The peanut controversy.

The Peanut Controversy

For anyone who's been responsible for providing quick, popular meals to hungry children or adults, an attack on peanut butter strikes close to home. How could this friendly, familiar sandwich staple possibly do harm?

Theoretically, scientists, too, should have little reason to suspect peanut butter as a threat to blood vessels. Peanut oil -- which contributes 80 percent of peanut butter's calories -- is largely unsaturated, the kind that doesn't raise blood cholesterol levels.

But some animal studies suggest that, despite its welcome effect on blood cholesterol, peanut oil clogs the arteries with cholesterol deposits, or plaques. The problem is that scientists stil don't know whether those animal studies apply to people. Until they do, the final word on the peanut's safety won't be in.

Peanuts Plus Cholesterol. The peanut's marred history goes back to the early 1970s, when Robert Wissler, of the University of Chicago, reported that diets high in peanut oil clogged the arteries of Rhesus monkeys more than did butterfat. [1] In animals, says Wissler, peanut oil has a "remarkable" ability to produce "raised plaques similar in most respects to those which we have observed at autopsy in people."

But recently, Wissler's attack on the ever-popular peanut has been challenged. Last year, K.C. Hayes, of Brandeis University, reported that peanut oil does not clog the arteries of another species of monkeys as long as the oil is fed as part of a diet that contains about as much cholesterol as most people eat. [2] In contrast, Wissler fed his monkeys 20 times more cholesterol than the typical American eats.

"Cholesterol swamped the peanut fat [in Wissler's experiments]," argues Hayes. "You can't draw conclusions about the fat because 99 percent of the effect is due to the cholesterol. No one has looked at peanut oil independent of its effect with cholesterol in the diet."

Wissler returns the criticism. First, he notes that his experiments compared peanut oil plus cholesterol to other fats, such as butterfat or corn oil, plus cholesterol. Therefore, Wissler argues, peanut oil's damage -- which was worse than any other fat's -- could not be due to cholesterol alone. And there's a reason for all that cholesterol, he points out.

"The low level of cholesterol in Hayes' study will not cause significant lesions in one year [the length of his experiment], even with the most damaging fat and the most susceptible species," contends Wissler. "Atherosclerosis generally requires one-third to one-half of a lifespan to develop in humans," he continues. "In non-human primates, this would be five to 10 years if one wanted to use nutritional regimens similar to those supporting disease in people."

In other words, only when the diet is loaded with cholesterol will an animal develop atherosclerosis in one to two years. Indeed, Hayes concedes that in his experiments, even butterfat would not have produced the plaques seen in humans.

No-Win Debate. Peanut butter's integrity, then, is wrapped up in a seemingly no-win debate over how to assess any fat's effect on arteries. "This has been a classic problem in the whole atherosclerosis field for years," says Mark Hegsted, of Harvard's New England Primate Center.

"If you load animals up with enough cholesterol, it gets difficult to evaluate the effect of fats. If you don't load them up, you don't get enough atherosclerosis to interest anyone in doing the study."

Instead, Hegsted suggests, scientists should rely on blood cholesterol levels and evidence from populations that eat different diets as indicators of heart disease risk.

When it comes to blood cholesterol, the peanut's fat is unassailable, since it clearly lowers the "bad" LDL cholesterol. As for populations, only the Chinese rely on peanut oil as a staple, and their heart disease rates appear low. But that doesnht prove peanut oil's innocence. First, mortality data from China may not be reliable. Second, the Chinese diet is so low in cholesterol and fat of all types, that any damage caused by peanut oil may be undetectable.

Skippy Can Stay. In short, the definitive word on the peanut's fat remains elusive. Fortunately, few people eat enormous quantities of any peanut product -- nuts, butter, or oil. Even Sid Schneider's family averages only about one teaspoon of peanut oil per person per day.

Still, cautious eaters may not want to use peanut oil as a staple for cooking. Recent animal studies suggest that, unlike several other unsaturated fats, olive oil may not promote cancer. But peanut oil's ability to promote tumors in animals has not been tested. In short, olive is still the oil of choice.

On the other hand, the evidence isn't strong enough to ban peanut butter from the cupboard. For the time being, Mr. Schneider, you needn't insist on tofu-and-jelly sandwiches for lunch.

References

[1] Atherosclerosis 20: 303, 1974.

[2] Arteriosclerosis 6: 465, 1986.