Study Shows Low-Carb Diet Improves Cholesterol
DURHAM, N.C. -- People who followed a low-carbohydrate diet
for six months raised their good cholesterol and lowered their
triglycerides, changes that can help lower the risk of heart
disease, Duke University Medical Center researchers found.
The Duke study compared the effects of a low-carbohydrate
diet, which included nutritional supplements, with a low-fat,
low-cholesterol, low-calorie diet. The two diets improved
cardiac risk in different ways, said lead researcher Eric
Westman, M.D., associate professor of medicine at Duke
University Medical Center.
The low-carb diet improved HDL, or good cholesterol levels,
and lowered triglycerides, the researchers found. The reduced
fat diet lowered total cholesterol levels and triglyceride
levels. Both diets brought down blood levels of small LDL
particles, the form of bad cholesterol most likely to lead to
hardened arteries, they found.
The results appeared early online November 16, 2005 in the
International Journal of Cardiology and will appear in print in
2006. The research was funded by an unrestricted grant from the
Robert C. Atkins Foundation. The study authors have no
financial interest in Atkins Nutritionals, Inc.
"I think the emerging science shows different diets improve
cardiac risk in different ways. We are moving from a
one-size-fits-all approach to considering many different diets
to fit the many different types of cardiac risk," Westman
Overall, both diets had positive effects on cholesterol,
Westman said. The triglyceride levels improved significantly in
both groups, falling 74.2 points for the low-carb group and
27.9 points for the low-fat group. People on the low-carb diet
showed an increase in HDL cholesterol by 5.5 points, a positive
change, while those following the low-fat diet did not have a
significant change. LDL cholesterol levels did not change
significantly in either group but small LDL particles decreased
17.4 points for the low-carb dieters and 19.2 points for the
low-fat dieters, a similar improvement. The total cholesterol
of the low-fat dieters saw a 13.7 point decline over 6 months
but did not change significantly in the low-carb dieters.
The 120 study participants were randomly assigned to either
the low-carbohydrate diet or the low-fat, low-cholesterol,
low-calorie diet. All were between 18 and 65 years old and in
generally good health, with a body mass index (BMI) between 30
and 60, indicating obesity, and a total cholesterol level of
more than 200 mg/dL. None had tried dieting or weight loss
pills in the previous six months.
The low-carbohydrate group was permitted daily unlimited
amounts of animal foods (meat, fowl, fish and shellfish);
unlimited eggs; 4 oz. of hard cheese; two cups of salad
vegetables such as lettuce, spinach or celery; and one cup of
non-starchy vegetables such as broccoli, cauliflower or
asparagus. They also received daily nutritional supplements --
a multivitamin; essential oils including flax seed oil, borage
oil and fish oil; and chromium picolinate. There were no
restrictions on total calories, but carbohydrates were kept
below 20 grams per day at the start of the diet.
The low-carbohydrate diet appears to have a favorable effect
on cardiac risk, Westman said. "While the low-carbohydrate
group received extra nutritional supplements, and experienced
greater weight loss, these differences did not fully account
for the changes in cardiac risk factors that we saw," he
The low-fat, low-cholesterol, low-calorie group followed a
diet consisting of less than 30 percent of daily caloric intake
from fat; less than 10 percent of calories from saturated fat;
and less than 300 milligrams of cholesterol daily. They were
also advised to cut back on calories. The recommended daily
calorie level was 500 to 1,000 calories less than the
participant's maintenance diet -- the calories needed to
maintain current weight.
Westman noted that the diets have one often-ignored
similarity. "It's possible that the common denominator of these
diets is what they're not eating – both diets did not allow
refined sugar or junk food," Westman said.
Study participants were encouraged to exercise 30 minutes at
least three times per week, but no formal exercise program was
provided. Both sets of dieters had group meetings at an
outpatient research clinic regularly for six months.
Co-authors include William Yancy, Jr., M.D., Maren Olsen,
Ph.D., Tara Dudley and John Guyton, M.D., all of Duke.