Diet and exercise are both important for weight loss. What you eat affects your health and physical activity has numerous health benefits. But, if you really want to see that number on the scale drop, what you put in your mouth matters most. People who simply cut calories to slim down lose about 2 pounds a week, says a study in the International Journal of Obesity and Related Metabolic Disorders. At the same time, people who exercise but don't restrict calories drop less than half a pound each week.
Why doesn't physical activity produce the same pound-dropping results as calorie restriction? One thought is that though exercise burns calories, it doesn't rev your metabolism, says a study in Obesity Reviews. It also doesn't prevent your metabolism from slowing as you lose pounds. As you slim down-via any method-your metabolism slows incrementally with your weight loss and, despite what many believe, exercising doesn't keep that from happening. As you lose weight, you burn fewer calories via exercise. For example, a 150-pound person who works the elliptical for 30 minutes burns about 306 calories. After losing 10 pounds, that person will burn about 286 calories doing the same workout. So to burn 306 calories, you'd need to extend your workout.
Think diet and exercise combined equals more weight lost? Guess again: research shows people who diet and exercise for weight loss drop the same amount of weight as people who only diet. They are, however, more successful keeping the weight off than their counterparts who simply eat less.
Bottom line: Cut calories to lose weight. But add in some activity to stay slim long term. Plus, exercise can boost your mood and energy.