Among the indignities of aging is a creeping tendency to put on weight, as our resting metabolism slows down—by roughly 1 to 2 percent every decade. But what's worse, at least for women, is a shift, around menopause, in where this excess flab accumulates. Instead of thickening the hips and thighs, it starts to add rolls around the belly—a pattern more typical of men—which notoriously reshapes older women from pears into apples.
The change is not just cosmetic. A high waist-to-hip ratio portends a greater risk of heart disease, stroke, diabetes, metabolic syndrome and even certain cancers—for both men and women. The shift helps to explain why, after menopause, women begin to catch up to men in their rates of cardiovascular disease. And those potbellies are costly. A 2008 Danish study found that for every inch added to a healthy waistline, annual health care costs rose by about 3 percent for women and 5 percent for men.
Researchers have been investigating “middle-aged spread” for decades, but there is still debate about why it happens, whether it is a cause or merely an indicator of health risks, and what can be done to avoid it. As we grow older, we deposit relatively more excess fat around our abdominal organs as opposed to under the skin—where most of our body fat sits. There are some ethnic and racial differences, however, notes endocrinologist Robert Eckel, director of the Lipid Clinic at the University of Colorado Hospital. For a given waist circumference, African-Americans tend to have less of this “visceral fat,” and Asians tend to have more. Visceral fat differs from subcutaneous fat in that it releases fatty acids and inflammatory substances directly into the liver rather than into the general circulation. Some experts believe this may play a direct role in causing the diseases linked to abdominal obesity.
But not everyone agrees. Samuel Klein, who heads the Center for Human Nutrition at the Washington University School of Medicine in St. Louis, has published data showing that key factors in those diseases—such as insulin sensitivity and triglyceride levels—are more tightly linked to the amount of fat inside the liver rather than outside it, although the two tend to track one another. Belly fat, he believes, is a marker of risk, not a cause, but it is an important indicator and a whole lot easier to size up than liver fat. Just use a tape measure.
Another area of uncertainty is why we pack on visceral fat with aging. Clearly, sex hormones are involved, given that the change occurs in women around menopause. But it is more complicated than just a drop in estrogen. Consider, for instance, that young women with polycystic ovary syndrome tend to have the apple shape and insulin resistance, although their bodies produce plenty of estrogen. Such women do, however, have high levels of androgens. Or consider that when transgender males—who are biologically female—take androgens to masculinize their body, they, too, develop more visceral fat and glucose intolerance. Both examples suggest that “a relative imbalance” of male and female hormones may be at work, says endocrinologist Margaret Wierman of the University of Colorado Denver. The same might also be true of healthy women at menopause.
But this isn't settled science. A newer theory made a splash last year after researchers reported in Nature that they could radically reduce body fat—including visceral fat—and raise metabolic rates in mice by blocking the action of follicle-stimulating hormone (FSH), a substance better known for its role in reproduction. Could FSH be the key to the midlife weight puzzle? The researchers had previously shown that blocking FSH could halt bone loss, raising the intriguing prospect of a medical twofer: one drug to combat obesity and osteoporosis. “The next step is to take this to humans,” says senior author Mone Zaidi of the Icahn School of Medicine at Mount Sinai.
Of course, many a thrilling discovery in mice has fizzled in humans, and combating the evolutionary programming for storing fat is particularly difficult. Klein, for instance, has tested whether removing body fat with liposuction or surgically excising visceral fat in obese patients would reduce risk factors for diabetes and heart disease. No dice. “They looked better,” he says, but in terms of metabolic benefits, “it was a bust.”
As far as we know, there's only one way to fight nature's plan for a thickening middle and its attendant risks—and you know where this is going. Eat less or exercise more as you age, or do both. Adding more muscle will also keep your metabolic rate perky, so best to hit the gym.