TORONTO – Which is better for weight loss – a low-fat or low-carbohydrate diet? It’s a question U.S. researchers attempted to answer, unknowingly unleashing an uproar from supporters dedicated to both diets.
Low-carb and low-fat diets each have a cult-like following. Just head over to your grocery store to see their appeal – cheese, yogurt, salad dressings, and even packaged goods are touting shiny ‘low-fat’ labels.
Bread and pasta have become villains to dieters ditching carbohydrates, replaced by low-carb substitutes.
In a Tulane University study published earlier this month, scientists crowned the low-carb diet as the best option for weight loss and heart health.
Then came the headlines: “Low-carb may trump low-fat in diet wars,” “Cutting back on carbs, not fat, may lead to more weight loss,” and “Low-carb emerges victorious over low-fat.”
These were fighting words. Global News looks at the study’s findings, the counter-arguments and the verdict from Canadian experts.
The study’s findings: 148 obese people were recruited and assigned to either a low-carb or low-fat diet.
On average, the patients weighed about 220 pounds. Those avoiding carbs were allowed to consume less than 40 grams of carbs per day – the low-fat dieters were allowed to have less than 30 per cent of daily calories coming from fat.
After a year, the low-carb group lost an average of 7.7 pounds more than the low-fat group, their blood levels of certain fats also improved and the low-carb group saw a spike in “good” HDL cholesterols.
Low-carb dieters lost an average of 11.7 pounds and the low-fat dieters lost only four.
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Low carb dieters got 41 per cent of their calories from fat – predominantly healthy fats, such as olive oil.
The sound bite: “Over the years, the message has always been to go low-fat. Yet we found those on a low-carb diet had significantly greater decreases in estimated 10-year risk for heart disease after six and 12 months than the low-fat group,” Dr. Lydia Bazzano said.
“It’s not a license to go back to the butter, but it does show that even high-fat diets – if they are high in the right fats – can be healthy and help you lose weight,” she said in a university statement.
The counter argument: Let’s just say the findings weren’t warmly received. For starters, critics didn’t even like the premise of the study of stacking these two longstanding, strict diets next to each other.
Yale University researcher Dr. David Katz called the study “dumb” with a “truly lousy question, resurrected from something like the Stone Age.”
Katz and Canadian obesity expert, Dr. Yoni Freedhoff, slammed the study, suggesting that the low-carb dieters were simply eating fewer calories.
“It’s been known for some time that low-carb diets lead those on them to automatically consume fewer total calories,” Freedhoff wrote in his blog, Weighty Matters.
The sound bite: “…It’s important not to forget that one person’s best diet is undoubtedly another person’s worst, and that folks who are stuck dogmatically promoting only one ‘best’ diet can be safely ignored,” Freedhoff concluded.
“…this was a study designed to generate a predictably useless, misleading, and potentially harmful answer to an egregiously silly and perhaps even willfully disingenuous question,” Katz wrote in his final thoughts on the paper.
Canadian experts weigh in:
Toronto-based registered dietitian Zannat Reza and Dr. Rena Mendelson, a Ryerson University nutrition professor, say that when consumers exclude a macronutrient from their diets – in this case carbohydrates or fat – it’s often replaced by something else.
“Lower carbs means higher fat but in this case, it also meant more protein. That’s going to have an impact on appetite,” Mendelson said.
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The extra protein in the low-carb diet may have helped consumers feel full and more satisfied with their meals. But it’s not entirely clear what the dieters were eating.
(Bazzano told NPR the low-carb dieters typically ate high-protein, high-fibre breakfasts of eggs on toast with butter. For lunch, they ate a lot of vegetables and salads with fish, chicken or red meat. They also ate “generous” portions of olive, canola and other plant-based oils.)
Fibre, in either diet, was also way too low. Study participants were eating only 18 grams at most of the tummy-filling nutrient.
It also sounds like a lot of work for little pay off.
“It’s not a very dramatic weight loss for a full year of pretty close-watched involvement. For all that effort, that’s not a major weight loss. It wouldn’t have even brought them into what we consider a healthy weight zone,” Mendelson said.
What’s also unclear is what happened post-study. Participants may have packed on more pounds.
It’s also hard to say if it was the low-carb diet that improved heart health – it could have been the general weight loss.
“I don’t know what the benefit of the study is because it causes more consumer confusion,” Reza said,
Her advice to consumers trying to lose weight? Stay away from any diet advice that’s screaming at you to avoid groups of food. It’s not sustainable and creates a negative relationship with food, she said.