According to a recent Which report, the last thing you should do if you want to lose weight is go on a crash diet. Dr Wynnie Chan explains why

With summer just around the corner, this is often the time we fall victim to fad diets. After all, who wants to expose a sun-starved and flabby body when it’s time to put on a bikini? Although many of these quick-fix eating plans claim instant gratification, most of the diets are not safe or effective ways to lose weight.

Most fad diets draw us in with their promise of miraculous weight loss in a short period of time. In fact, most of them will work only in the short term because they rely on a limited range of foods (like cabbage, egg or unlimited protein portions), so you eat less and reduce your calorie and fat intake.

Here’s a summary of what happens to your body when you follow a low-calorie diet:

• First, your body uses up carbohydrate stores (known as glycogen) in the liver and muscles. Water is stored with glycogen in the body, and as this is used up you may lose several pounds in water weight.
• Once all the stored carbs have been used up, your body enters a kind of starvation mode, and protein in the muscles is used as the main source of energy. As a result, toxic compounds called ketones are produced that make you feel fatigued and headachy.
• As you begin to lose weight, you also lose muscle mass (because the protein from your muscles is being used for energy), and your metabolism begins to slow down to conserve the small number of calories you’re now consuming. Your metabolism (the rate at which you burn calories) is directly related to the amount of muscle you have, so the more muscle you have, the faster you burn calories.
• If you lose a lot of weight initially on the diet, you’ll also lose a lot of muscle. So, even though you’re eating fewer calories, your body is burning calories at a slower rate than before you went on the diet, because you now have less muscle mass.
• Once you return to your pre-diet habits (which is inevitable), you’ll regain the weight that you initially lost, and potentially more. This is because your slow metabolism can’t process the amount of incoming calories and, therefore, stores them as fat.
• A low-carb, high protein diet may also cause dehydration, weakness, nausea and, in severe cases, gout, kidney problems and an increased risk of heart disease.

So, next time you see a crash diet promising instant weight loss, remember:

• These diets are boring, unrealistic and impossible to sustain for long periods of time
• Fad diets rarely give you optimal amounts of essential nutrients because they are often based on a single or limited range of foods
• A sensible and realistic diet can be followed for long periods of time, to maintain a desirable body weight, whereas fad diets require dramatic changes in the way you eat
• Crash diets fail to provide ways to keep excess weight off permanently
• A realistic exercise regime is rarely advocated with a fad diet, yet exercise is crucial to maintain weight loss over a long period of time

Despite what crash diets promise, the only sensible way to lose weight permanently is to eat less and increase your physical activity. If you want to lose weight, aim to drop one to two pounds per week, watch your total calorie intake and reduce fat in the foods you eat. A well-balanced diet should consist of not more than 35 percent fat, 50 percent carbs and 15 per cent protein.