Effect of Mediterranean Diets Based on Organic and Conventional Foods

The most recent systematic literature reviews and meta-analyses have indicated significant and nutritionally-relevant composition differences between organic and conventional foods (crops, meat and dairy products). Specifically, these systematic reviews reported that:

organic crops have 17% higher antioxidant activity and between 18% and 69% higher concentrations of a range of individual antioxidants; increased intakes of polyphenolics and antioxidants has been linked to a reduced risk of certain chronic diseases such as cardiovascular and neurodegenerative diseases and certain cancers.

conventional crops have 48% higher levels of the toxic metal cadmium, and are 4-times more likely to contain detectable pesticide residues; there are general recommendations to minimise the intake of pesticides and cadmium to avoid potential negative health impacts.

conventional crops also have 15%, 10%, 30%, and 87% higher concentrations of protein, nitrogen, nitrate, nitrite, respectively; increased intakes of these compounds have been linked to both positive and negative health impacts.

organic meat, milk and dairy products have approximately 50% higher concentrations of nutritionally-desirable omega-3 fatty acids; intakes of very long chain omega-3 fatty acids in Western diets and there are EFSA recommendation to at least double their intake.

organic milk has 70% lower concentrations of iodine and slightly lower concentrations of Selenium, which is nutritionally undesirables especially in the UK where (a) the Se content of cereals has decreased (due to reduced import of cereals grown on Se-rich soil (b) Iodine fortified table salt is not widely available and used and the iodine supply relies more on mineral fortification of animal, and especially dairy feeds.

Results from a small number of human cohort studies are also available and indicate that there are positive associations between organic food consumption and reduced risk/incidence of certain acute diseases (e.g. pre-eclampsia, hypospadias) and obesity/overweight .

Results from animal dietary intervention studies suggest that (i) switching to organic food consumption results in significant changes in hormonal balances and an increase in immune system responsiveness and (ii) differences in pesticide residue, cadmium, protein and antioxidant concentrations between organic and conventional foods are major drivers for hormonal balances and immune system parameters in animals.

However, there is virtually no published data from (i) long-term cohort studies focusing on chronic diseases (e.g. cardiovascular disease, diabetes, cancer and neurodegenerative conditions) and (ii) controlled human dietary intervention studies comparing effects of organic and conventional diets. It is therefore currently not possible to assess whether and estimate to what extent organic food consumption may affect human health.

The overall aim of the study is to get a quantitative understanding of (a) the uptake (and therefore potential to affect health) of food composition components (pesticide residues, toxic metals such as cadmium, antioxidants) that differ between organic and conventional foods and (b) the effect of organic vs conventional food consumption on selected physiological parameters in plasma linked to health.

This information will be essential to (a) carry out accurate statistical power analyses (based on uptake [=estimated from blood and urine concentrations] rather than food composition data) and (b) optimise designs for longer-term dietary intervention studies, designed to identify impacts of organic food consumption on health related physiological markers in humans and mechanisms for potential health impacts.

The main objectives of the proposed study are to:

1. Carry out a human dietary intervention study comparing the effects of switching to Mediterranean diets based on organic and conventional foods on concentrations of pesticides, toxic metals, mineral nutrients (e.g. Fe, Cu, Se, I) and antioxidants, and antioxidant activity and selected health-related markers in urine and blood.
2. Quantify concentrations of pesticide residue, mineral, toxic metal and antioxidants in both organic and conventional food samples consumed during the intervention period
3. Carry out both univariate and redundancy analyses to both quantify effects of different diets on urine and blood composition and to identify the most important food composition drivers for differences in urine/blood composition and health markers.