MUFA, thereby comprising a majority of the recommended 25% to
35% of total fat intake.
- No specific recommendations exist for MUFA intake with
regard to cancer or diabetes prevention.
- Most US authoritative bodies have not provided percentage
intake recommendations for MUFA; instead, appropriate
consumption levels need to be extrapolated from the quantity of fat
remaining from total fat intake recommendations after PUFA and SFA recommendations
are met.
- A recent FAO report indicated that MUFA intake be calculated by difference: Total
fat [%E] - SFA [%E] - PUFA [%E] – TFA [%E]
- This quantity determined through calculation by difference
allows for up to 15% to 20% of total energy.
- While considering intake recommendations for total fat and
fatty acids (discussed in their respective sections), one can extrapolate that MUFAs can comprise 9% to 29% of
energy
in our diet, assuming current intake levels of saturated and
trans fat
- For example, assuming no change from current consumption
of saturated and trans fat (approximately 12% combined), then MUFA intake should not be more than 17% of
energy in order to avoid consumption above intake recommendations for total
fat.
- This is important, as excess consumption of energy-dense
nutrients, such as fatty acids, can lead to weight gain and, depending on type
of fatty acid, be detrimental to health.
- Based on currently available information, consumption of
MUFA at a moderate level (15% to 20%) to account for appropriate PUFA intake,
while keeping within 20% to 35% of energy as fat is desirable.
MUFAs and Health
- Although current MUFA intake at 12% of energy falls within
total fat recommendations and supports recommended PUFA intake, investigating
the impact of MUFA in the diet is warranted.
- This is important because specific intake recommendations for MUFA are limited, specific health
benefits of MUFAs are unclear, and recent emphasis on olive oil consumption
by health professionals and the media can result in increases in MUFA intake.
- Understanding the role of MUFAs within the context of
substitutions for other macronutrients is also important.
- With consumption of oleic acid at 93% of total MUFA
intake, oleic acid is the primary focus in this section.
Older evidence suggest
benefits of higher oleic acid intake
- Oleic acid can be
synthesized in vivo, so measuring serum oleic acid as a marker of health
does not reflect intake.
- Although there is an inability to assess MUFA status, MUFA
intake has been linked to alterations in markers of health and disease, such as
reducing LDL cholesterol, triglycerides, total cholesterol to HDL ratio, and increasing
HDL cholesterol.
- In the context of macronutrient replacement, oleic acid
lowers total and LDL cholesterol when it replaces SFA (12:0 through 16:0 SFAs).
- Compared to carbohydrate, MUFA decreases triglycerides,
increases HDL cholesterol, and is inversely related to total-to-HDL cholesterol
ratio.
- In addition, compared to diets with ≤12% MUFA, dietary
regimens with high amounts of MUFA (>12%) resulted in lower fat mass,
systolic blood pressure, and diastolic blood pressure
Recent controversies surrounding oleic acid intake
- Despite evidence reporting health benefits from MUFA
consumption, some recent studies
have questioned these benefits.
- From a pooled analysis of 11 cohort studies, Jakobsen and
colleagues reported in 2009 that PUFAs are a preferred energy source over both MUFA
and carbohydrate; the analysis did not show that MUFA provided
cardioprotection.
- In addition, when coronary mortality was assessed over 30
years, serum MUFA levels were positively associated with coronary death.
- In contrast, however, there is a large body of evidence
reporting health benefits from consuming a Mediterranean diet (ie, a dietary
pattern that includes olive oil at approximately 20% of energy intake).
- Recent evidence also suggests benefits from olive oil
consumption for obesity, according to a 14-point screener for adherence to the
Mediterranean diet (PREDIMED [Prevención con Dieta Mediterránea] trial).
- The finding that, compared to a low-fat diet, a
Mediterranean diet enriched with either olive oil or nuts reduced the incidence
of major cardiovascular events supports potential health benefits from olive
oil; it should be noted that although the subjects in this study were free of heart
disease, they were at high cardiovascular risk and might not be considered
healthy adults, which is the focus of this article.
- Finally, and as recognized in the previously mentioned
PREDIMED trial, olive oil is only one
component of the Mediterranean diet.
