Fear of Fat The Medical Evidence
In 1985, a panel convened by the National Institutes of Health (NIH) declared that obesity is a disease and a potential killer. The panel deplored what might be termed "the rounding of America." The nation now has a "high prevalence" of obesity among adults, the panelists said. And the increasing incidence of obesity in childhood and adolescence, they warned, will result in greater numbers of obese adults in the future.
Anyone 20 percent or more overweight—now the standard definition of obesity—should try to reduce, the NIH panel urged. That advice, it said, applied to 34 million obese Americans, or one out of every five adults. For some people, the panel said, even five excess pounds can threaten health.
At the same time, the panel's chairman, Jules Hirsch, M.D., of Rockefeller University, acknowledged that his group relied primarily on a "feeling for the data" in citing the figure of 20 percent above standard weight as the point at which a person ought to reduce. That's because hard information about the nature and consequences of obesity is still skimpy. Nor is there any consensus yet about just what is a person's "desirable weight."
How Much Should You Weigh?
To find out their ideal weight, Americans for more than 40 years have turned to the height/weight tables published by the Metropolitan Life Insurance Co.
The most recent Metropolitan desirable-weight tables, published in 1983, use combined data from 25 insurance companies that followed more than 4 million policyholders for between one and 22 years. The tables (tables missing due voluntary work) show the range of weights that were associated with lowest mortality among the policyholders. The weights shown are based on what people weighed at the time their insurance policies were issued. No attempt was made to monitor their changing weight as the years passed.
The NIH panel relied on the Metropolitan Life data, plus several other studies, in concluding that "obesity . . . has an adverse effect on longevity." In defining obesity, the panel began with a concept of ideal weight—the midpoint of the Metropolitan tables' desirable weight range for a person with a medium frame. If you weigh 20 percent more than that, you are obese and should reduce, the panel declared.
Unfortunately, the Metropolitan Life weight tables are far from a perfect indicator. For one thing, weight alone doesn't always reflect obesity, which is a measure of body fatness. Muscular athletes, for example, may be well over normal weight but not at all obese.
The percentage of your body weight that is in the form of fat is a better indicator of obesity than weight alone. However, measuring the percentage of body fat requires specialized equipment. The most accurate method requires immersion in a tank of water, which is awkward and expensive. A moderately accurate technique involves using calipers to measure the thickness of certain fleshy areas. Physicians and patients customarily rely on straight weight as an indicator.
Most of the data in the Metropolitan weight tables comes from white middle-class males—not a representative sample of the general U.S. population. The tables apply to people aged 25 to 59 and therefore don't cover younger adults or the growing number of people over 60.
Perhaps most important, the Metropolitan tables make no allowance for aging. They assume that a 50-year-old man, for example, should weigh the same as he did at 20. And that may be a mistake.
Reubin Andres, clinical director of the Gerontology Research Center at the National Institute on Aging, analyzed the insurance data from which Metropolitan Life derived its tables and found that the desirable weight-for-height varied markedly with age. He then devised a new weight table providing weight ranges associated with lowest mortality by age group.
Remarkably, he found that the desirable weights for men and women of a given age and height were about the same.
Compared to the Metropolitan tables, Andres's table "permits" heavier weights for the middle-aged and elderly—but it's more restrictive for young people. The message of Andres's table is that average healthy individuals who are not overweight early in adulthood should not worry about putting on some extra pounds as they move into middle age. Andres has pointed to more than a dozen other studies also suggesting that middle-aged and older people live longer at weights the Metropolitan tables would consider too high.
Weight gain with age is certainly common in this country. Can some weight gain also be beneficial, as Andres contends? The NIH panel didn't think so. The panel mentioned Andres's work in its report but endorsed the Metropolitan tables as a guide for calculating desirable weights. However, a significant minority of obesity experts believe that the Metropolitan tables are too restrictive when they are applied to older people.
Obesity and Health Risks
When medical scientists speak of obesity raising the risk of mortality, they're mainly referring to the association between obesity and heart disease—the leading killer of Americans. It's not clear whether obesity per se directly promotes heart disease. What is certain is that obesity makes it much more likely that proven risk factors for heart disease will be present. Weight-related risk factors include hypertension (high blood pressure), high blood cholesterol levels, and diabetes. The NIH panel cited the following figures:
* Hypertension occurs about three times as often in overweight people as in those who are not overweight. Among adults aged 20 through 44, individuals 20 percent or more overweight are 5.6 times as likely as others to have hypertension.
* High blood cholesterol levels occur more than twice as often in overweight people.
* The prevalence of diabetes is nearly three times as high in the overweight.
Many studies have shown that weight loss can significantly improve all three of those heart-disease risk factors. If you're overweight and you have any of these risk factors or a family history of them, then losing weight should be a priority. Maintaining proper weight seems to be especially important for young males, obesity experts agree.
Recent evidence from several countries also suggests that where you're fat may be more important than how fat you are. So-called male-type obesity—the bulging abdomen sometimes known as beer belly or executive spread—seems to pose more of a threat than fat lower down around the hips and buttocks ("female type" obesity). Bulging bellies appear to increase the risk of developing cardiovascular disease and diabetes. Risk seems to increase sharply when the waist-to-hip ratio exceeds 1.0 in men and 0.8 in women. (In other words, men are at risk when their waist is larger than their hips; women are at risk when their waist measures more than 80 percent of their hips).
