Low-carb? High-protein? Or low-fat? If you're planning to shed some pounds, you
can stop fussing over which diet works best, according to a study published in
the New England Journal of Medicine.
Researchers at the Harvard School of Public Health randomly assigned 811
overweight adults to four different diets with varying ratios of fat,
carbohydrates and protein, then measured their weight loss at six months and two
years.
"All the diets we tested produced weight loss to the same extent," says the
study's lead author, Frank Sacks, a medical doctor and professor in the school's
department of nutrition. "No one diet was better for reducing calories or
increasing weight loss at six months or two years."
The four heart-healthy diets - all of which were low in saturated fat and
cholesterol and high in dietary fibre - were designed to cover many of today's
most popular options:
Low-fat, average-protein: 20 per cent of calories from fat, 15 per cent from
protein, 65 per cent from carbohydrates.
Low-fat, high-protein: 20 per cent fat, 25 per cent protein, 55 per cent carbs.
High-fat, average-protein: 40 per cent fat, 15 per cent protein, 45 per cent
carbs.
High-fat, high-protein: 40 per cent fat, 25 per cent protein, 35 per cent carbs.
Calorie counts were assigned individually to each dieter based on subtracting
750 calories from their daily caloric needs. Participants were asked to attend
group sessions and use self-monitoring tools, such as diaries. They were also
asked to exercise moderately for 90 minutes a week.
At the six-month mark, participants assigned to each diet had lost an average of
13 pounds (six kilograms). Among the 80 per cent who completed the program, the
average weight loss was nine pounds (four kilograms) at two years. Waistlines
were reduced by an average of two inches at the end of the two-year period.
All the diets improved cardiovascular risk factors in the participants, with a
few subtle differences that dieters may want to discuss with their doctors. For
instance, lower-fat diets reduced LDL cholesterol a little more than the
higher-fat diets.
Although none of the four diets were as extreme as some of today's trendy diets,
such as the high-protein, low-carb Atkins, Dr. Sacks says his findings show
there is "nothing magic about them."
Still, he isn't saying they're useless. "Some people like one of these popular
diets and if it works for them, all the better."
But for others, a less-rigid approach can work just as well. "It gives people a
lot of flexibility to try a diet that's comfortable for them, [that] they feel
they can stick with, and to focus on calories, not the particular type of
content of diet."
If there is magic to be had, it's in motivation. Dr. Sacks found that rather
than the ratios of fats to proteins, it was other factors, most notably the
counselling sessions participants attended, that most affected dieting success.
On average, people who attended sessions lost more weight than those who didn't,
he says.
"The biggest influence is in the individual response, not the diet type," he
says. "That's something we ought to delve into and understand better."
In an editorial appearing in the same issue of the journal, diet researcher
Martijn Katan, from the Institute of Health Sciences at VU University,
Amsterdam, suggests that Dr. Sacks's findings illustrate the need for a
societal, rather than individual, approach to combatting growing obesity rates.
He cites a French study that examined a town that implemented a number of
community-based efforts to encourage children to eat better and exercise more,
including building sports facilities and offering cooking workshops to families.
In five years, the prevalence of overweight children had dropped to 8.8 per
cent, compared with 17.8 in neighbouring towns.
"Like cholera, obesity may be a problem that cannot be solved by individual
persons but that requires community action," Dr. Katan writes.
Dr. Sacks agrees with this sentiment, but he says a two-pronged approach taking
both the individual and the community into account may be best.
"There are two equal parts to this," he says. "We should try to find out why
some people can do very well and some not. There may be biological factors we
don't know about."
