Gavin Stewart, one of the authors on the Leifert study has written a full explanation to clarify why the three studies (the others being Dangour, 2009 and Smith Spangler, 2012) differ in their conlcusions. Dangour, he says, employed a flawed methodology and "confused no evidence of effect with evidence of no effect". The conclusion of Smith Spangler, he says, was influenced by a difference in focus which lead them to look at individual antioxidants rather than pooling them as one. This meant they missed the large cumulative effect on health eating organics could produce, says Stewart.
This report offers a little bit for everyone. Those who already believed organic food is better for them have issued an immediate "I told you so". For those who see it differently there is plenty of uncertainty around what these results actually mean for human health. And for those who don't care, there's always the spectacle of a slightly undignified academic brawl.
I don't know how much heathier you will be if you eat organic food. Along with (for the most part I think) the authors of this report. The study has identified striking differences between organic and conventional farming produce. Antioxidant levels are higher. Pesticide occurance is reduced. Particularly stark is the result on cadmium, which is 48% lower in organic food. In so far as our knowledge of how these agricultural techniques affect what we put into our bodies. the study is of great value.
There are plenty of environmental, humane and social reasons to consider eating organic food. But many people intuitively believe organic food must be healthier. Partly, I think, because they adhere to a certain set of bucolic values people have about food and partly because it sounds right that spraying your food with poison can't be good for you. These feelings drive consumer choice and they may one day be proved correct by science.
But intuition should not be confused with empirical evidence. Drawing conclusions about human health from this study is impossible. We don't know what effect the cadmium in conventional food has, although the FSA assures us it is safe. Antioxidants are a mixed bag. What is needed is a study linking the consumption of organic food with long term health benefits. Until we have that, I'll stay on the fence, eating an apple (organic, just to be sure).
Updated at 8.15pm BST
This new study diverges dramatically from the conclusions of its 2009 predecessor, which was until now the largest of its kind. The authors of the previous work concluded:
"There is no evidence of a difference in nutrient quality between organically and conventionally produced foodstuffs. The small differences in nutrient content detected are biologically plausible and mostly relate to differences in production methods."
Another study, this time by researchers at Standford University in 2012, found:
"The published literature lacks strong evidence that organic foods are significantly more nutritious than conventional foods. Consumption of organic foods may reduce exposure to pesticide residues and antibiotic-resistant bacteria."
Updated at 7.23pm BST
What does the study actually say?
On antioxidants: "It is important to point out that there is still a lack of knowledge about the potential human health impacts of increasing antioxidant/(poly)phenolic intake levels and switching to organic food consumption."
On cadmium: "The exact health benefits associated with reducing Cd intake levels via a switch to organic food consumption are difficult to estimate."
On pesticides: "Potential health benefits associated with reducing pesticide exposure via a switch to organic food consumption are impossible to estimate." Although "complex mixtures of pesticides, as additive synergistic effects of pesticide mixtures have been documented and safety testing of pesticide mixtures is currently not required as part of the regulatory pesticide approval process."
On proteins: "The nutritional significance/relevance of slightly lower protein and amino acid concentrations in organic crops to human health is likely to be low."
On nitrites and nitrates: "The higher NO2 [nitrite] concentrations in conventional crops/crop-based foods are nutritionally undesirable… there is still controversy about the potential health impacts of crop-based dietary NO3 intake."
In summary, we don't know much about the significance of this report for human health.
Study team rounds on critics
Carlo Leifert, who lead on the study, has issued a fierce rebuke to the critics of his work, accusing them of impartiality and vested interest.
"I do not think they have read our paper properly before launching their criticisms and their criticism seems to me based on “accusing us of making statement in the paper that we in fact did NOT make” and then taking issues with them.
"I suspect, but obviously I do not know their real motivations, based on their very unbalanced criticism that both Prof. Sanders and Dr Dangour simply do not want to admit that the conclusion of their analyses were wrong."
Other key points:
- "Prof Saunders claims that we only found differences for cereals. This is in fact wrong. For fruit we had only 4 data-sets/comparisons available and could only carry out an unweighted meta-analysis and still detected a trent towards significantly higher Cd concentrations in fruit, but clearly to confirm that there are differences for Cd in fruit additional studies are required."
- "Prof Sauders claims that “Cadmium levels are dependent on the soil and have nothing to do with organic certification”. This shows his ignorance of what is going on in agriculture. If you follow his soils claim through, than to explain our results on Cd he thinks organic farms are, for some magical reason, based in regions with soils naturally low in Cd, while conventional ones are located on soils with high Cd soils”, that is complete utter non-sense."
- On antioxidants: "This does not mean there is no evidence, but only that there is not yet enough for health claims! There is a growing body of evidence that many of the antioxidants that we found significant differences for were shown to be linked to positive health indicators/impacts."
