Obesity is the result of imbalance of energy (food) intake and output. If energy intake is more than energy output, the energy is accumulated in the body as adipose (fat) tissue, mainly in the abdomen and in subcutaneous (just below skin) tissue. The bad part of fat accumulation is that fat is accumulated in the abdomen first and while reducing weight the abdominal fat is the last to go. This energy is stored for later use if the individual can not get energy supply. So, reduced calorie intake is the cornerstone in reducing weight.
The fundamental goal of obesity reduction is to consume energy (food) below that of expenditure. The fad diets does not have any scientific basis. The main regimen that is followed keeps certain facts in consideration relevant to food intake and weight loss. First, 7,500 kcal of energy is approximately one kilogram of fat. Therefore, consuming 100 kcal/day less for a year will produce weight loss of 5 kg, and eating 1,000 kcal/day less will produce weight loss of about one kg per week. Dieticians advice the above regimen for weight loss.
Obese individuals have a higher metabolic rate than normal persons and men have higher metabolic rate than women (due to greater lean body mass) the rate of weight loss is greater in more obese and among men (relative to women). With chronic calorie restriction, metabolic rate diminishes because of reduced lean body mass and possibly because of other adaptations. This fall in metabolic rate with food restriction slows down the rate of weight loss on a constant diet. This is the reason of faster weight loss at the beginning and much slower weight loss later on, if a person is on constant diet.
Weight reduction is not like treatment of a disease that once the disease is cured the person need not to worry. To remain within normal weight by previously obese person require lifelong change of behavior and lifestyle as well as lifelong change of food habit. This lifestyle change has to continue even after reduction of weight to normal. Typically behavior change is brought about by counseling in a group of people and requesting them to monitor and record the circumstances relating to extra eating. Unless the obese person continues to follow the new lifestyle after weight reduction he is bound to gain weight again.
An important aspect of diet therapy is educating the obese person how to prevent weight gain. Knowledge of calorie and nutritional content of food is very important in shaping the food habit for maintaining weight. Generally obese persons liking of food is of high calorie type and there knowledge of calorie and nutrition is very poor. There is no clear evidence that one type of diet is better than others that is why it becomes more important that obese persons should be educated in nutrition and calorie content of different types of foods. In general a diet containing lots of fruits, vegetables, whole grains, and low fat and oil diet is the best diet an obese person can follow. The diet should also contain enough quantity of proteins.