While low-carb diets have outperformed other diets when it comes to
weight loss, some researchers feared they might be worse for heart
health because they tend to be high in fat.
The new study shows that with proper nutritional counseling, people
can lose more weight and lower their risk factors for heart disease
on a low-carbohydrate diet, said the lead author, Dr. Lydia Bazzano
of Tulane University in New Orleans.
"This study shows if you are overweight and have cardiovascular
disease risk factors and haven't had success on other diets,
certainly a low-carbohydrate diet is worth a try," said Bazzano.
Carbohydrates are found in food and include sugar, fiber and
starches that give the body energy. Some carbs - like those in whole
grains and fruits - are healthier than others - like those in white
bread and other processed foods.
Bazzano and her colleagues write in Annals of Internal Medicine that
low-carb diets have become popular weight loss strategies in recent
years. Studies on their effects on cardiovascular risk factors have
produced mixed results, however.
For the new study, she and her colleagues recruited 148 obese men
and women between the ages of 22 and 75. None of the participants
had heart disease or diabetes.
Half were randomly assigned to follow a low-carbohydrate diet for a
year, and the other half were assigned to a low-fat diet for a year.
They were told to not change their physical activity throughout the
All participants attended regular meetings where they learned about
portion control, healthy eating and overall nutrition. They were
also offered one meal-replacement bar or shake per day.
The only difference between the groups was the proportions of
carbohydrate and fat in their diets.
Those in the low-carbohydrate group were told to eat at no more than
40 grams of digestible carbohydrates per day. ("Digestible carbs"
equals total carbs minus total fiber.)
Those in the low-fat group were told not to get more than 30 percent
of their daily energy from fat and no more than 55 percent of their
daily energy from carbohydrates.
Overall, about four of every five participants were still following
the diets 12 months later.
During that time, the researchers found, people on the
low-carbohydrate diet lost more weight and more body fat than those
on the low-fat diet.
The difference in lost weight between the two groups would represent
about eight additional pounds.
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Additionally, the researchers saw no increases in total cholesterol
or "bad" LDL cholesterol between the two groups. Bazzano said that's
good news since some thought a low-carbohydrate diet would increase
Those in the low-carbohydrate group had lower levels of fat
circulating in their blood and had lower scores on a measure often
used to predict the risk of a heart attack or stroke within the next
"I thought that was a very striking finding," Bazzano said. She
added that the score that predicts risk of future heart attacks and
strokes was computed after the study was finished and is less
reliable than the other risk factors they measured.
Dr. David Jenkins, who wasn't involved in the study, told Reuters
Health, "This doesnít look to me to say 'eat all the meats you want
to lower your carbohydrates.' Thatís just one way to do it."
Instead, Jenkins said, people in this study appeared to improve
their overall diets. For example, they were eating foods with
healthier fats, such as nuts and beans.
He also said they seemed to eat more fiber and cut down on processed
foods with more carbohydrates.
"I think itís another testament to what one can do with a more
plant-based diet using the right macronutrient profile," said
Jenkins of the Department of Nutritional Sciences at the University
of Toronto and the Keenan Research Centre at St. Michael's Hospital.
Bazzano agreed that the overall diets improved among the
participants and they were encouraged to eat healthier forms of
protein like chicken, fish, nuts and beans.
She also said her team is not sure why people on the
low-carbohydrate diets lost more weight and had lower risk factors
for heart disease after one year. It's not clear, she added,if there
would still be a difference after a longer period.
Annals of Internal Medicine, online September 1, 2014.
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