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Organic Food High in Antioxidants and Low in Toxic Metals

A meta-analysis of 343 studies has found that organic crops and crop-based foods are up to 60% higher in a number of key antioxidants and 50% lower in toxic heavy metals than conventional crops. But are these results biologically meaningful?

“This is yet another study that shows that there is little difference in nutritional content between organically grown food and conventionally grown food. There have been many attempts to measure the nutritional differences between conventional and organic food, with largely inconsistent results. This is not surprising, as the nutritional value of foods is very variable, influenced strongly by local regional factors, variations in growing seasons and rainfall, ripeness of food when harvested and time of harvest. Even different cultivars of the same crop may vary significantly in composition due to the factors above.

“To try and avoid these limitations, several studies have looked at large numbers of these single studies (a meta-analysis), and generally concluded that there is no meaningful difference between conventional and organic food.

“The paper by Baranski and colleagues in the British Journal of Nutrition follows in the footsteps of these large comparison studies, looking at the largest group of studies to date (343). Their findings are largely similar to previous meta-analyses: only a handful of nutrients are statistically different between organic crops and conventional crops, and only one is of plausible biological significance.

“While some organic crops (typically fruits) had statistically higher levels of antioxidants than conventional, the level variations were small and unlikely to significantly affect health. While consumption of antioxidant-containing fruit and vegetables have been associated with better health outcomes, the antioxidants themselves do not appear to have any role in this effect, and the extra amounts of antioxidants present in organic food are too low to be meaningful. Organically grown fruits tended to be higher in carotenoids, but fruit consumption is unlikely to boost carotenoid levels to those associated with higher risk of death.

“The levels of the toxic metal cadmium were lower in organic foods than conventional foods. Although most people’s intake of cadmium in conventional foods is below that associated with any health risk, this is one area where organic foods may have a larger margin of safety.

“Overall, organic foods generally have no biologically meaningful health benefits (with the possible exception of cadmium). Given their much higher price, people need to carefully consider any decision to consume organic foods.”

Dr Ian Musgrave is a Senior Lecturer in the Faculty of Medicine at the University of Adelaide.

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“The most interesting result of the meta-study is the difference in the content of some but not all antioxidant substances in organic produce. There is no obvious reasons for the differences, but whether they translate into better nutrition is a question that deserves further investigation. It’s no surprise that organic produce shows significantly lower pesticide residues and less contamination by metals, such as cadmium, that are found as trace impurities in some phosphate fertilisers.

“But … hang on … organic growers are not supposed to use these pesticides or fertilisers at all, so we would not expect to find any of these contaminants in their produce, not just lower concentrations. Are some ‘organic’ growers cheating?”

Professor Ian Rae is an Honorary Professorial Fellow at the University of Melbourne and Former President of the Royal Australian Chemical Institute.

Reference

Baranski et al. (2014) Higher antioxidant concentrations and less cadmium and pesticide residues in organically grown crops: A systematic literature review and meta-analyses. British Journal of Nutrition. doi:10.1017/S0007114514001366

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