Want to evade extra weight as you age?

Then try to maintain a high activity level over time. This is the message of a new 20-year study showing that adults who are highly active gain much less weight by middle age. However, moderate or inconsistent activity doesn't seem to help much.

Many studies have shown that regular physical activity helps people slim down if they're overweight or obese. But surprisingly few studies have explored how physical activity can help prevent weight gain in the first place. Of course, it makes sense that people who are more active burn more calories, so they gain less weight. But what level of activity is necessary for people to keep their weight down over time—particularly as their metabolism slows in middle age?

Most participants gained some weight during this time. However, the weight gain was much less for those who were highly active throughout the study, even after taking into account other factors that might have affected their weight (for example, their age, race, alcohol use, and diet).

Highly active women seemed to benefit most, gaining 13 pounds less, on average, than their low-activity peers. Among men, those who were very active gained about 6 pounds less. But they also ate more than their less active counterparts, which might explain why the weight difference wasn't as large for highly active men as it was for highly active women.

Interestingly, participants who maintained moderate activity levels during the study gained about as much as those in the low-activity group. The same was also true for participants with inconsistent activity levels. This suggests that physical activity needs to be sustained at a high level over time to help keep weight off.

So is "high activity" as daunting as it sounds? Not necessarily. It can involve many different things, say the researchers, including walking briskly, playing basketball, taking an exercise class, or performing physically demanding household chores, such as vacuuming. Doing 150 minutes of such activities a week would put you in the "highly active" group. This amounts to 30 minutes a day, five days a week.

What you need to know. Regular exercise provides many health benefits, ranging from boosting your mood, to improving your sleep, to lowering your risk of heart disease, osteoporosis, and other conditions. This study supports another benefit—less weight gain by middle age for those who keep their activity levels up.

—Sophie Ramsey, patient editor, BMJ Group

ConsumerReportsHealth.org has partnered with The BMJ Group to monitor the latest medical research and assess the evidence to help you decide which news you should use.

For more easy ways to get fit and stay fit, see our 2011 guide to diet and exercise.