Some new studies!

Low-Carbohydrate, High-Protein Diets

Physicians are often asked about the safety and efficacy of low-carbohydrate, high-protein diets. Unfortunately, very few controlled studies have evaluated these popular regimens. These diets, which are often high in fat, raise concerns about their effects on lipid levels.

One such diet, the Atkins Diet, restricts carbohydrates and encourages unlimited consumption of protein and fat. Preliminary results were presented from a 3-center (University of Pennsylvania, University of Colorado, Washington University) randomized controlled trial comparing the Atkins Diet with a conventional low-fat, high-carbohydrate plan that restricted daily caloric intake to 1200-1500 kcal for women and 1500-1800 kcal for men.

The study included 63 obese (BMI 33.8 ± 3.4 kg/m2) males and females who were randomized to 1 of the 2 diets. Subjects received an initial session with a dietitian to explain the assigned diet program.

At 12 weeks, the researchers found that the Atkins group had a lower rate of attrition (12%) compared with that of the conventional program (30%).

In addition, subjects in the Atkins group lost significantly more weight (8.5 ± 3.7%) compared with the conventional group (3.7 ± 4.0%).

In terms of serum lipids, the Atkins group demonstrated slight increases in total cholesterol (TC; 2.2 ± 16.6%) and low-density lipoprotein (LDL) cholesterol (6.6 ± 20.7%), whereas the conventional group showed significant decreases in these measures (TC -8.2 ± 11.5%; LDL -11.1 ± 19.4%).

High-density lipoprotein (HDL) cholesterol significantly increased in the Atkins group (11.5 ± 20.6%) but did not change in the conventional group, whereas triglycerides showed a significant decrease for the Atkins group (-21.7 ± 27.9%) and no change in the conventional group.

At 26 weeks, these changes persisted in both groups even though the sample size was smaller. The researchers concluded that the Atkins Diet produced favorable effects on weight, HDL, triglycerides, and retention compared with a conventional low-fat, low-calorie program, whereas the conventional plan was associated with more favorable effects on TC and LDL cholesterol.

A similar randomized-controlled trial from Duke University was also presented at the conference. The researchers in this study also compared the effects of a low-carbohydrate (LC) diet with a low-fat, low-calorie (LF) program.

This study included 120 obese (mean BMI 34 kg/m2) males and females, who all received group treatment for their respective diet programs.

At 6 months, both groups had similar rates of attrition, but the LC group lost considerably more weight (13.3 ± 4.6%) compared with the LF group (8.6 ± 5.9%). In addition, the LC group lost significantly more fat mass than the LF group (-9.7 kg for the LC group and -6.4 kg for the LF group).

Both groups showed decreases in triglycerides, with the LF group also showing a significant decrease in total cholesterol (-13.5 mg/dL).

The LC group showed significant increases in HDL and a significant decrease in Chol/HDL ratio.

This pattern of results was similar to those of the 3-center study described above. Longer-term studies are needed to more fully evaluate the safety and efficacy of these popular diet approaches.

The 2002 NAASO meeting will occur in San Diego, California, from February 23 as part of the First Annual Nutrition Week Conference.