Different Metabolic Effects Observed With Traditional and Atkins-Like Diets

Michael O'Riordan
January 2, 2008 (Adelaide, Australia) – A study comparing the metabolic effects of two diets, one a low-carbohydrate, high-fat, Atkins-like diet and the other a more traditional high-carbohydrate, low-fat diet, showed that both diets had similar improvements on a number of metabolic risk markers, although the traditional diet had more favorable effects on the blood lipid profile, including significant reductions in LDL-cholesterol levels [1].
"After six months, isocaloric energy-restricted very-low-carbohydrate, high-fat and high-carbohydrate, low-fat diets produced similar weight loss and substantial reductions in a number of cardiovascular disease risk markers," write Jeannie Tay (Flinders University, Adelaide, Australia) and colleagues in the January 1, 2008 issue of the Journal of the American College of Cardiology. "Neither diet displayed adverse effects, suggesting diverse dietary patterns, including very-low-carbohydrate, high-fat diets, may be tailored to an individual's metabolic profile and dietary preference for weight management."
The investigators note that while the traditional diet reduced LDL-cholesterol levels, the low-carbohydrate, high-fat diet resulted in greater increases in HDL cholesterol and larger reductions in triacylglycerol levels.
Weight loss as a confounding factor
As previously reported by heartwire, several studies have demonstrated greater weight loss among subjects who adhere to a low-carbohydrate, high-fat diet, such as the popular Atkins diet. One recent study, known as the Atkins-Traditional-Ornish-Zone (A TO Z) trial, found that premenopausal women randomized to the Atkins diet lost statistically more weight than women on the Zone diet and numerically more than the other two diets [2].
Despite the potential weight-loss advantages, there is still concern that long-term consumption of a high-fat diet, one high in saturated fat and cholesterol, will have adverse effects on blood lipids and cardiovascular disease risk. In this study, Tay and colleagues aimed to examine the metabolic effects of a low-carbohydrate, high-fat diet without the confounding effect of differential weight loss. The investigators compared the metabolic effects of the two diets, a traditional vs low-carbohydrate, high-fat one, under controlled dietary conditions where 88 subjects with abdominal obesity and at least one additional metabolic-syndrome risk factor consumed roughly the same amount of calories over a six-month period.
The subjects were randomly assigned to either of the moderately energy-restricted diet plans for 24 weeks. For those assigned to the very-low-carbohydrate, high-fat diet, 4% of total calories were obtained from carbohydrates, 35% from protein, and 61% from fat, including 20% from saturated fat. Subjects randomized to the high-carbohydrate, low-fat diet followed a more traditional macronutrient profile, with 46% of calories obtained from carbohydrates and 30% from fat, including <8% from saturated fat. Both treatment arms consumed the same number of calories daily.
Over the 24 weeks, there were significant reductions in body weight in both groups, but no significant difference between the two diets, either in absolute or relative terms. Total- and LDL-cholesterol levels decreased among subjects randomized to the low-fat diet but did not change significantly among those randomized to the Atkins-like diet. Those who consumed a high-fat, low-carbohydrate diet did experience greater increases in HDL-cholesterol levels as well as a greater reduction in triacylglycerol levels. Blood pressure, fasting glucose, insulin, and homeostasis model assessment were all reduced with weight loss, with no difference observed between the diets.
The investigators suggest that the anticipated increase in LDL cholesterol in the high-fat intervention arm, a result of higher saturated-fat intake, might have been mitigated by the effects of energy restriction and weight loss. However, there was no observed correlation between the change in LDL-cholesterol levels and the change in saturated-fat intake or weight, "suggesting the influence of other factors." They also note that there was wide variability in the LDL response in the low-carbohydrate, high-fat-diet arm, with approximately one-half of subjects showing a decrease. This suggests, Tay and colleagues write, that some individuals might have a more sensitive lipoprotein response to increases in saturated-fat intake.
Tay J, Brinkworth GD, Noakes M, et al. Metabolic effects of weight loss on a very-low-carbohydrate diet compared with an isocaloric high-carbohydrate diet in abdominally obese subjects. J Am Coll Cardiol 2008; 51: 59-67.
Gardner CD, Kiazand A, Alhassan S, et al. Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women: the A TO Z Weight Loss Study: a randomized trial. JAMA 2007; 297: 969-977. Abstract