To lose weight, is it better to eat less or exercise more?

Sunday, July 31, 2011 • Chicago, IL 60657


A calorie is a calorie is a calorie, according to the old-school, keep it simple school of nutritional thinking. But as we’ve seen, good health is a little more complicated than just matching the calories you eat to eh calories you burn. A study published in 2010 in the Journal Medicine & Science in sports & Exercise suggests that your body can tell the difference between a calorie burned through exercise and a calorie avoided through dieting – and both types turn out to be important.

            Researchers at Louisiana State University recruited 36 moderately overweight volunteers and divided them into three groups. One group was the control and stayed exactly the same throughout the six-month study. A second group cut their calorie intake by 25 percent, while the third group cut calories by 12.5 percent and increased their calories burned by an equivalent amount through physical activity. Tat meant both intervention groups had the same total “calorie deficit” – once through diet alone, and the other through a 50-50 mix of diet and exercise.

            As expected, the two intervention groups lost exactly the same amount of weight – a fairly impressive 10 percent of their starting weight. They also lost about 25 percent of their total body fat and 25 percent of their abdominal fat, again with no difference between the two groups. This confirms that the amount of weight you lose is a function of calorie deficit, whether you create the deficit through diet or exercise. But when the researchers took a closer look, they found some important differences between the two groups. Only the diet-plus-exercise group had significant improvements in insulin sensitivity, LDL cholesterol, and diastolic blood pressure – crucial risk factors that heart disease and diabetes, but changes you can’t measure by looking in the mirror or stepping on a scale.

            This research sheds new light on an ongoing “fitness v. fatness” debate. While some researchers believe that weight and body mass index are the simplest measure of cardiovascular risk, others – most prominently Steven Blair of the University of South Carolina – argue that aerobic fitness is more important than body shape. It’s difficult to tease apart eh effects because, in general, those who are fattest are the least fit and vice versa. The Louisiana State results support Blair’s position by showing that there are some key health benefits that you can’t get just by being skinny: you have to exercise too.

            But that’s not the final word. Two other risk factors measured in the Louisiana State study – systolic blood pressure and HDL Cholesterol – remained identical between the two experiment groups. That suggests that they depend on weight rather than aerobic fitness, so that “fat but fit” people may still be missing out on some health benefits. The challenging but inevitable conclusion is that both diet and exercise are important to optimize your health, and you can’t ignore either of them.