Restrictive dieting sends a signal to the body that there is a food shortage, and the body thinks its survival is threatened. It responds by slowing down its metabolic rate (the speed at which the body burns up energy). This means that body fat loss slows down and it becomes harder to lose weight.

Dieting makes the body respond by conserving fat. When dieting, weight loss is mainly water and muscle. The reduced muscle mass further slows down the rate at which the body uses up energy.

Research shows that people find it more and more difficult to lose weight after repeated dieting, and they rapidly regain weight. Over 90 per cent of dieters regain the weight they lost after they stop dieting, and often regain more weight than they started with.

Weight fluctuations increase the risk of heart disease. It is healthier to stabilise at a heavier weight than repeatedly gain and lose weight. Dieting deprives the body of essential nutrients and energy, and the body responds by wanting to binge. Strict avoidance of particular foods can cause cravings for those foods.

Women need to carry 25-30 per cent body fat for health and fertility. Genetics has a significant influence on each person’s metabolic rate, body shape and size, so dieting is not the only answer.

Basal metabolic rate (BMR)
The body uses up energy according to its basal metabolic rate, and is influenced by exercise and food intake.

The BMR is the rate at which the body burns up energy to breathe, keeps blood flowing around the body, and maintains body temperature. About two-thirds of the energy used by the body each day is used by the BMR.

BMR varies between people
People with a low BMR are ‘energy savers’, and do not use as much energy for the same body functions as people with a high BMR. Those with a low BMR are more likely to have excess energy to store as fat.

BMR can be changed
The goal for people wanting to lose weight is to increase their BMR, and thus become an ‘energy user’ - where the body uses up more energy for body functions.

Physical activity
Physical activity is the second-largest use of your energy. It is the energy used to move muscles during the day, for example, walking, reading, swimming, cleaning, gardening, and this energy expenditure varies a lot from person to person.

Food
The body uses energy to digest, absorb and convert the food eaten. The type of food eaten affects how much energy the body needs to use up to break down and convert the food. High carbohydrate or starchy foods require more energy to use up than high protein or fatty foods.

What happens to BMR when dieting?
The BMR slows down when the number of kilojoules eaten in food is reduced (as is the case with most weight-loss diets). The body thinks ‘hard times are coming, food seems less plentiful; I’d better start saving energy’. Thus the body becomes an ‘energy saver’. One way the body does this is by breaking down body tissue that needs energy just to exist - your muscle and organs.

The BMR drops, the body gets used to and needs less food. If a person stays on a low kilojoule diet for any length of time, they end up eating a very small amount of food just to maintain weight.

This style of eating is not very satisfying and a person soon begins to eat more. As soon as the body gets more food it says to itself, ‘Whoopee — a bit extra! I’ll save it for a rainy day’, and stores it as fat. Eventually, the body gets back to the weight it was before dieting started, often with a few more kilograms added.

People often don’t realise that they now have more fat and less muscle than when they started dieting (the fat goes back, not the muscle — the only way to get muscle back is through exercise).

People will then try another diet, lose some more weight, then regain it all plus extra; and end up being heavier still. This vicious cycle is called the ‘yo-yo syndrome’ and may result in dramatic changes in the body make up (more fat, less muscle), plus a very low BMR. (Remember, a low BMR means it is easier to gain weight.)

Remember - Fat needs no energy to exist - it just sits there!. So a lot of the weight lost on a diet is not fat, but muscle.

That's why at Gym In Motion, we believe in a lifestyle change which is a long term approach to nutrition and not one off dieting fads.