Obesity increases the likelihood of diabetes, some forms of cancer, hypertension, and other chronic diseases. According to the Centers for Disease Control and Prevention, as people age, their body composition gradually shifts — the proportion of muscle decreases and the proportion of fat increases. This shift slows their metabolism, making it easier to gain weight. In addition, some people become less physically active as they get older, increasing the risk of weight gain. But, weight gain can be prevented through good eating habits and daily physical activity.