New Evidence for Restricting Calories, But . . .

Cutting as few as 300 calories from the daily diet might offer significant health benefits –  even for people with a BMI in the normal or only mildly overweight range. That’s the primary finding of a new 2-year RCT in Lancet Diabetes and Endocrinology. Is this groundbreaking research? Or, is restricting calories an impractical option for promoting health?

An Important Confirmation

This randomized controlled study offers important confirmation for the potential value of restricting calories in humans. In the lab, animals live longer when you restrict the number of calories they can eat. But it’s been hard to prove a benefit in humans.

However, this study was rigorous enough to do just that. Researchers randomly assigned 218 subjects to either cut their calories by 25 percent or continue with their regular diet. In fact, the test group did not make their goal. They only cut calories by an average of 12 percent. Even so, they lost five kilograms of body fat while the control group added to their fat mass.

More important, though, was the gain in heart and metabolic health. Every measure improved: blood pressure, cholesterol measures, and insulin sensitivity. Any way you look at it, these are good outcomes for a rather small reduction in calories.

Easier Said Than Done

In a commentary published alongside this research, Frank Hu acknowledges the “groundbreaking” nature of these findings. But he goes on to question their practical value. In an obesogenic environment, cutting even 300 calories is hard to do, he says. He points to an 18 percent dropout rate in the restriction group to support his belief.

So instead, he says the best bet for public health is to promote “leanness induced by healthy lifestyles.”  Hu concludes that we should focus on sugar taxes, incentives for healthy foods, food labelling, and regulation of food marketing.

Building on Evidence

It’s odd to see a scientist reject the findings of a randomized, controlled trial as impractical while promoting policies with uncertain outcomes. Each of those policies have merit. But they also have practical issues. Latin America has been implementing these policies for a while now, with some advocates pointing to them as a “model.” And yet, the U.N. says “obesity is growing uncontrollably” in Latin America.

On the other hand, research has shown that it is possible to cut trillions of calories from the U.S. food supply. Somehow that seems relevant to the finding that restricting calories can have real health benefits.

We believe it’s important to take the evidence at hand more seriously. A bit more objectivity and curiosity would help.

Click here for the study and here for Hu’s commentary. For further perspective, click here and here.

One Cherry, photograph © Ted Kyle / flickr

Subscribe by email to follow the accumulating evidence and observations that shape our view of health, obesity, and policy.

July 19, 2019