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Written by: Matt Fitzgerald
Triathlete Magazine Senior Editor Matt Fitzgerald provides advice on the amount of food to intake while attempting to lose weight during training.
Should You Try to Eat Less?
It seems commonsensical to many people that if you want to lose weight, you need to make a conscious effort to eat less. However, many nutrition experts are not convinced that eating restraint is the best way to pursue weight loss, for two main reasons. First, reduced eating slows body metabolism, making it more difficult to sustain weight loss. Second, reduced eating increases hunger and the desire to eat urges that few people can resist very long. Consequently, reduced eating itself is difficult to sustain.
Skeptics of reduced eating believe that it’s better to pursue weight loss by altering the diet to reduce caloric intake without reducing food volume (the Volumetrics approach) and through exercise. However, some research suggests that physical exercise is in many cases a less effective way to lose weight than reduced eating, in part because it increases appetite, while at least one new study supports the effectiveness of eating restraint.
Let’s briefly examine both the case for and the case against reduced eating in pursuit of weight loss.
What is to blame?
Whether eating less is necessary for weight loss may depend to some extent on whether the current obesity epidemic is caused by reduced physical activity or by increased eating. A new study suggests that lack of physical activity may be less important than increased caloric intake as a cause of the current obesity epidemic. Researchers from Loyola University Health System compared activity levels and dietary patterns in Chicago-area African-American women and women living in rural Nigeria. The American women weighed 184 pounds on average, while the Nigerian women weighed 127 pounds. To their surprise, the researchers found no significant difference in activity levels between the two groups. Adjusted for body weight, the average American woman burned 760 calories per day through physical activity (not necessarily formal exercise), while the Nigerian women burned 800 calories. This is not enough of a difference to explain the large weight disparity between the two groups. There were major differences in their diets, however. The American women consumed significantly more fat and processed foods and less fiber.
Research clearly demonstrates that Americans are eating more than ever. According to one source, the average American now consumes in excess of 300 calories per day more than 25 years ago. That’s certainly enough to account for most of our weight gain over that time period. The connection between changes in activity levels and obesity over the same time period is more equivocal. On the one hand, we know that we watch substantially more television and spend more time using computers now, but there is no clear proof of a significant decrease in activity levels. Some exercise advocates point out that we are much less active than our ancient hunter-gatherer ancestors were, but the obesity epidemic began long after we ceased hunting and gathering.
In summary, then, it seems that increased eating is more responsible for our current weight problems than reduced activity.
The Downside of Eating Less
So, if eating more is the primary cause of our current weight problems, then the primary means by which we should address the problem is eating less. Right? Well, this is easier said than done. Low-calorie diets demand high levels of eating restraint and force the dieter to live with persistent hunger. When you go on a low-calorie diet, suddenly many of your favorite foods are off-limits. Your meals are too small to satisfy your hunger for very long, if at all. As a result, you end up being distracted by your rumbling stomach and thinking about food-especially your favorite off-limits foods-most of the day. It’s only a matter of time before you scream, “To hell with it!” and break the diet.
The difficulty of sustaining the popular low-calorie diets was demonstrated in a study conducted by researchers at Tufts University. The purpose of the study was to compare the effectiveness of four popular diet programs. The researchers who led the study found that the four diets were equally effective in those who stayed on them. The only problem was that more than half of the subjects on each diet dropped out before the one-year study period was completed!
There are both physiological and psychological reasons why diets make us miserable. A number of studies have shown that food restriction actually increases our baseline appetite. In other words, when we cut back on calories, we don’t just miss the calories we cut, but we want even more! This is because food restriction alters the action of key hormones including leptin, grehlin, and thyroxine that are involved in regulating our appetite. From an evolutionary standpoint it makes sense that our bodies would work this way. It ensures that, when we aren’t getting enough food (which was probably a common problem in human prehistory), we become highly motivated to seek out food and chow down. But while this adaptation may have been important for our survival in prehistoric times, it makes life hell for dieters.
