Image
Anyone
who has ever been on a diet knows that the standard prescription for
weight loss is to reduce the amount of calories you consume.
But a new study, published Tuesday in JAMA,
may turn that advice on its head. It found that people who cut back on
added sugar, refined grains and highly processed foods while
concentrating on eating plenty of vegetables and whole foods — without
worrying about counting calories or limiting portion sizes — lost
significant amounts of weight over the course of a year.
The
strategy worked for people whether they followed diets that were mostly
low in fat or mostly low in carbohydrates. And their success did not
appear to be influenced by their genetics or their insulin-response to
carbohydrates, a finding that casts doubt on the increasingly popular
idea that different diets should be recommended to people based on their
DNA makeup or on their tolerance for carbs or fat.
The
research lends strong support to the notion that diet quality, not
quantity, is what helps people lose and manage their weight most easily
in the long run. It also suggests that health authorities should shift
away from telling the public to obsess over calories and instead
encourage Americans to avoid processed foods that are made with refined
starches and added sugar, like bagels, white bread, refined flour and
sugary snacks and beverages, said Dr. Dariush Mozaffarian, a
cardiologist and dean of the Friedman School of Nutrition Science and
Policy at Tufts University.
Advertisement
“This
is the road map to reducing the obesity epidemic in the United States,”
said Dr. Mozaffarian, who was not involved in the new study. “It’s time
for U.S. and other national policies to stop focusing on calories and
calorie counting.”
The new research
was published in JAMA and led by Christopher D. Gardner, the director of
nutrition studies at the Stanford Prevention Research Center. It was a
large and expensive trial, carried out on more than 600 people with $8
million in funding from the National Institutes of Health, the Nutrition
Science Initiative and other groups.
You have 3 free articles remaining.
Subscribe to The Times
Subscribe to The Times
Dr.
Gardner and his colleagues designed the study to compare how overweight
and obese people would fare on low-carbohydrate and low-fat diets. But
they also wanted to test the hypothesis — suggested by previous studies
— that some people are predisposed to do better on one diet over the
other depending on their genetics and their ability to metabolize carbs
and fat. A growing number of services have capitalized on this idea by
offering people personalized nutrition advice tailored to their
genotypes.
The researchers recruited
adults from the Bay Area and split them into two diet groups, which were
called “healthy” low carb and “healthy” low fat. Members of both groups
attended classes with dietitians where they were trained to eat
nutrient-dense, minimally processed whole foods, cooked at home whenever
possible.
Soft drinks, fruit juice,
muffins, white rice and white bread are technically low in fat, for
example, but the low-fat group was told to avoid those things and eat
foods like brown rice, barley, steel-cut oats, lentils, lean meats,
low-fat dairy products, quinoa, fresh fruit and legumes. The low-carb
group was trained to choose nutritious foods like olive oil, salmon,
avocados, hard cheeses, vegetables, nut butters, nuts and seeds, and
grass-fed and pasture-raised animal foods.↚
Advertisement
The
participants were encouraged to meet the federal guidelines for
physical activity but did not generally increase their exercise levels,
Dr. Gardner said. In classes with the dietitians, most of the time was
spent discussing food and behavioral strategies to support their dietary
changes.
The new study stands apart
from many previous weight-loss trials because it did not set extremely
restrictive carbohydrate, fat or caloric limits on people and emphasized
that they focus on eating whole or “real” foods — as much as they
needed to avoid feeling hungry.
“The unique thing is that we didn’t ever set a number for them to follow,” Dr. Gardner said.
Of course, many dieters regain what they lose,
and this study cannot establish whether participants will be able to
sustain their new habits. While people on average lost a significant
amount of weight in the study, there was also wide variability in both
groups. Some people gained weight, and some lost as much as 50 to 60
pounds. Dr. Gardner said that the people who lost the most weight
reported that the study had “changed their relationship with food.” They
no longer ate in their cars or in front of their television screens,
and they were cooking more at home and sitting down to eat dinner with
their families, for example.
Image↚
“We
really stressed to both groups again and again that we wanted them to
eat high-quality foods,” Dr. Gardner said. “We told them all that we
wanted them to minimize added sugar and refined grains and eat more
vegetables and whole foods. We said, ‘Don’t go out and buy a low-fat
brownie just because it says low fat. And those low-carb chips — don’t
buy them, because they’re still chips and that’s gaming the system.’”
Dr.
Gardner said many of the people in the study were surprised — and
relieved — that they did not have to restrict or even think about
calories.
“A couple weeks into the
study people were asking when we were going to tell them how many
calories to cut back on,” he said. “And months into the study they said,
‘Thank you! We’ve had to do that so many times in the past.’”
Advertisement
Calorie
counting has long been ingrained in the prevailing nutrition and weight
loss advice. The Centers for Disease Control and Prevention, for
example, tells people who are trying to lose weight to “write down the foods you eat
and the beverages you drink, plus the calories they have, each day,”
while making an effort to restrict the amount of calories they eat and
increasing the amount of calories they burn through physical activity.
“Weight
management is all about balancing the number of calories you take in
with the number your body uses or burns off,” the agency says.
Yet
the new study found that after one year of focusing on food quality,
not calories, the two groups lost substantial amounts of weight. On
average, the members of the low-carb group lost just over 13 pounds,
while those in the low-fat group lost about 11.7 pounds. Both groups
also saw improvements in other health markers, like reductions in their
waist sizes, body fat, and blood sugar and blood pressure levels.
The
researchers took DNA samples from each subject and analyzed a group of
genetic variants that influence fat and carbohydrate metabolism.
Ultimately the subjects’ genotypes did not appear to influence their
responses to the diets.
The
researchers also looked at whether people who secreted higher levels of
insulin in response to carbohydrate intake — a barometer of insulin
resistance — did better on the low-carb diet. Surprisingly, they did
not, Dr. Gardner said, which was somewhat disappointing.
“It
would have been sweet to say we have a simple clinical test that will
point out whether you’re insulin resistant or not and whether you should
eat more or less carbs,” he added.
Advertisement
Dr.
Walter Willett, chairman of the nutrition department at the Harvard T.
H. Chan School of Public Health, said the study did not support a
“precision medicine” approach to nutrition, but that future studies
would be likely to look at many other genetic factors that could be
significant. He said the most important message of the study was that a
“high quality diet” produced substantial weight loss and that the
percentage of calories from fat or carbs did not matter, which is consistent with other studies, including many that show that eating healthy fats and carbs can help prevent heart disease, diabetes and other diseases.
“The bottom line: Diet quality is important for both weight control and long-term well-being,” he said.
Dr.
Gardner said it is not that calories don’t matter. After all, both
groups ultimately ended up consuming fewer calories on average by the
end of the study, even though they were not conscious of it. The point
is that they did this by focusing on nutritious whole foods that
satisfied their hunger.
“I think one
place we go wrong is telling people to figure out how many calories they
eat and then telling them to cut back on 500 calories, which makes them
miserable,” he said. “We really need to focus on that foundational
diet, which is more vegetables, more whole foods, less added sugar and
less refined grains.”
SOURCE ARTICL : https://www.nytimes.com/
Aucun commentaire:
Enregistrer un commentaire