Posted Sunday, June 29, 2003; 14:08BST
If we were to start from scratch, how would we design a diet to keep our weight under control? For starters, we could concentrate on diets geared for life rather than quick and easy weight loss. Over the years, we pick up a lot of bad eating habits, and it's tough to break them. "If you asked someone to get up and go to bed two hours earlier every day, they would have to completely change their lifestyles," says Coppack. "There's a lot of habit to break. You have to get them to pay attention to even the simple things, like the way they put food onto the plate." Second, we could stop paying such close attention to every jot and tittle in the diet debate. It will take decades for researchers to unravel all the reasons we eat what we do, and why we like to eat so much of it. But a few insights are emerging that should point us in the right direction, as long as we don't turn them into inviolable dietary laws. Not all carbohydrates seem to have been created equal. So-called simple carbohydrates, those found in white bread and cake, are so quickly digested by the body that they trigger a very rapid rise in the levels of glucose in the blood. The pancreas releases a massive amount of insulin to mop up the excess. Soon enough, however, blood- glucose levels plummet to the point where our brains may feel woozy, we become excessively hungry and are driven to eat again. Complex carbohydrates, on the other hand, particularly those rich in fiber, do not elicit the same kind of spike-and-crash response. Avoiding simple carbohydrates is part of the approach advocated by French diet guru Michel Montignac. The best-selling author of I Eat Therefore I Lose Weight concentrates not on the calorie content of food but its glycemic index. Researchers refer to the amount of glucose a single serving of a particular food releases in the bloodstream as its glycemic index. And there is growing evidence that we can manipulate it somewhat to control our hunger. Broccoli and peanuts, for example, have a low glycemic index, while instant rice and baked potatoes have an extremely high one. "The problem of calories is not quantitative," Montignac says, "but qualitative. It depends on the actual chemical composition of the food."

Dairy products and milk — which has been increasingly replaced by soft drinks in the diets of both children and adults — are also fast emerging as dietary "goods," despite the fact that a 0.35-L glass of skim milk has almost as many calories as a 0.35-L can of Coke. The reason may have to do with calcium, says Michael Zemel, professor of nutrition at the University of Tennessee. In the absence of calcium, levels of the hormone calcitriol increase. Among other things, calcitriol shuts off the mechanisms that break down fat and activates those that make it. Fats, too, are gaining new respect. Olives, nuts, avocados and other foods that are rich in mono- and polyunsaturated fat belong in our diets, many nutritionists believe. Not only do these good fats help lower the level of ldl, or bad, cholesterol, but they are also essential for the absorption of fat-soluble vitamins like E. So what's to be done? Crash diets are no good. Germans have long retreated to clinics for a "cure" that limits them to between 600 and 1,000 calories a day. A study found that during the fast people lost an average of 6.9 kg, but a year later weighed 0.9 kg more than they had done before the cure. At obesity clinics like the one run by Wilding, nutritionists recommend reducing fat intake from 40% to 30% of total calories, increasing mono-unsaturated fats like olive oil, and ensuring that a majority of carbohydrates come from fiber-rich sources like pulses, oats and rye bread. And we must get moving to use up more of those calories.

The question is whether the addition of new concepts like glycemic index can restore sanity to a collective eating binge that has spiraled out of control. And if not, then what can? An appetite suppressant that makes people eat less but has no side effects? A thermogenesis pill that one can take after overindulging in ice cream? Perhaps the future will bring better medications, at least for people who are morbidly obese. But for the broader population, the remedy must be sought elsewhere. And as we can't change the genes we are born with, we are left with one alternative — to change the environment that our genes have proved so ill equipped to handle. We, the species that invented barbecuing, domesticated corn and wheat and created foie gras and French fries, have powered through a series of food revolutions, says Oxford University historian Felipe Fernández-Armesto in his book, Food: a History. The purpose of the next revolution, he predicts, will be to undo the excesses of the last.

With reporting by David Bjerklie and Sora Song/New York, Dan Cray/Los Angeles, Alexandra Hartman/Paris, Elisabeth Kauffman/Nashville, Kate Noble/London, Ursula Sautter/Bonn and Steve Zwick/Cologne

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