On the psychological side, it’s important not to forget that eating is a pleasure, a comfort, and a habit that is sorely missed when we turn away from it. In a study performed back in the 1940s, researchers asked normal-weight men to drastically restrict their food intake for six months. In addition to losing weight, the participants became preoccupied with food and food-related activities such as collecting recipes and pictures of food. They also became irritable and apathetic, lost interest in sex, and fought with each other and their girlfriends. What’s more, when they resumed normal eating, these previously normal eaters developed binging behaviors and gorged themselves on favorite foods.
Another problem with reducing eating for weight loss is that, as I mentioned above, it lower the body’s metabolic rate. It is expected that the metabolic rate will decrease in those who lose substantial amounts of weight, because the metabolic rate is largely a function of total body mass. However, research has consistently shown that metabolism decreases more than would be expected based on loss of body mass alone. What has not been known up to this point is whether this exaggerated metabolic slowdown is transient or more or less permanent. Researchers from Columbia recently answered this question through a study in which they compared the metabolic rates of age- and weight-matched subjects who had not lost weight, subjects who had recently lost weight, and subjects who had succeeded in maintaining weight loss for a long period of time. They found that resting energy expenditure was significantly lower in both the recent weight loss and the long term weight loss subjects than in the non-weight loss subjects of the same body weight. Does that suck or what?
Is Eating Less Necessary Anyway?
The fact that eating less is difficult to sustain does not necessarily suggest that weight loss is possible without eating restraint. But the results of a new study from Brigham Young University suggest that eating restraint is critical to preventing weight gain in middle age. The study followed 192 middle-aged women for three years and tracked information on lifestyle, health and eating habits. Their analysis revealed that women who did not become more restrained with eating were 138 percent more likely to put on 6.6 pounds or more. More evidence of the necessity of eating restraint for weight loss comes from the National Weight Control Registry, a large pool of weight loss research subjects consisting of individuals who have lost large amounts of weight and kept it off for extended periods of time. The vast majority of this group’s members lost weight initially through reduced eating and exercise rather than through exercise alone, and those who keep the weight off most successfully score higher on measures of eating restraint than those who regain weight.
Where Exercise Fits In
Based on studies such as those just mentioned, some experts contend that exercise is not an effective tool for weight loss. They note that it is a less efficient way to create a negative caloric balance than eating less, and that exercise increases appetite, making its use as a weight loss tool self-sabotaging. Some studies comparing the effects of dieting only and exercise only on weight loss have seemed to suggest that dieting is much more effective.
But a 2000 review of this literature by researchers at Queens University concluded that these studies did not properly compare the two approaches to weight loss, and that an exercise program that burns X calories per day will indeed result in the same amount of weight loss as a diet in which eating is reduced by X calories per day. Indeed, in a study by the same research team, obese men who burned 500 calories per day by walking and obese men who reduced their daily caloric intake by 500 calories both lost 8 percent of their bodyweight in three months. The real question is this: Would you rather reduce your food intake by 500 calories per day or increase your activity level by 500 calories per day? Some people would clearly rather be hungry than sweat, while folks like me would much prefer to sweat. Indeed, I am living proof that it’s possible to lose weight with exercise alone. When I took up triathlon at age 26 I lost 20 pounds in six weeks despite actually eating more due to increased appetite.
Using exercise for weight loss is further recommended by the fact that it causes a whole host of health benefits such as increased insulin sensitivity, better immune function and improved brain health that weight loss through eating restriction cannot match. What’s more, exercise appears to be all but essential to prevent weight regain after weight loss. Remember the National Weight Control Registry? It so happens that exercise level is the number-one predictor of success in weight loss maintenance in this group.
Up to this point I’ve written as if you can choose to pursue weight either by eating less or by exercising more but not through a combination of these means. Of course, one can combine them, and it should not surprise you to learn that this is a more effective approach than using either dieting or exercising only. But the question this article asked is whether eating restraint is necessary for weight loss. The evidence suggests that in principle it is not, but on a practical level it is for most people.