Factoring exercise into the middle-aged fight against fat

The dread of the midlife spread, the battle of the bulge, the fight against fat: Whatever you call it, Americans are at war with their waistlines, and many are losing. But a new Public Health Sciences Division study shows that regular, long-term exercise is an effective way for middle-aged adults to keep the scale from creeping upward.

The observational study of more than 15,000 middle-aged adults, led by Dr. Alyson Littman, examined the associations between physical activity and weight change after age 45 in a subset of participants enrolled in the Vitamins and Lifestyle (VITAL) study. The participants recalled their physical activity — with a focus on activity type, intensity and frequency — and weight over the previous 10 years. The researchers found that people tended to gain about a pound each year between the ages of 45 and 55. Although no groups within the study were successful at maintaining or losing weight, the findings indicated that physical activities performed on a consistent basis over a long period resulted in significant reduction in weight gain.

Previous findings inconsistent

"A lot of previous studies had inconsistent results," Littman said. "There weren't a lot of longitudinal studies on this, so this seemed like a good opportunity in this cohort to look at this question. Also, it was very timely because obesity is such a big problem right now. There have been some recent studies showing that various commercial weight-loss programs are not that successful over the long-term."

Although midlife changes in metabolism, hormones, food intake and physical activity levels often cause weight gain, Littman speculates that she would have seen similar weight increases with most age groups. "I don't think it's necessarily specific to this age," said Littman, a postdoctoral research associate in PHS. "Especially in the last 10 years, surveys of the U.S. population indicate a general trend of weight gain from adolescence through adulthood."

Excess weight increases the risk of high cholesterol, high blood pressure and insulin resistance, which can lead to diabetes. All of these factors increase the risk of heart disease and other ailments.

"A tiny, daily imbalance in energy intake over expenditure, maintained for years, will lead to obesity," said co-author Dr. Alan Kristal, a researcher in the center's Cancer Prevention Program. "Even moderate exercise, like walking, can help maintain a normal weight as you age. You don't need to jog or climb mountains, but these won't hurt either."

Walking was the most common form of exercise reported by the study participants. Moderate and fast walking (two or more miles per hour) was associated with less weight gain, except in normal-weight men, as were running and jogging. Some types of activity proved more beneficial for one gender, in part because they were more commonly practiced by that gender: Aerobic classes or videos helped women stave off pounds, while fast cycling and stair-machine use proved effective for men. Swimming, weight lifting or a slow pace of cycling, walking or stair-machine use were not associated with less weight gain for men or women.

Since obese individuals burn more calories doing the same amount of activity as their leaner peers, a greater association between exercise and weight maintenance was seen in this group. Obese women and men who walked fast for 75 to 100 minutes each week gained 9 and 5 pounds less, respectively, than non-walkers. For equal weight maintenance or weight loss over time, lower-weight participants needed to exercise more than their heavier counterparts.

Increased activity needed

Littman and colleagues found that this cohort overall was not successful in maintaining or losing weight during the study's span. "There were certainly some individuals who lost weight or maintained weight. It's not impossible," she said. "I don't think it's necessarily easy, though. As a population, we're not moving in the right direction."

"Studies like ours say to maintain your weight, you really do have to be pretty active. The Surgeon General's recommendation of 60 to 90 minutes (of exercise per day) is right on. It's not an overestimate. You don't have to run for 60 or 90 minutes. The key is including activity, whether it's parking your car farther from work, taking the stairs, going for a walk at lunch, things like that — it doesn't have to be all at once. Just try to be as active as possible."

Dr. Emily White was the third author of the NCI-funded study. White is the principal investigator of the VITAL study. The findings were published in the Jan. 11 edition of the International Journal of Obesity.