Comparison of Weight Loss Diets? What Comparison?

Monday, March 2

You’ve probably heard or read about a recent diet comparison study published in the New England Journal of Medicine which concluded that it’s only calories that count for weight loss, not the type of diet such as high protein, high fat, low carb, low fat, etc. 

Well I hate to break it to you. 

Upon scrutinizing this study, I found that the researchers incorrectly defined what comprises a low carb diet, as well as a high fat diet.  Here’s the breakdown of the four diets they compared:

Diet #1: Fat 20%; Protein 15%; Carbs 65%

Diet #2: Fat 20%; Protein 25%; Carbs 55%

Diet #3: Fat 40%; Protein 15%; Carbs 45%

Diet #4: Fat 40%; Protein 25%; Carbs 35% 

First, all of these diets are variations on a high carbohydrate diet.  None of these could correctly be classified as low carb.  A low carb diet does not have a carbohydrate percentage as high as 35%.  That’s 140 grams of carbs on a diet of 1,600 calories a day! 

Diet #4 comes closest to a Mediterranean diet (40/20/40) or a Zone diet (40/30/30).  However, neither of these would be considered a low carb diet---not even close to Phase IV of Atkins (the Maintenance phase) which is the most liberal at 75-100 grams of carbs a day.  Because the authors made the critical error of incorrectly defining the types of diets they compared, the methodology is flawed, making the study invalid.  So of course it’s all going to come down to calories.  They’re variations of the same diet! 

Second, the authors did not compare high fat diets as they claim.  As a matter of fact, there isn't a high fat diet in this study.  40% fat is defined as a moderate fat diet most closely linked to the Mediterranean diet, which would never be classified as a high fat diet.  High fat diets are typically 50% fat and above.  So again, the researchers incorrectly defined the types of diets they compared, deeming the research invalid.   

As you’ve heard me say before, the concept of calories in, calories out is no longer the whole story.  There are reams of research that VALIDLY conclude that a high protein, high fat, low carb diet burns more calories (because it burns more fat) than a standard high carb, low fat diet.  This result has been replicated in the scientific literature ad nauseum.    

Here’s the icing on the cake:  The authors report using low glycemic index carbohydrates in the participant’s meal plans.  Well, I reviewed those meal plans.  I don’t recall apple juice, white potatoes or graham crackers as having a low glycemic index.  Do you?

This research was supported by a grant from the National Institutes of Health, our hard-earned tax dollars.  NIH should be more discriminating in their criteria for awarding grants.  I hate to see our tax dollars being wasted on research with flawed methodologies drawing invalid conclusions.    

And by golly the media takes the bait every time!

Sacks FM, Bray GA, Carey VJ, et al.  Comparison of Weight-Loss Diets with Different Compositions of Fat, Protein, and Carbohydrates.  N Engl J Med.  2009;360:859-73.