This past week has been hard on ordinary mortals as we watched some of the most toned bodies on Earth doing the most extraordinary things at the Olympics. It's enough to make the rest of us give up. But it shouldn't. There's something they're doing that we can all do: exercise. Throw out the pills, books, supplements and other nonsense the diet industry has convinced you to spend big money on. The beautiful body science jury is ready to bring down its verdict and the key words are: physical activity. While those in medical and nutrition circles like to blame McDonald's for the worldwide waistline explosion, more research is pointing to a drop in physical activity as the main reason that obesity rates are climbing. Sure, people who don't exercise are asking for trouble if they eat thousands of fast-food calories. And if you lie in front of the TV all day, then you do need to starve because only starvation energy levels are required to keep you going. But starving yourself means missing out on important components of your diet - vitamins C, A, all the B group, iron, calcium and fibre, to name a few. So, you end up paying big dollars for vitamin and mineral supplements and may also end up overdosing on them. Worse still, studies into what the obesity experts call 'cyclers' - people obsessed with dieting who gorge themselves in between - find they end up with worse bodies than they started with. 'Cyclers' simply recycle their fat, according to a number of reports published in this month's International Journal of Obesity, resulting in classic apple figures - big balls of fat on thin legs. The 'apple' figure is the one associated with all the serious complications of obesity - diabetes, heart disease and high blood pressure. This is one apple that doesn't keep the doctor away. The value of exercise isn't just based on the problems with diets and dieters. The most recent information added to the exercise or diet debate comes from Australia, where a team of researchers, collaborating with a team of muscle experts in Copenhagen, have found that a protein called Interleukin 2, which is produced by muscle cells during exercise, is a fat burner. Testing this protein, which I'll call IL2, on obese people intravenously, the rate of fat-burning increased. So, all you couch potatoes are asking, surely they can put this stuff in a pill and we can keep participating in the Olympics the only way we want to - from our couches? Bad luck, guys. Just like leptin, that other great hope for sweat-free creation of the perfect figure, the researchers say our clever, if annoying, bodies will adapt to chronically raised levels of IL2 and start ignoring its effects. There's plenty of evidence, though, that if the level of IL2 is raised along with the pulse, it will work as a fat burner. So, if you climb the stairs in your apartment block, go for a brisk half-hour walk each day or kick a ball with the kids, your metabolism is going in the right direction.