A healthy diet that replaces some carbohydrates with
either protein or monounsaturated fat can substantially
reduce blood pressure and cholesterol levels, resulting in
a substantial reduction in overall risk of heart disease,
according to government-funded studies by researchers at
Johns Hopkins and elsewhere.
The Johns Hopkins team found that shifting about 10
percent of calories from carbohydrate to either
protein-rich foods, mostly from plant sources, or to
monounsaturated fats, contained in olive and canola oils,
provided a major benefit to the heart.
"Our study provides strong evidence that replacing
some carbohydrate with either protein or monounsaturated
fat has important health benefits," said internist Lawrence
Appel, a professor of
medicine at the
Johns Hopkins School of Medicine and lead author of the
study. "There is already agreement that reducing saturated
fat lowers risk for heart disease, but the question of
which macronutrient to emphasize has been
controversial."
Appel makes clear that his study does not support
extremely high-saturated-fat, low-carbohydrate diets such
as the Atkins diet, which he says is not a healthy diet
plan.
The study, called the Optimal Macronutrient Intake
Trial to Prevent Heart Disease, or OmniHeart, evaluated
three healthy diets that differed mainly in the amount of
macronutrients — protein, fat and carbohydrate
— that provide calories used for energy in the body.
All three diets were low in saturated fat, cholesterol and
sodium and rich in fruits, vegetables, fiber, potassium and
other minerals. However, one diet was a traditional healthy
diet, rich in carbohydrate, while in the other two diets
approximately 10 percent of its calories from carbohydrate
were replaced with either monounsaturated fat or protein.
In the protein-rich diet, about half came from plants.
"All three diets reduced overall heart disease risk,
lowering blood pressure and improving cholesterol levels,"
Appel said. "But the protein and monounsaturated fat diets
had an edge over the carbohydrate-rich diet."
The Johns Hopkins findings from OmniHeart, presented
Nov. 15 at the American Heart Association's Scientific
Sessions 2005 and published simultaneously in the Journal
of the American Medical Association, underscore the
significant benefits from making dietary changes, the
researchers said.
Overall, the protein-rich diet, derived from plant and
animal sources, decreased cardiovascular disease risk by 21
percent. "Many people equate protein with meat, but it is
not the only source of protein," said study co-author
Phyllis McCarron, a dietitian at Johns Hopkins. "Excellent
plant sources of protein are beans, nuts, seeds and certain
grains."
The monounsaturated fat diet, enriched with olive and
canola oils, as well as various nuts and seeds, decreased
risk by almost 20 percent.
The carbohydrate-rich diet used in the study decreased
risk by roughly 16 percent. The carbohydrate-rich diet is
similar to the Dietary Approaches to Stop Hypertension, or
DASH, diet, which Appel helped develop in 1997.
For the current study, which lasted about three years,
researchers enlisted 164 generally healthy men and women
ages 30 and over. "Because of the huge risk of stroke and
heart attack in African-Americans, the results are
particularly applicable to this group, who made up roughly
55 percent of study participants," said study co-author
Jeanne Charleston, a research associate at the Bloomberg
School of Public Health. Charleston adds that all
participants either had high blood pressure (almost 20
percent) or were on the verge of having high blood
pressure.
For six-week intervals, participants ate all their
food--breakfast, lunch, dinner and snacks--from one of the
three diets. After a two-to-four-week break, participants
started the six-week feeding period over again, this time
with a different diet. The process was repeated until all
participants ate all three.
Researchers monitored each participant's levels of
blood pressure, cholesterol and triglycerides on each diet.
These measurements were then factored into a standard
mathematical model, called the Framingham risk equation,
for estimating heart disease risk.
Appel said the OmniHeart study results reconfirm the
powerful effects of a diet-based approach to improving
someone's cardiovascular risk profile, for blood pressure
and cholesterol levels, and lowering their overall risk of
heart disease. The OmniHeart Collaborative Research Group,
which conducted this study, plans further research on the
effects of carbohydrate on heart disease and its risk
factors.
Funding for this study, conducted at Johns Hopkins and
Brigham & Women's Hospital in Boston, was provided by the
National Heart, Lung and Blood Institute, and the National
Center for Research Resources; both are members of the
National Institutes of Health.
In addition to Appel, McCarron and Charleston,
researchers involved in the study were Edgar Miller III and
Thomas Erlinger, of Johns Hopkins; Frank Sacks, Vincent
Carey, Janis Swain, Paul Conlin, Bernard Rosner, Nancy
Laranjo and Louise Bishop, of Harvard Medical School; and
Eva Obarzanek, of the National Heart, Lung and Blood
Institute.
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