Which Matters More: What You Eat or How Much You Eat?

‘Tis the season to worry about weight gain. According to research, most adults add a pound or two between Thanksgiving and the New Year. This phenomenon is blamed on seasonal changes in diet. Runners, though, have an additional reason to worry about weight gain. For us, the holiday season is also the off-season—the time of year when we are not actively preparing for races and are therefore burning fewer calories through exercise.

Worrying about weight gain naturally leads to thoughts about how to prevent it. These thoughts, in turn, are based on beliefs or assumptions about what causes weight gain. That’s where things get tricky. There is much disagreement about the core cause of weight gain in our public discourse. One faction argues that weight gain is caused simply by eating too much. The other faction contends that it’s not how much but what you eat—particularly carbs or fat—that matters. Who is right? The answer will help you avoid gaining weight during this holiday/off-season.

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A Calorie is a Calorie

The idea that how much people eat is more important than what they eat where gain is concerned is summed up in the expression, “A calorie is a calorie.” Proponents of this view argue that if you eat too much of anything, you will gain weight, and that changing what you eat won’t cause you to lose weight unless the changes reduces the number of calories you consume.

Among the experts who encourage people to focus on how much rather than what they eat is Brian Wansink, author of “Mindless Eating.” Wansink’s research has shown that many people today eat food not because they’re hungry but because it’s there. If we simply pay more attention to what we’re doing and avoid eating more than necessary to satisfy our hunger, we can reduce our daily calorie intake by up to 20 percent and lose weight without changing what we eat.

John Cisna has demonstrated real-world proof that this approach can work by losing 56 pounds in six months eating nothing but McDonald’s. He pulled it off by limiting his total daily energy intake to 2,000 calories. You might assume that respecting this ceiling required him to avoid French fries and load up on salads instead. In fact, Cisna ate everything on the restaurant’s menu and had at least one serving of French fries almost every day.

Yet there are clear limits to the notion that all calories are the same. Most people who succeed in losing weight do make changes in what they eat, and there is plenty of science showing that it is possible to lose weight without making any conscious attempt to eat fewer calories if the right changes in food choices are made.

In a study performed at the University of Washington, overweight women spontaneously began to consume 441 fewer calories per day, on average, when their protein intake was increased to 30 percent of total calories. As a result, they lost weight despite not making any conscious effort to eat less. The reason is that protein is more filling than other calorie sources (carbohydrates and fat). Also, high-protein diets increase the body’s metabolic rate, so more calories are burned throughout the day.

However, loading up on protein isn’t the only way to lose weight without consciously reducing calorie consumption. In 2015, researchers at the University of South Carolina reported that volunteers placed on a vegan diet for six months lost an average of 7.5 percent of their initial body weight without making any attempts to eat less. In this case, dieters received more of their calories from vegetables and other foods that have a high content of fiber and water, which made them more filling than other foods, calorie for calorie.

If you want to see for yourself that all calories are not the same, try this experiment: At noon tomorrow, eat 500 calories worth of French fries or one large order of fries. Then at noon the next day, eat 500 calories worth of apples; that’s five and a half apples. In the unlikely event that you’re able to force down that much red delicious, you won’t want dessert, whereas you’ll still be hungry after eating the same caloric order of fries

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