Tuesday, February 27, 2018

Short Take: Calories Matter in Weight Loss, Despite Some Recent Headlines

A recently published clinical trial out of Stanford University found that high-quality low-fat and high-quality low-carbohydrate diets could be equally effective for weight loss.

It was a positive finding from a well-designed study.

Many news headlines about the study, however, focused on something else entirely: that calories don't matter for weight loss. Some examples:

The problem is: The study didn't really find that.

In the trial, approximately 600 overweight and obese adults were randomly assigned to one of two diet groups (low-fat or low-carbohydrate) and followed over a 12-month period.  During the study, participants attended regular nutrition classes where emphasis was placed on healthy, high-quality foods – such as whole grains, healthy fats, and minimally processed foods.

Participants were not specifically instructed to lower their calorie intake.

At the end of the study, each group had lost similar amounts of weight. The low-fat group dropped around 12 pounds, and the low-carbohydrate group dropped around 13 pounds. 

So, each group lost weight without being instructed to cut calories:  What's wrong with the "calories don't matter"-themed headlines?

A couple of things.

First, calorie counting was not a subject of study of the trial.   Clinical trials are designed to assess very specific things.  Because calorie counting was not something one group in the study did and another group in the study did not do, no conclusions can be made about its possible impact – or lack of impact –  on weight loss. Any headline implying otherwise is reaching beyond the findings of the current study.  

On top of that, while it’s true that participants were not coached to reduce their calorie intake, that does not mean that they did not eat fewer calories.  In fact, each diet group ate an average of 500 – 600 fewer calories per day during the course of the study than at the start of the study.  That is a large deficit that would lead to weight loss over time. 

For both of these reasons, it's inaccurate to imply that the study found that calories, and counting calories, aren't important for weight loss.

Of course, diet quality is important.  A largely plant-based diet that focuses on fruits, vegetables, whole grains, and healthy fats has long been shown to lower the risk of many diseases and help with weight control.

But diet quantity is key.  To lose weight, we need to take in fewer calories than we expend - whether we count them or not.

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