Saturday, August 16, 2008

Does Exercise Really Lead to Weight Loss?

     It's standard advice: to lose weight, exercise. But there are some who disagree, because physical activity makes you hungry. Or course, exercise has numerous benefits, but what is its real effect on hunger and weight?  
     The American College of Sports Medicine and the American Heart Association even said in a statement that “It is reasonable to assume that persons with relatively high daily energy expenditures would be less likely to gain weight over time, compared with those who have low energy expenditures. So far, data to support this hypothesis are not particularly compelling.”          Research has found that those who lose weight and keep it off tend to exercise. One recent study suggested 55 minutes, 5 days a week (or about 40 minutes every day.) But these studies don't isolate exercise as the sole factor contributing to the weight loss maintenance. In the study I mentioned, for instance, the women who lost weight exercised, but they ate less too.
     So does exercise contribute to weight loss, or do people who have healthy habits tend to exercise? 
     In New York Magazine, Gary Taubes points to Jean Mayer, influential nutritionist and former president of Tufts University,  as the person who pushed the "fitness revolution." Mayer is credited with defeating the current societal belief that exercise was bad for you. He noticed that thinner people exercised more, and concluded that exercise did not necessarily equal increased hunger. But Taubes claims the 2 studies that he used to prove this have never been replicated.
     Recent studies don't suggest that there is no connection between appetite and exercise. But one especially interesting study does suggest that appetite is related to the intensity of the exercise. Researchers studied the effect of high-intensity and low-intensity exercise on appetite in college women. (Low-intensity exercisers took an hour to burn 350 calories, equal to walking, high-intensity exercisers took about half an hour.) They found that high-intensity exercisers ate more after their work-out than low-intensity exercisers and a control group. 
     The study really got interesting when the researchers calculated "relative energy intake," or the calories each group consumed not included the calories they burnt off through exercise. The researchers concluded that there were "no significant differences" between the groups. However, it is worth noting that low-intensity exercises had the lowest food intake when the calories burnt from exercising were subtracted. Low-intensity exercisers consumed an average of 2397 calories a day, but 2100 a day after subtracting calories burnt from exercise. High-intensity exercisers consumed 2580, 2266 for relative energy intake. The control group had 2285. In other words, this study suggest that for those watching their weight, low-intensity exercise is best. 
     Jean Mayer suggested that exercise doesn't have to lead to increased hunger. This study helped show us where the line is. And if you want to engage in vigorous exercise, like I do, at least you'll now be a little bit more informed.


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