Though all the contestants lost dozens of pounds through diet and exercise at the end of the show, six years later, their waistlines had largely rebounded. Thirteen of the 14 contestants in the study put a significant amount of weight back on, and four contestants are even heavier today compared with before they went on the show. But the participants' metabolisms had vastly slowed down through the study period.
Their bodies were essentially burning about calories fewer about a meal's worth on average each day than would be expected given their weight. And this effect lasted six years later, despite the fact that most participants were slowly regaining the weight they lost.
Sandra Aamodt, a neuroscientist and author of the forthcoming book Why Diets Make Us Fat , explained this may be the body's way of vigorously defending a certain weight range, called the set point. Once you gain weight, and keep that weight on for a period of time, the body can get used to its new, larger size. When that weight drops, a bunch of subtle changes kick in — to the hormone levels, the brain — slowing the resting metabolism, and having the effect of increasing hunger and decreasing satiety from food, all in a seeming conspiracy to get the body back up to that set point weight.
In the Biggest Loser study, for example, the researchers found each participant experienced significant reductions in the hormone leptin in their bloodstreams. Leptin is one of the key hormones that regulate hunger in the body. By the end of the Biggest Loser competition, the contestants had almost entirely drained their leptin levels, leaving them hungry all the time. At the six-year mark, their leptin levels rebounded — but only to about 60 percent of their original levels before going on the show.
But not every kind of weight loss in every person results in such devastating metabolic slowdown. For example: That great effect on leptin seen in the Biggest Loser study doesn't seem to happen with surgically induced weight loss. Indeed, all the researchers I spoke to thought the effects in the B iggest Loser study were particularly extreme, and perhaps not generalizable to most people's experiences.
That makes sense, since the study involved only 14 people losing vast amounts of weight on what amounts to a crash diet and exercise program. The Mayo Clinic's Jensen said he hasn't found in his patients as dramatic a slowing of the metabolism in studies where people lose about 20 pounds over four months.
With slow, gradual weight loss, the metabolic rate holds out really well. There are some interesting hypotheses, however. One of the most persistent is an evolutionary explanation.
That ability would to some extent increase our ability to survive during periods of undernutrition, and increase our ability to reproduce — genetic survival. Today, the thinking goes, this inability to keep off weight that's been gained is our body defending against periods of undernutrition, even though those are much rarer now.
But not all researchers agree with this so-called "thrifty gene" hypothesis. As epigeneticist John Speakman wrote in a analysis , one issue with the hypothesis is that not everybody in modern society is fat:. We would all have the thrifty alleles, and in modern society we would all be obese.
Yet clearly we are not. If famine provided a strong selective force for the spread of thrifty alleles, it is pertinent to ask how so many people managed to avoid inheriting these alleles.
And, Rosenbaum added, "The evolution of our genetic predisposition to store fat is quite complex. It involves a frequently changing environment, interactions of specific genes with that environment, and even interactions between genes.
Jan 22 People often blame weight gain on a slow metabolism… but do you actually have one? Fortunately, there may be ways to tweak your metabolism to get it running in a healthier way. The myths of metabolism Some of the things you think you might know about your metabolism might not be true.
Signs of a fast metabolism You may have a naturally fast metabolism. Signs of a slow metabolism Do you think you might have a slow metabolism? On the positive side, having a slower metabolism might delay the aging process for you.
Here are important lifestyle modifications you can make to adjust your metabolism: Move your body, even in small ways, throughout the day. Reach and maintain your healthy weight. New York, N. Factors affecting weight and health. Accessed Feb.
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Reprint Permissions A single copy of these materials may be reprinted for noncommercial personal use only. Your BMR falls, or slows, with weight loss. To add to the frustration, your brain also sends signals to your body that increase hunger and reduce the number of calories you burn. Evolutionarily, this was a protective mechanism to keep you from starving. Today it is a major cause of weight regain. This may seem depressing, but you do have some control over the rate at which your metabolism falls.
You can keep your metabolism from slowing too much by losing weight slowly versus through a crash diet. Roberts, Ph. Once you have lost weight and stabilized, if you have been going at a moderate rate of one to two pounds per week, there does not seem to be a long-term impact. Your metabolism is lower because you are now a smaller person, but not disproportionately low.
Featured Recipe: Mexican Cabbage Soup. Weight loss isn't the only culprit for a slower metabolism. If you eat too few calories or go too long between meals more than three or four hours , your metabolism will slow down. This is known as "starvation mode" and is due to the same protective mechanism that happens when you lose weight.
Your body slows down the rate at which it's burning calories in order to conserve energy, because it doesn't know when you are going to feed it again. This is a double whammy if you are severely restricting calories to lose weight. The ratio of fat to muscle in the body also affects metabolic rate. Weight, or body composition, is made up of fat, muscle, bone and water.
Muscle is more metabolically active than fat. In other words, it burns more calories. When you lose weight, you lose both fat and muscle, unless you are doing something to preserve the muscle mass.
Losing calorie-burning lean muscle mass slows your metabolism. This can be influenced by maintaining muscle mass throughout the lifetime with weight-bearing physical activity.
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