- Because the dietary pattern also emphasizes vegetables and
fruits, n-3 fatty acid-rich foods, nuts, low-fat dairy, and moderate red wine
intake, reported benefits of a Mediterranean diet on CVD risk factors cannot be
attributed solely to the MUFA content. Indeed, nut consumption has been shown
to reduce total cholesterol, LDL cholesterol, and postprandial hyperglycemia
compared to meals high in carbohydrates
- In summary, MUFA consumption can be beneficial when replacing carbohydrate and
saturated fat, but not as beneficial when replacing PUFAs.
- Although MUFA is shown to have positive impact on
surrogate markers, the potential impact of MUFA intake alone on disease
outcomes, such as CVD or diabetes, remains unclear.
- Further understanding of the precise role of MUFAs on
health and disease when consumed within the context of an eating pattern (eg,
Mediterranean diet) is warranted.
- Although most of the research on MUFAs has focused on risk
of CVD and associated biomarkers, the relationship between MUFAs and cancer has
been investigated. The American Cancer Society guidelines state that olive oil
is not associated with an increased risk of cancer and likely has a neutral
effect on cancer risk.
3) SFAs
Specific Fatty Acids and
Food Sources
- SFAs are fatty acids that are fully hydrogenated.
- SFAs do not contain double bonds between carbon atoms in
the fatty acid hydrocarbon chain and therefore have a linear chain, a
structural property that allows the individual fatty acids to tightly pack and
exist at a solid state at room temperature.
- SFAs vary in length, but most commonly exist in the food
supply between 12 and 18 carbons: lauric
acid (12:0), myristic acid (14:0), palmitic acid (16:0), and stearic acid
(18:0).
- Less common in the food supply are shorter-chain SFAs,
specifically caprylic (8:0) and capric (10:0). These are medium-chain
triglycerides (MCTs), in the
category of fatty acids that are 8-12
carbons in length
- SFAs originate primarily
from animal sources, including meats, eggs, and butter, or from processed
food products containing naturally saturated vegetable oils.
- Animal fats such as butter,
lard, and beef tallow predominantly contain palmitic acid (16:0) and
stearic acid (18:0) (see Table 1).
- Specifically, food fats high in stearic acid (18:0) include beef
tallow (19% of fat as 18:0) and cocoa
butter (33% of fat as 18:0).
- It should be noted that stearic acid does not negatively impact serum cholesterol levels;
as a result, foods high in stearic acid can affect health in ways different
from other SFAs.
- Although the primary sources of SFAs are animal products, tropical vegetable oils such as palm
and palm kernel oil are commonly used in processed foods, principally because
of their physical properties.
- Although palm oil and palm kernel oil both originate from
the oil palm tree, these oils have different fatty acid profiles; palm oil contains 49% of fat as SFA
(primarily 16:0) and palm kernel oil
contains 82% of fat as SFA (primarily 12:0).
- In comparison, 87% of the fatty acids in coconut oil (from the coconut palm) are
saturated, with 12:0 (medium chain) in the highest concentration.
- Although coconut oil is not commonly used in processed foods,
new food products on the market (eg, milk, spreads, yogurt) containing coconut
oil are touting the purported health benefits of MCTs (see section on SFAs and
Health).
- In addition to SFA that occur naturally in foods,
vegetable oils are industrially hydrogenated
(the process of adding hydrogen atoms to unsaturated bonds to create saturated
bonds) to produce fats that have properties ideal for food production. In this
process of creating fully hydrogenated fatty acids (SFA), partially
hydrogenated fatty acids (TFAs) are
also produced.
SFAs from Supplements
- SFAs are not commonly marketed in supplement form; MCTs
are an exception.
- MCT supplements
contain primarily 8:0 and 10:0 fatty
acids in capsule or liquid form.
- However, some MCT supplements are derived from coconut
oil.
- More than 50% of the fatty acids in coconut oil are MCTs
(58.7% are 6 to 12 carbons in length) and due to this are marketed as having
health-promoting properties.
- It is important to note that supplemental MCT oil is used for
medical nutrition therapy in patients who lack the ability to properly
metabolize longer-chain lipids.