- "We do not claim that both reduced “nitrate and nitrite in organic vegetables would be beneficial to health” because we agree with him that for nitrate the evidence on whether it has beneficial or deleterious effects is controversial, and it will probably turn out that it can have both."
Updated at 6.42pm BST
What are antioxidants?
The body is under constant attack from free radicals (which always sounded like the name of a 90s soft rock band to me, turns out I was almost right) which strip electrons from the body's own molecules.
"This electron theft can radically alter the “loser’s” structure or function. Free radical damage can change the instructions coded in a strand of DNA. It can make a circulating low-density lipoprotein (LDL, sometimes called bad cholesterol) molecule more likely to get trapped in an artery wall. Or it can alter a cell’s membrane, changing the flow of what enters the cell and what leaves it."
An antioxidant is any substance that gives up electrons to these free radicals without harming the body, acting as a firewall against the attack. Harvard again:
"There are hundreds, probably thousands, of different substances that can act as antioxidants… Some substances that act as antioxidants in one situation may be prooxidants—electron grabbers—in a different chemical milieu. Another big misconception is that antioxidants are interchangeable. They aren’t. Each one has unique chemical behaviors and biological properties… This means that no single substance can do the work of the whole crowd."
The website says there is little evidence that supplementing your diet with "vitamin C, vitamin E, beta-carotene, or other single antioxidants provides substantial protection against heart disease, cancer, or other chronic conditions. The results of the largest such trials have been mostly negative". And that a few studies have even shown they can be harmful.
A spokesperson from the UK Food Standards Agency said the levels of cadmium and other harmful chemicals in food are strictly controlled and there is little reason to think a further reduction in these levels comes with a health benefit.
“Many factors can influence the level of cadmium and nitrates in foods, such as the chemistry of the soil or the climate, and so levels can vary considerably. Maximum limits have been set for cadmium and nitrates in some foods by the EU and these apply whether food is conventionally produced or organic.
"EU maximum limits are set at levels which are as low as reasonably achievable by following good agricultural, fishery and manufacturing practices. The permitted levels take into account the risk related to the consumption of the food. The FSA considers that they are sufficiently protective of the heath of the general population (and vulnerable groups such as infants and young children) on the basis of the current scientific evidence. This evidence is kept under review."
Response from study lead author
Cadmium variation usually results from soil variation:
"We are pretty certain that soil type is averaged out over the many studies [we analysed]."
Higher cadmium levels in conventional crops are still within safe legal limits:
"But cadmium accumulates in the body – you really want to avoid eating it if possible."
Pesticides levels is conventional foods are also beneath maximum recomended levels:
"But there are some conventional crops that do exceed levels (eg 6% of spinach – see paper for more examples). If you want to avoid that it would be helpful to eat food with a lower chance of pesticides. until they start testing combinations of pesticide I am not confident in the regulatory testing regime."
There were many "poor quality" studies included in the analysis:
"If you exclude lots of studies you can be accused of bias. If you include lots, you get accused of including bad studies. We have done a lot of sensitivity analysis for example if you exclude the studies with low levels of replication – about the bottom 20% – that doesn't really change the result."
Will eating a broad organic diet have long term health effects?
"We don't know if eating organic food would give a healthy life.
"If you feel you want to have higher antioxidant intake maybe you should consider eating organic food and if you want to avoid increasing intake of cadmium and pesticide this is a way to do it."
He said those long term, broad diet studies have not been conducted. Although he said studies showing links between high-antioxidant foods (red wine, coffee etc) do show health benefits.
Are increases in antioxidants seen in the data big enough to help health?
"We don't know but it is in the range we would expect to see effects."
The study underplayed the evidence for lower protein in organic cereals:
"We probably eat too much protein in the west anyway though the issue would be more significant for vegetarians."
Updated at 6.05pm BST
Large studies have repeatedly shown that, with the possible exception of vitamin D, antioxidant supplements have negligible positive effect on healthy people, at least in terms of important things such as preventing people getting cancer or dying prematurely. And some supplements – notably vitamins A, E and beta-carotene – even seem to slightly raise the risk of disease and early death.
So said Henry Scowcroft from Cancer Research UK in an article in the Guardian last year.
The Guardian, 16 February, 1960: "Organic experts had been commenting on the continuous rise in the numbers of deaths due to degenerative diseases and clamouring to know if there was a connection between this and the increasing use of artificial techniques in agriculture and food processing."
This spat has been going for a while then… click here to read the full article.
Updated at 4.38pm BST
More scientific reaction
Alan Dangour, who conducted a similar 2009 study for the FSA said that the quality of some of the data included in the study was poor. He questioned if the authors had substituted accuracy for scope.
“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."
He said the public health signicance was "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."
Catherine Collins, principal dietitian at St George’s Hospital NHS Trust, said:
“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.”
