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How to Diet

How to Diet

The battle of low-carb versus low-fat

Are all calories equal? Or is the body more likely to store—rather than burn—a calorie of carbs than a calorie of fat?

That was the first question tackled by the Nutrition Science Intitiative’s Energy Balance Consortium of 10 obesity experts. (NuSI was largely financed by billionaire former hedge fund manager John Arnold and his wife, Laura.)

Kevin Hall, senior investigator at the National Institute of Diabetes and Digestive and Kidney Diseases, led two studies designed to answer the question: Do carbs drive you to gain more body fat because they boost levels of the hormone insulin?

“The argument is that people are consuming too many carbohydrates, which drive up insulin levels in the blood,” explains Hall.

“Insulin causes the body’s fat cells to suck in too many calories, and because calories are trapped in the fat cells, the rest of the body is starving. That makes you hungrier, so you eat more calories.”

And because the body is starving, adds Hall, “it slows down its metabolic rate, so it burns fewer calories.” So cutting carbs should boost calorie burning and shrink body fat.

At least that’s the theory.

Opposite Results

Hall’s first study housed 19 people in a lab where they ate only the food the researchers provided. Those diets cut 800 calories either from carbs (about half of the cuts came from sugar) or from fat for one week each.1

“When we cut carbs, daily insulin secretion went down,” says Hall. If the carbohydrate-insulin theory were correct, “that should have released fat from their fat cells, boosting fat loss while relieving the internal starvation and therefore causing calorie burning to go up.”

It didn’t. “The number of calories they were burning went down,” says Hall. “So we found the opposite NuSIresult.” Instead of speeding up fat loss, the low-carb diet actually slowed it down.

But that study didn’t cut carbs enough or last long enough, argued some critics. So Hall did a longer study using a very-low-carb diet.2

“After one month of eating a high-​sugar, high-carbohydrate diet, we cut the carbs down to 5 percent, cranked the fat up to 80 percent, and kept protein and calories constant,” Hall explains.

The result: “The rate of fat loss actually slowed down for the first two weeks, and then picked back up to the normal rate again for the last two weeks,” says Hall. So the low-carb diet didn’t speed fat loss.

“We did see a very slight increase in the number of calories that were being burned—57 more a day—on the very-low-carb diet,” adds Hall. But NuSI’s Energy Balance Consortium had agreed beforehand that only an increase of at least 150 calories a day would be meaningful.

“Our results add to the evidence from many other controlled feeding studies on more than 500 people,” says Hall. Those studies failed to show that cutting carbs boosts calorie burning or fat loss more than cutting fat.3

“If anything,” says Hall, “there is a statistically significant greater fat loss and calorie burning on a low-fat diet. But the effects are so small that they’re physiologically meaningless.”

It’s still possible that a very-low-carb diet curbs dieters’ appetites. “We didn’t test that,” says Hall.

If so, that might explain why some studies report that people tend to lose more weight over the first few months when they are prescribed a low-carb diet.

“But over the long term that doesn’t seem to persist either,” says Hall. In studies that last a year or more, the difference in weight loss is negligible.4

“Sometimes you can’t see any significant difference, and sometimes you can see a few pounds difference that is clinically meaningless,” notes Hall.

The DietFits Study

“This study should be able to document, for the first time ever, what happens when free-living participants maintain compliance with a very-low-fat diet and a very-low-carbohydrate diet for an entire year,” says the NuSI website.

Christopher Gardner, professor of medicine at Stanford University, led that trial—called DietFits—which randomly assigned 609 overweight or obese people to either a healthy low-fat diet or a healthy low-carb diet.

“We told everyone in both groups to eat as little white flour and sugar and as many higher-fiber vegetables as possible,” Gardner explains.

But the participants weren’t told 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.’” And, whether they cut fat or carbs, “each group reported a 500-calorie reduction.”

After a year, each group had lost an average of about 13 pounds.5 And, as in earlier studies, the results varied dramatically. “Someone lost 60 pounds, someone gained 20 pounds, and we saw everything in between,” notes Gardner. “The range, which was similar in both diet groups, was stunning.”

