Replacing Carbs in the Diet with Protein or Monounsaturated Fat Reduces CHD Risk

JUNE 02, 2007
Wayne Kuznar

From the American Heart Association

Dallas—A comparison of 3 diets with recommended levels of saturated fat revealed that one that emphasizes protein or monounsaturated fat has a greater effect on coronary heart disease (CHD) risk factors than one that favors carbohydrates, said Lawrence J. Appel, MD, of Johns Hopkins University, Baltimore, Md, at the American Heart Association’s Scientific Sessions 2005.

In a multicenter, randomized, cross-over study, blood pressure (BP) and lipid risk factors were improved with diets that partially replaced carbohydrates with protein or unsaturated fat, said Dr Appel. The study was supported by the National Heart, Lung, and Blood Institute.

“We now have several options,” he said. “All 3 diets tested were healthy and beneficial. We have shown that replacing some carbohydrate is of benefit.” He added that increasing protein intake from plants may be particularly beneficial, as shown in observational studies.

The study included 164 adults with prehypertension or stage 1 hypertension (systolic BP of 120-159 mm Hg and/or diastolic BP of 80-99 mm Hg). About one half of the participants were African American.

The participants were randomized to 1 of 3 diets for 6 weeks and then crossed over to the other diets for 6 weeks each, with at least a 2-week washout period between diets. All of the diets studied were vast improvements over the typical American diet. The 3 diets were as follows:

• The diet emphasizing carbohydrates derived 58% of calories from carbohydrates, 15% from protein, and 21% from unsaturated fat. (In the other 2 diets, carbohydrates comprised 48% of calories.)

• The diet emphasizing protein in­creased protein intake to 25% of calories. It also derived 21% of calories from unsaturated fat, as in the diet rich in carbohydrates.

• The diet emphasizing unsaturated fat used fats and oils pri­marily rich in monounsaturated fat (ie, olive oil) to increase unsaturated fat to 31% of calories. As in the carbohydrate diet, it contained 15% of calories from protein.

Each diet was low in saturated fat (6% of calories) and cholesterol and rich in fruits, vegetables, and fiber. Patie­nts’ weight was kept constant throughout the study.

Compliance with the 3 diets was excellent; all 164 patients com­pleted 2 feeding periods, and 159 of them completed all 3.

Compared with the patients’ prestudy diets, all 3 diets reduced systolic BP by 8.2 to 9.5 mm Hg and low-density lipoprotein (LDL) cholesterol by 11.6 to 14.2 mg/dL. Compared with the diet that emphasized car­bohydrates:

• The protein diet further reduced systolic BP by 1.4 mm Hg and LDL cholesterol by 3.3 mg/dL, but also significantly reduced high-density lipoprotein (HDL) cholesterol by 1.4 mg/dL.

• The unsaturated fat diet further reduced systolic BP by 1.3 mm Hg, had no significant effect on LDL cholesterol levels, but raised HDL cholesterol levels by 1.1 mg/dL.

Compared with baseline, the pro­tein and unsaturated fat diets reduced triglycerides by 16.4 and 9.3 mg/dL, respectively, while the carbo­hydrate diet had no significant effect.

When the 10-year risk of CHD was estimated using the Framingham risk equation, all 3 diets were found to lower risk compared with baseline, but the 10-year estimated risk was reduced by 16% with the carbohydrate diet and by 20% with the protein and unsaturated fat diets.

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