Why is abdominal fat worse? Researchers speculate that fat cells there may be more metabolically active, perhaps pumping more fat into the bloodstream and onto the artery walls.
Most of the population studies that have linked obesity to heart disease have focused on men, since they're much more likely to develop heart disease than women are. While obese women may or may not face the same heart-disease threat as men, they do face a cancer risk. Compared to nonoverweight women, obese women have a greater incidence of cancer of the gallbladder, uterus (including both cervix and endometrium), and ovaries. Postmenopausal obese women also have a heightened risk of breast cancer. Researchers believe that the uterine and breast cancers in obese women may result from the higher estrogen levels resulting from their obesity (fat stores can convert certain male adrenal hormones into female hormones). On the other hand, postmenopausal osteoporosis occurs less often among the obese for this same reason.
Obesity is also associated with several types of cancer in men: cancer of the colon, rectum, and prostate. Gallstone formation occurs much more often in obese people—especially women—than in others. The prevalence of arthritis and gout is also high among the obese.
Beyond its physiological effects, obesity can cause embarrassment and humiliation. The NIH panel even went so far as to say that the psychological burden of obesity may be "its greatest adverse effect."
While better health and greater longevity might be the reward of normal weight, the road there from obesity is paved with difficulties and potential health hazards of its own.
Diets and Exercise
About 30 years ago, an authority on the treatment of obesity had this to say: "Most obese persons will not stay in treatment of obesity. Of those who stay in treatment most will not lose weight and of those who do lose weight, most will regain it." The evidence behind that pessimistic assessment hasn't changed much. The problem facing dieters can be summed up this way: Losing weight is hard, but keeping it off is much harder.
There are complex and unresolved disputes about why people become overweight and remain that way despite strenuous efforts to reduce. Most experts believe that obesity results from an interaction among many factors—genetic, social, psychological, environmental, and hormonal. A number of explanations have been offered for how obesity occurs. Two hypotheses currently receiving a good deal of attention are the fat-cell theory and the set-point theory.
The fat-cell theory of obesity holds that a high-calorie diet in childhood leads the body to produce excessive numbers of fat cells, which a person then carries for life. Diet and exercise can help shrink these fat cells. But studies show that the number of fat cells can't be diminished—though they can still increase, especially in cases of extreme obesity.
According to the set-point theory of obesity, each of us is "programmed" to maintain a certain weight—much as a home's temperature is regulated by a thermostat. What we regard as an attempt to lose weight our body regards as famine—and responds accordingly. Shrunken fat cells, crying out to be filled, urge us to eat more. The body further defends its "set point" weight by lowering its metabolic rate, the rate at which energy is used by normal bodily processes. If valid, the set-point theory may help explain why diets often fail. After a person has shed a few pounds, losing weight becomes increasingly difficult, requiring more drastic calorie reductions. However, some proponents of the set-point theory believe that vigorous exercise can alter the body's "set point."
Regardless of the mechanism of obesity, resorting to fad and crash diets can cause serious illness and even death. Even ordinary dieting can cause frustration and depression. Weight-loss drugs can cause serious side effects. And the all-too-common "yo-yo" cycle of weight loss followed by weight gain may leave you worse off than before.
Some studies, mainly involving test animals, suggest that yo-yoing may actually cause some of the health problems that are blamed on obesity itself. In addition, people may regain increasingly more weight in successive cycles—and studies suggest that the regained weight contains an increasingly higher percentage of fat.
Since losing weight and keeping it off is so difficult, the best approach to managing obesity is to avoid it in the first place. People who really want to lose weight
must forget about "going on a diet." Instead, they must undertake a permanent change in eating and living habits.
Your weight reflects the balance between calories ingested and calories expended. But many people still believe that overweight results solely from overeating. So when trying to lose weight, they usually limit themselves to dieting, and fail to achieve the desired result. Studies indicate that combining exercise with dieting may be the most effective way to lose weight and keep it off. As one report put it, overweight people can be thought of as underexercised rather than overfed.
Some people believe—mistakenly—that exercise increases appetite, making it even harder to limit eating. Actually, moderate exercise usually has very little effect on appetite.
Others contend that the modest calorie loss through exercise isn't worth the effort. Take jogging, they say: If one hour of jogging bums up only 500 calories, you need to jog for seven hours to lose one pound of body fat (3500 calories). That's true. But it's also true that jogging one-half hour a day for two weeks gives you those seven hours—and a one-pound loss. By jogging one-half hour per day for one year, while keeping food intake constant, you'd shed 26 pounds—far more than most crash diets promise, let alone deliver.
Ideally, when you diet you should lose fat, not muscle. Without exercise, you'll lose both. Dieters who also exercise lose weight mostly as fat.
If you're overweight, exercise can help you be healthier even if your caloric intake keeps you at the same weight. Besides improving muscle tone, exercise appears to help in reducing high blood pressure, lowering blood cholesterol levels, and improving blood sugar levels
in diabetics, even when no weight loss occurs. Those changes, in turn, reduce the risk of heart disease.
Source: http://www.healthguidance.org/authors/716/Luis-Treacy
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