A systematic review 1 including 5 studies with a total of 447 subjects was abstracted in DARE. All arms of the 5 trials showed weight loss after the diet: After 12 months, the low-carbohydrate groups showed weight losses between -7.2 and -2.1 kg. Weight losses in the low-fat group ranged from -4.4 to -3.1 kg in the 3 studies that provided these data. The participants on low-carbohydrate diets were more likely to complete the trial. After 6 months, individuals on low-carbohydrate diets had lost significantly more weight than individuals randomised to low-fat diets (WMD -3.3 kg, 95% CI: -5.3 to -1.4; 5 trials). The results showed statistical heterogeneity (P=0.02), which was traced to one trial allowing 10% energy intake from fat compared with 30% in the other trials. After 12 months, the difference was reduced to a mean of -1.0 kg (95% CI: -3.5 to 1.5; not significant; based on 3 trials). No differences in blood-pressure were found. A low-carbohydrate diet had favourable effect on triglyceride levels (WMD -22.1 mg/dL, 95% CI: -38.1 to -5.3; 4 trials) and high-density lipoprotein cholesterol values (WMD 4.6 mg/dL, 95% CI: 1.5 to 8.1; 4 trials). A low-fat diet showed favourable results on total cholesterol (WMD 8.9 mg/dL, 95% CI: 3.1 to 14.3; 4 trials) and low-density lipoprotein cholesterol values (WMD 5.4 mg/dL, 95% CI 1.2 to 10.1; 4 trials).
The authors conclude that potential favourable changes in triglyceride and high-density lipoprotein cholesterol values should be weighed against potential unfavourable changes in low-density lipoprotein cholesterol values when low-carbohydrate diets are considered.
An additional RCT 2 with a total of 311 overweight/obese (BMI 27-40), nondiabetic premenopausal women compared 4 weight-loss diets representing a spectrum of low to high carbohydrate intake. Participants were randomly assigned to follow the Atkins (very low in carbohydrate, n = 77), Zone (low in carbohydrate, n = 79), LEARN (Lifestyle, Exercise, Attitudes, Relationships, and Nutrition; low in fat, high in carbohydrate, based on national guidelines, n = 79), or Ornish (very high in carbohydrate, n = 76) diets and received weekly instruction for 2 months, then an additional 10-month follow-up. Weight loss was greater for women in the Atkins diet group compared with the other diet groups at 12 months, and mean 12-month weight loss was significantly different between the Atkins and Zone diets (P<0.05). Mean 12-month weight loss was as follows: Atkins, -4.7 kg (95% CI -6.3 to -3.1 kg), Zone, -1.6 kg (95% CI -2.8 to -0.4 kg), LEARN, -2.6 kg (-3.8 to -1.3 kg), and Ornish, -2.2 kg (-3.6 to -0.8 kg). Weight loss was not statistically different among the Zone, LEARN, and Ornish groups. At 12 months, secondary outcomes (included lipid profile: low-density lipoprotein, high-density lipoprotein, and non-high-density lipoprotein cholesterol, and triglyceride levels; percentage of body fat; waist-hip ratio; fasting insulin and glucose levels; blood pressure) for the Atkins group were comparable with or more favourable than the other diet groups.
Weight-loss trajectories for each group had not stabilized at 12 months and the trajectories of weight change between 6 and 12 months suggest that longer follow-up would likely have resulted in progressively diminished group differences
Comment: The quality of evidence is downgraded by sparse data.
Primary/Secondary Keywords