Inactivity leads to loss of muscle, obesity, and reduced functional ability. Low physical fitness increases risk for cardiovascular disease, diabetes, and some types of cancer. Individuals who are physically fit can do more things, have better endurance for activities and tasks, and are healthier than persons who have low fitness. Obesity and low physical fitness are often related, but thin persons are not necessarily physically fit just because they are thin. Even small increases in physical fitness can make a big difference to a person's health. Incorporating small changes into daily activities can slowly and gradually improve fitness, leading to better health. The December 21, 2005, issue of JAMA includes an article about physical fitness and its effects on cardiovascular diseases.