Karen Collins, MS, RD, CDN
American Institute for Cancer Research
Surveys reveal that many Americans are confused by the conflicting messages about nutrition and wellness that inundate magazines, newspapers and TV news programs. Unfortunately, messages about physical activity can be just as erratic. Fortunately, research is now providing evidence on just how much activity is needed to stop weight gain and support weight loss.
The STRRIDE study is one example of researchers taking a closer look at how activity alone can be used to combat obesity without any changes to diet. Participants in the study (sedentary overweight and mildly obese men and women) were assigned to one of four groups that differed in amount and intensity of exercise.
Researchers saw a direct relationship between amount of physical activity and changes in weight. After eight months, almost 75 percent of those assigned to the no-exercise control group gained weight. Among the exercisers, participants needed to accumulate the equivalent of six to seven miles of walking each week (an average of about 20 minutes a day of moderate walking) just to prevent weight gain.
Dietary interventions in addition to increased activity are almost always needed if someone is looking to lose weight and maintain that leaner frame. One study followed women who began a program to change eating and exercise habits for two years. Those who achieved and sustained at least a 10 percent weight loss had added about 275 minutes of moderate activity a week to their sedentary lifestyle – the equivalent of about 40 minutes of daily activity or 55 minutes, 5 days a week.
In an earlier study, maintaining weight loss took more activity than that. The study began following over two dozen women within three months after they reached their weight loss target. One year later, sedentary women had gained more than 15 pounds compared to an average 5-pound gain among women who created a physically active lifestyle. According to the researchers, the threshold to maintain weight loss averaged 80 minutes a day of moderate activity or 35 minutes a day of vigorous activity.
We don’t know all the reasons for the different levels of physical activity necessary to maintain weight loss in these and other studies. But experts speculate that the actual activity level needed varies for each of us depending on metabolism, how much we sit or move throughout our day’s activities and how many calories we consume. The one consistent finding, however, is that for almost everybody, some daily physical activity is essential.
Inherited genetic tendencies can also impact weight gain. Although some people may want to give up the battle altogether if they feel their weight woes are genetic, new research suggests that at least some inherited tendencies may be overcome with adequate physical activity. One study found that carriers of a common weight-related gene were more likely to be overweight if they exhibited below average physical activity. That same genetic variable had little impact on weight among those with above-average activity levels.
Physical activity influences weight by burning calories and increasing metabolic rate as muscle tissue is built and maintained. But it may also impact weight as part of a “constellation” of health behaviors. Since physically active people tend to eat more healthfully, some researchers question whether activity’s impact on stress, mood, self-image or other factors might help support the dietary behavior changes that are usually vital to long-term weight control.