DISCUSSION
To our knowledge, this is the first study to assess the in- dependent effect of weekly physical activity and dietary energy intake on the development of kidney stones. Postmenopausal women who performed greater amounts of physical activity were less likely to develop an incident kidney stone than inactive women, in adjusted analyses. A protective effect was identified even with small amounts of physical activity, and this protective effect increased as physical activity increased up to approximately 10 METs/wk. This threshold represents a moderate amount of weekly activity and is comparable to just over 3 hours of average walking (2–3 miles per hour), 4 hours of light gardening, or 1 hour of moderate jogging (6 miles per hour).23 This effect appears to be driven primarily by the total amount of activity rather than the intensity of exercise.
Dietary energy intake .2200 kcal/d was associated with an increased risk of incident kidney stones. This risk increased with higher energy intake. However, women with the lowest dietary energy intake did not have a decreased risk of incident kidney stones. This effect appeared to be independent of mac- ronutrient intake typically associated with kidney stone forma- tion, including water, sodium, animal protein, and calcium. Thus, separate from the risk imparted by BMI and diet, a woman