High Carb Diets Affect Weight Independent of Total Calories
Consuming a diet high in carbohydrates has long been shown to contribute to overweight and obese states and ultimately to type 2 diabetes and the metabolic syndrome. However, in most cases this is primarily the association of excess calories from carbohydrates not exclusively to carbohydrates themselves.
A recent report in the journal, European Journal of Clinical Nutrition, has shown that the effects of high carbohydrate consumption, when total calories are equivalent across diets, is related to changes in fat tissue (adipose tissue) rates of mitochondrial oxidation:
This study involved a randomized-controlled trial involving a weight-loss maintenance feeding schedule in which participants consumed the same number of calories but in one group (high carbohydrate) the amount of calories from carbohydrate was 60% of total calories, while in the other two groups the amount of carbohydrate was 40% (moderate carbohydrate) or 20% (low carbohydrate) of total calories, respectively.
Participants in this study all had BMI values greater than 25, considered an overweight state (a BMI greater than 30 is considered obese). All participants consumed prepared diets that consisted of 60% of estimated caloric (energy) needs to produce weight loss in the range of 10%-14%. Following the targeted weight loss the participants were fed a prepared diet to achieve a stabilized weight. These individuals were then randomly assigned to diet groups that consisted of equivalent total calories but were low- (20%), moderate- (40%), or high- (60%) in carbohydrate. These diets were maintained for a period of 20 weeks, test diet phase. Regardless of carbohydrate content all the diets contained 20% of calories from protein, derived from similar sources across diets, with the remainder of the total energy derived from fat.
Adipose tissue samples were collected from participants by needle biopsy from subcutaneous abdominal fat before and after the implementation of the various diets. Mitochondrial respiration assays were then performed on the adipose tissue biopsies and normalized to total protein in each sample.
Participants that were consuming the high carbohydrate diet had lower rates of maximal adipose tissue mitochondrial respiration than those consuming a moderate or low carbohydrate diet. The effects of the high carbohydrate diet on mitochondrial respiration may be the result of increased secretion of insulin which promotes fat storage (triglycerides) in adipose tissue while inhibiting fatty acid oxidation and triglyceride production.
TAKE HOME: The results from this study, although preliminary, allow for the postulation of the mechanism for calorie-independent effects of dietary composition, specifically carbohydrates, on energy expenditure and fat deposition in adipose tissue and that this is most likely the result of the actions of insulin on fuel partitioning.
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