Lack of suppression of circulating free fatty acids and hypercholesterolemia during weight loss on a high-fat, low-carbohydrate diet

Abstract

Background: Little is known about the comparative effect of weight-loss diets on metabolic profiles during dieting.

Objective: The purpose of this study was to compare the effect of a low-carbohydrate diet (< or =20 g/d) with a high-carbohydrate diet (55% of total energy intake) on fasting and hourly metabolic variables during active weight loss.

Design: Healthy, obese adults (n = 32; 22 women, 10 men) were randomly assigned to receive either a carbohydrate-restricted diet [High Fat; mean +/- SD body mass index (BMI; in kg/m(2)): 35.8 +/- 2.9] or a calorie-restricted, low-fat diet (High Carb; BMI: 36.7 +/- 4.6) for 6 wk. A 24-h in-patient feeding study was performed at baseline and after 6 wk. Glucose, insulin, free fatty acids (FFAs), and triglycerides were measured hourly during meals, at regimented times. Remnant lipoprotein cholesterol was measured every 4 h.

Results: Patients lost a similar amount of weight in both groups (P = 0.57). There was an absence of any diet treatment effect between groups on fasting triglycerides or on remnant lipoprotein cholesterol, which was the main outcome. Fasting insulin decreased (P = 0.03), and both fasting (P = 0.040) and 24-h FFAs (P < 0.0001) increased within the High Fat group. Twenty-four-hour insulin decreased (P < 0.05 for both groups). Fasting LDL cholesterol decreased in the High Carb group only (P = 0.003). In both groups, the differences in fasting and 24-h FFAs at 6 wk were significantly correlated with the change in LDL cholesterol (fasting FFA: r = 0.41, P = 0.02; 24-h FFA: r = 0.52, P = 0.002).

Conclusions: Weight loss was similar between diets, but only the high-fat diet increased LDL-cholesterol concentrations. This effect was related to the lack of suppression of both fasting and 24-h FFAs.

FIGURE 1

A: Decrease in 24-h insulin (baseline – 6 wk) for both the high-fat- and high-carbohydrate-diet groups (High Fat and High Carb). B: Lack of free fatty acid (FFA) suppression with meal intake over 24 h for the High Fat group. In both panels, baseline data show the trend for all participants (High Fat/High Carb groups combined). Data for the 2 separate groups (n = 16 per diet condition) were collected 6 wk into the weight-loss period. Arrows indicate meal times.

FIGURE 2

A: Relation between the difference in fasting free fatty acid (FFA; baseline − 6 wk) and the difference in LDL cholesterol (baseline − 6 wk; r = 0.41, P = 0.02; n = 16 per diet condition) in high-fat- and high-carbohydrate-diet groups (High Fat and High Carb). B: Relation between the difference in 24-h area under the curve (AUC) for FFA (baseline − 6 wk) and the difference in LDL cholesterol (baseline − 6 wk; r = 0.52, P = 0.002; n = 16 per diet condition).