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For years, I've been trying to eat properly. You know what that means: lean meat; not too much fat; lots of fruit, vegetables and healthy whole grains. Sullenly, I embraced fibre. Reluctantly, I gave up butter and cheese. Conscientiously, I ate as much broccoli and Brussels sprouts as I could stomach. (Cruciferous vegetables are especially good for preventing cancer.)

I even tried switching to fake salt, which was awful. My dad did the same after his second heart attack. He gave up booze and fat and salt, chowed down on tasteless, skinless chicken and lived to a relatively ripe old age, griping all the way.

Here is what the latest scientific findings have to say about all that: Feh.

The science isn't settled after all. Almost everything the medical establishment, the health commissars and the nutrition nannies have been telling us for the past 60 years is just flat-out wrong.

To start with, saturated fat won't raise your cholesterol and give you heart attacks. Neither will butter or cheese. Do you hanker after a juicy marbled piece of steak? Help yourself! New research published this March in the Annals of Internal Medicine found that saturated fat doesn't cause heart disease. This, despite decades of advice that we should restrict saturated fat to as little as 5 per cent of our daily caloric intake – equivalent to about two tablespoons of butter a day.

Next, the salt wars. Salt vigilantes have been warning us for years that our habit is killing us. We consume an average of 3,400 milligrams a day, mostly through processed foods. Health Canada says we should cut back to 2,000. The American Heart Association says 1,500 – less than three-quarters of a teaspoon. Not only is this virtually impossible, it also turns out to be unnecessary, and perhaps even harmful.

A study published last October in JAMA Internal Medicine concluded: "The lack of evidence of benefit and concerns for harm suggest that low sodium intake (less than 2,300 mg/day) should not be recommended." According to Dr. Gilbert Ross of the American Council on Science and Health, anthropological studies suggest that humans are hard-wired to consume between 3,500 and 4,000 milligrams of sodium a day – about what we do now. "To try to cut it in half, or less, is both fruitless and more likely to harm than benefit," he says.

As for fruits and vegetables and all the rest: If you hate Brussels sprouts, you're in luck, because they don't do any good. As recently as 1997, leading cancer authorities told us that eating lots of fruits and veg might cut our cancer risk by more than 20 per cent. They told us to stay away from saturated fat, too. But today, decades of research into the links between nutrition and cancer have reached a dead end. As Harvard's Walter Willett, perhaps the world's leading cancer epidemiologist, told The New York Times, "Diet and cancer has turned out to be more complex and challenging than any of us expected."

What happened? How could so many people have been so wrong for so long? How did all this flawed science become the foundation for everything we thought we knew about nutrition and our health?

The answer, in a nutshell, is food politics, big egos, flawed research and heavy institutional investment in the status quo.

Science journalist Nina Teicholz is author of The Big Fat Surprise, a new book that explores the origin of the spurious link between saturated fat and heart disease. It's quite a tale. It all began in the 1950s with a brilliant self-promoter named Ancel Keys, a scientist who rose to the top of the nutrition world by arguing that saturated fats were behind the postwar explosion in heart disease. Although his research was full of holes, it quickly became dogma. Leading health authorities endorsed his diet advice. Millions of people cut back on red meat, eggs, butter and cheese, and replaced them with vegetable oils, pasta, grains, fruits and potatoes.

The results were catastrophic. Carbohydrates break down into glucose, and too many carbohydrates have unleashed an epidemic of obesity, Type 2 diabetes, and possibly heart disease. Even unrefined carbs are bad. As Ms. Teicholz wrote in The Wall Street Journal, "The reality is that fat doesn't make you fat or diabetic. Scientific investigations going back to the 1950s suggest that actually, carbs do." On top of that, she writes, there's "growing evidence that women on diets low in saturated fat actually increase their risk of having a heart attack."

As you can imagine, these findings are not welcome news to the experts and institutions that have invested so heavily in the status quo. How are they supposed to break the news to the rest of us? They also expose the awkward truth about diet and nutrition studies: that they're very, very difficult to do well. They often have so many confounding factors that the supposed link between cause and effect can be extremely shaky. And many diet studies yield results that later studies can't replicate.

None of this means the vigilantes are about to go away. Salt warrior Thomas Farley, former commissioner of health for the city of New York, still insists that sodium is killing us, and wants to impose sweeping laws and standards to reduce the threat. He's the perfect picture of a modern Puritan – a lean, ascetic type who is convinced that we are on the fast track to hellfire and damnation.

People are already highly skeptical of nutrition advice delivered from on high. They figure that whatever we're told not to eat today will probably be okay again next week. But these revelations are yet more blows to the public's faith in experts. If they can't even get this stuff right, what else are they wrong about?

So … sorry about that, Dad. You gave up steak for nothing. As for the rest of us, here's my best advice: Eat real food that you like, but not too much. Avoid sugar and carbs. Stay hydrated. And if you go to Paris, make sure to have lots of cheese.