Slender, physically active hunter-gatherers in Tanzania were part of a research program. They use more energy in their daily lives than most of us. However, researchers found that their low weight is not because of physical activity, but rather because of their moderate eating habits.
Most people believe that you use more energy when you exercise. However, another study showed that high levels of physical activity can actually result in the use of less energy as the body becomes more fit. If you use less energy while you exercise, your weight loss will be slower.
Scientists developed a calculator (it may take some time to open this link) to help people lose weight by dieting. You enter your sex, age, height and weight. The calculator tells you how many calories you need to maintain your current weight. You tell it how many calories you are willing to give up each day. It will tell you how much weight you will lose over time.
Exercise is still important for conditioning and strengthening your heart health.