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The Americans have been more and more fat in the recently years. The gym coaches and government officers said that if they return to the traditional food habits or walk for 20 minutes every day, they will lose the fat gradually.

Scientists are not so optimistic, they believe that most of the ideas about obesity are based upon the inference of simplifying the medical conclusions, even though diet and exercise will indeed play a role but will not determine a person's weight. Fat or thin is mainly decided by the DNA, and affected by the brain; of course, the power of will is also important. It is a good idea that taking a slow walking after supper. At least it is much better than sitting in front of the TV for a whole evening. However, the evidence shows that moderate exercise is not of great importance for losing weight.

Dr. Medellin, a weight management expert at the clinical center of the University of Pittsburgh said, "peopel may not know that it'll only burn 100 calories of fat by walking for 20 minutes, but that fact is people always overestimate the fat burnt by exercise and underestimate the fat they consume." Secondly, scientists have recently discovered that the brain`s enormous influence in controlling body's weight and food intake. Harvard Medical School obesity- preventing project leader, Dr. Matthew said: "Some physiological mechanism will automatically stop us from reducing weight."

Nowdays it is widely believed among scientists that everyone has a range of weight decided by gene, which spans less than 30 pounds. Those who are trying to lose weight will eat more because of starvation. Also, metabolism will slow down, as the body wants to store energy and gain weight in this way, so as to reach the weight preset by gene. While the people who want to reduce large pounds of weight will face the opposite situation: the metabolism becomes faster. The temptation of environment as comfortable life of sitting for long time and having enough food are not the main causes of increasingly rising rate of obesity.

The only one of influential external factors is the uterus. According to research, a mother's physical condition during pregnancy, including her menu, will affect the level of child's thinness or fatness after growing into adults. What amazes people is that if the pregnant woman eats little, the baby will be very fat as he grows up. The mothers smoke when they are pregnant, their children also tend to be fat later.