Is low carb diet better for weight loss?

ribsA new study pits low carb vs low fat with interesting results

Dedicated dieters can be divided into two armed camps: Low Carb and Low Fat.  The Low Fat concept is promoted by large organizations (American Heart, etc) while the Low Carb diet advocates are primarily diet book authors and individual medical professionals.  Getting the two groups together can be like a religious war; both sides are adamant about the virtues of their diet.  When research results favor one or the other diet for health benefits, the opposing camp immediately attacks the study as poorly designed.

Yet another study was released this summer, and the results seem to favor low carb diets.  Headlines in the popular press certainly promoted that conclusion: Low carb vs low-fat: best diet for weight loss.  Is that actually what the study concluded?

The study, done at Tulane University, looked at the effect of a low carb diet (less than 40 grams of digestible carb/day) or low fat diet (less than 30% fat) on weight and heart health risk indicators in obese adults.  Unlike other studies comparing diet composition, these subjects did not already have heart disease or Type 2 diabetes.  The study went on for 12 months, and the participants were assessed for diet, weight, waist circumference and numerous health measures such as blood pressure and lab values.

Results:

  • Everyone ended up eating fewer calories, although they were not told to restrict.  The low carb diet group had, on average, a lower calorie intake (1260-1450) than the low fat group (1420-1530)*.
  • The low carb dieters ate about 10 grams more of protein daily.
  • The low fat dieters averaged less than 30% of their calories as fat, while the low carb group averaged over 40%.
  • Everyone lost weight.  But the people on the low carb diet lost significantly more weight, and more of that weight loss was body fat.
  • While everyone experienced some improvements in heart disease risk factors, several of those indicators, such as HDL cholesterol, triglycerides and waist circumference, improved more in the low carb group.

It’s interesting that the low carb dieters spontaneously ate fewer calories than the low fat dieters.  This could account for some of the extra weight loss.  It could also mean that it’s easier for people to stick to a lower calorie intake on a low carb diet.  One of the arguments against low fat has always been that it’s really hard to stick to a low fat diet.  And if you can’t stick to a diet, then it doesn’t work, no matter how wonderful it looks on paper.  Higher fat foods are more satisfying, and the higher protein intake common to low carb diets can improve satiety.

The study authors speculated that the low carb diet also had metabolic effects that improved weight loss, and that might be true.

So is low carb diet better?

This study certainly supports the argument that a low carb diet is better for weight loss and improvement in heart disease risk factors.  Well, this low carb diet.  There are other versions of “low carb” that are more strict about carbs and more liberal about fat.  Some even advocate 50% or more of daily calories as fat.

And this version of “low fat” wasn’t all that strict either.  The average percent fat was just below the 30% recommendation, in line with general recommendation from organizations like the American Heart Association.  Many low fat diet advocates believe 20% fat or even 10% are advisable.  Those are extreme levels, and would be hard for anyone to stick with long term.

Some low carb diets encourage you to eat as much as you want, as long as you don’t eat carbs.  But if calories aren’t restricted, significant weight loss is unlikely.  Unfortunately, much of the improvement in heart disease risk factors depends on weight loss.  The low carb group in this study ate fewer calories, which certainly helped them lose weight.

And there might be a psychological benefit to low carb: you automatically restrict all the high carb foods that are so easy to overeat, like chips, candy, cakes, cookies, doughnuts, breads, pasta and desserts.  Some dieters find these strict rules helpful.  On the other hand, if at some point you return to eating some of those foods, you might go overboard.  The low carb diet never taught you how to control portions.  This study did not follow the dieters beyond 12 months to see how they were doing months later, and whether a return to normal food choices resulted in weight re-gain.

Take Away Message: A low carb diet can be a good choice for weight loss, as long as you also cut calories.  You might find it easier to stick to a low carb diet, which is another key to diet success.

*These are average calorie ranges over the 12 month study.  Calorie intake was lower at the beginning and gradually increased to the higher number at 12 months.  But it remained below the average pre-study calorie intake of roughly 2000 calories/day.

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