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“You can eat healthy in three different ways, and two of
them are a bit better than the other.” Lawrence J. Appel, M.D., M.P.H., Johns
Hopkins School of Medicine (AP)
“[People] don’t have to be restricted. If they have a
certain preference, they should know that they can follow any of these
[diets].” Eva Obarzanek, PhD, National Heart, Lung and Blood Institute (AP)
If people start by cutting back on saturated fat and
eating plenty of fruits and vegetables, they have a wide range of eating choices
to arrive at a healthy diet. That’s the basic finding of a study published
November 16, 2005 in the Journal of the
American Medical Association (Vol. 294, pages 2455-2464).
The Optimal Macronutrient Intake Trail to Prevent
Heart Disease (Omni-Heart Trial), based in Boston and Baltimore and funded by
the National Heart, Lung, and Blood Institute, recruited 164 mostly overweight
individuals with borderline or mild high blood pressure and rotated them through
three different diets for 6 weeks each with a few weeks of break between diets.
Calorie intake was adjusted to keep weight constant. Activity level was also
unchanged.
They checked blood pressure and LDL “bad”
cholesterol (and several other secondary measures) at the beginning and end of
each diet period. In addition, the researchers monitored change in heart
disease risk for each diet variation.
Each diet was a variation of the well-known DASH diet
(Dietary Approach to Stop Hypertension), which is relatively low in salt and
includes generous amounts of fresh fruits and vegetables, and low-fat dairy
products. The macronutrient breakdown of the DASH diet is 55% carbs, 18% protein and 27% fat. The three variations were
as follows: rich in carbs (58
carbs, 15 protein, and 27 fat), rich in protein (48-25-27),
and rich in unsaturated fat (48-15-37). As indicated, the primary distinguishing feature
of the three diets is their macronutrient composition, or carb-protein-fat
ratio. All three diets were low in saturated fat, cholesterol and sodium, and
rich in fruits, vegetables, fiber, potassium and other minerals. The carb diet
cuts back on protein and adds carbs. The protein diet is the reverse; it cuts
back on carbs and adds protein, about half from plant sources (legumes, grains,
nuts and seeds). In the unsaturated fat diet, they cut back on protein and added
healthy fats, such as olive and canola oil, and a variety of nuts and seeds.
This is a bit hard to follow, I know. The key is to
focus on the big picture; don’t miss the forest for the trees. The point is
that you can makes adjustments to suit your taste buds, and still eat a healthy
diet. You’ll see this in the outcome measures.
All three diets improved blood pressure and
cholesterol readings from baseline levels when the participants were eating on
their own. The protein and unsaturated fat diets produced slightly
better results, however. Systolic blood pressure (the top number in BP readings)
fell by an average of about 8 points on the carb diet; 9.5 points on the protein
diet, and 9.3 points on the good fat diet. LDL-cholesterol levels fell about 12
points on the carb diet, about 14 points on the protein diet, and about 13
points on the good fat diet.
The improvements produced by all three diets were
enough to reduce estimated 10-year cardiovascular disease risk:
minus 16.1% on the carb diet, -21.0% on the protein diet, and –19.6%
on the unsaturated fat diet. Again, the protein and healthy fat diets did a
little better than the carb diet.
Lead researcher Lawrence J. Appel, MD, of Johns
Hopkins School of Medicine, told Associated
Press reporter Lindsey
Tanner that all three diets would be beneficial for most Americans. “Most
people aren’t following anything close to any of these [diets],” he said.
“You can eat healthy in three different ways, and two are a bit better than
the other.”
Co-author Eva Obarzanek, PhD, a researcher at the
National Heart, Lung and Blood Institute, said, “[People] don’t have to be
restricted. If they have a certain preference, they should know that they can
follow any of these [diets].” She added, “None of these diets are
extreme.”
In an editorial in the same issue of JAMA,
Myron H. Weinberger, MD, of Indiana University Medical Center, called
the calorie-adjustment to avoid weight loss “a confounding variable.”
Observing that the majority of the study participants were overweight or obese,
he said weight loss would be “perhaps [the] most important intervention.”
Another recent study did look at the effect
of increased protein on appetite and body composition.
In
the JAMA study, carbs were reduced from 58 to 48 percent to make room for more
protein or fat. In the second study, published in the American
Journal of Clinical Nutrition (July
2005), carbohydrates were kept constant at 50%, while fat was cut from 35% to
20% and protein was increased from 15% to 30%; the resulting carb-protein-fat
ratio was 50-30-20. Rather than blood pressure and LDL cholesterol, the focus
was on appetite and weight loss. (Dr. Weinberger would no doubt approve.) Note
that carb intake was kept relatively high in both studies; these are not
“low-carb” diets.
Lead
author David S Weigle and his colleagues at the University of Washington School
of Medicine and the Oregon Health and Science University in Portland theorized
that adding protein while maintaining carbohydrate content would lower body
weight by curbing appetite and voluntary calorie intake. That’s what happened.
They
placed 19 healthy weight-stable adult volunteers, all at their lifetime high
body weight, on three different diets:
first, two weeks on a weight-maintenance diet (50% carbs, 15% protein, and 35%
fat); next, two weeks on a diet with exactly the same number of calories, but
more protein and less fat (50-30-20); and then, another 12 weeks on the same
high-protein diet. But this time they were allowed to eat all they wanted—as
long as they stuck to the high-protein, low-fat ratio. Significantly, the
subjects were told that it was not a weight-reduction study and that they should
not expect to lose weight.
The
subjects reported a clear reduction in appetite and increase in fullness during
the initial two weeks on the high-protein diet, but they ate the same number of
calories, as required, and they did not lose weight. During the final 12-weeks
on the high-protein diet, however, when allowed to eat as much as they wanted,
they spontaneously reduced their food intake by an average of 441 calories a
day—and lost an average of 10.8 pounds in body weight and 8.2 pounds of fat.
In
an accompanying editorial in AJCN, Arne Astrup, MD, PhD, head of the Institute of Human Nutrition at the
Royal Veterinary and Agriculture University in Copenhagen, Denmark, wrote that
the results “clearly showed that protein is more satiating than is fat, and
previous studies have shown that protein is more satiating than is
carbohydrate.” He, however, acknowledged:
“We do not yet understand how protein increases satiety.”
Since
there is no clear evidence that moderately increasing protein is harmful, Astrup
says it is probably advisable for people trying to control their weight to cut
back on refined carbohydrates and fat, and eat more lean meat and low-fat dairy
products. Don’t reduce your intake of fruits, vegetables and whole grains, he
emphasized.
I agree with both studies. I include some good
quality protein or “good” fat with each meal or snack, but I don’t worry
about the precise ratio of carbs to protein or fat. As Astrup suggests, I also
eat plenty of fruits, vegetables and whole grains. Do that, and exercise, and
you can probably stop worrying about your heart or your waistline. (For more
details, see my book Challenge
Yourself, pages
27-30.)
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