Dieting

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Dieting is the practice of eating food in a regulated fashion to achieve or maintain a controlled weight. In most cases dieting is used in combination with physical exercise to lose weight in those who are overweight or obese. Some athletes, however, follow a diet to gain weight (usually in the form of muscle). 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 calorie-reduced diet types cause equal weight loss irrespective of the macronutrients emphasized.

The first popular diet was "Banting", named after William Banting. In his 1863 pamphlet, Letter on Corpulence, Addressed to the Public, he outlined the details of a particular low-carbohydrate, low-calorie diet that had led to his own dramatic weight loss.

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Types of diets

Low-fat diets

Low-fat diets involve the reduction of the percentage of fat in one's diet. Calorie consumption is reduced because less fat is consumed. Diets of this type include NCEP Step I and II. A meta-analysis of 16 trials of 2–12 months' duration found that low-fat diets (without intentional restriction of caloric intake) resulted in average weight loss of 3.2 kg (7.1 lb) over habitual eating.

Low-carbohydrate diets

Low carbohydrate diets such as Atkins and Protein Power are relatively high in protein. Low-carbohydrate diets are sometimes ketogenic (i.e. they restrict carbohydrate intake sufficiently to cause ketosis).

Low-calorie diets

Low-calorie diets usually produce an energy deficit of 500–1,000 calories per day, which can result in a 0.5 kilogram (1.1 lb) to 1 kilogram (2.2 lb) weight loss per week. Amongst some of the most commonly used low-calorie diets include DASH diet, Diet to Go, and Weight Watchers. The National Institutes of Health reviewed 34 randomized controlled trials to determine the effectiveness of low-calorie diets. They found that these diets lowered total body mass by 8% in the short term, over 3–12 months.

Very low-calorie diets

Very low calorie diets provide 200–800 calories per day, maintaining protein intake but limiting calories from both fat and carbohydrates. They subject the body to starvation and produce an average weekly weight loss of 1.5–2.5 kilograms (3.3–5.5 lb). "2-4-6-8", a popular diet of this variety, follows a four-day cycle in which only 200 calories are consumed the first day, 400 the second day, 600 the third day, 800 the fourth day, and then the cycle repeats. These diets are not recommended for general use as they are associated with adverse side effects such as loss of lean muscle mass, increased risks of gout, and electrolyte imbalances. People attempting these diets must be monitored closely by a physician to prevent complications.

Detox diets

Detox diets claim to eliminate undesirable "toxins" from the human body rather than claiming to cause weight loss.

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Fat loss versus muscle loss

Weight loss typically involves the loss of fat, water and muscle. Overweight people, or people suffering from obesity, typically aim to reduce the percentage of body fat. Additionally, as muscle tissue is denser than fat, fat loss results in increased loss of body volume compared with muscle loss. Reducing even 10% body fat can therefore have a dramatic effect on a person's body shape. To determine the proportion of weight loss that is due to decreased fat tissue, various methods of measuring body fat percentage have been developed.

Muscle loss during weight loss can be restricted by regularly lifting weights (or doing push-ups and other strength-oriented calisthenics) and by maintaining sufficient protein intake. Those on low-carbohydrate diets, and those doing particularly strenuous exercise, may wish to increase their protein intake. According to the National Academy of Sciences, the Dietary Reference Intake for protein is 0.8 grams per kilogram of body weight for adults.

Excessive protein intake, though not connected to declined kidney functioning in healthy individuals, may be harmful to those with certain kidney diseases. There is no conclusive evidence that moderately high protein diets in healthy individuals are dangerous; it has only been shown that these diets are dangerous in individuals already suffering from kidney and liver problems.

The Basal Metabolic Rate, which is the amount of calories the body expends at rest, meaning without performing any physical activity, is influenced by the person's total weight and total amount of muscle. The more muscle, the more calories a person can burn naturally. When the amount of muscle is increased, then more calories can be ingested without gaining weight. Conversely, if the amount of fat is increased, increasing the number of calories ingested will only add weight.

Normally, when people lose weight, they lose a combination of fat and muscle. If the diet plan includes a daily caloric intake greater than the basal metabolic rate (BMR), the person will most likely lose fat. In contrast, if the person follows a diet that includes a lower caloric intake than the BMR, this person will lose fat but also a higher percentage of muscle.[citation needed] Severe diets may make people lose 50% fat and 50% muscle weight thus affecting their metabolism because by losing muscle the BMR is affected.

Maintaining muscle mass while losing fat is therefore a key factor to reach both the ideal weight and body composition. To achieve this goal, experts advise not to reduce carbohydrates aggressively. Fat can be lost by reducing the calorie intake by 20% of daily needs for two days.[citation needed] This reduced calorie intake, even in the presence of 100% carbohydrate consumption, allows for reduction of fat without muscle loss because the glycogen in the muscle is properly replenished.

Exercising on days when the highest amount of carbohydrates is consumed, 1.5 to 2 hours after eating, is also helpful to achieve a balanced fat reduction in the absence of muscle loss. Within this window of time, sugar and insulin levels are undergoing a slow decline. When insulin levels start dropping, the pancreas then produces the hormone glucagon while releasing nutrients stored in the fat cells to the blood to be turned into energy. Conversely, if blood sugar levels suffer a high increase, insulin feeds the muscle cells and deposits excess into fat cells. Furthermore, if insulin levels decrease too much, the muscle cells do not receive the appropriate amount of food they require. There should always be a meal left during the day after exercising to allow the muscles to recover from exercise.[8]