What if bad fat isn’t so bad?

For example, eastern Finland had five times as many heart-attack fatalities and twice as much heart disease as western Finland, despite only small differences between the two regions in animal-fat intake and cholesterol levels. And while Keys provided that raw data in his report, he glossed over it as a finding. Perhaps a larger problem, though, was his assumption that saturated fat has an unhealthy effect on cholesterol levels.

Trio of saturated fats
Although more than a dozen types of saturated fat exist, humans predominantly consume three: stearic acid, palmitic acid, and lauric acid. This trio comprises almost 95 percent of the saturated fat in a hunk of prime rib, a slice of bacon, or a piece of chicken skin, and nearly 70 percent of that in butter and whole milk.

Today, it's well established that stearic acid has no effect on cholesterol levels. In fact, stearic acid — which is found in high amounts in cocoa as well as animal fat — is converted to a monounsaturated fat called oleic acid in your liver. This is the same heart-healthy fat found in olive oil. As a result, scientists generally regard this saturated fatty acid as either benign or potentially beneficial to your health.

Palmitic and lauric acid, however, are known to raise total cholesterol. But here's what's rarely reported: Research shows that although both of these saturated fatty acids increase LDL ("bad") cholesterol, they raise HDL ("good") cholesterol just as much, if not more. And this lowers your risk of heart disease. That's because it's commonly believed that LDL cholesterol lays down plaque on your artery walls, while HDL removes it. So increasing both actually reduces the proportion of bad cholesterol in your blood to the good kind. This may explain why numerous studies have reported that this HDL/LDL ratio is a better predictor of future heart disease than LDL alone.

All of this muddies Keys's claim of a clear connection between saturated-fat intake, cholesterol, and heart disease. If saturated fat doesn't raise cholesterol in such a way that it increases heart-disease risk, then according to the scientific method, the diet-heart hypothesis must be rejected. However, in 1977 it was still a promising idea.

That was the year Congress made it government policy to recommend a low-fat diet, based primarily on the opinions of health experts who supported the diet-heart hypothesis. It was a decision met with much criticism from the scientific community, including the American Medical Association. After all, officially endorsing a low-fat diet could change the eating habits of millions of Americans, and the potential effects of this strategy were widely debated and certainly unproved.

We've spent billions of our tax dollars trying to prove the diet-heart hypothesis. Yet study after study has failed to provide definitive evidence that saturated-fat intake leads to heart disease. The most recent example is the Women's Health Initiative, the government's largest and most expensive ($725 million) diet study yet. The results, published last year, show that a diet low in total fat and saturated fat had no impact in reducing heart-disease and stroke rates in some 20,000 women who had adhered to the regimen for an average of 8 years.

But this paper, like many others, plays down its own findings and instead points to four studies that, many years ago, apparently did find a link between saturated fat and heart disease. Because of this, it's worth taking a closer look at each.

The Los Angeles VA Hospital Study (1969) This UCLA study of 850 men reported that those who replaced saturated fats with polyunsaturated fats were less likely to die of heart disease and stroke over a 5-year period than were men who didn't alter their diets. However, more of those who changed their diets died of cancer, and the average age of death was the same in both groups. What's more, "through an oversight," the study authors neglected to collect crucial data on smoking habits from about 100 men. They also reported that the men successfully adhered to the diet only half the time.

The Oslo Diet-Heart Study (1970) Two hundred men followed a diet low in saturated fat for 5 years while another group ate as they pleased. The dieters had fewer heart attacks, but there was no difference in total deaths between the two groups.

The Finnish Mental Hospital Study (1979) This trial took place from 1959 to 1971 and appeared to document a reduction in heart disease in psychiatric patients following a "cholesterol-lowering" diet. But the experiment was poorly controlled: Almost half of the 700 participants joined or left the study over its 12-year duration.

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