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AMES IS NOT ALONE in his findings. A comprehensive review of some 400 scientific papers on the health impacts of organic foods, published by Faidon Magkos and colleagues in 2006 in the journal Critical Reviews in Food Science and Nutrition, concluded there was no evidence that eating organic food was healthier.

Even if it can't be proved that eating organic is healthier, advocates claim it is nutritionally superior. Some studies, especially those reported by the organic farming advocate group, the British Soil Association, show that organic produce has a higher content of vitamin C, minerals and anti-oxidants such as flavonols, polyphenols, lycopene and resveratrol.

However, some of the compounds present at higher levels in organic food are actually natural pesticides. According to Bruce Ames, a variety of insect-resistant celery had to be taken off the U.S. market in the late 1980s because its psoralen levels were eight times higher than normal and caused a rash in people who handled it. There was a similar story with a naturally pest-resistant potato variety that ended up being acutely toxic because of its high levels of solanine and chaconine – natural toxins that block nerve transmission and cause cancer in rats. Organic farmers who rely on 'naturally resistant' plant varieties may also be producing plants with high levels of 'natural' toxins. And in this case, 'natural' is not likely to mean better. Think of Abraham Lincoln's poor mother, who died after drinking the milk of a free-range cow that had grazed on a snakeroot plant.

Regardless of how it is grown, the nutritional content of fruit and vegetables is more likely to be affected by freshness or varietal differences. One study reported by Magkos tried to narrow things down by growing the same variety of plums in adjacent fields, with one using organic and the other conventional methods: the conventionally grown plums contained 38 per cent more of the potentially beneficial polyphenol compounds than the organically grown ones did.

The bottom line is that there is tremendous variation in the nutritional make-up of fruit and vegetables regardless of whether they were grown by organic or conventional means.

In fact, it is so difficult to support the claim that organic food is healthier that the Britain's Advertising Standards Authority has directed the British Soils Association – an organic foods advocacy group – to desist from making it.

IF CHEMICAL PESTICIDES ARE hazardous to health, then farm workers should be most affected. The results of a 13-year study of nearly 90,000 farmers and their families in Iowa and North Carolina — the Agricultural Health Study – suggests we really don't have much to worry about. These people were exposed to higher doses of agricultural chemicals because of their proximity to spraying, and 65 per cent of them had personally spent more than 10 years applying pesticides. If any group of people were going to show a link between pesticide use and cancer, it would be them. They didn't.

A preliminary report published in 2004 showed that, compared to the normal population, their rates of cancer were actually lower. And they did not show any increased rate of brain-damaging diseases like Parkinson's. There was one exception: prostate cancer. This seemed to be linked to farmers using a particular fungicide called methyl bromide, which is now in the process of being phased out. According to James Felton, of the Biosciences Directorate of the Lawrence Livermore National Laboratory in California, who also chairs the study, "The bottom line is the results are coming out surprisingly negative. It's telling us that most of the chemicals we use today are not causing cancer or other disease."

And as a flurry of papers cited in Faidon Magkos's review will attest, organic food has been subject to its own food scares. There have been bacterial outbreaks which have been blamed on the fact that organic production involves manure but not antibacterial techniques such as food irradiation or chemical washes. Another concern is the growth of moulds such as aflatoxin B1, commonly found on mouldy peanuts and one of the most carcinogenic compounds known to exist. Among the most notorious recent toxic mould scares was one linked to organic apple juice, where levels of the toxin patulin were 10 times greater than those found in regular apple juice. Levels of the mould toxin deoxynivalenol have also been reported to be higher in organic wheat. Because organics are not treated with fungicides, there is a higher risk of these toxins creeping in.

But as with anything to do with plants, the variations in the levels of these toxins is enormous, and contamination can be found in conventional as well as organic produce. Probably the only lesson to be learned from all this is that as far as human health is concerned, pesticide residues in fruit and vegetables are probably the least of our concerns.

Historically, most food-related diseases are due to bacterial and fungal contamination, so in terms of health consciousness, focussing on pesticides is probably barking up the wrong tree.

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