the nutritionist Gayl Canfield plucked off the shelf a can of Pam, the spray-on 'fat-free' cooking oil. The 'fat-free' serving, it turned out - according to the label - was a one-third-of-a-second spray. Anything more was hugely high in calories.

At the fat-free dairy, Canfield took out a fruit-flavoured yogurt and looked at the label. "Excuse me, 'fat-free?'," she said, pointing out the elevated calories in the fruity yoghurt. "When they add fruit, they add tons of sugar, which multiplies your calories. Add your own fruit to natural yoghurt."

The eternal vigilance at Pritikin about food is also applied to exercise, which is crucial to the reduction of hunger. "Research shows that most of the people who burn up 500 calories in exercise, don't eat more calories than they burn off," resident nutritionist Jay Kenny said.

Although any exercise is good, for the maximum weight loss and health benefits Pritikin preaches an exercise gospel of 45-90 minutes six times a week.

By 10am at Pritikin, the exercise regime is

over; by then, having risen for breakfast in the moonlight at 6.30, the clients have stretched, run for three-quarters of an hour in the gym, and been dispatched to lift weights, work their core, develop their flexibility and manage their stress in yoga, or, if they wish, get an extra aerobic workout in the amoeba shaped pool.

The rest of the day is given over to a combination of educational lectures, voluntary exercise (spinning classes, salsa dancing among them), and whatever leisure pursuits capture the imagination. (Some play tennis on the nearby courts; others prefer shopping at the local mall; some sit around until Happy Hour schmoozing in the mahogany-lined main room.)

Many of the guests are returning clients who enjoy the rigour of the Pritikin lifestyle or recidivists who merely want to lose a few pounds so they can go back to their old bad habits; some, like Anne Sanan of Tampa, Florida, who was accompanying her unwell husband for three weeks, most definitely did not get the Pritikin religion.