Critical Mass

If you can't get a grip on a problem, it's sometimes convenient just to stop letting it bother you. When the Metropolitan Life Insurance Co. published its famous height-weight chart in 1959, a woman standing 5 feet 5 inches was supposed to weigh between 111 and 142 pounds. Today's government guidelines, tailored to a fatter population, tell the same woman that 162 pounds is acceptable if she's at least 35 years old. But last week brought stark evidence that our accommodation has come at a cost. In a study of more than 100,000 nurses, researchers at Harvard Medical School and Boston's Brigham and Women's Hospital found that women weighing at least 15 percent less than average were the least likely to die prematurely, and that death rates rose steadily with increasing heft even in women who weren't officially obese. The study concludes that weight-related illnesses now kill 300,000 Americans a year, placing fat second only to smoking as a cause of preventable death. And the findings set a new ideal for leanness.

To gauge the relationship between weight and mortality, the researchers, led by endocrinologist JoAnn Manson, tracked 115,000 nurses from 11 states who were 30 to 55 years old in 1976. For 16 years, the participants provided periodic updates on their weight and health, and the researchers recorded deaths from cancer, heart disease and other causes. The results, published in last week's New England Journal of Medicine, suggest that excess weight accounted for nearly a third of all cancer deaths and half of those from cardiovascular disease among nonsmoking women. Those who weighed the most for their height were four times as likely as their leanest counterparts to die of cardiovascular disease, and twice as likely to die of cancer. (In postmenopausal women, fat tissue fosters the production of tumor-promoting estrogens, and high-fat diets raise the level of cancer-causing bile salts in the co-Ion.) The trend toward higher mortality was evident even among women of average or mildly excessive weights. For example, a hypothetical 5-foot 5-inch woman was 20 percent more likely to die during the study if she weighed 135 pounds than if she weighed less than 120. If she weighed 170 pounds, her risk was 60 percent higher, and at 195 pounds her risk more than doubled.

The obvious message is that leaner is healthier. But statistical trends provide only a rough guide to personal health. The pattern revealed in the new study is based on a single figure known as body mass index (BMI), an expression of weight in relation to height. To compute your BMI, measure your weight in kilograms (pounds multiplied by .45), and divide that number by the square of your height in meters (inches multiplied by .0254). (The chart on this page gives a shortcut for these calculations.) The new findings suggest that a BMI of 19 or less is optimal, at least for middle-aged women, and that indexes of 25 or more grow increasingly risky. But people's ideal BMIs can vary depending on what their weight consists of. A person with small bones and few muscles could carry an unhealthy amount of fat while maintaining a fairly low BMI. By the same token, an athlete with thick bones and a lot of lean muscle could qualify as overweight on the BMI scale despite her excellent health.

Alas, few of us face that problem. A typical American spends just 16 minutes a day exercising, and the average weight of U.S. adults has risen by 8 pounds since 1980. The government's current guidelines recommend BMIs of 21 to 27 and sanction weight gains of up to 20 pounds in middle age. Yet even by those lax standards, a third of U.S. adults--32 million women and 26 million men--are at least 20 percent overweight. Even before the new study came out, the U.S. Department of Agriculture was revising its recommendations to reflect the growing awareness that we needn't expand as we age. The new guidelines, due out later this year, could render half of the adult population officially overweight.

Some critics complain the Harvard study will leave women feeling utter failures if they don't look like teenage models. "This perpetuates an obsession with weight rather than healthy lifestyle choices," says Lynn Jaffee of the Melpomene Institute in St. Paul, Minn., which studies the link between exercise and women and girls' health. But Manson is hardly promoting crash diets. Obesity's toll would drop sharply if average-size women simply avoided gaining weight with age, she observes. Most Americans grow heavier throughout their 30s and 40s, as their metabolism slows and the demands of work and family conspire to make regular exercise difficult. People know that from their mirrors, and most would like to do something about it. If vanity can't suppress our appetites, actuarial tables probably won't have much success either. But as the new study makes clear, there is ample reason to keep trying.

Statistical trends offer only a rough guide to personal health. But a 16-year study of 115,000 nurses suggests that extremely lean women are the least likely to die prematurely.

Increased risk of early death

Source: Adapted from New England Journal of Medicine, Dr. Joann E. Manson

            _B_Weight Watch_b_

Standards have changed since 1959.

                         WEIGHT GUIDELINE

YEAR                      FOR 5'5" WOMAN

1959[a]                    116-130 lbs.

1983[a]                    127-141

1990                       126-162

1995                       110-149