By Barbara Berkeley
I’d be rich if I had a dollar for every time I’ve heard the word “metabolism.” Skinny people love to credit their “good metabolisms” for keeping them lean. Heavy people are certain that they have some kind of awful metabolic sluggishness. Diet books talk about ways to influence it and magazine articles tout foods that “boost” it. Personal trainers claim that building muscle speeds it up. Everyone seems to know everything about metabolism. Everyone, that is, except the people who study and research metabolism for a living.
Before we explore that issue, let’s take a minute to review what metabolism is. In scientific terms, it is simply the number of calories a person burns each day. It you burn a lot of calories, I guess you could say you have a “fast” metabolism. But here’s the paradox: heavy people burn more calories than thin ones! In other words, the very people who think they have slow metabolisms actually have “fast” ones.
ere’s the reason. The number of calories each one of us burns in a day can be calculated by a formula. We burn more if we are male, younger or bigger. Heavy people grow muscle along with their fat. This muscle acts like a scaffolding that holds up their larger weight. And since muscle burns calories, heavy people burn quite a few. In addition, any movements done by a heavy person will require more calories than those of their thin counterparts. That part is simple common sense. Moving a larger mass through space requires more energy.
With the exception of people with endocrine problems such as an underactive thyroid or those who are taking medicines that slow them or speed them up, pretty much everyone has a calorie burn that can be estimated by the standard formula.
However, one question has bedeviled metabolism scientists.
During weight loss, the amount of calories a dieter burns slows down inappropriately. This is a response to the restriction of food. Essentially, the body turns its burn process to “low” in order to conserve available energy. This is probably the reason that people reach plateaus when they diet. It is also the reason why that last 10 pounds is so tough to lose. While this phenomenon has been well described for years, there has been controversy about another question. Does this inappropriate calorie burn persist after the weight is gone?
If your metabolism is changed by weight loss and stays inappropriately low while you are maintaining, it will obviously be easier for you to regain your weight. Since you would burn fewer calories than normal, whatever you ate would tend to put pounds back on. Theoretically.
Many scientific studies have been done to figure out whether weight loss permanently lowers metabolism. Most of them have shown that metabolism after loss is normal. Recently, however, a paper by some well-known researchers at Columbia cast doubt on this finding.
You can find this research on the Science Page. It’s a tough read, so I will interpret.
Basically, the researchers put seven groups each with three people into a hospital unit where they could be observed. In each group was one person who was at their usual weight, one who had lost weight recently, and one who had lost the same amount but had kept it off for a long time. The three people were matched so that their weights and amount of muscle were very close. They were then fed a liquid diet which was fine tuned to keep them at exactly what they currently weighed. Their exercise was kept as identical as possible. Measurements of metabolism were then performed.
The result showed that in both recent dieters and longer term maintainers, the amount of calorie burn per day was lower than would be expected for their size, age and sex. In other words, there did seem to be a persistent problem with metabolism that was caused by the weight loss. Remember that this is only one study and that many others have failed to show this effect. Nevertheless, this study was well controlled and reputably done.
Perhaps most interesting was the area of metabolism that was slowed. The problem did not appear to be in the number of calories burned by the resting body. Instead, it appeared that when muscles worked, they burned less calories than would have been predicted. This effect would be camouflaged in people who exercised a lot. Because they were forcing the muscles to burn large amounts of extra calories, they were counteracting the muscle problem.
If these results turn out to be true, they will go a long way in explaining why exercise seems to be such a vital component of successful weight maintenance. The National Weight Control Registry reports that their average successful maintainer walks the equivalent of four miles per day. Most of us who are maintaining have found that we can’t do it without physical activity. On the other hand, it is perfectly possible to lose large amounts of weight without ever taking a step.
We must also keep in the mind the fact that this study did not look at people who were years into maintenance. Might their metabolisms reboot after a period of time? We don’t know.
The important message is: stay as active as possible in maintenance. Vigorous, daily exercise may be your best hedge against weight regain.
