The Obesity Code. Jason Fung

obesity has galloped ahead full steam. It is highly improbable that decreased exercise played any role in causing obesity in the first place.

      If lack of exercise was not the cause of obesity epidemic, exercise is probably not going to reverse it.

       CALORIES OUT

      THE AMOUNT OF calories used in a day (Calories Out) is more accurately termed total energy expenditure. Total energy expenditure is the sum of basal metabolic rate (defined below), thermogenic effect of food, non-exercise activity thermogenesis, excess post-exercise oxygen consumption and, of course, exercise.

      Total energy expenditure = Basal metabolic rate + Thermogenic effect of food + Nonexercise activity thermogenesis + Excess post-exercise oxygen consumption + Exercise.

      The key point here is that total energy expenditure is not the same as exercise. The overwhelming majority of total energy expenditure is not exercise but the basal metabolic rate: metabolic housekeeping tasks such as breathing, maintaining body temperature, keeping the heart pumping, maintaining the vital organs, brain function, liver function, kidney function, etc.

      Let’s take an example. Basal metabolic rate for a lightly active average male is roughly 2500 calories per day. Walking at a moderate pace (2 miles per hour) for forty-five minutes every day, would burn roughly 104 calories. In other words, that will not even consume 5 percent of the total energy expenditure. The vast majority (95 percent) of calories are used for basal metabolism.

      Basal metabolic rate depends on many factors, including

      •genetics,

      •gender (basal metabolic rate is generally higher in men),

      •age (basal metabolic rate generally drops with age),

      •weight (basal metabolic rate generally increases with muscle mass),

      •height (basal metabolic rate generally increases with height),

      •diet (overfeeding or underfeeding),

      •body temperature,

      •external temperature (heating or cooling the body) and

      •organ function.

      Nonexercise activity thermogenesis is the energy used in activity other than sleeping, eating or exercise; for instance, in walking, gardening, cooking, cleaning and shopping. The thermogenic effect of food is the energy used in digestion and absorption of food energy. Certain foods, such as dietary fat, are easily absorbed and take very little energy to metabolize. Proteins are harder to process and use more energy. Thermogenic effect of food varies according to meal size, meal frequency and macronutrient composition. Excess post-exercise oxygen consumption (also called after-burn) is the energy used in cellular repair, replenishment of fuel stores and other recovery activities after exercise.

      Because of the complexity of measuring basal metabolic rate, non-exercise activity thermogenesis, thermogenic effect of food and excess post-exercise oxygen consumption, we make a simple but erroneous assumption that these factors are all constant over time. This assumption leads to the crucially flawed conclusion that exercise is the only variable in total energy expenditure. Thus, increasing Calories Out becomes equated with Exercise More. One major problem is that the basal metabolic rate does not stay stable. Decreased caloric intake can decrease basal metabolic rate by up to 40 percent. We shall see that increased caloric intake can increase it by 50 percent.

       EXERCISE AND WEIGHT LOSS

      CONVENTIONALLY, DIET AND exercise have been prescribed as treatments for obesity as if they are equally important. But diet and exercise are not fifty-fifty partners like macaroni and cheese. Diet is Batman and exercise is Robin. Diet does 95 percent of the work and deserves all the attention; so, logically, it would be sensible to focus on diet. Exercise is still healthy and important—just not equally important. It has many benefits, but weight loss is not among them. Exercise is like brushing your teeth. It is good for you and should be done every day. Just don’t expect to lose weight.

      Consider this baseball analogy. Bunting is an important technique, but accounts for only perhaps 5 percent of the game. The other 95 percent revolves around hitting, pitching and fielding. So it would be ridiculous to spend 50 percent of our time practicing the bunt. Or, what if we were facing a test that is 95 percent math and 5 percent spelling? Would we spend 50 percent of our time studying spelling?

      The fact that exercise always produces less weight loss than expected has been well documented in medical research. Studies lasting more then twenty-five weeks found that the actual weight loss was only 30 percent of what was expected.^{8, 9} In one recent controlled study, participants increased exercise to five times per week, burning 600 calories per session. Over ten months, those who exercised lost an extra ten pounds (4.5 kilograms).¹⁰ However, the expected weight loss had been 35 pounds (16 kilograms).

      Many other longer-term randomized studies have shown that exercise has minimal or no effect on weight loss.¹¹ A randomized 2007 study of participants who did aerobics for six days per week¹² over one year found that women reduced their weight, on average, by 3 pounds (approximately 1.4 kilograms); men, by 4 (1.8 kilograms). A Danish research team trained a previously sedentary group to run a marathon.¹³ Men averaged a loss of 5 pounds (about 2.3 kilograms) of body fat. The average weight loss for women was . . . zero. When it comes to weight loss, exercise is just not that effective. In these cases, it was also noted that body-fat percentage was not much changed.

      The Women’s Health Study, the most ambitious, expensive and comprehensive diet study ever done, also looked at exercise.¹⁴ The 39,876 women were divided into three groups representing high (more than one hour per day), medium and low levels of weekly exercise. Over the next ten years, the intense exercise group lost no extra weight. Furthermore, the study noted, “no change in body composition was observed,” meaning that muscle was not replacing fat.

       COMPENSATION: THE HIDDEN CULPRIT

      WHY DOES ACTUAL weight loss fall so far below projected? The culprit is a phenomenon known as “compensation”—and there are two major mechanisms.

      First, caloric intake increases in response to exercise—we just eat more following a vigorous workout. (They don’t call it “working up an appetite” for nothing.) A prospective cohort study of 538 students from the Harvard School of Public Health¹⁵ found that “although physical activity is thought of as an energy deficit activity, our estimates do not support this hypothesis.” For every extra hour of exercise, the kids ate an extra 292 calories. Caloric intake and expenditure are intimately related: increasing one will cause an increase in the other. This is the biological principle of homeostasis. The body tries to maintain a stable state. Reducing Calories In reduces Calories Out. Increasing Calories Out increases Calories In.

      The second mechanism of compensation relates to a reduction in non-exercise activity. If you exert yourself all day, you are less likely to exercise in your free time. The Hadza, who were walking all day, reduced their physical activity when they could. In contrast, those North Americans who were sitting all day probably increased their activity when given the chance.

      This principle also holds true in children. Students aged seven and eight years who received physical education in schools were compared to those who did not.¹⁶ The physical education group received an average of 9.2 hours per week of exercise through school, while the other group got none.

      Total physical activity, measured with accelerometers, showed there is no difference in total activity over the week between the two groups. Why? The phys ed group compensated by doing less at home. The non-phys ed group compensated by doing more when they got home. In the end, it was a wash.

      In addition, the benefit of exercise has a natural upper limit. You cannot make up for dietary indiscretions by increasing exercise. You can’t outrun a poor diet. Furthermore, more exercise is not always better. Exercise represents a stress on the body. Small amounts are beneficial, but excessive amounts are detrimental.¹⁷

      Exercise