A new analysis appears to refuel the debate about the nutritional value of organic versus conventional foods, by finding that organic crops and crop-based foods contain up to 69% more of certain antioxidants, are four times less likely to contain pesticide residue, and have significantly lower levels of the toxic heavy metal cadmium.

Led by Newcastle University in the UK, the international team of experts reports its findings in the British Journal of Nutrition. In what is thought to be the largest study of its kind, the researchers describe how they pooled and analyzed data from 343 studies comparing the compositional differences of organic and conventionally grown fruit, vegetables and cereals.

Share on Pinterest Researchers say organic foods contain more antioxidants and less pesticide residue than conventionally grown crops.

Study leader Carlo Leifert, professor of ecological agriculture at Newcastle University, says the evidence is “overwhelming,” and shows that:

“[…] choosing food produced according to organic standards can lead to increased intake of nutritionally desirable antioxidants and reduced exposure to toxic heavy metals. This constitutes an important addition to the information currently available to consumers which until now has been confusing and in many cases is conflicting.”

Prof. Leifert and colleagues say their findings suggest that by switching to organically grown crop foods, and foods made from them, people would consume additional antioxidants equivalent to eating between one and two extra portions of fruit and vegetables per day.

They would also be consuming less cadmium, one of the three metal contaminants – the other two being lead and mercury – for which the European Commission has given maximum permitted levels in food.

In their analysis, the team found cadmium levels were nearly 50% lower in organically grown than conventionally grown crops.

For a crop to qualify as “organic,” the grower is not allowed to protect it with synthetic chemicals or feed it with certain mineral fertilizers (for example, nitrogen compounds, potassium chloride and superphosphate). This is in order to reduce environmental impact from nitrates and phosphorous, and to avoid pesticide contamination in groundwater.

Instead, organic crop growers are expected to give regular feeds of organic fertilizers, such as manure and composts, to enrich the nitrogen in the soil by rotating legume crops, and use non-chemical crop protection methods, such as crop rotation, mechanical weeding and biological pest control.