= Full article availableThe shifting scientific story on “carbs” in your diet took another twist at the American Heart Association’s recent Scientific Sessions: Results from the OmniHeart study presented at the conference showed that substituting protein or monounsaturated fats for 10% of carbohydrates in an already healthy diet can reduce heart-disease risk. The findings suggest a possible improvement in the Dietary Approaches to Stop Hypertension (DASH) diet, which has been viewed as the “gold standard” in hypertension-fighting nutrition since the mid-1990s.
“Both the general public and the scientific research community are extremely interested in the health effects of shifting calories from carbohydrates,” said Lawrence J. Appel, MD, professor of medicine at Johns Hopkins University and lead author of the study, which was published simultaneously in the Journal of the American Medical Association. “Our study provides evidence that substituting carbohydrates with protein (about half from plants) or with unsaturated fat (mostly monounsaturated fat) can lower blood pressure, improve cholesterol levels, and reduce heart disease risk.”
Rather than studying the standard American diet, researchers tested three healthy diets. “All three diets are good; it’s just that two of these diets are somewhat better,” said Frank Sacks, MD, lead investigator from the study center at Brigham & Women’s Hospital, Harvard Medical School. “These diets improved the whole cardiovascular risk spectrum. A lot of patients are tough to control with the medications we have. Patients might not even need drugs if they go on these diets.”
Researchers studied 164 adults, average age 53.6, most of whom had elevated blood pressure not requiring medication (“prehypertension”) and 21% of whom had hypertension. Just over half were African American, a population that has a greater-than-average risk of developing hypertension. Rather than comparing the reduced-carbohydrate diets to the standard American diet, the researchers tested against a diet very close to the DASH plan, which has proven to lower blood pressure; the 2,000-calorie DASH diet emphasizes fruits, vegetables and low-fat or fat-free dairy products. Subjects tried each of three diets for six weeks, with a “washout period” in-between:
- The DASH-like diet, with 58% of calories from carbohydrates, 15% from protein and 27% from fat (13% from monounsaturated fat).
- A diet shifting 10% of calories from carbs to protein, with 48% of calories from carbohydrates, 25% protein and 27% fat; about half of the protein came from plant sources such as beans, nuts and seeds and vegetable-based meat substitutes, plus roughly six ounces per day of chicken, fish, meat and egg-product-substitutes, all low in saturated fat.
- A diet shifting 10% of calories to unsaturated fat, mostly olive and canola oils, with 48% of calories from carbohydrates, 15% protein and 37% fat (21% monounsaturated fat).
All of the diets were extremely low in saturated fat (6% of calories). Researchers kept the patients’ weight and exercise levels the same.
Compared to baseline levels, all three diets lowered systolic blood pressure by 8.2 mm Hg to 9.5 mm Hg and low-density lipoprotein (LDL) or “bad cholesterol” by 11.6 milligrams per deciliter (mg/dL). The protein diet further reduced systolic blood pressure by 1.4 mm Hg overall and lowered LDL by 3.3 mg/dL overall; it also significantly decreased high density lipoptotein (HDL)—the “good cholesterol”—however. The unsaturated-fat diet reduced systolic blood pressure by 1.3 mmHg more than the DASH diet; it had no significant effect on LDL but raised levels of HDL by 1.1 mg/dL. Both test diets reduced triglycerides (another fat in the blood), with the protein diet having a larger effect.
Researchers estimated each diet’s effect on the 10-year risk of coronary heart disease based on well-established formulas. While all three diets lowered risk, the researchers concluded that the risk was lowest for people following the protein and the unsaturated-fat diets. Compared to baseline, each diet reduced heart disease risk—16% reduction in the DASH-like diet and about 20% reduction in the carb-cutting unsaturated fat and protein diets.
“There are many aspects of diet that we know affect heart disease risk,” added Dr. Appel. “This study provides convincing evidence that the amount of carbohydrates, protein and fat people eat also influence risk.”
To learn more: Journal of the American Medical Association, Nov. 16, 2005. American Heart Association.
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