Low-Carb Diet Doesn't Up Heart Risk
Researchers Say It's Best to Avoid Extreme Diets, Whether Low-Fat or Low-Carbohydrate
Nov. 8, 2006 -- Critics of low-carbohydrate diets claim that they promote
heart disease, but one of the first studies to examine the long-term effects of
low-carb eating suggests otherwise.
Researchers from the Harvard School of Public Health found no evidence of an
association between low-carbohydrate diets and increased cardiovascular risk,
even when these diets were high in saturated animal fats.
Low-carb eating even seemed to be protective against heart disease when
vegetables were the main sources of fat and protein in the diet.
The study, which appears tomorrow in the New England Journal of
Medicine, included almost 83,000 female nurses in the Nurses' Health Study
who provided detailed information about their eating patterns once per year for
more than 20 years. The nurses were not asked to follow any particular
A clear message from the research was that extreme diets, which severely
restrict either fats or carbohydrates, are not the best choices for
cardiovascular disease prevention, researcher Thomas L. Halton, ScD, tells
Pros and Cons
"Neither a very low-fat diet or a very low-carbohydrate diet proved to
be ideal," he says. "There were pros and cons to both of these
Low-fat diets are by definition low in saturated fats, which is good for the
heart, Halton says. But they also tend to be higher in refined carbohydrates
like sugar and white flour, which spike blood sugar levels.
"Americans tend to pick the wrong carbohydrates," he says. "So
the benefits of eating lower amounts of saturated fat and cholesterol are
offset to some degree by the poor quality of the carbohydrates they
The most protective diet, in terms of heart disease risk, was a
low-carbohydrate that was also low in saturated fats and cholesterol where
vegetables were the main sources of fats and protein.
"The vegetable-based low-carbohydrate diet combined the best features of
low-fat and low-carbohydrate eating," Halton says.
Following this diet was associated with a 30% reduction in heart disease
risk over 20 years.
"The quality of fat and carbohydrate is more important than the
quantity," says study researcher Frank Hu, MD, PhD. "A heart-healthy
diet should embrace healthy types of fat and carbohydrates."
The Glycemic Load
Hu was talking about carbohydrates that are slow to convert to sugar, or
so-called low-glycemic-load foods.
Most fruits, vegetables, whole grains, and nuts have low glycemic loads.
Refined white flour and sugar, as well as white rice and potatoes, have high
Women in the study whose diets had the highest glycemic loads had a 90%
increased risk of developing heart disease
during the 20 years of follow-up, compared with women whose diets had the
lowest glycemic loads.
"This is just one study, but the findings suggest that eating a
high-glycemic-load diet may be even more harmful than eating a diet that is
high in saturated fat and cholesterol," Halton says.
Frank Sacks, MD, also studies diet and heart disease risk at the Harvard
School of Public Health, but he was not involved with the study by Halton and
His research also suggests that following a strictly low-fat diet is less
protective against heart disease than following a diet that includes fat from
vegetable sources like olive and canola oil.
He is currently assessing the cardiovascular risks and benefits of some of
the most widely promoted commercial diets, including Atkins, the South Beach
Diet, and the Zone.
"One problem with very restrictive diets is that people don't stay on
them very long," he says. "It doesn't matter how good they are or how
protective they are if people don't follow them."