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 "These findings showed that all calories are not alike to the body,"
said study coauthor Dr. David Ludwig, who codirects the New Balance
Foundation Obesity Prevention Center at Boston Children's Hospital.
"Restricting carbohydrates might be a better strategy than
restricting calories over the long term."
The new study did not focus on losing excess pounds, but rather on a
factor that makes it hard to maintain weight loss: the fact that the
body adapts as pounds are shed by slowing metabolism, which results
in fewer calories being burned. And for most that means weight is
regained.
Ludwig subscribes to a theory, known as the carbohydrate-insulin
model, which suggests that increases in the consumption of so called
high-glycemic foods – which raise blood sugar sharply right after
they're eaten - trigger hormonal changes that increase hunger and
lead to weight gain.
To see if metabolism and hunger can be shifted by types of foods
people eat, Ludwig and his colleagues enlisted 164 overweight adults
aged 18 to 65 who had already lost 10 percent of their body weight,
and randomly assigned them to one of three carb-varying diets for 20
weeks.
The volunteers' meals, provided by the researchers, had the same
daily calorie count and all contained 20 percent protein. But one
group's diet consisted of 20 percent fat and 60 percent carbs,
another got a diet with 40 percent fat and 40 percent carbs and the
third group ate 60 percent fat and 20 percent carbs.
After tracking the volunteers' weight and measuring energy
expenditure through the study period, it was clear that those who
had consumed the lowest levels of carbs had burned the most
calories. Perhaps just as important, their levels of the
hunger-regulating hormones, ghrelin and leptin, were lower too.
Volunteers in the low-carb group burned 209 to 278 calories a day
more than those on the high-carb diet, which meant they were burning
50 to 70 calories more a day for every 10 percent decrease in carbs
to their total energy intake, according to the report in The BMJ.
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The volunteers with the highest insulin secretion at the start of
the study had an even more dramatic difference in energy
expenditure: those on the low-carb diet burned as much as 478
calories a day more than those consuming the highest level of carbs.
This kind of extra calorie burn would translate "into about 20
pounds of weight loss in a year among those on the low carb diet
compared to those in the high carb group," Ludwig said.
The new study is "exciting and unique," said Dr. Rekha Kumar, an
endocrinologist and obesity medicine specialist at NewYork-Presbyterian
and Weill Cornell Medicine in New York City. "Most studies are
looking at inducing weight loss," Kumar said. "This one is about
weight maintenance. And it's asking, is there a particular macro
nutrient composition that can result in a higher calorie burn?"
The fact that people with higher insulin levels "had the biggest
impact allows you to say this is quite valid," said Kumar, who was
not involved in the study. "That's because these are the people -
the ones who have issues with blood sugar and insulin - that you
would expect to respond."
The findings offer hope that modifying nutrients in the diet could
affect energy expenditure, said Lisa Martich, a dietician specialist
at Magee-Womens Hospital at the University of Pittsburgh Medical
Center.
And it may end up being used as "another tool," in weight loss
programs, said Martich, who was not involved in the study.
"I think there's a tendency to go all or nothing, saying just eat a
low carb diet and it will keep the weight off," Kumar explained.
"Maybe a low-carb diet can help, but so can increasing exercise."
SOURCE: https://bit.ly/2PFm3i0 The BMJ, online November 14, 2018.
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