Weighty Decisions

For years, the message "fat is bad" has rung loud and clear. But older folks should heed another warning: Lightening up could be dangerous, too.

Losing weight has become as much a part of American culture as baseball and apple pie. And perhaps it's just as well. Tubbier folks succumb to heart attacks, high blood pressure, and diabetes more readily than do individuals of normal weight. And for the elderly, obesity can lead to years of disability.

But trimming down can pose serious health threats for the senior set. Compared to their weight-stable counterparts, older folks who shed pounds break their hips more easily, land in nursing homes more often, and are more than twice as likely to die. So although obesity has its dangers, experts warn, supersized seniors should think twice about passing on the peach cobbler and reaching for the Slim-Fast.

Although most people don't think of shedding unwanted weight as being potentially hurtful, weight loss can cause trouble for older folks. According to a 2003 analysis of bone injury in more than 6700 elderly women in the United States, individuals who lost 5% of their body weight over a period of 5 to 6 years--regardless of how big they were when they started or whether they intended to slim down--had twice the risk of hip fracture as did those who either held their weight steady or gained. And in a Canadian study of 288 frail seniors, losing 5 kilograms or more inflated by 70% a person's odds of being sent to a nursing home.

Why slenderizing can spell death or disability for seniors is not entirely understood, but researchers have a few theories. As people lose weight, fat breaks down and trickles into blood vessels, where it adds to plaques that have been building up for years. The new constituents might be "the last straw to cause you to have a heart attack or stroke," suggests John Morley, a geriatrician at Saint Louis University in Missouri. The breakdown of fat, some speculate, might also release accumulated toxins, sending the harmful substances into circulation, where they can damage other tissues.

But perhaps the most crippling part of slenderizing stems from the complex relation between fat and muscle. When people shed excess weight, they lose muscle as well as fat. But when they put it on again, only a portion of the lost muscle returns. In older folks, such muscle wasting sets the stage for disability (see "Seventy and Going Strong"). To make matters worse, muscle loss can subsequently promote fat buildup, thanks in part to the action of insulin. Muscle cells sport receptors that bind to the hormone, and losing muscle not only depletes this receptor reserve, but--through a complex chain of molecular events--renders the remaining receptors less responsive, says Ronenn Roubenoff of Tufts University's Friedman School of Nutrition Science and Policy in Boston. This lack of sensitivity translates into insulin resistance--a condition that often leads to obesity.

Obesity, in turn, can further exacerbate muscle depletion. Some scientists say this effect is mediated by an immune chemical called tumor necrosis factor-α (TNF-α). When people are ill, TNF-α--some of which is produced by fat cells--directs muscles to decompose. Overweight individuals have a surplus of circulating TNF-α, which could be giving their muscles too strong a "break down" signal, accelerating muscle decline, Roubenoff says.

For older individuals, carrying too much weight--and too little supporting muscle--is a fast track to disability. In a 1994 epidemiologic study, Dutch researchers found that older women in the United States who were overweight or obese became disabled more often than did those of average weight. And in a study of more than 8000 people aged 70 or older--published last month in The Gerontologist--Sandra Reynolds of the University of South Florida in Tampa and colleagues found that the odds of becoming disabled went up about 50% in obese seniors relative to the nonobese group.

The extra pounds, however, don't seem to translate into lost years. A recent study of adults aged 25 or over showed that overweight people live as long as--and might even outlive--individuals of normal weight. Using data from national health surveys spanning 3 decades, Katherine Flegal, an epidemiologist with the Centers for Disease Control and Prevention in Atlanta, Georgia, and colleagues divided more than 35,000 adults into weight categories based on their body mass index (BMI), a measure of body weight relative to height. Taking into account factors such as age, gender, race, and smoking habits, the researchers then estimated the number of deaths expected per year for each group. When they compared the estimated and actual death totals, they found that underweight (BMI less than 18.5) and obesity (BMI of 30 of greater) were linked to 34,000 and 112,000 more deaths than predicted, respectively. But the death tally in the overweight group (BMI between 25 and 30) came out 86,000 fewer than estimated.

In Reynolds's hands, even outright obesity did not cut into seniors' longevity. She found that "if you've survived to the age of 70 being obese, you're no more likely to die than the same person who's not obese." Although the numbers suggest that chubby folks live just as long--if not longer--than their normal-weight counterparts, they aren't necessarily as healthy, Flegal cautions. And Reynolds's data on disability bear out that notion.

Sadly, because weight loss can also pose health hazards, portly seniors who want to slim down can find themselves stuck in an unpalatable situation: Disabled if you do, disabled if you don't. To avoid this predicament, Morley says that plump patients should try to lose weight before they're ready for retirement. "They should exercise like mad before they're 50," he says. "Then they should stabilize their weight." And for normal-weight seniors who want to trim down because of conditions such as diabetes or high blood pressure, Morley advises holding tight: Dropping clothing sizes could ultimately cause more problems than benefits.

For many seniors, however, being chunky is the least of their problems, notes Alfred Fisher, a geriatrics physician at the University of Pittsburgh in Pennsylvania. For instance, for overweight individuals with severe Alzheimer's disease, slimming down won't improve their most disabling condition. "Eating might be one of their few remaining pleasures," Fisher says. That said, most folks should probably pause to think before reaching for that second slice of apple pie.

Esther Landhuis is a science writer in the San Francisco Bay Area who finds that thinking too heavily about a topic can be hazardous to her health.