Free fatty acids, insulin resistance, and corrected qt intervals in morbid obesity: effect of weight loss during 6 months with differing dietary interventions.

OBJECTIVE: To assess whether shortening of the corrected QT (QTc) interval is most closely associated with changes in weight, insulin resistance, or free fatty acids (FFAs) (or some combination of these factors). METHODS: We randomized 75 severely obese subjects without diabetes to either a low-carbohydrate or a conventional low-fat weight-loss diet for 6 months. We measured QTc, insulin sensitivity, body mass index, and FFAs at baseline and at 6 months. Analysis was performed to determine whether improvement in weight, in insulin resistance, or in FFAs has the greatest effect on reducing the QTc interval. RESULTS: "Completers" of both the low-carbohydrate diet (N = 25) and the low-fat diet (N = 22) had a decrease in weight, but the weight loss was greater in the low-carbohydrate group. A statistically significant decrease in QTc from baseline was observed only in the low-carbohydrate group. QTc in the low-carbohydrate group correlated with improvement in insulin resistance, but this finding was not significant after correction for the greater weight loss. FFAs or weight loss was not correlated with QTc in either dietary group. CONCLUSION: Low-carbohydrate dieting is associated with a greater decrease in the QTc interval in comparison with low-fat dieting. Improvements in insulin resistance seem to have a relatively weak mechanistic role, and a decrease in FFAs has no apparent role in the reduction of the QTc interval.

A randomized study comparing the effects of a low-carbohydrate diet and a conventional diet on lipoprotein subfractions and C-reactive protein levels in patients with severe obesity.

PURPOSE: To compare the effects of a low-carbohydrate diet and a conventional (fat- and calorie-restricted) diet on lipoprotein subfractions and inflammation in severely obese subjects. METHODS: We compared changes in lipoprotein subfractions and C-reactive protein levels in 78 severely obese subjects, including 86% with either diabetes or metabolic syndrome, who were randomly assigned to either a low-carbohydrate or conventional diet for 6 months. RESULTS: Subjects on a low-carbohydrate diet experienced a greater decrease in large very low-density lipoprotein (VLDL) levels (difference = -0.26 mg/dL, P = 0.03) but more frequently developed detectable chylomicrons (44% vs. 22%, P = 0.04). Both diet groups experienced similar decreases in the number of low-density lipoprotein (LDL) particles (difference = -30 nmol/L, P = 0.74) and increases in large high-density lipoprotein (HDL) concentrations (difference = 0.70 mg/dL, P = 0.63). Overall, C-reactive protein levels decreased modestly in both diet groups. However, patients with a high-risk baseline level (>3 mg/dL, n = 48) experienced a greater decrease in C-reactive protein levels on a low-carbohydrate diet (adjusted difference = -2.0 mg/dL, P = 0.005), independent of weight loss. CONCLUSION: In this 6-month study involving severely obese subjects, we found an overall favorable effect of a low-carbohydrate diet on lipoprotein subfractions, and on inflammation in high-risk subjects. Both diets had similar effects on LDL and HDL subfractions.

The effects of low-carbohydrate versus conventional weight loss diets in severely obese adults: one-year follow-up of a randomized trial.

BACKGROUND: A previous paper reported the 6-month comparison of weight loss and metabolic changes in obese adults randomly assigned to either a low-carbohydrate diet or a conventional weight loss diet. OBJECTIVE: To review the 1-year outcomes between these diets. DESIGN: Randomized trial. SETTING: Philadelphia Veterans Affairs Medical Center. PARTICIPANTS: 132 obese adults with a body mass index of 35 kg/m2 or greater; 83% had diabetes or the metabolic syndrome. INTERVENTION: Participants received counseling to either restrict carbohydrate intake to <30 g per day (low-carbohydrate diet) or to restrict caloric intake by 500 calories per day with <30% of calories from fat (conventional diet). MEASUREMENTS: Changes in weight, lipid levels, glycemic control, and insulin sensitivity. RESULTS: By 1 year, mean (+/-SD) weight change for persons on the low-carbohydrate diet was -5.1 +/- 8.7 kg compared with -3.1 +/- 8.4 kg for persons on the conventional diet. Differences between groups were not significant (-1.9 kg [95% CI, -4.9 to 1.0 kg]; P = 0.20). For persons on the low-carbohydrate diet, triglyceride levels decreased more (P = 0.044) and high-density lipoprotein cholesterol levels decreased less (P = 0.025). As seen in the small group of persons with diabetes (n = 54) and after adjustment for covariates, hemoglobin A1c levels improved more for persons on the low-carbohydrate diet. These more favorable metabolic responses to a low-carbohydrate diet remained significant after adjustment for weight loss differences. Changes in other lipids or insulin sensitivity did not differ between groups. LIMITATIONS: These findings are limited by a high dropout rate (34%) and by suboptimal dietary adherence of the enrolled persons. CONCLUSION: Participants on a low-carbohydrate diet had more favorable overall outcomes at 1 year than did those on a conventional diet. Weight loss was similar between groups, but effects on atherogenic dyslipidemia and glycemic control were still more favorable with a low-carbohydrate diet after adjustment for differences in weight loss.

A low-carbohydrate as compared with a low-fat diet in severe obesity.

BACKGROUND: The effects of a carbohydrate-restricted diet on weight loss and risk factors for atherosclerosis have been incompletely assessed. METHODS: We randomly assigned 132 severely obese subjects (including 77 blacks and 23 women) with a mean body-mass index of 43 and a high prevalence of diabetes (39 percent) or the metabolic syndrome (43 percent) to a carbohydrate-restricted (low-carbohydrate) diet or a calorie- and fat-restricted (low-fat) diet. RESULTS: Seventy-nine subjects completed the six-month study. An analysis including all subjects, with the last observation carried forward for those who dropped out, showed that subjects on the low-carbohydrate diet lost more weight than those on the low-fat diet (mean [+/-SD], -5.8+/-8.6 kg vs. -1.9+/-4.2 kg; P=0.002) and had greater decreases in triglyceride levels (mean, -20+/-43 percent vs. -4+/-31 percent; P=0.001), irrespective of the use or nonuse of hypoglycemic or lipid-lowering medications. Insulin sensitivity, measured only in subjects without diabetes, also improved more among subjects on the low-carbohydrate diet (6+/-9 percent vs. -3+/-8 percent, P=0.01). The amount of weight lost (P<0.001) and assignment to the low-carbohydrate diet (P=0.01) were independent predictors of improvement in triglyceride levels and insulin sensitivity. CONCLUSIONS: Severely obese subjects with a high prevalence of diabetes or the metabolic syndrome lost more weight during six months on a carbohydrate-restricted diet than on a calorie- and fat-restricted diet, with a relative improvement in insulin sensitivity and triglyceride levels, even after adjustment for the amount of weight lost. This finding should be interpreted with caution, given the small magnitude of overall and between-group differences in weight loss in these markedly obese subjects and the short duration of the study. Future studies evaluating long-term cardiovascular outcomes are needed before a carbohydrate-restricted diet can be endorsed.