Abstract 18552: Six Months of a Low-Carbohydrate versus Low-Fat Weight Loss Diet Plus Exercise: Effects on Resting and Postprandial Endothelial Function

Background: A worry about low-carbohydrate (CHO) diets is that higher fat meals may adversely affect vascular function acutely, and the regular eating of such meals may lead to chronic vascular impairment. We hypothesized that the effects of a low-CHO vs. low-fat weight loss diet, each combined with exercise training for 6-months, would have similar effects on resting and postprandial endothelial function. Methods: Persons (n=77), BMI 25-42 kg/m2, 30-65 years, were randomly assigned to a low-CHO or low-fat diet, plus exercise. At 0 and 6 months, reactive hyperemia was induced after 5 minutes of upper arm occlusion of SBP. The reactive hyperemia peripheral arterial tonometry index (RH-PAT), a measure of endothelial function, was obtained at rest and 4 hours after eating a McDonald’s breakfast (900 calories, 50 fat grams). We also measured body weight, BMI, and total body fat and trunk fat % by dual-energy X-ray absorptiometry. Results: Sixty subjects (low-CHO group: n=31, 74% female; low-fat group, n=29, 72% female) completed the study. At 0 months, there were no group differences in the following and the combined values are: age, 50.0±8.7 years; weight, 215.4±32.7 lbs; BMI, 34.2±3.8 kg/m2; total body fat, 43.3±7.2%; trunk fat, 46.4±5.7%; RH-PAT, 2.32±0.44%. At 0 months, RH-PAT did not change in response to the meal in either group, overall -0.05±0.64, p=.58. At 6 months, low-CHO vs. low-fat subjects had a greater reduction in weight, -28.9±11.0 vs. -18.7± 2.0 lbs., p<.01; BMI, -4.7±2.0 vs. -2.9±1.7, p<.01; body fat, -6.8±4.5 vs. -4.0±3.9%, p<.02. The groups did not differ in loss of trunk fat, with an overall drop of - 5.5±5.7%, p<.01. At 6 months, there was no change in resting RH-PAT in either group vs. 0 months, overall +0.03±0.53, p=.64 and no group difference in resting vs. postprandial RH-PAT, overall -0.08±0.69, p=.34. Though the 6-month mean resting RH-PAT did not improve, each absolute 1% drop in trunk fat % was associated with an absolute 0.29% (relative 12.5%) increase in RH-PAT, p=.05. Body composition changes did influence postprandial RH-PAT. Conclusions: We found no adverse effects of 6-months of a low-CHO diet on resting or postprandial endothelial function. Central fat loss was associated with improved vascular function, regardless of diet.