(paraphrased from nytimes.com magazine 04/2018)
I find this article a fascinating expose’ of what our bodies are encountering in a weight loss journey. It’s not the straight and narrow math that we’re led to believe will miraculously take the pounds off. But if one understands the process, you will hang in there longer to witness the body finally responding to your efforts.
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How exercise affects body weight is one of the more intriguing and vexing issues in physiology. Because exercise burns calories, it should in theory, produce weight loss, a fact that has prompted countless people to undertake exercise programs to shed pounds. Without significantly changing their diets, few succeed.
The newest science suggests that exercise alone will not make you lose weight, but it may determine whether you keep the weight off once you achieve the loss. It’s not about abandoning exercise as a weight-loss tool, but understanding what exercise can and cannot do. Exercise impacts metabolism, appetite and body composition, though the consequences of exercise can vary. Women’s bodies, for instance, seem to direct them to eat more compared with men, after exercise.
Barry Braun, an associate professor of kinesiology at the University of Massachusetts at Amherst, notes that. “The body aims for homeostasis, it likes to remain at whatever weight it’s used to. So even small changes in energy balance can produce rapid changes in certain hormones associated with appetite, particularly acylated ghrelin, which is known to increase the desire for food, as well as insulin and leptin, hormones that affect how the body burns fuel.
In a 2009 a study was undertaken at University of Mass Amherst to study exercise’s impact on appetite between men and women. Eighteen overweight or obese men and women completed four bouts of exercise on a treadmill for four days. The study showed that after exercise, the hunger hormone acylated ghrelin increased and insulin levels decreased in women compared with before exercise. This change was not observed in the men. Women’s bodies were directing them to eat more to make up for the expended energy, most likely a result of the biological need to maintain energy stores for reproduction. So yes women, it can be harder for us to lose weight compared with men.
Thankfully there has been encouraging news about exercise and weight loss. In a women’s health study published by The Journal of the American Medical Association, researchers looked at the weight-change histories of more than 34,000 participants.
The women began the study middle-aged (at an average of about 54 years) and were followed for 13 years. During that time, the women gained, on average, six pounds. The subset that gained the least amount of weight over this time period reported exercising almost every day for an hour or so. The exercise involved was not strenuous, the equivalent of brisk walking.
In another representative experiment, 97 healthy, slightly overweight women were put on an 800-calorie diet until they lost an average of about 27 pounds each. Some of the women were then assigned to a walking program, some were put on a weight-training regimen and others were assigned no exercise; all returned to their old eating habits. Those who stuck with either of the exercise programs regained less weight than those who didn’t exercise and, even more striking, did not regain weight around their middles. The women who didn’t exercise regained their weight and preferentially packed on these new pounds around their abdomens. It’s well known that abdominal fat is particularly unhealthful, increasing risk of heart disease, stroke and type 2 diabetes. These results strongly suggest that if you can somehow pry off the pounds, exercise may be the most important element in keeping the weight off.
Braun says scientists are “not really sure yet” just how and why exercise is so important in maintaining weight loss in people, but in animal experiments, exercise seems to remodel the metabolic pathways that determine how the body stores and utilizes food. In a study performed at the University of Colorado at Denver, rats were put on diets and divided between those who were required to exercise and those that were sedentary. In the last month the rats were allowed to go back to eating as much as they wanted. The rats that had not been running on the treadmill fell upon the food eagerly. Most regained the weight they lost and then some.
But the exercising rats metabolized calories differently. They tended to burn fat immediately after their meals, while the sedentary rats’ bodies preferentially burned carbohydrates and sent the fat off to be stored in fat cells. The running rats’ bodies, meanwhile, also produced signals suggesting that they were satiated and didn’t need more kibble. Although the treadmill exercisers regained some weight, their relapses were not as extreme. “Exercise “re-established the homeostatic steady state between intake and expenditure to defend a lower body weight,” the study authors concluded. Running had remade the rats’ bodies so that they ate less.
So here’s a thought, just like the body initially fights weight loss by increasing hunger and slowing metabolism, it initially fights weight gain by more efficiently utilizing calories which is helped along with exercise! Use this information to your advantage, especially if you are at or close to your desired weight.
And women, no you’re not crazy when you complain how difficult it is to lose weight. But knowing what you’re up against is a big part of the battle to lose it.
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