Monday, September 1, 2014

Low-carbohydrate vs. Low-fat diets for Weight Loss: New Evidence

A new high-profile study compared the weight loss and cardiovascular effects of a low-carbohydrate diet vs. a low-fat diet.  Although many studies have done this before, this one is novel enough to add to our current understanding of diet and health.  Unlike most other studies of this nature, diet adherence was fairly good, and carbohydrate restriction produced greater weight loss and cardiovascular risk factor improvements than fat restriction at the one-year mark.  Yet like previous studies, neither diet produced very impressive results.

The Study

Lydia A. Bazzano and colleagues at Tulane University randomly assigned 148 obese men and women without cardiovascular disease into two groups (1):
  1. Received instructions to eat less than 40 grams of carbohydrate per day, plus one low-carbohydrate meal replacement per day.  No specific advice to alter calorie intake.  Met regularly with dietitians to explain the dietary changes and maintain motivation.
  2. Received instructions to eat less than 30 percent of calories from fat, less than 7 percent of calories as saturated fat, and 55 percent of calories from carbohydrate, plus one low-fat meal replacement per day.  No specific advice to alter calorie intake.  This is based on NCEP guidelines, which are actually designed for cardiovascular risk reduction and not weight loss.  Met regularly with dietitians to explain the dietary changes and maintain motivation.
Participants were followed up for one year, with data reported for 3 month, 6 month, and 12 month timepoints.  This study actually measured body fat percentage, but unfortunately did so using bioelectrical impedance (like on some bathroom scales), which is essentially meaningless in this context.

Results

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