The research, which claims to be the largest analysis of its kind, looked at data from 343 studies into the compositional differences between organic and conventional crops.
The international team of experts led by Newcastle University, UK, found that a switch to eating organic fruit, vegetable and cereals – and food made from them – could provide additional antioxidants equivalent to eating between 1-2 extra portions of fruit and vegetables a day.
“This study demonstrates that choosing food produced according to organic standards can lead to increased intake of nutritionally desirable antioxidants and reduced exposure to toxic heavy metals,” said lead author Professor Carlo Leifert of Newcastle University.
“This constitutes an important addition to the information currently available to consumers which until now has been confusing and in many cases is conflicting.”
Writing in the British Journal of Nutrition, the review and meta-analysis also shows significantly lower levels of toxic heavy metals in organic crops. Cadmium, which is one of only three metal contaminants along with lead and mercury for which the European Commission has set maximum permitted contamination levels in food, was found to be almost 50% lower in organic crops than conventionally-grown ones, said the team.
The question of whether organically grown foods offer any nutritional benefit has been hotly debated for decades – with a plethora of research suggesting that organic food has no nutritional benefit over foods and crops grown using conventional methods.
The review and analysis directly contradict those of a 2009 UK Food Standards Agency (FSA) commissioned study which found there were no substantial differences or significant nutritional benefits from organic food.
“The main difference between the two studies is time,” explained Leifert. “Research in this area has been slow to take off the ground and we have far more data available to us now than five years ago”.
"The much larger evidence base available in this synthesis allowed us to use more appropriate statistical methods to draw more definitive conclusions regarding the differences between organic and conventional crops,” added Dr Gavin Stewart – a co-author of the study.
But commenting on the new analysis, Professor Tom Sanders of King’s College London warned that the current meta-analysis is misleading “because it refers to antioxidants in plants as if they were a class of essential nutrients, which they are not.”
“The compounds referred to are mainly plant phenolics and are produced in higher quantities when plants are environmentally stressed,” he said.
“The article shows differences in cadmium concentrations in cereals but not in fruit and vegetables. Cadmium levels are dependent on the soil in which the plant is grown and have nothing to do with organic certification.”
Richard Mithen, leader of the food and health programme at the Institute of Food Research (IFR) in the UK noted that while the research provides evidence that organic production could lead to increases in certain phenolic compounds in some fruits and vegetables, it also reports a decrease in protein, nitrates and fibre in the organically grown crops, “which may be undesirable, and which are maybe unsurprisingly not referred to by the authors in their advocacy of organically grown produce.”
“Of greater significance is that there is no evidence provided that the relatively modest differences in the levels of some of these compounds would have any consequences (good or bad) on public health,” he added. “The references to ‘antioxidants’ and ‘antioxidant activity’, and various ‘antioxidant’ assays would suggest a poor knowledge of the current understanding within the nutrition community of how fruit and vegetables may maintain and improve health.”
The study, funded jointly by the European Framework 6 programme and the Sheepdrove Trust, found that concentrations of antioxidants such as polyphenolics were between 18-69% higher in organically-grown crops.
Substantially lower concentrations of a range of the toxic heavy metal cadmium were also detected in organic crops (on average 48% lower).
Leifert and his colleagues also reported that nitrogen concentrations were found to be significantly lower in organic crops, with total nitrogen, nitrate and nitrite concentrasions, 10%, 30% and 87% respectively lower in organic compared to conventional crops.
Pesticide residues were also four times more likely to be found in conventional crops than organic ones, they said.
“Our results are highly relevant and significant and will help both scientists and consumers sort through the often conflicting information currently available on the nutrient density of organic and conventional plant-based foods,” commented study co-author Professor Charles Benbrook of Washington State University
“The organic vs non-organic debate has rumbled on for decades now but the evidence from this study is overwhelming – that organic food is high in antioxidants and lower in toxic metals and pesticides,” concluded Leifert.
The authors added that they welcome a continued public and scientific debate on the subject – noting that the entire database generated and used for this analysis is freely available on the Newcastle University website for the benefit of other experts and interested members of the public.
Source: British Journal of Nutrition
Published online ahead of print, doi:
“Higher antioxidant concentrations and less cadmium and pesticide residues in organically-grown crops: a systematic literature review and meta-analyses.”
Authors: Baranski, M. et al