The excercise myth
The idea that the best way to lose weight and get fit is to run a couple of kilometres a day is simply wrong. If you see a group of overweight men and women jogging or doing a vigorous aerobics class, panting, sweating and straining, they are kidding themselves. They are doing nothing to burn their fat, and are probably cannibalising their muscles. The irony is that their over-vigorous exercise may be worsening their fat to muscle ratio.
High intensity aerobic exercise that causes a rapid pulse, fast breathing and lots of sweating may make you fitter, but is not an effective way to build up your muscles and shed fat. Rather than burning fat, this kind of exercise uses the energy that is most quickly and easily available to your body – the glucose stored as glycogen in your muscles and liver. If the glycogen runs out, the next quickest and easiest source of glucose is your muscles. It makes little use of your stores of fat.
To burn the fat stored around your body, your aerobic exercise should be at a moderate level, and of long duration. The secret is that your breathing should be deep and controlled, with no sense that you are out of breath. Fat needs plenty of oxygen to burn.
When you start to exercise, your body first uses the energy stored as glycogen. However, after about 30 minutes of sustained but comfortable exercise, your body makes an important switch. Instead of burning mostly glycogen, it starts to burn more and more stored fat. After 30 minutes, more than half the energy you are using comes from your fat! If you exercise at least three times a week, an even higher proportion of fat is used.
A fat-breaking enzyme called hormone sensitive lipase is released after half an hour of exercise, with significant amounts available after an hour of continued exercise with deep comfortable breathing. This enzyme remains active for up to 12 hours. The longer you exercise at this sustained, moderate level, the more the enzyme is activated. It has a long lasting and direct effect on breaking down the fat in your body. It also cleans your blood vessel walls of fatty plaque and deposits.
Oxygen is one of the keys to using fat. Fat, at 9 calories per gram, contains more than twice the energy of glycogen (4 calories per gram). Fat, being calorie dense, needs plenty of oxygen to burn. If you breathe deeply and sufficiently while doing aerobic exercise, you can burn fat. However, as you exercise harder, less oxygen is available in your body. If you exercise at a rate where you become short of breath, your body will be forced to get its glucose energy from easier sources - your stored glycogen, or next, the protein in your muscles.
If you are unfit and overweight, the best exercise to shed fat and get back into shape is sustained walking. Active housework, swimming, gardening, or other non-exhausting activity is also suitable. Keep it to a level you can sustain, but not to the point where you are out of breath or over-exerting.
After age 40, adults lose 100-150 grams of muscle a year and gain that much body fat, a condition known as sarcopenia. People who do not exercise lose their muscle bulk, and develop a pudgy, flabby ‘old person’ look. A diet with insufficient protein can also lead to muscle loss. These people have a high fat / muscle ratio, slow metabolism, and a distorted sense of hunger, making them want to eat more than they need.
Even if you do not look fat, you can still have a high fat to muscle ratio. Some thin people – particularly women who have been sporadically dieting - have lost a lot of their muscle. Their high fat to muscle ratio makes it easy to put on weight again, and accelerates their ageing.
Muscles need glucose and burn calories, even when they are resting. However, fat has a very low rate of metabolic activity – it uses almost no energy. So as fat replaces muscle you get into a vicious circle where your metabolic rate falls and you burn even fewer calories. While eating exactly the same amount of food, and doing the same amount of exercise, you will put on more and more fat. As your bodyweight shifts from muscle to fat, it becomes much harder to lose that weight.
Your bathroom scales will not tell you that you are losing muscle and gaining fat. Fat weighs little compared to muscle, so at first you will not gain much weight. For a fifty-year-old person, a four-kilogram weight gain over ten years is a lot worse than it sounds. This person is likely to have lost two kilograms of muscle and gained six kilograms of fat.
Conversely, when you start to build up your muscles again, and lose fat, you will initially put on weight. Your bathroom scales are misleading. You will look taught, trim and fantastic, and will feel better than you have for years. But your new muscle bulk will at first add to your weight!
Copyright © David Niven Miller 2003
Excerpts from Grow Youthful
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