People who avoid carbohydrates and eat more fat, even saturated fat, lose more body fat and have fewer cardiovascular risks than people who follow the low-fat diet that health authorities have favored for decades, a major new study shows.
The
findings are unlikely to be the final salvo in what has been a long and
often contentious debate about what foods are best to eat for weight
loss and overall health. The notion that dietary fat is harmful,
particularly saturated fat, arose decades ago from comparisons of
disease rates among large national populations.
But
more recent clinical studies in which individuals and their diets were
assessed over time have produced a more complex picture. Some have
provided strong evidence that people can sharply reduce their heart
disease risk by eating fewer carbohydrates and more dietary fat, with
the exception of trans fats. The new findings suggest that this strategy
more effectively reduces body fat and also lowers overall weight.
The new study was financed by the National Institutes of Health
and published in the Annals of Internal Medicine. It included a
racially diverse group of 150 men and women — a rarity in clinical
nutrition studies — who were assigned to follow diets for one year that
limited either the amount of carbs or fat that they could eat, but not
overall calories.
“To
my knowledge, this is one of the first long-term trials that’s given
these diets without calorie restrictions,” said Dariush Mozaffarian, the
dean of the Friedman School of Nutrition Science and Policy at Tufts
University, who was not involved in the new study. “It shows that in a
free-living setting, cutting your carbs helps you lose weight without
focusing on calories. And that’s really important because someone can
change what they eat more easily than trying to cut down on their
calories.”
Diets
low in carbohydrates and higher in fat and protein have been commonly
used for weight loss since Dr. Robert Atkins popularized the approach
in the 1970s. Among the longstanding criticisms is that these diets
cause people to lose weight in the form of water instead of body fat,
and that cholesterol
and other heart disease risk factors climb because dieters invariably
raise their intake of saturated fat by eating more meat and dairy.
Many
nutritionists and health authorities have “actively advised against”
low-carbohydrate diets, said the lead author of the new study, Dr. Lydia A. Bazzano
of the Tulane University School of Public Health and Tropical Medicine.
“It’s been thought that your saturated fat is, of course, going to
increase, and then your cholesterol is going to go up,” she said. “And
then bad things will happen in general.”
The new study showed that was not the case.
By
the end of the yearlong trial, people in the low-carbohydrate group had
lost about eight pounds more on average than those in the low-fat
group. They had significantly greater reductions in body fat than the
low-fat group, and improvements in lean muscle mass — even though
neither group changed their levels of physical activity.
While the low-fat group did lose weight, they appeared to lose more muscle than fat.
“They
actually lost lean muscle mass, which is a bad thing,” Dr. Mozaffarian
said. “Your balance of lean mass versus fat mass is much more important
than weight. And that’s a very important finding that shows why the
low-carb, high-fat group did so metabolically well.”
The
high-fat group followed something of a modified Atkins diet. They were
told to eat mostly protein and fat, and to choose foods with primarily
unsaturated fats, like fish, olive oil and nuts. But they were allowed
to eat foods higher in saturated fat as well, including cheese and red
meat.
A
typical day’s diet was not onerous: It might consist of eggs for
breakfast, tuna salad for lunch, and some kind of protein for dinner —
like red meat, chicken, fish, pork or tofu — along with vegetables.
Low-carb participants were encouraged to cook with olive and canola
oils, but butter was allowed, too.
Over
all, they took in a little more than 13 percent of their daily calories
from saturated fat, more than double the 5 to 6 percent limit
recommended by the American Heart Association. The majority of their fat
intake, however, was unsaturated fats.
The
low-fat group included more grains, cereals and starches in their diet.
They reduced their total fat intake to less than 30 percent of their
daily calories, which is in line with the federal government’s dietary
guidelines. The other group increased their total fat intake to more
than 40 percent of daily calories.
Both
groups were encouraged to eat vegetables, and the low-carbohydrate
group was told that eating some beans and fresh fruit was fine as well.
In the end, people in the low-carbohydrate group saw markers of inflammation and triglycerides — a type of fat that circulates in the blood — plunge. Their HDL, the so-called good cholesterol, rose more sharply than it did for people in the low-fat group.
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