Prof. Carlo Leifert (Professor of Ecological Farming) at Newcastle University's Nafferton Ecological Farm in Northumberland
Landmark research led by Newcastle University shows that there really are differences between organic and non-organic produce.
A new scientific paper published in the British Journal of Nutrition shows that there are significant differences in the nutritional composition and quality of organic and non-organic crops, such as vegetables, fruit and cereals.
The most striking differences revealed in the study are: higher concentrations of antioxidants, lower levels of cadmium, nitrate and nitrite, and less frequent presence of pesticide residues in organic crops compared with non-organic.
The study is the most up-to-date analysis of the nutrient content in organic compared to conventionally produced foods, taking in the results of many more studies than previous analyses. The findings are the result of a groundbreaking new systematic literature review and meta-analysis by an international team of scientists led by Professor Carlo Leifert at Newcastle University.
This study contrasts markedly with some previous studies, in particular with the findings of a 2009 UK Food Standards Agency (FSA)-commissioned study (Dangour et al. Am. J. Clin Nutr. 90, 680-685). The new analysis of organic crops is based on 343 peer-reviewed publications solely focusing on organic crops, fruit and vegetables, whereas the FSA-commissioned study based its conclusions on just 46 publications covering crops, meat and dairy. With more than half of the publications included in the new analysis published since 2006 (and therefore not available to the FSA-commissioned researchers and other earlier studies), this review is a landmark in the advancement of our knowledge of the subject.
While people should still eat their five-a-day of fruit and vegetables, this study demonstrates that choosing food produced according to organic standards can lead to increased intake of antioxidants without increased calorie intake. With greater nutrient and antioxidant density, every mouthful of fruit and vegetables produced organically can count for more. This constitutes an important addition to the information currently available to consumers.
Farming method matters
The analysis indicates that the quality of food is strongly influenced by the way it is produced, and that organic farming methods lead to increased levels of nutritionally desirable compounds and reduced concentrations of undesirable ones. In particular, there is increasing evidence that higher levels of manufactured chemical fertilisers, most notably the nitrogen-and phosphate-based fertilisers that are prohibited or heavily restricted by organic farming standards, lead to substantially lower concentrations of antioxidants in conventional crops.
Organic farming prohibits the use of synthetic chemical pesticides, and promotes the use of balanced crop nutrition, crop rotation and mechanical, biological and cultural methods for weed, pest and disease control. This explained the very low incidence of pesticide contamination in organic compared to conventional crops found in the study, and demonstrated that organic food consumption is an efficient way to reduce dietary pesticide exposure.
Organic crops and crop-based food products were found to have significantly higher concentrations of antioxidants, including phenolic acids, flavanones, stilbenes, flavones, flavonols and anthocyanines, compared with their conventionally produced counterparts. The mean percentage difference for most antioxidant compounds was between plus 18 and 69 per cent. Smaller, but still statistically significant, composition differences were also detected for a number of carotenoids and vitamins.
A switch to eating organic fruit, vegetable and cereals, and food made from them, would lead to a 20 to 40 per cent increase in crop-based antioxidant consumption without any increase in calories. This is important as there is strong scientific evidence of the health benefits of increased consumption of (poly)phenolics and other plant secondary metabolites with antioxidant activity, most notably protection against chronic diseases, including cardiovascular and neurodegenerative diseases and some cancers.
Less toxic metals
Substantially lower concentrations of a range of toxic heavy metals were detected in organic crops, particularly cadmium, which was almost 50 per cent lower. Cadmium, along with lead and mercury, are the only toxic metal contaminants for which the European Commission has set maximum permitted contamination levels in food. Since it is known to accumulate in the body, especially the liver and kidneys, any reduction in cadmium consumption can only be positive.
Nitrogen concentrations were also found to be significantly lower in organic crops. Concentrations of total nitrogen in organic crops were 10 per cent lower, while nitrate was 30 per cent and nitrite 87 per cent lower compared with non-organic crops. The higher nitrate and nitrite concentrations of non-organic crops are believed to be linked to the use of mineral nitrogen fertiliser, which is strictly banned under organic farming standards. Also, the higher nitrite concentrations in non-organic crops can be considered nutritionally undesirable, as nitrite has been described as potential risk factors for stomach cancer and other conditions.
Less pesticide residue
Pesticides featured in the study too. The frequency of occurrence of detectable pesticide was found to be four times higher in non-organic crops. The greatest difference was detected in fruit with the frequency of pesticide residues being about seven times higher than in organic fruit. In non-organic vegetables and crop-based processed foods the frequency of pesticide residues was three to four times higher than in organic.
Knowing that organic foods contain lower levels of pesticides is already a key factor motivating some consumers to choose organic foods, so this additional evidence is useful for consumer choice.
While further studies are needed to clarify the health benefits of reducing pesticide exposure, any reduction can be considered desirable, especially since we know that a significant proportion of non-organic crop samples regulated by the European Food Safety Authority (EFSA) contain pesticide residues above permitted levels. For example, in recent EFSA surveys pesticide residues above the Maximum Residue Levels (MRL) were found in 6.2 per cent of spinach, 3.8 per cent of oats, 3 per cent of orange, 2.9 per cent of strawberry and lettuce, and 2.7 per cent of apple samples. The fact that pesticides are found twice as frequently in non-organic fruit than in non-organic vegetables is also significant and may point to greater use of persistent chemicals and/or pesticides being applied closer to harvest time in fruit crops.
More studies needed
This study identified serious deficiencies in a large proportion of previously published studies. These include a lack of standardised measurements and reporting, and evidence of duplicative or selective reporting of data collected in experiments. The statistical methods used in the Newcastle University study were an advance over previous research syntheses that did not balance out the contribution of larger studies versus smaller ones. As well as having less evidence and not accounting for the amount of information, earlier syntheses used less reliable methodologies and inclusion criteria, and some included results from the same experiment multiple times.
Talking about the research, Professor Leifert said: “The organic versus 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. But this study should just be a starting point. We have shown without doubt there are composition differences between organic and conventional crops, now there is an urgent need to carry out well-controlled human dietary intervention and cohort studies specifically designed to identify and quantify the health impacts of switching to organic food.”