After being maligned for decades for its caloric density and heart-clogging effects, fat’s place in our diet is being reconsidered — and a new study argues that there wasn’t enough evidence to curb our consumption of butter and cheese in the first place.
Restrictions on eating fat have been questioned recently: Documentaries like “Fed Up” make the argument that sugar is a bigger problem than fat in the current obesity and diabetes epidemic, and a well-cited recent study found that saturated fat didn’t seem to be as bad for heart health as guidelines make it out to be.
Dietary guidelines in the US still say that we should restrict saturated fat to under 10% of daily caloric intake and that adults shouldn’t get more than 20-35% of their daily calories from fats.
The American Heart Association is even stricter, recommending limiting saturated fat to 5-6% of daily caloric intake — though those recommendations are based on what the evidence suggests is best for adults at risk of heart disease, says Dr. Alice H. Lichtenstein, the director of the Cardiovascular Nutrition Laboratory at Tufts and a member of the nutrition committee at the AHA.
Guidelines restricting fat consumption to present day levels went into effect in the US in 1977 and in the UK in 1983. But a new look at the research behind those guidelines, published Feb. 9 in the BMJ journal Open Heart, comes to the conclusion that there wasn’t evidence to support them in the first place.
After looking at the research on fat consumption that existed at the time, the authors of the new analysis conclude that the “dietary advice not merely needs review; it should not have been introduced.“
The evidence for limiting fat when the guidelines were introduced
The authors of the newly published study say that they wanted to understand the evidence used to establish present-day guidelines for dietary fat consumption. In particular, they wanted to see whether the dietary guidelines that affected 276 million people in the US and UK at the time had been tested using randomised controlled trials, which are considered the gold standard and most informative test for any clinical decision.
But when the low-fat guidelines were put into place more than 30 years ago, neither the UK or US cited any of the randomised controlled studies available at the time. And even if they looked at them, it would have been hard to use them as evidence that dietary fat was a problem.
The authors of this new study found eight different randomised trials that would have been available to policy makers, which would have included 2,467 men and no women. Testing various dietary changes involving fat had no impact on their likelihood of death, either from heart disease or any other cause.
So hundreds of millions of people were given dietary guidelines that were arguably not supported by the evidence.
It seems that even at the time, researchers didn’t think they had a conclusive recommendation — the authors of the study cite a 1977 exchange between Dr. Robert Olson of St. Louis University and the chair of the dietary committee, Sen. George McGovern.
“I pleaded in my report and will plead again orally here for more research on the problem before we make announcements to the American public,” said Olson.
But McGovern replied, “Senators don’t have the luxury that the research scientist does of waiting until every last shred of evidence is in.”
How cutting fat could have been bad for our health
Recently, there’s been more research that says that saturated fats — like those in butter and cheese — just aren’t as bad for you or your heart as we thought.
Some researchers have even said that the focus on fat led people to consume carbohydrates instead, especially from refined sugar, which they say has lead to a more serious increase in the diabetes rate. When a low fat diet was tested against a low carbohydrate diet — as long as both were low in calories overall — the latter was much more beneficial, the researchers showed. People on the low carb diet lost abdominal fat and body mass, had improved glucose tolerance, better cholesterol, and less inflammation. All of those measurements got worse on the low fat diet, where fat was replaced with carbs.
When the low fat craze swept society, people didn’t necessarily consume fewer calories by steering clear of fat — they just ate trans fats instead of saturated fat, which turned out to be much worse for health, or they consumed carbs instead, especially sugars and processed “low-fat” snacks, which may also be much worse for us.
Throw out the guidelines and eat endless cheeseburgers?
Should we rejoice and celebrate that, as food writer Mark Bittman writes, butter is back?
Not so fast.
First of all, says Lichtenstein, no one — not the AHA or national health guidelines — is promoting a “low fat” diet anymore. She says that health experts agree that directing people towards low fat diets caused them to consume carbs and sugar “with abandon,” which clearly had negative consequences. Now, she says, health experts promote a moderate fat diet, still getting around 30% of calories from fat, but replacing saturated fats with healthier fats when possible, like those from vegetable oils.
Further, she says that some of these reviews that seem to vindicate saturated fat are too broad and incorporate too many different types of studies — some that just cut saturated fat when it might be replaced by carbs (not healthy), others where healthier fats are consumed instead of saturated fats. She says that if the focus is on consuming “healthy fat” instead of saturated fat, those health benefits are clear.
As for the history of nutritional guidelines, randomised controlled trials may not have provided evidence telling us to cut fat out of our diets, but as cardiologist Rahul Bahl points out in an editorial published along with the new study in Open Heart, that doesn’t mean there’s no evidence at all.
As the American Heart Association notes, eating more saturated fat is associated with a rise in cholesterol, and while not all cholesterol is bad, higher levels of one type of cholesterol from saturated fat are associated with a greater risk of heart disease and stroke.
Others point out that those associations don’t mean the link between saturated fat and heart disease has been proven. Even so, cutting fat is still one of the easiest way to cut calories — as long as they aren’t replaced by something else that’s less healthy.
Bahl also points out that the people in the trials the researchers looked at may not have really changed their behaviour, which would explain why there was no change in health outcomes — people do not always accurately self-report their diets to researchers, and may be inclined to say they ate more healthfully than they actually did.
Dietary guidelines don’t normally depend on evidence from randomised clinical trials, says Bahl, so to withdraw guidelines based on a lack of those trials would be unusual. It’s also hard to complete long term randomised nutrition studies, since people don’t tend to stick with proscribed diets consistently, and it’s not feasible to provide all the meals for a large population for a number of years.
Normally, he explains, those guidelines are made based on evidence that’s observed in large populations over time. He says that one example occurred due to political changes in Eastern Europe in the 1990s, when large populations started consuming more healthy fat from vegetable oils, which was associated with improved heart health.
He tells Business Insider that he does think it’s worth revisiting nutritional guidelines to incorporate new evidence and to take a more thorough look at carbohydrates, especially sugar.
“There is certainly a strong argument that an overreliance in public health on saturated fat as the main dietary villain for cardiovascular disease has distracted from the risks posed by other nutrients,” he writes in the editorial.
But that doesn’t mean it’s the end of the story. “I think the real relationships between all these nutrients and health outcomes is probably more complicated then we have examined in most studies so far,” he tells Business Insider.
For now, though, one thing is certain: The low-fat guidelines jumped the gun. For most people, it’s long past time to give fats — especially healthy ones — a prominent place on your plate.
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