- Although the MCT oil used for patient care often
originates from coconut or palm oil and might contain primarily 12:0 (rather
than 8:0 or 10:0) as its fatty acid source, individuals with a medical indication
for MCTs differ from the needs of the healthy individual.
- Caution should
be taken when considering MCT
supplements as the impact of the
different MCT fatty acids on human health are not fully elucidated and many over-the-counter supplements do not
identify which fatty acids they contain (see section on SFAs and Health)
Current Intake of
SFAs
- On average, both men and women consume 11% of energy from SFAs; this is higher
than the recommendation from most authoritative bodies to consume <10% of
energy as SFA.
- No differences in saturated fat intake exist based on
race/ethnicity (range of 10.0% to 11.3% of intake) or income.
- The majority of
saturated fat consumed is from palmitic
acid (16:0) and then stearic acid
(18:0) (54% and 25% of saturated fat intake, respectively).
- Food sources of SFA in the American diet, listed as greatest
to least, are cheese, pizza, grain-based desserts, and dairy-based desserts;
together these foods comprise 31% of SFA intake
- Most stearic acid is consumed from grain-based desserts,
cheese, and various meats.
- From a global
perspective, saturated fat intake (based on food availability) varies by continent
and country, with lower intakes in Asia
(3.1% to 10.6% of kilocalories) to
higher intakes in Europe (8.9% to 16.5%).
- Finally, because energy intake is often greater than
energy need, evaluating SFA intake solely as a percentage, rather gram quantities, provides a somewhat
limited view
SFA Recommendations
- No current AI or RDA exist, in part because SFA is synthesized
in the body to meet physiological needs and because of the recognized role of
SFA in CVD
- The AMDR states that SFA should be as low as possible
while consuming a nutritionally adequate diet.
- The DGA recommend that <10% of calories come from saturated
fat and should be replaced with MUFA and PUFA; <7% SFA intake was suggested
for further reduction of CVD risk.
- The guidelines also recommend limiting foods that contain
solid fats (SFA and TFA), sugars, and sodium; this is especially important as these
foods comprise 19% of total energy intake.
- The AHA’s Diet and Lifestyle Recommendations (2006)
recommended SFA intake be <7% of calories (approximately 16 g based on a
2,000 kcal diet) for the general population for CVD risk reduction.
- In addition, the AHA and American College of Cardiology
recently released a report indicating a dietary pattern that achieves 5% to 6% of
calories from saturated fat best for those that want to achieve lipid lowering.
- In 2010, the FAO reported that SFA intake should be no
more than 10% of energy and replaced with PUFAs.
- Although the American Diabetes Association has a recent
position on fat in diabetes management, no recommendations exist for SFA in
primary prevention of either diabetes or cancer.
- A current American Cancer Society guideline, however,
recommends limiting consumption of red and processed meats, recognizing their
role as major contributors to total and saturated fat intake.
- Based on recent
literature and consensus, the goal
for SFA intake for the population should be 7% to 10% of total energy. The current intake of SFA at 11% exceeds
the amount recommended for healthy individuals.
SFAs and Health
- The linear structure of SFA and its ability to tightly
pack in cell membranes, along with its signaling properties, have consequences
often considered detrimental to health.
- As with the other fatty acid groups, individual SFAs have
differing impacts on health.
- The SFAs 12:0,
14:0, and 16:0 have similar effects on serum lipoproteins; specifically,
they increase LDL cholesterol
- In contrast, stearic
acid (18:0) has a neutral impact
on LDL cholesterol. However, because stearic acid is consumed in foods that should
otherwise be limited (eg, grain-based desserts, cheese, processed meat), it is
prudent to make the same intake recommendations for stearic acid as the other
SFAs
- When evaluating the impact of replacing SFA with carbohydrates
on CVD risk, SFA increases LDL
cholesterol but lowers triglycerides and raises HDL cholesterol, and
apolipoprotein B is not changed.
- Inclusion of 12:0, 14:0, or 16:0 increases LDL cholesterol
and HDL cholesterol when replacing carbohydrate at 5% of the diet; however, a recent pooled analysis of large cohort
studies indicate there is a significantly
greater relative risk for CHD with
carbohydrate intake vs SFA intake (Jakobsen
et al. Am J Clin Nutr.
