General principle of diets

A weight loss diet is a food practice intended to lose weight. Most often, plans are based on a decrease in the amount of energy ingested by controlling the main families of food intake (calories) and nutrients (proteins, lipids, carbohydrates). In practice, the dietary advice without accompaniment are effective moderate and limited in time (high likelihood of weight regain).
Practice of a sport, of medium intensity (heart rate of 160 less age) but still, and during more than a half hour (e.g. endurance sports like walking on foot or by swimming), is recommended in addition to dietary changes, and helps improve the weight loss.


General principle

When the amount of ingested energy is less than the amount of energy expended, the body uses the energy stored in the form of fat. Conversely, if ingested energy is greater than the amount of energy expended, the body stores the excess as fat. Schemes are intended to increase expenditure through the exercise and decrease the amount of energy ingested.
Changes in behaviour are usually only temporary. The people who have lost weight, see their metabolism decrease. The resumption of the old behaviour is accompanied by so a resumption of very rapid weight because energy consumption is lower (less exercise and lower basal metabolism).

Energy requirement

It is often recommended when dieting to calculate its daily energy needs. There are complex formulas to calculate it based on age, weight, frequency of physical exercises, etc. In general, it stands at around 2,000 calories for women and 2,500 kcal for men. This energy requirement (BEN) is the number of calories needed to maintain weight. To lose a kilogram of fat, the body must be in deficit of 7,000 kcal compared to its energy needs. This means that by consuming 500kcal less than his BEN every day, it will take 14 days to lose a kilogram.

effectiveness evaluation

The evaluation of the effectiveness of these regimes is tricky, because published studies attempting to do so are 'open' (the patient knows what kind of regime it is submitted) and their interpretation is therefore likely some bias. In addition, they are of short duration.
The effectiveness of these schemes appears to be comparable to two years3.
A report  published in November 2010 identifies nutritional imbalances caused by 15 plans (including the Atkins diets, California, lemon detox, chrononutrition, Cohen, Dukan, Fricker, Mayo, the cabbage soup diet, Zone diet (in) and Weight Watchers): protein intakes above the recommended dietary allowances (RDA) for 80% of plans, contributions greater than the ANC, fiber intakes below the ANC in 3 schemes on 4, ANC insufficient iron, and vitamin C (Dukan and Fricker plans) or calcium (Mayo, Montignac regimes in phase 2, Fricker in phase 3). The Agency captures also the decrease in bone mineral mass (risk of fracture), the reduction in essential polyunsaturated fatty acids, the risk of gallstones with low-calorie diets or the risk of colorectal cancer with complex carbohydrates and fibre diets.
There is frequently a "yo-yo" effect: the patient follows a diet then quickly regains its original weight then goes beyond. For example, a person of 1, 75 m, 40 and 85kg its metabolic rate can be estimated at 1789 kcal. Dieting with a power supply providing less 220kcal per day (or a slice of cake under a day) this person is expected to reach a weight of 73kg to 41 years. If it persists the weight will stabilise to 65kg (without modification of physical activity). If it returns to its previous power weight stabilizes at 86kg to 42 years because basal metabolism decreases with age.


Some examples of dieting

Diets are of several kinds:
"balanced" caloric restriction (for example: 50 to 55% carbohydrates, 30-35% lipid, and 10-20% protein) and moderate, which consists of a decrease (for example, 600 kcal per day) compared to the usual ration.
the food changes inducing calorie reduction via increased satiety, without caloric restriction: reduction of fat, increase in fruit, grains and vegetables.
very low calorie diet: less than 800 less than 600 kcal/d. They can be sources of deficiencies if they are prolonged. Sudden deaths have even been reported.

the fat diets where lipids represent more that 10 to 15% of inputs (Dukan diet for example). Its effectiveness is controversee6.
diets, low-carb (Atkins Diet), but high in fat and protein, not imposing any caloric restriction but allowing to increase satiety. They have a certain efficacite7 and would be similarly, short-term, slightly higher than other diets.
therapeutic fasting in specialized clinics is increasingly practiced, particularly in Russia, in Ukraine, in Germany (the first clinic of Dr. Otto Buchinger was founded in 1920; many clinics exist today throughout the world, in Spain (therapeutic fasting is taught graduate in the Faculty of Medicine of Zaragoza, in Japan, in the USA, in Canada, in Thailand, in India, in the Philippines...