Nutrition-related health effects of organic foods: a systematic review

Introduction

- Organic foodstuffs are produced according to specified standards that emphasize the protection of the environment and control of the use of chemicals in crop production and medicines in animal production.

- A recent systematic review of peer-reviewed evidence published in the past 50 y concluded that organically and conventionally produced foodstuffs are broadly comparable in their nutrient content

- Aim: to assess the strength of evidence of the nutrition-related benefits to human health of consumption of organic foodstuffs

- This systematic review did not address: potential health effects of differences in contaminant content (such as herbicide, pesticide, and fungicide residues) of organically and conventionally produced foodstuffs or of potential wider environmental or occupational health effects of different agricultural practices.

Method

- Search period: from 1 January 1958 to 15 September 2018 (A systematic review until 10 March 2010 was done before publication)

- Database: PubMed, ISI Web of Science, CAB Abstracts, Embase (gray literature were not included)

- Language: At least English language abstract

- Inclusion criteria: Exposure to foodstuffs from organic (reported as organic, ecologic and bioorganic) or conventional (reported as conventional and intensive) farming system

- Exclusion criteria: concerned with occupational health outcomes unrelated to consumption of organic or conventional foodstuffs, investigated animal health from an exclusively veterinary perspective, or concerned with the effects of nonnutrient contaminant content (eg, chemical residues and heavy metals),

- Study type included:

i) Randomized and nonrandomized controlled trials and studies with cohort, case-control, and crosss ectional designs

ii) In vitro and ex vivo studies in human or animal cell lines and serum used to investigate human-related cell mechanisms;

iii) Animal studies that were explicit models of physiologic, biochemical, or other processes in humans

- Study quality, assessed by 4 a priori criteria (Satisfactory quality if met all criteria):

i) Clear definition of the organic production methods for the food stuffs (including name of the organic certification body)

ii) A statement on the nature (ie, type, amount, or proportion) of the organic component of the foodstuff or diet under investigation,

iii) A clear definition of the health outcome and how it was measured

iv) A statement of the statistical methods used for data analyses

- Data analyses: no meta-analysis was performed because of the marked heterogeneity of the included studies

- Result synthesis: according to 1) study hypothesis, 2) study design, 3) exposure, and 4) health outcome

Results:

- Number of studies included: 12 (8 human in vivo studies, 3 human in vitro studies, 1 animal study)

- Quality: 4/12 studies (33%) met the predefined quality criteria

1) Study Hypothesis

- 8/12 studies (67%) hypothesized that organic production methods result in higher nutrient concentrations in foodstuffs and that these compositional differences would result in different health responses

- Remaining 4 studies hypothesized that agricultural production methods differentially affect markers of carcinogenesis or the bioavailability of carotenoids or polyphenolic substances

2) Study designs

- 8 human studies: 6 clinical trials, 1 cohort and 1 cross-sectional study

- 4 experiments conducted in animals (rats) or human cell lines or serum

- Clinical trials: small (sample size, n=6-43) and short (exposure period 1-28 d)

- Cross-sectional and cohort: larger size (n=312-2764), both derived from KOALA Birth Cohort Study. Design shortcomings: self- or proxy-reported measures of exposure, a lack of information on the duration of exposure, and proxy-reported measures of primary outcomes

- Remaining 4 experiment studies used contrasting approaches to test different biological materials in animal or human samples

3) Exposures

- 10 studies investigated the effects of specific foodstuffs (fruit or vegetables, n=7; wine, n=2; livestock products, n=1)

- 9 studies investigated foodstuffs known to be rich in antioxidants such as tomatoes, grapes, apples, carrots, and strawberries

- 2 studies investigated organic foodstuffs as part of the whole diet

- 10 studies compared a specified exposure or dose of a foodstuff as part of a controlled-exposure study

- The 2 large studies used measures of self- or proxy-reported exposure and proxy reports of diet when necessary (16% of study participants)

4) Health outcomes

- 10 studies: primary outcome was the change in antioxidant activity (Antioxidant status and activity are useful biomarkers but do not directly equate to a health outcome)

- 1 study recorded proxy-reported measures of atopic manifestations as its primary health outcome

- 1 study examined the fatty acid composition of breast milk and implied possible health benefits for infants from the consumption of different amounts of conjugated linoleic acids from breast milk

Discussion:

- Evidence of nutrition-related health effects from the consumption of organic food is currently lacking.

- The strength of evidence of other public and environmental health benefits that arises from the consumption of organic foods would warrant further systematic review.

-Clinical trials included: small sample size, none reported power calculation, inadequate reporting etc

- Most studies investigated the health effects of specific foodstuffs rather than the diet as a whole, and there was rarely any rationale provided for the quantity and duration of exposure to foodstuffs in clinical trials

- A surprising and important finding of this review is the extremely limited nature of the evidence base on this subject, both in terms of the number and quality of studies. This is particularly surprising given the increasing public and policy-level interest in the question of whether there are health benefits from the consumption of organic foods.

Conclusion:

- Evidence is lacking

- Taken together, the 12 included articles did not provide evidence of health benefits or harm from consuming organic foods

Future studies:

- The International Research Association for Organic Food Quality and Health aims to develop novel methods to study the effect of organic food on human health and has recently provided some useful guidelines on study design

- Recommendation for future studies: sufficient sample size, longer and more realistic dietary exposures, and more accurate and objective approaches to measure dietary intake and outcomes of public health relevance

Dangour et al. Am J Clin Nutr 2010; 92:203-10. doi: 10.3945/ajcn.2010.29269

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