'Naturally Dangerous': Surprising Facts About Food Health and the Environment

Why natural may not equal healthy by John Krebs, Head of the Food Standards Agency and Department of Zoology, University of Oxford, United Kingdom.

This is a review of a new book by James P Collman of the title above. University Science Books, 19.99 / US$29. This review was published in the leading International Journal of Science, Nature 415:117. Visit www.nature.com for original article.

If you ask people what they fear about their food, typically the top half-dozen concerns are food poisoning, BSE, growth hormones used in animals, animal feed, pesticides and genetically modified (GM) food (http://www.food.gov.uk). But how do these perceived risks stack up with the estimates of deaths caused by food? Acknowledging that these are only approximate, and that great uncertainties surround some of the numbers, two food risks tower above the rest the dietary contributions to cardiovascular disease and to cancer. These risks, taking a fairly conservative estimate, probably account for more than 100,000 deaths per year in Britain. Food poisoning probably accounts for between 50 and 300 (similar in range of magnitude to the risk of choking to death on food or suffering a fatal accident while getting into or out of bed). As far as we know, growth hormones (banned in Europe) and pesticides in food, as well as GM food, are not responsible for any deaths.

A generally accepted psychological explanation for the discrepancy between perceived and actual risk is the one based on Paul Slovic's identification of the range of factors that make risks seem more frightening. Thus, for example, risks that are under someone else's control, potentially catastrophic and unfamiliar are perceived as greater than those with the opposite features. That is why most of us view riding our bicycle in a busy street as a more acceptable risk than living near a nuclear power station, although rational analysis says that you should stay off your bike.

James Collman writes about another important dimension of risk perception naturalness: "Many Americans are under the mistaken impression that if something is 'natural' it is safe." As far as food is concerned, Collman covers similar ground to that in Julian Morris and Roger Bate's Fearing Food (Butterworth-Heinemann, 1999) and Douglas Powell and William Leiss's Mad Cows and Mother's Milk (McGill-Queens University Press, 1997).

Perhaps one of the most telling arguments against the 'natural equals safe, man-made equals dangerous' view of foods is the one put forward by Bruce Ames and colleagues. Fundamental to the safety assessment of any potentially toxic substance is the maxim attributed to Paracelsus, that the effects on the body of any substance, good or bad, depend on the dose. Ames pointed out that if the same precautionary criteria that are used to set pesticide safety levels toxicological data, including tests on rodents for carcinogenicity were applied to the natural toxins in plants that have evolved to deter predators, many foods would be deemed unsafe. For example, potatoes, grilled food and peanuts would be banned if they underwent the same kind of scrutiny as pesticide residues.

According to Ames, half of the natural toxins that have been tested (most have not) are rodent carcinogens, and each year the average American consumes about 10,000 times more of these natural pesticides than of synthetic residues. A single cup of coffee contains natural carcinogens equal at least to a year's worth of carcinogenic synthetic residues in the diet. The organic sector has claimed that its produce is lower in synthetic residues (fewer pesticides are used) but higher in natural toxins. From Ames's line of argument, consumers of organic produce may well be trading a minute amount of synthetic residue for equally if not more dangerous natural pesticides. This should, of course, be kept in perspective: any potentially detrimental effect of natural pesticides or synthetic pesticide residues is far outweighed by the health benefits of consuming five portions of fruit and vegetables per day.

Collman's quirky and erratic account, more a series of vignettes than a narrative, makes an effective case for not accepting the simple equation 'natural = safe'. In addition to food, he covers herbal medicines, environmental pollution, global warming, electromagnetic radiation and radioactivity. I would have liked a slightly less triumphalist tone, in recognition that there are still many uncertainties in our understanding of both environmental and diet-related impacts on human health. For instance, the toxicological consequences of exposure to cocktails of residues and the potential effects of long-term exposure are not well documented. As new data emerge, the experts, quite correctly, sometimes change their minds about safety limits. This recently happened for dioxins, for which the safety level has been reduced by a factor of five.

When viewed from the perspective of scientific uncertainty, some of the fears about unknown consequences may seem less irrational. A challenge for those responsible for translating science into regulatory policy is to find an effective way of taking people's concerns into account without straying from the bedrock of scientific evidence. There are no easy answers, but a start may be for scientists both to explain the uncertainties more fully, and to emphasize that evidence is dynamic and evolving rather than a set of ineluctable facts.

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