Dangers of dietary fat instilled in us

Last week’s column ended with the 1977 release of the McGovern Commission’s report urging all Americans to drastically reduce intake of dietary fat. The report became an immediate controversy among various agencies and interest groups lining up pro or con on the evils of dietary fat.

In response, the U.S. Department of Agriculture issued a publication, “Using the Dietary Guidelines for Americans,” which was a virtual copy of the McGovern report’s recommendations. The National Academy of Sciences countered with its own report, “Toward Healthful Diets,” that said, in essence, dietary fat was no more harmful than many other components of the diet such as carbohydrates. The academy was castigated for this stand with The New York Times writer Jane Brody accusing it of “being in the pocket of the industries being hurt.”

In the 1980s, this is where matters stood with the public firmly convinced that dietary fat was an unmitigated evil. Now, Gary Taubes in the March 30 issue of Science, examines whether this belief has stood the test of time.

One of the concerns connected with dietary fat was that it caused cancer. This was such a given that, in 1982, a NAS report equated researchers who questioned the connection to those who denied any link between smoking and cancer. In 1997, however, the connection was far less clear. A 15-year study by the World Cancer Research Fund and the American Institute for Cancer Research could not find convincing or even probable reasons to believe that dietary fat caused cancer. The same was true for another widely held belief, that a low-fat diet was the only sure route to weight loss.

The $100 million Women’s Health Initiative was undertaken and 50,000 women enrolled in the study were directed to obtain only 20 percent of their calories from fat. After three years on this stringent diet, the women lost, on average, only 1 kilogram each.

Decades of research on links between dietary fat and heart disease have produced murky results at best. The problem, says Taubes, is that there are two separate and distinct propositions involved. One is simply that lowering cholesterol reduces heart disease. There is no argument on this point since years of studying cholesterol-lowering drugs have shown dramatic results in preventing first or reoccurring heart attacks. These drugs are now a $4 billion business annually in the United States.

The other proposition, which holds that eating less dietary fat prolongs life in general, is very iffy on the basis of current evidence. Taubes reviews many studies for and against this proposition in his article, but his analysis of one of many people’s favorite sinful foods, a well-marbled steak, is the most interesting.

We have all been taught the differences between HDL, the good cholesterol, and LDL, the bad variety. Different types of fat contribute in varying degrees to either or both of these types. Polyunsaturated fats lower overall cholesterol levels. Monounsaturated fats raise HDL and lower LDL and are thereby classified good fat. Saturated fats, in general, tend to raise both HDL and LDL, but one, stearic acid, raises HDL while having little effect on LDL.

Saturated fats, says Taubes, are classified bad to neutral. Taubes then applies this criteria to a broiled porterhouse steak with about a half-centimeter of fat before cooking. After broiling, about 51 percent of fat is monosaturated, of which more than 90 percent is oleic acid, the healthy fat component in olive oil. There is 45 percent saturated fat but, of that, 15 percent is stearic acid which is classified as a good fat. The remaining 4 percent is polyunsaturated fat so, in sum, up to 70 percent of the fat in a cooked porterhouse steak will improve cholesterol levels while 30 percent affects LDL and HDL more or less equally.

There is even evidence, says Taubes, that low cholesterol levels may lead to hemorrhagic stroke. In 1986, even as Americans were being advised to adopt low-fat diets, Japanese doctors were advising patients to raise their cholesterol levels because Japanese men were dying from stroke in numbers equal to the death rate for American men from heart disease.

So where does all this conflicting data leave the consumer? Taubes says the long-standing warnings against dietary fat will undoubtedly remain in place. Limiting fat consumption is considered reasonable advice because, whatever else it may accomplish, it will help to keep the caloric intake down. And then there is the effectiveness of the early campaigns against dietary fat that have been instilled in the American consciousness.

“In America, we no longer fear God or the communists,” says David Kritchevsky of Philadelphia’s Wistar Institute, “but we fear fat.”