Physical Activity Alone Doesn't Prevent Weight Gain for Most Women

I am often asked by my patients if it is possible to prevent weight gain by maintaining high activity levels, without giving special consideration towards food intake. An important study from the Journal of the American Medical Association tells us that physical activity is not enough to prevent weight gain for most women.
The study by I-M Lee and colleagues surveyed over 34,000 American women over a 16 year period, and asked them to report their weight and physical activity levels. They were classified into one of three levels of activity:

less than 150 minutes of moderate intensity exercise per week
150-420 minutes of moderate intensity exercise per week
420 or more minutes of moderate intensity exercise per week (at least 1 hour per day)

The study found that for women who were overweight, there was no difference in weight gain over time between each activity group. It did not seem to matter how much exercise overweight women engaged in; weight gain was the same regardless.
Interestingly, they found that physical activity was helpful to prevent weight gain in some women who were not overweight (ie, with a Body Mass Index of ≤ 25; you can calculate your own BMI here, in the right hand column). It is no cake walk, though (so to speak) - in order for normal weight women to prevent weight gain with exercise, they had to engage in at least one hour of exercise per day.
The take home messages, as I see them, are:
1. For most women, exercise alone is not enough to prevent weight gain. Weight management is more about watching what you eat, rather than how much you exercise.
2. Regardless of whether or not exercise will prevent further weight gain, it is still very important to exercise for its other health benefits! Exercising for 150 minutes per week has been clearly shown to lower the risk of chronic diseases, so it remains of crucial importance to continue to exercise for the benefit of your overall health. (Before engaging in, or stepping up, an exercise program, be sure to speak with your doctor to make sure you are making changes safely.)
3. For normal weight women, at least an hour a day of moderate activity is necessary for exercise alone to prevent weight gain over the long haul.
You can read about the Canadian Physical Activity guidelines here to find out how much exercise is recommended. Check out Health Canada's website for further details, and some great ideas as to how you can work exercise into your daily life!
Dr. Sue © 2011 www.drsue.ca drsuetalks@gmail.com