Williams reports these findings in the May issue of the American Journal of Clinical Nutrition . They are the latest results from the National Runners' Health Study, ongoing research that is headed by the Berkeley Lab life scientist.

Aside from the sagging egos that are associated with bulging beltlines, there are also serious health consequences.

Expanded waists usually are the result of increased abdominal fat. According to a large body of scientific evidence, this fat is linked to high cholesterol, high blood pressure, diabetes, and heart disease.

Williams says the current study was designed to explore the fundamental question of whether middle-age weight gain is a basic physiological consequence of aging or the result of declining activity levels.

The study showed that in 4,769 runners between the ages of 18 and 50, weight gain occurred at the same rate almost regardless of the number of miles run per week. Per decade, the average six-foot-tall man gained about 3.3 pounds and about 3/4 inches around the waist.

Over the years, this weight gain adds up. Among the under-30 age group of runners in the study, 21 percent were moderately overweight; in the 45-49 age group, 30 percent were overweight.

Says Williams, "Our data suggests that you can probably compensate for middle-aged weight gain by becoming more active. By annually increasing weekly running distance by about 1.4 miles, we estimate that the effects of exercise should compensate for the expected weight gain during middle age. What this means is that runners who average 10 miles per week at age 30 should increase their weekly running distance to 24 miles by age 40 if they plan to still fit into the tuxedo they bought a decade earlier."

The findings in this study reveal a contradiction inherent in the current national health policy.

The widely following guidelines for recommended weight -- the Department of Agriculture's 1995 Dietary Guidelines for Americans -- set the same overweight standards for young and old alike. Likewise, the federal guidelines for physical activity are the same, calling for equal amounts of exercise for both younger and older adults. Both the Surgeon General and the Centers for Disease Control and Prevention recommend 30 minutes of moderate physical activity for everybody on most days of the week.

Williams says the government's recommendations for physical activity and for weight are in conflict.

"If the federal weight standard is going to make no distinction for age, then we believe that physical activity guidelines should recommend substantial increases in activity over time. The alternative," says Williams, "is to adopt a weight standard that accommodates the normal consequences of aging. Earlier versions of the federal weight guidelines allowed people to gain weight as they age."

Without doubt, physical inactivity and dietary choices play a major role in the prevalence of obesity in this country. However, says Williams, the results of this study indicate that physiological changes that occur as we age also lead to weight gain. The underlying cause of these physiological changes remains an enigma. Some suggest declining testosterone or "male menopause" as a cause. Several genes recently have been identified that may regulate weight. Williams suggests that runners may be ideal subjects for a study to reveal the biological basis of middle-age weight gain since running appears to reduce the influences of inheritance and diet, but not middle age.

Women may wonder what this study portends for them. Currently, WIlliams is examining the pattern of weight gain in women runners, a pattern which could be fundamentally different from that observed in men. Prior to menopause, women tend to gain fat in their hips and thighs rather than in their waists, and they may be particularly vulnerable to weight retention after pregnancy.

Berkeley Lab conducts unclassified scientific research for the U.S. Department of Energy. It is located in Berkeley, California and is managed by the University of California.