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updated 10/8/2004 2:52:10 PM ET 2004-10-08T18:52:10

Dieting may be as American as apple pie, but repeated attempts at dieting could be harmful. Although excess body weight increases the risk of many health problems, new research suggests that going through cycles of weight loss and regain may damage your emotional and physical health. Your immune system could also be impaired.

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One type of immune cell thought to play a major role in cancer prevention is called natural killer cell. These cells attack viruses and cancer cells. One study links low levels of natural killer cells with an increase in cancer incidence.

A new study draws a link between repeated weight loss and injury to the immune system. In this study, natural killer cell activity dropped in women who lost and regained at least 10 pounds two times or more.

In contrast, natural killer cell activity stayed the same in women who had never or only once lost more than 10 pounds. Weight lost following childbirth was not counted for any of the women.

Despite this study’s findings, a link between repeated weight loss and lowered immune function is still tentative. Consequently, the impact of repeated weight loss on a person’s cancer risk is unknown. The few studies looking at the link show inconsistent results. And natural killer cell activity is just one part of our immune system. There are other parts to protect us from cancer.

Emotional health at highest risk
The psychological damage caused by repeated dieting efforts may be more harmful than the physical effects and a better reason to avoid diet cycles. In one recent study, the more times women had dieted, and the younger they were when they began, the more overweight they tended to be. The majority of women in this study had dieted over 11 times, using a wide range of strategies. All were obese, and many were extremely obese.

The authors of this study point out the psychological damage brought on by repeated weight loss “failures” and deprivations, especially when diets are forced on young people. A long history of diet attempts could make it difficult for someone to ever permanently establish healthy behaviors.

An overweight person could, in fact, be better off never dieting, if she or he belongs to a small group called “obese but metabolically normal.” Although the weight and body fat of these people appear high, they lack the insulin resistance that seems to link obesity with health problems. Medical tests also show that they have no dangerous, excess fat, which is stored around the abdominal organs. Some researchers believe that obesity may not be a health risk for this small subgroup of people.

Healthy lifestyles key
Like everyone, however, this subgroup still needs to exercise regularly to keep fit. People who are overweight but physically fit remain healthier longer than people of a normal weight who are inactive and unfit. Although exercise can improve everyone’s health, overweight people are still more likely to develop arthritis of the knees, as well as suffer an increased risk of some hormonally related cancers.

Adults who have attempted losing weight in the past dieting should try, for a change, to build a lifestyle of healthy eating and regular exercise. By looking at more than the loss of pounds, your overall state of health could improve.

Experts emphasize, however, that children and adolescents should not diet. Instead, parents should practice family-wide healthful eating, encourage physical activity, limit sedentary time, and teach children to fill emotional needs without food.

Nutrition Notes is provided by the American Institute for Cancer Research in Washington, D.C.

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