There has been a fairly hostile response from the academic community to this study.
The researchers failed to mention some less desirable findings from the study, says Richard Mithen, leader of the Food and Health Programme at the Institute of Food Research (IFR).
“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."
He suggested that the greater damage organic crops are exposed to from pests makes them produce more phenolic compounds (antioxidants) as part of their natural defence system.
“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."
“This article is misleading because it refers to antioxidants in plants as if they were a class of essential nutrients, which they are not," says Tom Sanders, head of nutrition at King's College London.
"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 suggests 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."
He said that polyphenols could actually inhibit the absorbtion of vital nutrients such as iron and zinc. And that cadmium quantity was dependent on soil type and couldn't be affected by organic farming processes.
“This study provides no evidence to change my views that there are no meaningful nutritional differences between conventional produced and organic crops.”
Updated at 3.55pm BST
The effects of cadmium, one of the heavy metals found to be higher in conventional cereals than organic cereals, on human health are well documented.
A study in 2008 concluded that cadmium "is one of the most toxic elements to which man [presumably also woman] can be exposed at work or in the environment. Once absorbed, Cd is efficiently retained in the human body, in which it accumulates throughout life. Cd is primarily toxic to the kidney". The article goes on to list many other horrible effects that the chemical can have on the human body where it persists and collects for up to 30 years.
Cadmium, nitrates and nitrites are controlled by food safety standards. To which conventional foods also have to adhere. According to the European Food Safety Authority (EFSA) cadmium is not absorbed readily by the human body (3-5%) when consumed in food or liquids. There is also conjecture over whether nitrates and nitrites are in fact unhealthy.
Damian Carrington writes that "the researchers argue that cadmium accumulates over time in the human body and that some people may wish to avoid this, and that pesticide limits are set individually, not for the cocktail of chemicals used on crops."
Updated at 3.45pm BST
What is organic food?
It seems obvious, but actually organic food is a tough thing to define. It essentially amounts to a labelling system that allows consumers to preference certain farming practices. The rules governing what can be considered organic differ from country to country.
Here is the Soil Association's take:
Our definition of organic farming recognises the direct connection between our health and how the food we eat is produced. Artificial fertilisers are banned and farmers develop fertile soil by rotating crops and using compost, manure and clover.
Strict regulations, known as ‘standards’, define what organic farmers can and cannot do – and place a strong emphasis on the protection of wildlife and the environment.
For foods to be labelled as organic [in the EU], at least 95% of the ingredients must come from organically produced plants and animals.
Updated at 3.35pm BST
Summary of report
- The most up-to-date analysis of the nutrient content in organic compared to conventionally produced foods.
- Based on 343 peer-reviewed publications solely focusing on organic crops, fruit and vegetables.
- Sought to identify and quantify compositional differences between organic and conventional crops (primarily cereals, vegetables and fruit) and crop-based products (e.g. seed oils, wine and baby food) based on a systematic review of all the available literature and data.
- 50% of the publications reviewed were published after 2006.
- Earlier benchmark 2009 UK Food Standards Agency (FSA) study based its conclusions on just 46 publications covering crops, meat and dairy.
Differences revealed in the study are:
- Higher concentrations of antioxidants,
- Lower levels of cadmium, nitrate and nitrite,
- Less frequent presence of pesticide residues in organic crops compared with non-organic.
The study authors say:
"While people should not eat less fruit or 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."
Welcome to the eco audit
Switching to organic foods could be equivalent to eating one or two extra portions of the recommended "five vegetables a day", say the team responsible for the most comprehensive study of organics to date.
The international scientific team behind the new work… say the increased levels of antioxidants is equivalent to "one to two of the five portions of fruits and vegetables recommended to be consumed daily and would therefore be significant and meaningful in terms of human nutrition, if information linking these [compounds] to the health benefits associated with increased fruit, vegetable and whole grain consumption is confirmed."
Consumption of antioxidants has been linked to better health. This, along with the revelation that levels of cadmium, which is poisonous to humans, were considerably lower in organic food, has lead organic advocates to claim the study vindicates their long held belief that organic food is better for you.
"The crucially important thing about this research is that it shatters the myth that how we farm does not affect the quality of the food we eat," said Helen Browning, chief executive of Soil Association, which campaigns for organic farming.
But questions have been raised over the study's methodology and assumptions. And whether it is possible to draw health conclusions from the results.
Tom Sanders, a professor of nutrition at King's College London, told Carrington: "the question is are they within natural variation? And are they nutritionally relevant? I am not convinced."
Join in today’s discussion by contributing in the comments below, tweet me or email me. If you are quoting figures or studies, please provide a link to the original source. Follow me on @karlmathiesen for updates throughout the day and later I will return with my own verdict.
Updated at 2.24pm BST
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