In a study
of overweight people maintaining weight loss, those on a
low-carbohydrate diet burned about 250 more calories per day
than those on a high-carbohydrate diet.
The study of
164 people, published recently by The BMJ medical journal,
notes the challenge of maintaining weight loss in the face of
the resulting hunger and metabolism slowdown, and says that
the calorie-burning effect of a low-carb diet “may improve
the success of obesity treatment.”
findings show that all calories are not alike to the body, and
that restricting carbohydrates may be a better strategy for
long-term weight loss than restricting calories,” said study
co-author Dr. David Ludwig, co-director of the New Balance
Foundation Obesity Prevention Center at Boston Children’s
addresses one of the most vexing problems in weight loss: As
the weight comes off, the body fights back, burning fewer
calories and bombarding us with hunger signals.
recipe for failure,” Ludwig said.
something of a mystery: Why does the body react as if it’s
starving when it clearly is not? For some researchers,
including Ludwig, the answer lies in the carbohydrate-insulin
model, the theory that processed carbohydrates such as white
bread trigger hormonal changes that lead to hunger, metabolic
slowdown and weight gain.
carbohydrates digest quickly into sugar, raising insulin
levels, Ludwig said. Insulin, in turn, programs fat cells to
store excess calories. When calories are locked up in fat
cells, the brain can’t perceive them and thinks the body
needs more food.
The authors of
the study collaborated with Framingham State University, where
164 overweight people — students, staff, faculty and
community members — agreed to eat only study-supplied food.
First, study participants lost about 12 percent of their body
weight, roughly 20 to 25 pounds for the average participant.
that’s going to stress their metabolism,” Ludwig said.
Then for the
20-week test phase, study participants were randomly placed in
three groups: those who ate diets composed of 20 percent
carbohydrates, 40 percent, or 60 percent. Each diet contained
20 percent protein, with the remaining portion composed of
fat. Diets used healthy foods and were as similar as possible,
Ludwig said. The goal at this stage was to maintain the weight
loss, not to lose any more weight.
Those on the
low-carb diet burned 209 to 278 more calories per day than
those on the high-carb diet, a difference that would lead to
an estimated 22-pound weight loss over three years if
researchers weren’t intervening to maintain weight.
And the effect
was even larger for those who produced high levels of insulin
in response to carbohydrates; they burned 308 to 478 more
calories a day on the low-carb diet than they did on the high-carb
How do you know
if you’re a high insulin secreter? “Look in the mirror,”
Ludwig advised. “If your fat distribution is predominantly
around the midsection — so you are more like an apple than a
pear — you’re more likely to be a high insulin secreter.”
activity levels were very similar for the three diet groups
before the study began, Ludwig said.
encouraged all participants to maintain their usual level of
physical activity, which was monitored. During the study, the
low-carb group showed a tendency toward more moderate-vigorous
physical activity, perhaps as a result of the diet, Ludwig
said via email. But he emphasized that exercise was only a
minor component of the total effect on calories burned.
A co-author of
a 2015 PloS One journal article comparing low-fat and low-carb
diets praised the precision and design of the new study,
including the direct calculation of energy expenditure, which
is difficult and labor intensive.
“I think they
brought a level of sophistication that you don’t tend to see
in these kinds of trials,” said Dr. Jonathan Sackner-Bernstein,
a former Food and Drug Administration associate center
director for technology and innovation who does consulting for
drug and device companies.
said the study reinforced his belief that the more sensitive
you are to carbohydrates, in terms of your insulin response,
the more important it is to be on a carbohydrate-restricted
Ludwig said the
study’s findings are very close to what the authors
predicted, but more work needs to be done.
“This is one
study, so the findings need to be replicated and examined in a
broader population — although we did have quite a
demographic variety in our participants,” he said. “We
need to see how this effect might play out in other studies,
how other populations would respond.”