Why crash dieting often doesn't work

The latest dieting craze may seem attractive, but often these diets are only a set-up for failure or worse. Here's why.

• Skip the fad diets. They simply don't work, partly because they are usually too drastic to maintain for the rest of your life.
• Also, many of these diets lack sufficient scientific research to support their occasionally ridiculous claims. Even though you might seem to lose a lot of weight at the beginning of such diets, most of that weight loss is actually water loss; your body is burning up stored sugars that previously soaked up excess water. Then you reach the "plateau" phase, after which further weight loss is increasingly difficult — that's when most people become discouraged.
• One review of 31 studies shows clearly how often deliberate dieting fails in the long term. While the subjects lost weight in the first six months, within five years, two-thirds put on more weight than they had initially lost. The truth is that the human body has evolved to survive periods of reduced food intake by going into "starvation mode." This involves adjusting its metabolism — the rate at which it burns calories — to try to conserve energy. So, if you drastically reduce your calorie intake, your body will react by starting to burn fewer calories to keep your body's normal processes functioning. It learns to expect a lower food intake. As soon as your calorie intake increases, you are even more likely to gain weight until your body adjusts again — and that could take months.

• Even worse than one-off crash diets is the phenomenon known as "yo-yo" dieting, or weight cycling, in which people get trapped in a pattern of weight loss followed by weight gain, followed by further dieting to lose weight again.
• Typically, someone who is overzealous about losing weight quickly picks an extreme diet and — if they can stick to it for a while — is initially overjoyed at the amount of weight lost in a short time. But diets that deprive you of too much are impossible to follow for long, and they make you irritable, tired and depressed. They also intensify food cravings and encourage you to eat too much when you stop the diet. As a result, you feel like a failure — even though it was the fad diet that failed, not you.

• If you lose weight too quickly through crash dieting alone, the big danger is that you will lose muscle mass as well as body fat, particularly if you are not doing exercise.
• Since muscle burns far more calories than fat, losing muscle mass is bad news. When you stop dieting and start eating more, you will only gain fat unless you are exercising as well. So what crash dieting does is swap muscle for fat, increasing your fat-to-muscle ratio as well as slowing your metabolism, and causing weight gain in the long term.
• Studies show that crash dieting reduces levels of HDL (the "good" cholesterol), slows cardiac blood flow in post-menopausal women and actually increases your proportion of body fat.
• You are much more likely to lose weight permanently by making small, sustained changes to your eating habits.
• To ensure that you achieve steady gradual weight loss, it is best to combine healthier eating with more exercise. Most overweight or obese people should aim to lose between five and 10 per cent of their starting weight in the first three months of a weight-loss program. You should soon notice the positive effect on your health, particularly if you are already suffering from high blood pressure, diabetes or arthritis.