The Anti-Obesity Actions of Exercise

Longitudinal (long-term) and cross-sectional studies have consistently shown a highly significant relationship between low levels of physical activity and obesity. A lack of exercise is believed to be one of the primary causes for the dramatic rise in obesity prevalence that has occurred in this country and throughout the industrialized world over the last several decades.

Technology has nearly eliminated exercise from our lives. Over the last half century, major technological developments have influenced dramatically levels of occupational and leisure physical activities.

The majority of jobs fifty or so years ago involved considerable physical exertion whereas most jobs today are sedentary. In the past, there were far fewer automobiles and it was not unusual to find people walking or cycling to work, to the market, church, or to visit friends. Today, most families have several automobiles, generally one for each licensed member. Walking and cycling are not only rare modes of travel in the U.S. but dangerous, as well, due to the large numbers of automobiles on public roads, few sidewalks or cycle lanes, and high crime.

Household labor-saving devices, escalators and elevators have also contributed significantly to the decline in physical activity. And, as discussed in the December issue of Beyond Change, studies have found that turning on the TV ‘turns on the pounds’ and that Americans are spending 3 to 4 hours per day watching TV. Time spent in front of the TV, as well on the computer, significantly reduces that available for physical activity. One survey found that 24% of Americans participate in no leisure time activity and another study found that nearly 60% of the population exercise occasionally or not at all.

An individual becomes obese when energy intake (food intake) exceeds energy expenditure (calories burned). Physical activity increases metabolic rate above resting levels, and the body burns more calories. Take for instance, a 150-pound man watching TV. During a 30-minute program, he will have burned a total of approximately 30-35 calories. Had he spent that same amount of time jogging, his body would have burned 250 calories; swimming, 286 calories; or walking briskly, 161 calories. Furthermore, even though he may return to his chair in front of the TV after the exercise bout, his metabolic rate will remain elevated above resting levels for some time following, dependent upon the exercise intensity and his level of fitness.

Increased metabolic activity associated with exercise, however, is only one of a number of reasons why numerous studies have found that exercise lowers the risk for weight gain, assists diet in inducing weight loss, and helps to maintain weight loss long-term.

Walking, jogging, cycling, swimming, dancing and other so-called ‘aerobic’ exercises change the way the body metabolizes fat. Exercise increases the release of certain nerve messengers and adrenalin that increase fat breakdown of stored fat, reducing the size of fat storage depots and making more fat available to be burned for energy by the muscle during exercise. Aerobic activities performed on a regular basis also alter muscle metabolism in such a manner as to increase the amount of fat the body uses during exercise. Overall, such changes would reduce body fat by stimulating fat breakdown and by increasing the amount of fat burned for fuel.

Exercise also lowers blood sugar and reduces the production of the hormone, insulin. Sugar can be converted into fat. A reduction in blood sugar would reduce fat production and storage. A decrease in blood sugar would also lower the need for high insulin production. Insulin causes fat accumulation by inhibiting the breakdown of fat and by driving fat into storage depots. Lower insulin levels with exercise would lead to an increase in fat breakdown and utilization, resulting in a reduced risk for fat accumulation.

In addition to its lowering effects on insulin, exercise temporarily increases levels of hormones that stimulate the breakdown of fat, such as growth hormone, prolactin, glucagon, and testosterone. And, exercise is believed to assist in weight loss efforts by increasing production of specific endorphins that reduce appetite.

Exercise may also be beneficial in reducing or maintaining body weight by increasing the production or activities of the brain messenger, serotonin. Studies have shown that the obese have low levels of serotonin and that low levels are associated with high carbohydrate cravings and intake (particularly sweets), as well as binge eating, emotional overeating and other aberrant eating behavior. Raising serotonin levels or activities reduces food cravings, improves eating behavior, and causes weight loss.

Raising serotonin also helps to improve mood, i.e. reduce feelings of depression and anxiety. Such improvement in mood may increase one’s desire for physical activity and, thereby, chance for weight loss success.

The desire to be active is also influenced by physical well-being and there are numerous studies that have shown a beneficial role of exercise in health and in disease prevention. Regular exercise lowers blood pressure and improves lipid levels, respiratory functions, and other cardiovascular indices that could contribute to heart disease and stroke.

Physical activity also reduces the risk for diabetes or improves the diabetic state and need for certain anti-diabetic medications that increase body weight. And, moderate exercise performed regularly, in addition, may lower one’s chance of cancer and various other conditions by increasing anti-oxidant defenses and by enhancing immune function. One large long-term epidemiological study has even reported that mortality risk (chance of dying) is higher for an unfit lean individual than for someone who is obese but physically active.

Perhaps, one of the most important consequences of increased physical activity is the influence that such has on the maintenance of, or increase in, muscle mass. Muscle is very metabolically active and an increase in muscle would not only increase the potential for greater energy expenditure (calorie burned) with activity but also increase resting metabolic rates, causing the body to burn more calories even while at rest or asleep.

The muscle-building influence of exercise is also a very important reason to exercise during and following a weight-loss program, including obesity surgery. Weight loss with reduced calorie intake (from diet or surgery) not only represents a loss of body fat but, often, a loss of muscle, as well. A decrease in muscle mass would lower resting metabolic rate, making it more difficult to lose weight. Exercise can help to prevent muscle loss, and some exercises can even build muscle during the weight reduction period.

For all the reasons discussed above, and many more, exercise plays an important role in the ‘battle of the bulge’. The American Heart Association recommends that we exercise at least 30 minutes a day for most days, if not every day, of the week.

According to the American College of Sports Medicine, studies have found that the benefits of exercise are additive and that the benefits of walking for three 10-minute bouts, for instance, are comparable to walking for 30 continuous minutes. This is good news for the individual who has shortness of breath or joint pain or even for the individual who just feels they do not have the time to take 30 minutes or so out of their busy routine for physical activity.

Studies have also shown that individuals who increase their daily activities or reduce time spent in sedentary activities are more successful in weight loss or weight maintenance efforts. Daily physical activities can be increased in a variety of ways, such as choosing to take the stairs instead of the elevator, walking around the mall before shopping, parking a distance from the store, starting and maintaining a garden, and numerous other ways that you or members of your family may find to increase levels of daily activity. And, of course, the best way to reduce sedentary activity is to turn off the TV and limit time spent on the computer.

Next month, discussion of the anti-obesity benefits of exercise will continue with the assistance and expertise of Justine Clark, exercise physiologist, who is studying the importance of specific types of exercise (strength, aerobic, isometric) in health improvement and weight loss success of the morbidly obese surgical patient before and after bariatric surgery.

Dr. Buffington is Chief of Research at Bariatric Centers for Weight Loss Surgery, which are under the direction of Dr. Robert Marema with main offices located in Ft. Lauderdale, FL.