Do calories matter?

“The Key to Weight Loss Is Diet Quality, Not Quantity, a New Study Finds,” reported the New York Times online last year. Here’s what the study actually found.

You can cut carbs or fat for weight loss. The key: load up on veggies and limiting added sugars and white flour.

The study, called DietFits, was designed to see if people lose more weight on a healthy low-fat diet or a healthy low-carb diet.

“Healthy” meant minimally processed whole foods, not junk.

“We told everyone in both groups to eat as little white flour and sugar and as many higher-fiber vegetables as possible,” says lead investigator Christopher Gardner, professor of medicine at Stanford University.

The year-long trial, involving 609 people, was funded by the National Institutes of Health and the Nutrition Science Initiative.

The low-fat group was advised to eat high-quality carbs like lentils, low-fat yogurt, steel-cut oats, quinoa, fresh fruit, and beans. The low-carb group was told to eat high-quality fats like salmon, avocados, nuts, seeds, hard cheeses, and olive oil.

And no one told the participants to cut calories. “If you prescribe calorie restriction, people feel deprived,” says Gardner. “So we just said, ‘Eat as low as you can on fat or carbs and don’t be hungry.’”

The results

Whether they cut fat or carbs, “each group reported a 500-calorie reduction,” says Gardner. And after a year, the people in each group had lost an average of about 12 pounds.

In other words, when it comes to weight loss, it doesn’t matter if you cut carbs or fat. Although the study participants weren’t told to count calories, calories still mattered.

“Dr. Gardner said it is not that calories don’t matter,” explained the Times, near the end of the article.

What’s more, the study couldn’t show that “The Key to Weight Loss is Diet Quality, Not Quantity,” because it didn’t compare diet quality to quantity. (To do that, Gardner would have had to tell a third group of dieters to count calories.)

DietFits’ most surprising finding

It didn’t matter if people were resistant to their body’s insulin when they entered the study.

“We assumed that insulin-resistant people would do better on a low-carb diet—as they did in some earlier studies—but they didn’t,” says Gardner.

Maybe that’s because both groups were told to eat healthy foods, he suggests. “In some older studies, when researchers told people to eat less fat, they weren’t particular about which low-fat foods. Coke and white flour and sugar are low-fat.”

Gardner also noted that—as in earlier studies—the results varied dramatically. “Someone lost 60 pounds, someone gained 20 pounds, and we saw everything in between,” he says. “The range, which was similar in both diet groups, was stunning.”

Bottom Line

You can lose as much weight on a healthy low-fat diet as a healthy low-carb diet. If you find it cumbersome to count calories, eat as little white flour and  added sugar and as many fiber-rich vegetables as possible. You’ll likely end up cutting calories without thinking about it, but that doesn’t mean that calories don’t matter.


Photo:  Sweetgreen.

The information in this post first appeared in the May 2018 issue of Nutrition Action Healthletter.

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8 Replies to “Do calories matter?”

  1. 1. How did the authors confirm subjects’ dietary intake? Self-report? Were there blood tests throughout the study? I read the original JAMA article (as far as allowed without a subscription) but saw no mention of these items.
    2. CSPI’s suggestion to simply “eat healthy” (i.e., reduce empty calories), whether low-fat or low-carb, and calories will automatically be cut, is tried-and-true. Calories matter, and that advice not only makes intuitive sense but has been demonstrated via evidence-based research for many decades. So how does this recommendation answer Dr. Berg’s suggestion that driving the body into a state of ketosis via a high-fat diet provides the “healthiest” weight loss?
    Thank you.

    1. Thanks for your question, Teri. Diet was confirmed based on unannounced 3-day 24-hour recalls and analyzed via the Nutrition Data for System Research software. There were also blood tests throughout the study (at 3, 6, and 12 months, though the data are only presented for baseline and 12 months).
      To your second question, we haven’t explored the ketogenic diet, specifically, though we will consider it for a future article. However, you can check out the results from this study (, which was small but well-designed. There have been no long-term studies on ketogenic diets for weight loss.

  2. Just curious about what the outcomes for heart health would be comparing the two diets…low fat or low carb. Was that checked at all? I am trying to avoid another bypass operation, so that is important to me. Thanks so much

    Nancy Nowak

    1. Hi Nancy,

      Thanks for your question. Relative to baseline values, LDL-cholesterol increased on the healthy low-carb diet group and decreased in the healthy low-fat group. However, triglycerides went down and HDL went up more in the low-carb group. Unfortunately, it isn’t clear if the increased risk associated with higher LDL would be offset by the improvement in HDL and triglycerides in the low-carb group.

    2. Nancy, I am not your MD, but the evidence is out there that a Whole Food Plant Based diet can prevent and in most reverse CAD. Look at the work of Dr.’s T. Colin Campbell, C. Esselstyn and Dean Ornish for a start. Dr M. Gregor’s book “how not to die” covers the top 15 leading causes of death in N. America and provides the references to support the claim for a WFPB diet

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