You hear this,"No wonder you are fat.All you ever d0 is eat."You feel sad."I skip my breakfast and supper.I run every morning and evening.What else can I do?" Basically you can do nothing.Your genes,not your life habits,determine your weight and your body constantly tries to maintain it. Albert Stunkard of the University of Pennsylvania found from experiments that"80 percent of the children of two fat parents become fat,as compared with no more than 14.percent of the children of two parents of normal weight." How can obese people become thinner through dieting? Well,dieting can be effective.but the health costs are great. Jules Hirsch,a research physician at Rockefeller University,did a study of eight fat people.They were.given a liquid formula providing 600 calories a day.After more than 10 weeks,the subjects lost on average 45 kg.But after leaving the hospital,they all regained the weight. The results were surprising:by metabolic measurement,fat people who lost large amounts of weight seemed like they were starving.They had psychiatric problems.They dreamed of food or of breaking their diet They were anxious and depressed.Some wanted to kill themselves.They hid food in their rooms. Researchers warn that it is possible that weight reduction doesn't result in normal weight,but in an abnormal state lust like that of starved non.obese people. Thin people, however,suffer from the opposite.They have to make a great effort to gain weight  Ethan Sims of the University of Vermont got prisoners to volunteer to gain weight.In four to six months--they ate as much as they could.They succeeded in increasing their weight by 20 to 25 percent. But months after the study ended,they were back to normal weight and stayed there. This did not mean that people are completely without hope in controlling their weight.It means that those who tend to be fat will have to constantly battle their genetic inheritance if they want to significantly 1ower their weight. The findings also provide evidence for something scientists thought was true--each person has a comfortable weight range.The range might be as much as 9kg.Someone might weigh 60--69kg without too much effort.But,going above or below the natural weight range is difficult.The body resists by feeling hungry or full and changing.the metabolism to push the weight back to the range it seeks. From the text,we know that the body can still feel comfortable
when the weight goes up or down by 6 kg when the weight goes up or down by l0 kg when the weight is increased by 20 to 25 percent when the weight is decreased by 20 to 25 percent