Physically active communities have minimal obesity rates. This was true for all hunter–gatherer societies, for subsistence farmers, and for children who played outdoors.1 So, how could a Time magazine article from last year advise people not to exercise for weight loss?2

The author of the article noted disappointing results for weight loss programs and wanted people to focus on other great benefits of exercise in terms of health, longevity, and happiness. Experiments using exercise to promote weight loss typically provided subjects with approximately 30 minutes per day of moderate exercise such as brisk walking. These manipulations mostly failed to produce any lasting weight loss in people who were overweight.

Does this mean that we should abandon exercise as a means of weight control? Hardly. After all, it is clear that people living in physically active communities are not overweight.3 The problem is not that physical activity does not control body weight but that these subjects did not get enough exercise to regulate body weight at a healthier level. How much is enough? Among indigenous people whose activity levels were studied in careful research, none averaged less than 90 minutes per day of vigorous physical activity.3

Imagine an experiment in which people received one-third of an aspirin to treat a headache. The researchers would falsely conclude that aspirin does not relieve pain.

In the minority of studies that had overweight subjects complete 90 minutes of exercise per day, positive results were obtained in terms of permanent weight loss. Not all of the participants benefited, however. This is because modern patterns of inactivity and nutrition alter human physiology in ways that make it difficult to maintain healthy body weight. Sugar in the diet plays a key role, as does insulin, the hormone that regulates sugar levels in the blood.

The Story of Insulin Resistance

A diet high in sugar causes obesity as established in animal experiments many decades ago in which rodents had unlimited access to sugar-laden drinking water. This principle was confirmed in a natural experiment on humans finding that people who drink a lot of sugary soft drinks are at greater risk of obesity. It is curious that we would, in effect, repeat the animal experiments on our own children and expect different results.

How does sugar in the diet produce obesity? When people consume sugary snacks, or sweet drinks, their blood sugar rises and insulin is released that draws sugar out of circulation and promotes the synthesis and storage of fats.

When the diet contains a lot of sugar, insulin levels are elevated much of the time. Consequently, insulin receptors lose their sensitivity so that blood sugar remains elevated. This condition is known as secondary diabetes and it is associated with obesity as well as many related health problems including high blood pressure, kidney disease, and liver disease.

Secondary diabetes is a tragic outcome of poor diet and exercise habits that are entrenched in modern life. It is a chronic condition and was widely considered incurable so that overweight adolescents could anticipate lifelong health challenges. Yet there is encouraging evidence that behavioral measures increasing physical activity and adopting a better diet improve weight regulation and normalize blood sugar.

Going Back to Nature

One of the most intriguing pieces of evidence involved urban Aborigines who were overweight and suffered from secondary diabetes. When they returned to their ancestral lifestyle of hunting and gathering, they lost weight and their blood sugar returned to normal levels.4 These beneficial outcomes reflected greatly increased levels of physical activity and a diet that was more varied, contained more fiber, and lacked refined sugar. Other promising evidence comes from experiments on weight loss using high levels of exercise.


The problem with exercising to lose weight is not that it is ineffective; rather, it’s that the time commitment is perceived as unreasonable. Overweight people may also suffer injuries from prolonged physical activity that discourage further exercise. This is unfortunate given the many benefits of exercise for health and longevity. Indeed, the exercise time could be more than repaid by increased longevity and improved quality of future life.

The benefits of physical activity do not require strenuous activities like running and lifting weights although such activities compress the amount of time required. For many people, it is preferable to select lower-intensity pursuits such as walking, gardening, or crafts like woodwork and house painting. Prolonged bouts of intrinsically interesting hobbies are good at mobilizing fats and save us from the dangers of spending too long sitting down. So, we should exercise to lose weight as well as to reap many other potential benefits, from better health and increased longevity to improved mood and social integration.

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