Did you know that the human body is programmed to work against your weight loss efforts? In fact, it’s programmed to defend its weight and, when it senses weight loss, it starts cutting down its energy expenditure.
To understand why this is, it’s important to first know how the body expends energy (or burns calories). Roughly 65-70% of calories burned each day are used just to keep the routine body functions going, like pumping blood. The body burns about another 10% of calories digesting what we eat, and it’s called the “thermic effect” of food. The rest, approximately 20%, is spent by the muscles in physical activity. (You can read in more detail about how the body burns calories here.)
Researchers have over two decades of data looking at the daily resting metabolic rate (RMR) of obese women who had lost weight (and were no longer obese) compared with women who were never obese. RMR is the number of calories a body needs to just exist. The researchers found that the post-obese women had metabolic rates around 15% lower than the never-obese group–and they ate less. The research points to the conclusion that the metabolism in people who have lost weight and those who are lean may not be the same.
In another study, 10 women with moderate obesity and 10 lean women were measured during periods of eating and exercise. Eating prior to exercise increased the exercise metabolic rate in lean women by 11% but only by 4% in obese women. The “thermic effect” of food was only 1.02 times greater during exercise than at rest for women with obesity, but 2.54 times greater for the lean women.
In 1995 important research was uncovered about how when the body loses weight, it adjusts by reducing its energy expenditure. This effect is so strong that an obese person who went from 250 pounds to 200 pounds would have to consume about 30% less than a 200 pound person who had not lost weight just to maintain the same weight. And for the person to maintain their weight loss, this extra-reduction in calories would need to continue indefinitely. The researchers called this process “adaptive thermogenesis”, and it can persist after active dieting for up to a year, according to one study.
Some scientists blame adaptive thermogenesis for the “plateau” we often see while dieting, the increase in hunger and weight regain. Adding to the complexity, individuals will have different adaptions to weight loss. In some cases, the effect can be significant, while for others it is not. What’s important to know is that our bodies contain a defensive mechanism against losing weight or especially against maintaining weight loss and thus, fighting obesity is much more difficult than many people presume.
Dr. Gregory Walton, expert bariatric surgeon in Oklahoma said, “As bariatric surgeons we have long known about metabolic set points and how our bodies defend them to maintain body mass. Our “knowledge” was observational only. . .until now. Research (current and others) have uncovered some of the details behind the “metabolic set point” curtain. After all, obesity is a metabolic disease–not a disease of weak willpower, as many are apt to assign blame. A mountain of willpower cannot make our metabolic rate move up or down 30%.”
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Weight Loss Studies & Clinical