2009;89(5):1425-1432)
- When stearic acid is replaced by carbohydrate, there is a
nonsignificant change in these CVD risk factors. (Mensink et al. Am J Clin Nutr. 2003;77(5):1146-1155)
- In addition, replacing SFA with PUFA lowers CVD risk by
approximately 10% (5% energy substitution).
- There is limited evidence about any impact of saturated
fat on inflammation.
- Despite documented influence of saturated fat on surrogate
disease markers, the effect of saturated fat intake on disease end points is
not clear.
- A recent systematic
review reported insufficient
evidence to link saturated fat intake with CHD. (Mente et al. Arch Intern Med. 2009;169(7):659-669)
- Several studies show that reducing fat consumption,
especially saturated fat, can reduce risk for diabetes with improvements in
weight; however, this is not supported by other trials.
- Although known to be an important component of breast
milk, MCTs are gaining in popularity among healthy adults.
- Unlike longer chain SFAs, MCTs are transported in portal
circulation and more readily oxidized through the β-oxidation pathway.
- These fatty acids are oxidized rather than stored as triglyceride
in the body could be advantageous.
- The oxidation rate of MCTs, as well as their impact on
thermogenesis, has been shown to be beneficial
in decreasing adiposity and improving weight loss when compared to olive
oil. However, these results were from supplementation with oil containing 8:0 and 10:0 and not 12:0 fatty acids
- New food products containing coconut oil and other palm
oils (eg, milk, spreads, yogurt) are touting health benefits of MCTs.
- Given that 44% of coconut oil is 12:0 and 16% is 14:0, and
these fatty acids are hypercholesterolemic, consumption of coconut products is not currently recommended.
- There is, however, cause to focus on the impact of different
MCT fatty acids in human health.
- As research is completed, the Academy will disseminate
findings to RDNs with appropriate recommendations.
- Dietary patterns that are high in saturated fat include
the Western dietary pattern, characterized as high in total fat, saturated and
trans fat, refined carbohydrate, and sodium.
- Although distinguished in part by its saturated fat
content, saturated fat is only one component of the Western dietary pattern.
- The saturated fat content of red meat can contribute to
disease risk, but other components such as iron, sodium, and compounds created
when cooking red meat can also contribute.
- Compared to red meat, consumption of fish, poultry, dairy
products, and nuts is associated with a lower risk of CHD when the same
servings are consumed
- Although this risk reduction could be due to a reduction in
heme iron, sodium, or saturated fat, or an increase in PUFA, examining whole foods rather than
individual components is important.
- In addition, although evidence on the impact of SFAs on
disease end points such as heart disease, diabetes, and cancer is mixed, replacing of SFA with PUFA instead of
refined carbohydrate appears to be beneficial.
- Finally, decreasing
SFA without caloric replacement is an effective strategy for reducing total
energy content of the diet and promoting healthy body weight.
4) TFA
Specific Fatty Acids
and Food Sources
- Partial hydrogenation results in the formation of a large
number of positional and geometric isomers of the naturally occurring cis-fatty
acids.
- A major TFA in industrially hydrogenated oils is elaidic acid (18:1, t9), although many
other trans isomers are formed
- TFA are present in ruminant meat and milk fats as a result
of biohydrogenation of unsaturated fatty acids (18:2 and 18:3) in the rumen.
- The major TFA
in ruminant meat and dairy products
are c9,t11-CLA, with vaccenic acid (18:1, t11),
predominating at 50% to 80% of total ruminant TFA (rTFA) produced. - Recent
efforts to increase c9,t11-CLA content in ruminants has increased the presence
of rTFA in both meat and dairy products
- As previously stated, CLA is classified as an n-6 fatty
acid and not a TFA and, therefore, will not be discussed here.
- Sources of commercially
partially hydrogenated TFA include hydrogenated vegetable and marine oils;
these oils have been commonly used in
commercial baked goods.
