Dieting

is the practice of ingesting food in a regulated fashion to achieve or maintain a controlled weight. In most cases the goal is weight loss in those who are overweight or obese, but some athletes aspire to gain weight (usually in the form of muscle) and diets can also be used to maintain a stable body weight.

Diets to promote weight loss are generally divided into four categories: low-fat, low-carbohydrate, low-calorie, and very low calorie A meta-analysis of six randomized controlled trials found no difference between the main diet types (low calorie, low carbohydrate, and low fat), with a 2–4 kilogram weight loss in all studies.At two years all diet types cause equal weight loss irrespective of the macronutrients emphasized.

Types of dieting

There are several kinds of diets:

• Weight-loss diets restrict the intake of specific foods, or food in general, to reduce body weight. What works to reduce body weight for one person will not necessarily work for another, due to metabolic differences and lifestyle factors. Also, for a variety of reasons, most people find it difficult to maintain significant weight loss over time. Among individuals that have lost 10% or more of body weight, only 20% are able to maintain that weight loss for a full year.
• Athletes participating in professional sports may sometimes undertake weight-gain diets to increase their body mass and gain advantage in their field.
• Individuals who are underweight, such as those recovering from anorexia nervosa or starvation, may adopt weight-gain diets which, unlike those of athletes, have the goal of restoring normal levels of body fat, muscle, and stores of essential nutrients.
• Actors, and people participating in similar activities, may pursue weight loss or gain in order to better portray a particular role.

Physical exercise is an important complement to dieting in securing weight loss. Aerobic exercise is also an important part of maintaining normal good health, especially the muscular strength of the heart.

Though the energy for muscle activity is primarily derived from the glycogen stored in the body, continued activity results in an increased use of the fatty acids as well. After the available glycogen stores are exhausted, fatty acids alone are used. It is often recommended that muscle activity be maintained for 20 minutes or more for increased usage of fatty acids.

The energy burnt during physical exercise has only a limited effect on weight loss, since an hour of aerobic exercise for a man in reasonable physical shape would burn about 2 megajoules (500 kilocalories), which is equivalent to only 60 grams (2 oz) of fat.

Both aerobic and anaerobic exercise would increase the basal metabolic rate (BMR) for some time after exercising. This leads to an additional caloric loss.