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 you actually work at whichever one you choose.
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.
"Our 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," says first author Bradley Johnston, a senior scientist at the Hospital for Sick Children's Research Institute.
"If 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 another."
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 reveals.
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," says 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 agrees with that premise.
Freedhoff 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," says 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 diet."
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 says.
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 says that work is currently underway.