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Monica Reinagel, MS, LDN, CNS Headshot

Carbs and Weight Gain

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There's been a lot of buzz recently about a new study that punched a few new holes in the already-tattered notion that weight gain and loss is simply a matter of "calories in vs. calories out."

What Did the Study Find?

One big challenge with losing weight is keeping it off after you've lost it. Most people eventually end up regaining most or all of the weight they've lost. So, researchers took people who had recently lost a significant amount of weight and compared the effectiveness of three different maintenance plans:

  • One plan was low in fat but high in refined carbohydrates. (Think of this one as the "Snackwells" approach.)
  • The second plan had a moderate level of carbohydrates (neither high nor low), but emphasized carbohydrates with a low glycemic load -- things like legumes, vegetables, intact grains. In place of the missing carbohydrates, they substituted fats. In other words, a Mediterranean-style diet.
  • The third diet was extremely low in carbohydrates and higher in fat and protein. Basically, an Atkins-style diet.

All three plans had the same number of calories -- precisely calibrated to match the number of calories each person burned each day. Not surprisingly, over the course of the study, no one lost or gained any weight.

The big news was this: People burned, on average, 300 more calories a day when they were eating the very low carb plan than they did on the high-carbohydrate plan. The low-glycemic diet was somewhere in between. The study authors concluded that, over time, people eating a low-fat diet would have a much harder time maintaining their weight loss than people on a lower-carbohydrate regimen.

Unfortunately, the study authors also noticed some negative effects from the very low carbohydrate diet. While on the low-carb regimen, subjects experienced increased levels of stress hormones and inflammation markers -- both of which might increase the risk of obesity over the long term. People on the moderate-carb, low-glycemic diet seemed to fare best of all. They burned extra calories but with none of the negative effects.

As news of the study spread, my inbox filled up with questions from journalists, news directors, medical colleagues, and readers. How significant is this finding? Is this really something new? Will this study change my advice regarding diet and weight loss?

Is This a New Finding?

It's not surprising (to me, anyway) that eating more protein and fewer refined carbohydrates would affect metabolism. (See my article "Protein and Weight Loss.")

I think what's most striking about this study is the magnitude of the effect -- 300 calories a day is a pretty big deal. I suspect that one reason that this study produced such dramatic results is that the subjects had just lost a significant amount of weight in a short period of time. Rapid weight loss produces some very dramatic changes in energy metabolism, and the fact that the subjects were in that exaggerated state of metabolic flux when they started the study may have amplified the effects of the three diets.

I think the effect was further exaggerated by the fact that the high-carbohydrate diet wasn't just high in carbs, it was high in refined carbohydrates -- foods that send blood sugar soaring and trigger big rushes of insulin, a hormone that promotes fat storage. And while there are still a few die-hards out there promoting a low-fat, high-carb diet, none of them are recommending that you load up on refined carbohydrates. Had the high-carbohydrate portion of the trial used the same low-glycemic foods as the moderate-carbohydrate diet (just more of them), I'm not sure the difference between those diets would have been as large.

Furthermore, if the moderate-carbohydrate diet had been as high in protein as the low-carbohydrate diet, it might have closed up the gaps even further. Finally, both the moderate- and low-carbohydrate diets featured a much higher proportion of monounsaturated fats -- which have been found to promote fat oxidation and weight loss. Had all three diets used the same types of fats, the differences might not have been as dramatic.

In other words, there were a lot of differences between the diets besides just the quantity of carbs.

It also must be said that the study was too small and too short to be considered the final word on the subject. But it certainly got everyone's attention!

Do Calories Still Matter?

"Carbs, not calories, lead to weight gain," blurbed the New York Times. But, as a take-home message, that's a little misleading. The study didn't find that you could eat as many calories as you want without gaining weight, as long as none of them are carbs. Remember, the amount of calories consumed by the dieters was strictly controlled to ensure weight maintenance. It's just that they got to eat a bit more when they backed off the refined carbs -- without gaining weight.

So, here's my slightly more nuanced take-home lesson:

Excess calories still lead to weight gain -- but excess calories from refined carbohydrates will do it faster than calories from other sources. In other words, all calories matter but some calories matter more than others.

At the end of the day, however, most of us don't have scientists measuring our metabolic rate and precisely calibrating our meals for us. And as the researchers pointed out (but the media largely ignored), identifying the ideal mix of carbs, fats, and proteins is only one part of the puzzle.

"A strategy to reduce glycemic load rather than dietary fat may be advantageous," they wrote. "[But] ultimately, successful weight loss maintenance will require behavioral and environmental interventions."

Does This Change My Advice?

So, how does this research translate into the real world? Does it change my previous advice? Not really. Here, by way of review, are the basic tenets of my approach -- all of which are in line with these new findings:

  1. Limit your intake of added sugar, especially sweetened beverages. See my article, "How (and Why) to Limit Added Sugars."
  2. Choose whole and minimally processed grains instead of refined grain products. And, even then, practice portion control. See my article, "The Truth About Whole Grains."
  3. Dial up the protein and healthy fats to make meals more satisfying and satiating. See my article, "How to Eat Less Without Feeling Hungry."
  4. Eat lots of vegetables. See my article, "How to Get More Vegetables in Your Diet."
  5. Do eat for pleasure but not for entertainment. See my article, "Mastering the Art of French Eating."

For more by Monica Reinagel, MS, LDN, CNS, click here.

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