Christopher Labos is a cardiologist and epidemiologist at the McGill University Health Centre. He is currently a fellow in global journalism at the Munk School of Global Affairs at the University of Toronto.
New doctors are often told that five years after medical school half of what they learned will be proven wrong.
Problem is, nobody knows which half. That seems to be what's going on with the current debate over fatty foods like bacon, butter and cheese.
For years, doctors said, fat was bad for your health and your waistline. But fat is back and it's even touted as being good for you.
A slew of editorials and news reports are claiming that scientists had it all wrong. And a new book called The Big Fat Surprise by journalist Nina Teicholz has popularized the controversial message to eat more fat.
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While many people might be puzzling over this new theory and rethinking their eating habits, most experts do not think of the book as controversial. They just think its advice is flat-out wrong.
The connection between fat and heart disease goes back to the 1960s. A series of epidemiologic studies, most notably the Seven Countries Study run by American physiologist Ansel Keys, established links between dietary fat, cholesterol and heart disease.
It's this research that informed how the medical establishment thought about fat for years, and that Teicholz takes down in her new book, claiming that more recent data invalidates it.
She claims that the low-fat diet that this research inspired has led to the growing obesity epidemic around the world, as sugars and carbs took the place of dietary fats.
But obesity experts are not so sure that claim is valid.
"We over simplify the message of fat, just like we oversimplify the message around calories," says Dr. Yoni Freedhoff, director of the Bariatric Medical Institute and assistant professor in the faculty of medicine at the University of Ottawa.
He says the real reason that obesity rates have risen is because large numbers of people are consuming more calories and larger portion sizes than they used to.
He points to a 2009 Cornell study that looked at how the popular cookbook, The Joy of Cooking, has evolved over 70 years.
It turns out that in 14 of the 18 recipes published in every edition, the number of calories jumped by 43.7 per cent over 70 years. Since 1996, portion sizes have risen by 33.2 per cent.
"There are a million reasons why we're eating more," says Freedhoff, "but the bottom line is we're eating more."
The notion that we should be eating more meat, butter and fat doesn't strike him as particularly sensible. "I don't think we should be eating more of anything," he says. He recommends eating less.
Low-fat junk food
The problem with focusing on fat, or on any one nutrient, as a diet strategy is that it distracts us from what is really important, says Dr. David Katz, director of the Yale University Prevention Research Centre and president of the American College of Lifestyle Medicine.
He says that when Keys and others initially recommended a low-fat diet, what they meant was eat less fatty food and more fruits, vegetables, whole grains, beans and lentils.
These are all nutritious foods that also happen to be low in fat. But that was not what happened.
"We just invented low-fat junk food," Katz told me.
As consumers sought out low-fat alternatives to their favorite snacks, companies simply took out the fat and added more sugar. Thus they were able to preserve the taste while still being able to label their food fat-free, which was a brilliant marketing strategy.
The public ate it up — literally — and never ate those healthy fruits and vegetables.
Consequently, the low-fat diet, as it was being practised in North America, was not associated with any health benefits.
That doesn't surprise Katz. He says that if you invent new ways to eat badly, your health won't improve.
The new movement to redeem fat was fuelled by a 2014 study in the Annals of Internal Medicine.
This review of 32 studies is often cited as proof that saturated fats are good for you.
However, that is not what the study actually showed, says Katz.
The study found no difference between high-fat and high-sugar diets when it came to cardiovascular disease.
But that does not mean that saturated fat is good for you, says Katz. "Whether it was low-sugar, high-fat or high-sugar, low-fat, the rates of heart disease were basically the same and really high. Everybody lost."
You can cut the fat and eat badly, just like you can cut carbs and eat badly.
"There's a simple shortcut that's even better," Katz says. That's eating wholesome foods — things like fruits, vegetables, nuts, seeds, lentils and fish — in sensible combinations.
If your diet is mainly made up of good stuff, Katz says, you can't get it wrong, because then there is no room for the bad stuff.
And junk food like low-fat potato chips, just like low-carb brownies, are the bad stuff.