Weight Gain Prevention - An Hour of Exercise Every Day?

If you've been watching or reading the news at all this week, you've probably seen the headlines ( "Women need hour of exercise to keep off pounds," "Women should exercise an hour a day to maintain weight, study says") about a recent study published in JAMA concerning women and weight gain prevention. To summarize, the study involved following 34,079 women over 13 years to learn about their exercise habits and how those habits affected their weight. Throughout that time period, these women would report their physical activity and body weight. The women who successfully maintained their weight exercised at least 21.5 MET hours a week, which study authors averaged out to be 60 minutes of moderate exercise a day.
Obviously, plenty of media outlets have covered this story and many of our About.com Guides (like Wendy, our Walking Guide) and have done a stellar job of covering it as well, but headlines like this drive me crazy for a variety of reasons. For one, there are many flaws in a study like this and Dr Rich, our Heart Disease Guide does an amazing job of spelling out these flaws. My beef has to do with what I think are the two biggest issues:
Diet. This study involved only exercise habits, not diet which is a crucial part of both losing weight and preventing weight gain. The study claims these women were following a 'usual diet,' but what does that mean? Maintaining a balance of calories can be accomplished with both exercise and diet. Using only exercise without changing how you eat is better than nothing, but if you're eating an unhealthy diet, you'll absolutely have to exercise more to offset the extra calories and prevent weight gain.
Intensity. The study concluded that the women averaged 60 minutes of moderate exercise a day, but this broad generalization doesn't take into account different intensity levels. They actually based this amount of exercise on how many METs (Metabolic Equivalent Tasks) the women expended each week. A MET is a ratio that compares your metabolic rate while at rest to other activities. So that means when you're at rest, you expend 1 MET every hour. Taking a stroll might burn twice as much as being at rest, expending 2 METs an hour. Jogging at a 12-minute-per-mile pace would expend 8 METs an hour. That means that if one of these women jogged for an hour at a 12-minute per mile pace 3 times a week, she would easily surpass the 21.5 METs of the successful women in the study, all with just 3 days of exercise. The harder you exercise, the more METs you expend and the more calories you burn, which can change how often and how long you need to exercise.
The truth is, no one can tell you exactly how much exercise you need. It depends on so many things - how active you are, your diet, age, gender, genetics, metabolism and proper planet alignment. Headlines like these can scare people who already struggle to stay active, but the kind of broad generalizations that come from these kinds of studies are just that: Broad generalizations that will never fit every person.
What do you think about this study and how the media is handling it? Will this discourage people or encourage them? Leave a comment and tell us what you think.
Weight Gain Prevention - An Hour of Exercise Every Day? originally appeared on About.com Exercise on Friday, March 26th, 2010 at 05:00:53.