Exercise Equals Weight Loss? Or Hunger?

Taubes' intro is masterful:
"If lean people are more physically active than fat people—one fact in the often-murky science of weight control that’s been established beyond reasonable doubt— does that mean that working out will make a fat person lean? Does it mean that sitting around will make a lean person fat? How about a mathematical variation on these questions: Let’s say we go to the gym and burn off 3,500 calories every week—that’s 700 calories a session, five times a week. Since a pound of fat is equivalent to 3,500 calories, does that mean we’ll be a pound slimmer for every week we exercise? And will we continue to slim down at this pace for as long as we continue to exercise?"

Read more: Does Exercise Really Make Us Thinner? -- New York Magazine http://nymag.com/news/sports/38001/#ixzz0e7FSe0yV"

The answer is - no.  Once thought through, that answer seems the commonest of common sense.  After all, if it were not true, lumberjacks would all have starved to death, leaving only typists and other office workers to rule the world.  In other words - the body must have a mechanism to increase hunger based on increased physical activity or we would starve to death with our first bout of several days of increased physical activity.

“Vigorous muscle exercise usually results in immediate demand for a large meal,” noted Hugo Rony of Northwestern University in his 1940 textbook, Obesity and Leanness. “Consistently high or low energy expenditures result in consistently high or low levels of appetite. Thus men doing heavy physical work spontaneously eat more than men engaged in sedentary occupations. Statistics show that the average daily caloric intake of lumberjacks is more than 5,000 calories, while that of tailors is only about 2,500 calories. Persons who change their occupation from light to heavy work or vice versa soon develop corresponding changes in their appetite.” If a tailor becomes a lumberjack and, by doing so, takes to eating like one, why assume that the same won’t happen, albeit on a lesser scale, to an overweight tailor who decides to work out like a lumberjack for an hour a day?"

The speculation - that populations and individuals fatten due to too little physical activity - has an appeal to the moralist in us; "it's their own fault."  It's a moral failing.  But what if it isn't?  What if we're eating the wrong foods, egged on by governments and impassioned vegetarians and other interest groups?

The conjecture that inactivity throws off the body's fat regulatory systems seems to be supported the observation that the obese are less active than the lean.  However, as with any correlate, the challenge for science is to utilize the scientific method to determine causality.  In this case, scientists have been unable to show that in fact, sloth leads to obesity.  Instead, what they find is that the obese often eat fewer calories than the lean, and that increasing the activity level of the obese does not prove to be a long term solution to their body fat problem.

Taubes continues:  "Meanwhile, the evidence simply never came around to support Mayer’s hypothesis, even though our beliefs did. My favorite study of the effect of physical activity on weight loss was published in 1989 by a team of Danish researchers. Over the course of eighteen months the Danes trained nonathletes to run a marathon. At the end of this training period, the eighteen men in the study had lost an average of five pounds of body fat. As for the nine women subjects, the Danes reported, “no change in body composition was observed.” That same year, F. Xavier Pi-Sunyer, then director of the St. Luke’s–Roosevelt Hospital Obesity Research Center in New York, reviewed the studies on exercise and weight, and his conclusion was identical to that of the Finnish review’s eleven years later: “Decreases, increases, and no changes in body weight and body composition have been observed,” Pi-Sunyer reported."

"As for the authorities themselves, the primary factor fueling their belief in the weight-maintaining benefits of exercise was their natural reluctance to acknowledge otherwise. Although one couldn’t help but be “underwhelmed by” the evidence, as Mayer’s student Judith Stern, a UC Davis nutritionist, wrote in 1986, it would be “shortsighted” to say that exercise was ineffective because it meant ignoring the possible contributions of exercise to the prevention of obesity and to the maintenance of weight loss that might be induced by diet. These, of course, had never been demonstrated either, but they hadn’t been ruled out. This faith-based philosophy came to dominate scientific discussions on exercise and weight, but it couldn’t be reconciled with the simple notion that appetite and calories consumed will increase with an increase in physical activity. Hence, the idea of working up an appetite was jettisoned. Clinicians, researchers, exercise physiologists, even personal trainers at the local gym took to thinking and talking about hunger as though it were a phenomenon exclusive to the brain, a question of willpower (whatever that is), not the natural consequence of a body trying to replenish itself with energy."

It does not matter how you try to starve the body - the result is the same.  Hunger, listlessness, irritability, feeling cold relative to the real temperature; one or more of these symptoms will be evident as the body responds to deprivation of energy by trying to conserve what is available.  Fat loss, then, results from making available the fat stores as an energy source, such that the body is never starved for energy.  Theoretically, exercise might contribute to that process by improving insulin sensitivity, but such has not yet been proved.