July 11, 2014

expert reaction to study comparing the nutritional content of organic and conventional foods

A meta-analysis published in the British Journal of Nutrition looked at 343 studies into compositional differences between organic and conventional crops, reporting differences including higher levels of certain anti-oxidants and lower levels of cadmium in organic crops. A before the headlines analysis accompanied this roundup.

Catherine Collins, Principal Dietitian at St George’s Hospital NHS Trust, said:

“Is organic food better for you than non-organic? That’s a question hotly debated for decades, and this large review of the evidence will be widely supported by the pro-organic lobby as evidence of a bigger ‘Health Halo’ with the organic cousins of the fruit and vegetable family compared to their non-organic equivalent.

“One of the key problems facing researchers in this field over the years is how to compare, well, apples and pears. Do you buy them at the supermarket and measure the difference in plant substances found in each type of produce at ‘point-of-sale? (so-called ‘basket studies’). Or do you choose two farms close to each other, one to grow organic and one to grow non-organic produce, and compare the two as picked? This removes the natural variation in soil richness as an influence of plant content. Or should you rely on formal experiments with sample crops? All these methods are valid but each generate very different answers depending on soil type, use of permitted plant additives to each type of produce, storage methods and time from farm to fork.

“That’s why in this large review the results show such a wide range of values for different plant substances. For example, the antioxidant chlorogenic acid was sometimes lower and sometimes higher in organic foods when compared to non-organic varieties. So what to do? As a dietitian I’d suggest forget the big ‘O’ title, and just enjoy your morning coffee or a juicy peach as a between meal snack as a rich source of this particular antioxidant, without the worry of how it was grown.

“The key plant substances that appeared higher in organic fruits and vegetables were some of the plant antioxidants. Polyphenol antioxidants such as flavanones and flavonols were higher in organic produce than non-organic versions, as were antioxidant anthocyanins. When you compare the price and availability of the organic version of foods rich in these antioxidants, paying double for organic didn’t provide you with double the antioxidant benefits – but it does reduce the amount of money left to spend on the rest of your diet.

“It’s also worth remembering that all of the massive national, European and international studies showing the significant health benefits of eating at least 5 portions of fruit and vegetables daily have never made a distinction between organic and non-organic varieties. When it comes to health insurance all fruits and vegetables count.  Bottom line?  Just eat more.”

Prof Richard Mithen, Leader of the Food and Health Programme at the Institute of Food Research (IFR), said:

“This paper provides some evidence that under organic agronomic regimes, there may be an increase in the concentration of certain phenolic compounds in some fruits and vegetables.  The paper 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.

“The increase in phenolic compounds may not be entirely unexpected due to the greater pest and pathogen damage that crops under organic systems are exposed to which can results in the induction of these toxic defence compounds.  Moreover, one can enhance the levels of phenolic compounds in crops through many different ‘organic’ or ‘conventional’ agronomic systems, or indeed through plant breeding and genetic modification, but this does not necessarily mean that the modes of production and the increases in these compounds are beneficial to health or the environment.

“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.  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 additional cost of organic vegetables to the consumer and the likely reduced consumption would easily offset any marginal increase in nutritional properties, even if they did occur, which I doubt.  To improve public health we need to encourage people to eat more fruit and vegetables, regardless of how they are produced.”

Prof Tom Sanders, Head of Diabetes and Nutritional Sciences Division, School of Medicine, King’s College London, said:

“This article 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. Plant phenolics have both toxic as well as potential beneficial effects. Some vitamins have anti-oxidant properties such as vitamin E, vitamin C and beta-carotene but the differences between organic and conventional produce are trivial.

“The article misleadingly suggest health benefits result from a high consumption of antioxidants particularly cancer protection.  While the World Cancer Research Foundation in its systematic reviews concluded there is a relationship between fruit and vegetable consumption and a lower risk of cancer, they did state that there was insufficient evidence to make any claim for antioxidants and plant phenolics.

“Polyphenols also have an adverse effect on metal absorption and are considered as anti-nutrients. For example their antioxidant properties inhibit iron and zinc absorption.

