weight.

One of the crucial problems in dieting is that many of the calorie-dense foods which we eat (peanuts, potato chips, bread, biscuits and most fatty, greasy and oily things) don't provide enough satiety per calorie; so, to feel full you have to eat more. (An extra 100 calories a day is 10lb a year.) Eight ounces of peanuts, for instance, is 1,400 calories; a pound of strawberries is 300 calories. Many potentially healthy options become calorie-dense by what we put on them. For instance, a potato, which is only 80-90 calories and has great satiety value, doubles in calories if you add just two teaspoons of butter and skyrockets to 600 with sour cream on it.

Pritikin's strategy is to fill up on lowest calorie density food first; to dilute calorie-dense foods with calorifically light ones; and to favour water-rich foods ('eat your water') which are filling but not fattening. For instance, fresh fruit, which is rich in water, is 300 calories a pound; dried fruit is 1,300 calories.

Pritikin is against the dieting mentality; instead of skipping meals or going hungry, it tries to establish healthy eating habits. To this end, Pritikin counsels the following: avoid processed foods, don't drink your calories (27 per cent of an average American diet of 2,000 calories is taken in drink; fruit juices and alcohol are calorie-dense), eat four servings of fruit and five servings of vegetables each day, limit poultry and wild game to one hand-sized serving a week; limit red meat to once a month. "After we stop growing we have a limited need for protein," said Kenny.

By eating fewer calorie-dense foods, the body fills up and, at the same time, takes in fewer and better calories. The Pritikin solution is to lose weight and be well-nourished at the same time. "If you're not putting the right fuel into your body, it's not going to run well," Jay Kenney said. "Diet is the single most significant determinant to how long you're going to live."

TOMORROW: LYING FOOD LABELS