As part of the study, the nurses periodically fill out questionnaires about their health, weight, diet and behavior.
The new analysis, published in the June 28 issue of Archives of Internal Medicine, looked at weight change and behavior from 1989 to 2005.
Researchers found women in their 30s and 40s who increased physical activity like brisk walking and bicycling by 30 minutes a day during the 16-year period maintained their weight and even lost pounds.
But those whose exercise was slow walking did not lose any weight.
Anne C. Lusk, a research fellow at the Harvard School of Public Health and author of the paper said the findings are "highly suggestive that bicycling is highly beneficial in women."