By Barbara Berkeley
I’d be rich if I had a dollar for every time I’ve heard the word “metabolism.” Skinny people love to credit their “good metabolisms” for keeping them lean. Heavy people are certain that they have some kind of awful metabolic sluggishness. Diet books talk about ways to influence it and magazine articles tout foods that “boost” it. Personal trainers claim that building muscle speeds it up. Everyone seems to know everything about metabolism. Everyone, that is, except the people who study and research metabolism for a living.
Before we explore that issue, let’s take a minute to review what metabolism is. In scientific terms, it is simply the number of calories a person burns each day. It you burn a lot of calories, I guess you could say you have a “fast” metabolism. But here’s the paradox: heavy people burn more calories than thin ones! In other words, the very people who think they have slow metabolisms actually have “fast” ones.
ere’s the reason. The number of calories each one of us burns in a day can be calculated by a formula. We burn more if we are male, younger or bigger. Heavy people grow muscle along with their fat. This muscle acts like a scaffolding that holds up their larger weight. And since muscle burns calories, heavy people burn quite a few. In addition, any movements done by a heavy person will require more calories than those of their thin counterparts. That part is simple common sense. Moving a larger mass through space requires more energy.
With the exception of people with endocrine problems such as an underactive thyroid or those who are taking medicines that slow them or speed them up, pretty much everyone has a calorie burn that can be estimated by the standard formula.
However, one question has bedeviled metabolism scientists.
During weight loss, the amount of calories a dieter burns slows down inappropriately. This is a response to the restriction of food. Essentially, the body turns its burn process to “low” in order to conserve available energy. This is probably the reason that people reach plateaus when they diet. It is also the reason why that last 10 pounds is so tough to lose. While this phenomenon has been well described for years, there has been controversy about another question. Does this inappropriate calorie burn persist after the weight is gone?
If your metabolism is changed by weight loss and stays inappropriately low while you are maintaining, it will obviously be easier for you to regain your weight. Since you would burn fewer calories than normal, whatever you ate would tend to put pounds back on. Theoretically.
Many scientific studies have been done to figure out whether weight loss permanently lowers metabolism. Most of them have shown that metabolism after loss is normal. Recently, however, a paper by some well-known researchers at Columbia cast doubt on this finding.
You can find this research on the Science Page. It’s a tough read, so I will interpret.
Basically, the researchers put seven groups each with three people into a hospital unit where they could be observed. In each group was one person who was at their usual weight, one who had lost weight recently, and one who had lost the same amount but had kept it off for a long time. The three people were matched so that their weights and amount of muscle were very close. They were then fed a liquid diet which was fine tuned to keep them at exactly what they currently weighed. Their exercise was kept as identical as possible. Measurements of metabolism were then performed.
The result showed that in both recent dieters and longer term maintainers, the amount of calorie burn per day was lower than would be expected for their size, age and sex. In other words, there did seem to be a persistent problem with metabolism that was caused by the weight loss. Remember that this is only one study and that many others have failed to show this effect. Nevertheless, this study was well controlled and reputably done.
Perhaps most interesting was the area of metabolism that was slowed. The problem did not appear to be in the number of calories burned by the resting body. Instead, it appeared that when muscles worked, they burned less calories than would have been predicted. This effect would be camouflaged in people who exercised a lot. Because they were forcing the muscles to burn large amounts of extra calories, they were counteracting the muscle problem.
If these results turn out to be true, they will go a long way in explaining why exercise seems to be such a vital component of successful weight maintenance. The National Weight Control Registry reports that their average successful maintainer walks the equivalent of four miles per day. Most of us who are maintaining have found that we can’t do it without physical activity. On the other hand, it is perfectly possible to lose large amounts of weight without ever taking a step.
We must also keep in the mind the fact that this study did not look at people who were years into maintenance. Might their metabolisms reboot after a period of time? We don’t know.
The important message is: stay as active as possible in maintenance. Vigorous, daily exercise may be your best hedge against weight regain.