- Although the TFA content in foods has decreased recently
(through food reformulation), it is important to monitor the type of fat used
to replace TFA, as it might be SFA
- An FDA labeling
requirement that went into effect in 2006 required food labels to list TFA
on their Nutrition Facts panel (on a separate line under the saturated fat
listing) when present at 0.5 g or more
per serving (not required if TFA < 0.5 g per serving)
- Dietary supplements were also required to list TFA in the
Supplement Facts panel.
- Consumption of
foods that contain TFA but at <0.5 g per serving contribute to overall TFA
intake, so foods commonly containing TFA should continue to be limited (eg,
commercial pastries, cookies, fast food).
- In addition, the FDA has recently issued a Federal
Register notice preliminarily determining that trans fats (partially hydrogenated oils) are no longer “generally
recognized as safe,” or GRAS.
- RDNs should monitor the determination of the FDA regarding
GRAS status of trans fats and what this means to the availability of trans fats
to the consumer.
TFA from Supplements
- No TFA supplements currently exist, as their negative
health impacts are widely known.
- However, this excludes CLA, considered a TFA, as the
cis-9, trans-11
- CLA isomers contain a trans bond at cis-11.
- Although nutritional supplements in liquid or powder form can
contain trans fats, and must declare it on the label if ≥0.5 g per serving, the majority of the products do
not contain appreciable quantities.
Current Dietary
Intake of TFAs
- Recent intake data estimates that TFA intake is 3 to 4 g/day in North America; intake
is similar in northern European
countries and less in eastern Asian
countries (<1 g/day).
- This is a reduction from previous consumption, which was estimated
to be 10 g/day worldwide
- Data from the European TRANSFAIR study indicate that in
the United States, 1.2 g/day of TFA originates from ruminants. This is
comparable with other countries, as consumption of rTFA in Europe ranges from
0.8 to 1.7 g/day
- More recent evidence (2007) reports the consumption of
rTFA is 20% of total TFA intake, with most (85%) of this coming from milk fat.
- Recent analysis of NHANES 2003-2006 dietary data indicate industrially
produced TFA intake at 1.3 g per person per day. TFA intake is declining; a
recent comparison using NHANES data indicated a 58% decrease in serum TFA levels
from 2000-2009
TFA Recommendations
- The 2005 Daily
Reference Intake has not set an AI or RDA for TFAs.
- No upper limit is set, as any TFA intake increases CHD
risk; in light of this, intake of TFA should be kept as low as possible.
- The DGA also recommend TFA consumption to be as low as possible,
especially by limiting foods that contain synthetic sources of TFA, such as
partially hydrogenated oils, and by limiting other solid fats.
- The AHA’s Diet and Lifestyle Recommendations advocate that
TFA be <1% of calories.
- In 2008, the FAO/World Health Organization recommended a
TFA upper limit (both ruminant and industrially produced) to be <1% of
energy; a 2010 report acknowledged that the <1% recommendation might need to be revisited due to unknown
distribution of intake and potential negative impact on subgroups with higher
consumption
TFAs and Health
- The impact of TFA intake is generally undisputed.
- There is convincing evidence that consumption of
commercial partially hydrogenated vegetable oils increases CHD risk factors, as
well as in metabolic syndrome and diabetes risk
- For example, trans-C18:1 increased serum levels of
lipoprotein(a), an atherogenic protein associated with apolipoprotein B-containing
lipoproteins; as this is the most commonly consumed TFA, this finding may be important
with regard to risk of disease in healthy individuals
- Limited research has examined the different impacts of
industrially produced TFA and rTFA on CHD risk.
- The amount of TFA
is also relevant when considering the impact on disease risk markers. At 3.7%
of energy, both ruminant and industrial TFA have been shown to have adverse
effects on blood lipids, specifically increases in LDL cholesterol and decreases in HDL cholesterol. However, when examined at
lower doses (1.5% of energy from rTFA or 0.8% total TFA), no significant
differences in blood lipids or lipoproteins were seen
- A relationship between trans fats and cancer has not been
determined.
- In summary, foods containing industrially derived TFA
should be minimized. Due to recent changes in commercial food composition,
there is less TFA in foods. Nonetheless, consumers should be cognizant of
potential TFA in processed foods and limit fast food in the diet in
order to reduce TFA intake, ideally to <1% of energy.
- Replacing TFA with other fatty acids or carbohydrate is an
improvement, but replacing TFA with PUFA is most beneficial for health.