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

The full study hasn’t been published yet, Gardner’s team hasn’t yet analyzed data looking at the participants’ gut microbes, and two more NuSI studies are still in progress.

But the Arnolds are not funding new NuSI studies. If NuSI was looking for clear-cut answers, it didn’t find them.

References

1 Cell Metab. 22: 427, 2015.
2 Am. J .Clin. Nutr. 104: 324, 2016.
3 Gastroenterology 2017. doi:10.1053/j.gastro.2017.01.052.
4 JAMA 312: 923, 2014.
5 http://professional.heart.org/idc/groups/ahamah-public/@wcm/@sop/@scon/documents/downloadable/ucm_492225.pdf.

Add Your Comments

8 Comments

  1. terim8
    Posted April 12, 2017 at 8:38 am | Permalink

    Isn’t the ultimate finding that if you want to loose weight, cut calories, period?

    • Caitlin
      Posted April 12, 2017 at 3:02 pm | Permalink

      Generally speaking, yes. We also know that you don’t necessarily want to cut down on protein when during weight loss because you can lose muscle mass. It’s also important to eat healthy food while losing weight, like the study that Dr. Gardner describes (cutting down on calories isn’t license to eat low-calorie junk).

  2. Cheryl
    Posted April 12, 2017 at 2:43 pm | Permalink

    Well, I followed a 50 carb a day diet strictly, and list 35 pounds in three months: no increased exercise. Did that for 2 years and weight stayed off– felt great, lots of energy… when I began to transition to calorie based diet I added more carbs– slowly fell back to eating more carbs and put weight back on. How does this study explain that?

    • Caitlin
      Posted April 12, 2017 at 3:08 pm | Permalink

      As Dr. Gardner describes, responses to different diets are extremely variable. You can have two people on the same diet – one that loses 60 pounds and one that gains 20. These studies simply show that there isn’t strong evidence that low-carb diets beat low-fat diets for weight loss for the general population.
      The bottom line is that the best diet for weight loss is the one that cuts calories, is healthy, and that you can stick with for your whole life. It sounds like low-carb works well for you, which is great!

      • Cheryl
        Posted April 12, 2017 at 4:27 pm | Permalink

        Agreed. Thanks.

    • hyokl2
      Posted April 13, 2017 at 1:53 pm | Permalink

      Various studies have shown that people, even Registered Dietitians, are poor at measuring calories. Most likely, when you added carbs back in, you also increased calories. It is also possible that you were eating less protein, as you moved away from low carb. Protein is the most satiating macronutrient, and may help with overeating.

      Many people report feeling great on a low carb diet. But, for many, the good feelings don’t last.

  3. Andries
    Posted April 16, 2017 at 11:12 pm | Permalink

    i FEEL 100% BETTER ON THE LOW CARB, BUT I ALSO SUSPECT THAT IT IS BECAUSE I’M NOT EATING MY FRIED OKRA AND FRIED CHICKEN ONCE A WEEK, AND WET BURRITO ONCE A WEEK. I’M IN LOVE WITH LOW CARB FOODS RIGHT NOW, ESPECIALLY CAULIFLOWER RICE ….SO MUCH I CAN DO WITH IT. WILL THIS GOOD FEELING LAST, ? I THINK SO AS LONG AS I CONTINUE TO THINK BEFORE PUTTING JUNK INTO MY MOUTH. LOW CARB, LOW FAT, COUNTING CALORIES…NONE OF IT WORKS IF I DON’T MAKE CHOICES IN A HEALTHY WAY. YES, I LOVE FRIED OKRA BUT AS WITH ALL THINGS, NOW IN MODERATION.

  4. L.
    Posted April 17, 2017 at 10:17 am | Permalink

    T. Colin Campbell, Ph.D. cites information claiming complex carbohydrates to be the most satiating macronutrient. Is there peer-reviewed scientific evidence that places protein in that spot? I am interested in reading some studies to support this view.

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