Unless you drink two litres of water a day, your body won't be properly hydrated. People in the west consume far too much salt, increasing their risk of high blood pressure. Non-organic foods are covered in harmful pesticides. The incidence of obesity would be drastically reduced if only we stopped gorging on Big Macs.
Many people would regard all of the above claims as true. After all, they are repeated incessantly in the media, by health officials and in general conversation. They have become nuggets of wisdom that shape our understanding of the relationship between what we eat and the healthiness of our bodies. So they must be true, mustn't they?
Well, not according to the authors of a bold new book: Panic Nation: unpicking the myths we're told about food and health (John Blake). Edited by two biochemists, Stanley Feldman and Vincent Marks, it sets out to demonstrate that, when it comes to food, we are collectively the victims of an incredible amount of hogwash.
The basic problem, according to the authors, is that our society is in thrall to the "precautionary principle". Ours is a worse-case-scenario mentality whereby any small or medium-sized risk is converted into a portent of near-certain catastrophe. Relatively trivial dangers - such as the recent Sudan 1 scandal - are magnified out of all proportion. Food is a natural focus for scaremongering, since it is common to everyone. According to Feldman and Marks, this is why so many of us believe that the food we eat is killing us, even though life-expectancy is longer than at any time in human history.
It is hard not to concede that they have a point. The tone of the book may be trenchant, but the arguments are sensible and even-handed. The authors do not deny that the food we eat affects us, or that it is important to eat healthily. What they do say is that our ability to look rationally at the issues is hampered by the prevalence of all sorts of myths. The chapter on junk food is particularly thought-provoking. The term "junk food", it is suggested, is an oxymoron, since if a substance has nutritional value, then by definition it cannot be junk. Fat is fat, whether it comes from processed ground beef or from an Aberdeen Angus steak. Big Macs may not be good for you, but they are not outrageously unhealthy either: in fact, they contain roughly the same calories as a Safeway tomato, chicken and basil salad.
Fine, but does this matter? Is it really a problem if we exaggerate the danger of Big Macs? Well, Feldman and Marks would retort, it does matter, because it changes the way we view an issue such as obesity. At present, the responsibility for obesity is placed squarely at the door of a group of foods that we arbitrarily choose to label "junk". If these foods were banned, or at the very least taxed, then obesity would disappear. In fact, the issue is more complex. A number of factors cause obesity, among them exercise levels, metabolism and diet. Whether or not a person habitually visits McDonald's may not be all that important.
The book makes other provocative claims. Pesticides are not present in large enough quantities to be remotely dangerous. The virtues of organic food are largely mythical, as are the hazards of GM. And as for fluid intake, it seems that you can safely put that bottle of mineral water away. Of the two litres the average person requires daily, half is provided as an inevitable consequence of the food they eat, and the rest by two cups of coffee and a glass of beer.