EMERGING POPULATION
RESEARCH
-In a recent study, associations between type of dietary fat
intake—PUFA, MUFA and SFA—and CHD risk were assessed using data from 11 American
and European cohort studies to address the question of the best macronutrient
substitution for SFA in the diet. From follow-up data over 4 to 10 years
including 344,696 persons, researchers identified that replacing SFA with PUFA was preferable to MUFA and carbohydrate for
reducing CHD risk; a 5% decrease in SFA that was replaced with PUFA showed
an inverse and significant relationship with CHD
- The EPIC (European Prospective Investigation of
Cancer)-Norfolk study involving 25,639 individuals reported blood levels of SFA
were positively associated with CHD risk, while an inverse association was seen
with PUFA levels.
- A 2012 study from a prospective cohort among 91,981 women
in the Nurses’ Health Study reported that consumption of PUFAs as a proportion
of fat was inversely associated with risk of sudden cardiac death, independent
of traditional CHD risk factors
- Together, these data support dietary guidelines to replace
intake of SFAs with n-3 and n-6 PUFAs
ROLE OF DIETITIAN
- Provides guidance on the quantity and quality of dietary
fat in addition to meal planning and food preparation.
- The guiding philosophy is to encourage food-based consumption first and supplements second
- Monitoring total
fat is important because it is abundant in the diet and contributes to
excessive energy intake; however, it aids absorption of fat-soluble nutrients
and provides desirable cooking and sensory qualities.
- Monitoring type of
fatty acid is important because they each have different biological effects
in the body and some are essential in human nutrition
- Recommendations for specific foods (eg, avocados) or fatty
acids (eg, more n-3) might be more practical than general statements.
- The concept of caloric
density is relevant because fat
contains 9 calories per gram, more than double the calories per gram of protein
and carbohydrates.
- Replacing fat with
less calorically dense foods or without caloric replacement, within the context of adequate nutrition,
are effective strategies for limiting excess energy intake; helping patients
make appropriate substitutions is equally important.
- Understanding, for example, that individuals who consume
fried fish tend to consume higher amounts of SFA and TFA is useful when
offering guidance
- Providing
clients with helpful tools and resources,
for example, how to choose snack foods with less SFA or fish that is
recommended by environmental organizations, will support ongoing healthful
choices.
- Teaching
consumers how to understand and apply Nutrition
Facts labels and ingredient lists
has lasting results
- In addition to current knowledge, information on how fatty acids influence health through gene expression is forthcoming.
- For example, both the type and amount of PUFA influence
peroxisome proliferator-activated receptor activity and its regulation of lipid
metabolism, including lipogenesis, oxidation, and transport.
- In addition, research on how an individual’s genetic
variation influences fatty acid utilization is underway; this work will provide
rationale and direction for future individualized dietary prescriptions.
- For example, individuals carrying >2 signal transducer
and activator of transcription 3 (STAT3) risk alleles have increased risk of obesity
with a SFA intake of >15.5% of energy, compared with those with ≤1 risk allele.
- Knowledge gained in this area of research will enable RDNs
to customize diets for optimal
health outcomes.
- Nutrition science has moved beyond fat as a macronutrient;
a commanding knowledge of food sources and health impact of individual fatty
acids is a vital piece of RDN training and continuing education.
- It is essential
that RDNs understand the current literature
on dietary fat and fatty acids and build
knowledge as science expands.
- Translating fat and
fatty acid literature into dietary recommendations is a complex process yet
highly suited for the skills and training of RDNs.
- New technologies are changing the types of fatty acids in
the food supply: new sources of fatty acids are being discovered, structural
changes within the fatty acids and how they are positioned within the
triglyceride molecule are being made, and genetically engineered
fatty acids are being incorporated into new foods.
- As modified fatty acids and their sources become
available, RDNs will be called on to provide leadership and guidance in areas where
the science is still emerging
Vannice et al. J Acad Nutr Diet. 2014;114:136-153. http://dx.doi.org/10.1016/j.jand.2013.11.001
Note:
DGA 2015-2020 was published recently.
Note:
DGA 2015-2020 was published recently.
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