You're fat because YOU EAT TOO MUCH. There isn't any other reason." These bracing (or shattering) words are from the Better Homes and Gardens Diet Book of 1955. Published before slimming became an industry worth £1 billion a year, and before diet gurus had to sell their books by flattering their public or blinding them with science, the editors felt no need to mince their words. Forty years on, however, the overweight can toy with dozens of excuses: slow metabolism or "big bones", food into l erance (as in the Nutron diet), enzyme deficiency (the pineapple-pushing Beverley Hills diet), digestive difficulties (the "don't mix starch and protein" Food Combining diet). So it's really not our own fault if we're plump rather than svelte. Or is it?
The Dunn Clinical Nutrition Centre, a medical research centre at Addenbrooke's Hospital in Cambridge, has been analysing the nation's diet for over 60 years. Nutritionists Dr Andrew Prentice and Dr Susan Jebb, both whippet-slender and bubbling with enthusiastic energy, have been investigating the failed slimmer's favourite cop-out: the notion that their metabolism is out of kilter. Discouraged dieters claim the rate at which they convert fuel into energy is sluggish, so that their body insists on layingfood down as fat, however little they eat.
Dr Prentice is in charge of the Calorimeters; three small neat boxlike rooms, each furnished with a bed, a desk, a phone and a television plus video. "We try to make it as comfortable as possible but it is in fact a scientific instrument," he says; sure enough, a fearsome array of tubing and piping leads from each one to a huge winking bank of computers.
In one of the rooms, a plumpish woman is puffing away on an exercise bike; nearby on a plate are carefully weighed (small) rations of fruit cake, ready for tea-time. Volunteers spend five days in the sealed Calorimeter. Fresh air is circulated through the room from the outside, sucked out again, and analysed for oxygen and carbon dioxide levels; from these, the subject's energy output and metabolic rate can be calculated.