Wednesday, March 13, 2019

Carbohydrate intake and energy expenditure after weight loss

The Study
Following weight loss, resting energy expenditure drops significantly. This is a big reason why so many dieters quickly regain their lost weight. A recently published randomized trial examined if the ratio of carbohydrate to fat impacts resting energy expenditure post weight loss. After a 12% weight loss, 164 overweight subjects were randomized to one of three diets for a period of 20 weeks:

-High Carbohydrate: 60% carbohydrate, 20% fat, 20% protein.

-Moderate Carbohydrate: 40% carbohydrate, 40% fat, 20% protein.

-Low Carbohydrate: 20% carbohydrate, 60% fat, 20% protein.

The primary outcome was total energy expenditure, which was measured by doubly labeled water. The results were fascinating. Subjects consuming the higher levels of carbohydrates had greater decreases in total energy expenditure. Subjects on the moderate carbohydrate diet burned 91 more calories per day when compared to subjects on the high carbohydrate diet. Subjects on the low carbohydrate diet burned 209 more calories per day when compared to the high carbohydrate diet. British Medical Journal 2018;363:k4583.

Take Home Message
This is a really interesting study. The differences in energy expenditure found in this study are highly relevant. Compared to the high carb diet, the extra calories burned in the moderate and low carb diets could prevent 10-20 lbs. of weight regain in a year. 

The researchers believed that the differences in energy expenditure could be due to a lower glycemic index, a lower glycemic load, thermic effects, brown adipose activity, autonomic tone, nutrient cycling, changes in ghrelin levels and/or changes in leptin sensitivity.  

The low carb subjects were found to have lower levels of ghrelin. Ghrelin has been shown to lower energy expenditure and promote fat deposition. The low carb group also had lower levels of leptin. Previous research has shown that lower levels of leptin after weight loss predict less weight regain.

Although more research is needed in this area, going lower carb may make it a lot easier to keep lost weight off permanently. This study provides further evidence that low-fat high carbohydrate diets do not seem to be the path to permanent weight loss.

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