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Study looks at effectiveness of diet for weight loss

September 2, 2014
By Helen Branswell The Canadian Press


Sept. 2, 2014 – It's a question that bedevils dieters on a regular basis: Is a low-fat or a low-carb diet the true path to weight reduction?

A new study suggests either will do – so long as one actually works at whichever one chooses.

The study is what is called a meta-analysis; it groups together and reanalyzes data from 48 different randomized trials of various diets.


The work was done by researchers at Toronto's Hospital for Sick
Children, McMaster University and a number of other institutions in
Canada and the United States.

The authors say that of the
so-called branded diets, those that espouse a low-fat or a
reduced-carbohydrates approach work better than the others.

But when those two approaches are compared, the results are more or less equal.

research has shown that… low-carbohydrate and low-fat diets result in
the most weight loss, about 18 pounds (8.2 kilograms) in six months and
16 pounds (7.3 kg) in 12 months, and there's very small differences
between the two,” said first author Bradley Johnston, a senior scientist
at the Hospital for Sick Children's Research Institute.

there's minimal differences between the diets, both at the brand level
and at the diet class level… individuals shouldn't buy into the latest
study that comes out that shows that maybe one diet is better than

The publication of the work – in the Journal of the
American Medical Association
– is timely. On Monday, a study published
in the Annals of Internal Medicine reported that people who eschew
carbohydrates and eat more fats lose more weight than people who follow a
low-fat diet.

Johnston acknowledges it is hard for people to
interpret the shifting sands of dietary science. So he and his
colleagues set out to try to see what the compilation of studies

While their study talks about diets by name, Johnston is
keen not to appear to be promoting one over the other. But he says the
findings make it clear that these diets can lead to weight loss, if
people do the work.

That said, the results were modest. The
median weight loss for people following a low-carb diet was nearly nine
kilograms at six months; the median loss for low-fat diet followers was
eight kilograms. At 12 months, both groups slipped a bit – a common
occurrence in diet studies – to just over seven kilograms for both types
of diets.

“For those who believe that they don't work,
short-term, this evidence suggests that they do. And we need a lot more
research in terms of the long-term effectiveness of these types of
interventions and we need to look closely at adherence,” said Johnston,
who began the project while doing post-doctoral studies at McMaster.

“If they're relatively equal, then you should choose something that you feel that you can adhere to.”

Obesity expert Dr. Yoni Freedhoff agreed with that premise.

practises at the Bariatric Medical Institute of Ottawa and is the
author of The Diet Fix: Why Diets Fail. He says it has been clear for
quite some time that there is no one single answer.

“The quest
for the holy diet is one that society's been on for quite a long time.
And I don't think there is such a thing, just like I don't particularly
believe in a Holy Grail,” said Freedhoff.

“The key to picking the
best diet for a person as an individual is the one they actually like
enough to keep living with… Ultimately people need to live lives that
they enjoy enough to sustain. And the same for sure goes for food and

He doesn't believe in weight loss by suffering, saying it
simply isn't sustainable over the long term. And weight shed by cutting
carbs or avoiding fat will come back if the intervention is treated as a
short-term fix.

“Not enjoying your low-carb diet versus not
enjoying your low-fat diet will have the same likely outcome, which is
you quitting your diet down the road,” Freedhoff said.

The study
looked only at the ability to lose weight on various diets. It did not
examine whether some diets do a better job of reducing cardiovascular
disease risks, such as lowering cholesterol. Johnston said that work is
currently underway.

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