We'll get more into gaining muscle mass in Part 3, which focuses on exercise. As we age, our metabolism begins to naturally slow down. When our metabolism decreases, our calorie intake must also decrease to compensate, or weight gain occurs. Another reason that weight increases with age is that we begin to lose muscle tissue, which, as mentioned above, burns many calories even at rest. Certain medical conditions can play a role in obesity, but they are rarely the primary cause.
Many people have a condition known as hypothyroidism, or an underactive thyroid gland.
However, people with hypothyroidism generally only gain between 5 and 10 pounds due to the condition in and of itself. In addition, most of this weight is usually fluid. It is also a critical factor in maintaining lost weight. Activity on some level is critical in keeping our metabolism elevated so we can burn more calories each day. Some exercises even help you burn more calories at rest.