A new study suggests that all those people trying to lose weight through diet alone may be wasting their time. Or does it?
The study in question involved female monkeys, not humans. After several years of a high fat (and we assume high calorie) diet, the monkeys were placed on a low fat diet with 30% fewer calories than they were used to for a month. While the monkeys did not lose weight, their activity level plunged! The second month, the monkeys’ diet was reduced still further to 60% fewer calories than their original diet, and activity levels dipped yet again with only some weight loss. Not surprisingly, their metabolisms ran more slowly than at the beginning of the experiment. From the abstract of the research paper: “We conclude that a diet-induced decrease in physical activity is the primary mechanism the body uses to defend against diet-induced weight loss”.
So, the only thing they really seem to have proven is that starvation diets don’t work.
There was a second group of monkeys that did not experience the severe calorie restriction but were made to “work out” on a treadmill for an hour a day. Those monkeys did lose weight.
That being said, the American Council on Exercise points out that the overwhelming majority of people who lose weight and keep it off more than a year used a combination of diet and exercise. There are several reasons why this may be so: exercise encourages a healthy metabolism; exercise builds strong muscles that burn some calories even at rest; exercise burns excess calories, giving the dieter a little more leeway with food.
Don’t make yourself into a monkey. Starvation diets never work for very long, but physical activity works for a lifetime.
Her take: Well, we did initially lose our weight through diet alone! It was hard, took a lot of discipline, and meant we ate a lot of foods that the diet books said were good for us but didn’t necessarily taste very good (here’s the long version of my story). Now, we eat reasonable meals, don’t obsess about what we can eat at restaurants, and are in the best shape of our lives because we combine a sensible attitude about food with a sensible daily workout. While I hope to address the topic of low fat dieting in depth at a later date, I thought the more important aspect of this particular study was the severe caloric restriction.