FOr for every 100 calories we can expect to burn as a result of a workout, most of us will actually net less than 72, according to an eye-opening new study into how physical activity affects our metabolism.
Studies have found that our bodies automatically replenish at least a quarter of the calories we burn during exercise, reducing our efforts to lose pounds by working out. The results also show that while carrying extra pounds unfortunately adds to calorie compensation, losing weight through exercise is even more elusive for people who are already overweight.
But studies also show that calorie compensation varies from person to person, and learning how your metabolism responds to workouts can be key to optimizing exercise for weight control.
In theory – or in a merciful, alternate universe – exercise would aid in weight loss to a great extent. When we move, our muscles contract, requiring more fuel than at rest, while other organs and biological systems also expend extra energy. Thanks to previous laboratory studies, we know how much energy is required in these processes. For example, walking a mile burns about 100 calories depending on one’s body size and walking speed.
Until recently, most people, including exercise scientists, assumed that the process would be additive—that is, walk a mile, burn 100 calories. Take two walks in a logical, mathematical way, burn 200, etc. If we don’t replace those calories with extra food, we should stop burning more calories than we did during the day and start dropping pounds.
But that rational result is rarely the case. In study after study, most people who start a new exercise program lose less weight than expected based on calories burned during the workout, even if they strictly monitor their diet.
So some scientists speculate that energy expenditure may be less elastic than we thought. In other words, it may have limitations. That prospect gained traction in 2012 with the publication of an influential study of African hunter-gatherers. This showed that, although the Aborigines regularly walked or jogged for hours, they burned almost the same number of total daily calories as the relatively sedentary Western men and women. Somehow, the study authors realized, the bodies of active tribesmen were compensating, dialing back overall calorie burning, so that they could avoid starvation while chasing their food.
Other smaller studies have since confirmed the conclusion that more activity does not result in greater daily caloric expenditure. But few large-scale experiments have tried to figure out how much our bodies compensate for the calories we burn while walking, because measuring metabolic activity in people is complicated and expensive.
As part of an ambitious new scientific initiative, however, dozens of researchers recently collated their metabolic data from several studies involving thousands of men and women. These studies involved drinking double-labeled water, the gold standard in metabolic research. It contained isotopes that allowed researchers to track how many calories a person burned throughout the day.
for new Study, which was published in August current biologySome scientists set out to see what happens to our metabolism when we walk. They pulled data for 1,754 adults that included their dual-label water results, as well as measures of their body composition and basal energy expenditure, which are how many calories they burn simply by living, even if they are otherwise inactive. . By subtracting the basal numbers from the total energy expenditure, the researchers estimated people’s energy expenditure from exercise and other movement, such as standing, walking, and walking in general.
Then, using statistical models, the researchers can find out whether the calories burned during activity resulted in an expected increase in people’s daily energy expenditure — that is, whether or not people burned total daily calories when they walked more. But, the researchers found, they didn’t tend to burn more calories. In fact, most people find that given their activity level, on average, they are burning only about 72 percent of the extra calories they expect.
“People seem to be energy-compensating for at least a quarter of the extra calories burned through activity,” says lead author of the study, Louise Halsey, a professor of life and health sciences at the University of Roehampton in London.
Unexpectedly, the researchers also found that people with relatively high levels of body fat had increased levels of energy compensation. They tended to compensate for 50 percent or more of the calories burned by being active.
It is important to point out that the study did not look at people’s food intake. It focuses entirely on energy outlay and how our bodies seem to be able to offset some of the calories we burn during exercise by reducing biological activity elsewhere in the body.
However, how we unconsciously orchestrate this feat, and which internal systems may be most affected, is unclear, Halsey said. He and his colleagues speculate that the operation of the immune system, which requires considerable energy, may be reduced somewhat. Or we may unintentionally splurge less or otherwise become more sedentary overall the days we exercise. Perhaps, some of the internal functioning of our cells may also slow down, reducing our body’s overall energy expenditure.
But the new science of exercising and replenishing calories isn’t entirely discouraging. Even people whose bodies compensate for 50 percent or more of the calories they expend during physical activity will burn more calories per day than if they stayed still, Halsey explains. A more difficult problem with using exercise for weight loss is that actual exercise burns few calories, full stop. To lose pounds, we also have to eat less.
“Half a cookie or half a can of cola” is followed by a half-hour walk, and you’ll take in more calories than you burn, he says, although you compensate for more or less.
This article originally appeared in the new York Times.
Credit: www.independent.co.uk /