How much weight lifting or other exercise is optimal for fitness? What is the right amount of carbohydrate restriction or fasting for sustained weight loss and health? What level of exposure to allergens will reduce allergies? How many hours of sun tanning is healthy? How frequently should plus lenses be worn to reduce myopia? Do I need to take cold showers every day to get their benefit? How much stress is enough — and how much is...

There are many different reasons that people exercise: weight loss, cardiovascular health, strength improvement, stress reduction, recreation, and more. If you are looking for recreation and stress reduction, mildly aerobic exercise such as walking, jogging or swimming can be beneficial. If you want to lose weight, the evidence is fairly clear that dietary changes have a much more significant impact than most forms of exercise. If y...