“The article also claims that the lower levels of nitrate and nitrite in organic vegetables would be beneficial to health. However, this is opposite to more recent research, including some carried out at the University of Newcastle, which shows that nitrate in vegetables in fact lowers blood pressure because it is converted to the vasodilator nitric oxide (1).

“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. There are naturally occurring areas (1,2) in the UK where cadmium levels of are high (e.g. Shipham in Somerset) and home-grown/organic food grown in these areas would therefore be high in cadmium.  Cadmium can be high in soils derived from spoil from former lead, zinc and tin mines. Generally, shellfish are regarded as far more important source of cadmium in the diet, especially if fished from areas where sediment is naturally high in Cadmium (ie. South Coast) or from smelting.

“In terms of macronutrients (i.e. protein, carbohydrate, fat) ­ the organic products contained less protein. Other nutrient differences were trivial and well inside the normal range of variation that occurs with different varieties, soil types and variations in weather.

“This study provides no evidence to change my views that there are no meaningful nutritional differences between conventional produced and organic crops.”

Refs:

1. Lidder S, Webb AJ. Vascular effects of dietary nitrate (as found in greenleafy vegetables and beetroot) via the nitrate-nitrite-nitric oxide pathway. Br JClin Pharmacol. 2013

Mar;75(3):677-96

2. Davies BE, Bailinger RC. Heavy metals in soils in north Somerset, England,with special reference to contamination from base metal mining in the Mendips Environ Geochem Health. 1990 Dec;12(4):291-300

3. Morgan H, Smart GA, Sherlock JC. The Shipham report. An investigation into cadmium contamination and its implications for human health. Intakes of metal.

Sci Total Environ. 1988 Aug 15;75(1):71-100.

Dr Alan Dangour, Reader in Food and Nutrition for Global Health at the London School of Hygiene & Tropical Medicine, said:

“Systematic reviews are powerful tools that are increasingly being used to help to resolve areas of controversy in science.  By bringing together all of the available evidence, critically assessing its quality, and synthesising the findings in a standardised and pre-specified manner, systematic reviews substantially reduce bias and enhance the reliability of the ‘answer’.

“The authors of this new systematic review that primarily aims to identify differences in nutrient content between organically and conventionally produced foods have brought together a large number of studies published over a 20 year period.  The quality of the available data varies greatly and it is therefore very surprising that, in their analysis, the authors decided to include all the data that they found, irrespective of their quality.  In fact the study authors themselves note that there are significant concerns with the consistency and reliability of some of their findings.  Mixing good quality data with bad quality data in this way is highly problematic and significantly weakens confidence in the findings of the current analysis.  It is a shame that greater care was not taken in trying to ensure that the analyses were based only on reliable and scientifically robust data from satisfactory quality studies.

“Furthermore, the public health significance of the reported findings have been worryingly overstated.  There is no good evidence to suggest that slightly greater antioxidant or polyphenolic intake in the human diet has important public health benefits, and there is no robust evidence to support the claim that consumption of greater amounts of these compounds reduces the risk of chronic diseases such as cardiovascular disease and cancer in human populations.

“All natural products vary in their composition for a wide variety of reasons.  This paper provides no convincing evidence to refute our earlier finding¹, fully supported by a recent US-led systematic review², that there are no important differences in nutrient content between organically and conventionally produced foods.”

Refs:
(1) Dangour AD, Dodhia SK, Hayter A et al. (2009) Nutritional quality of organic foods: a systematic review. American Journal of Clinical Medicine, 90, 680-685.
(2) Smith-Spangler C, Brandeau ML, Hunter GE et al. (2012) Are organic foods safer or healthier than conventional alternatives? A systematic review.  Annals of Internal Medicine, 157, 348-366.

‘Higher antioxidant concentrations and less cadmium and pesticide residues in organically grown crops: a systematic literature review and meta-analyses’ by Carlo Leifert et al. published in the British Journal of Nutrition on Tuesday 15th July 2014.

Declared interests

Dr Dangour was project lead and lead author of the systematic reviews on the nutritional quality (2009) and nutrition-related health benefits (2010) for the Food Standards Agency.  He is also an expert reviewer for the Department of Health and Public Health England.