Recently a septuagenarian friend complained about the fare generally put on his plates when he visits his peers. "It's all so boring, so bland and dry. Everybody is so scared of cholesterol that they're eating stuff I wouldn't have touched when I was a baby. And it's not fair. Here I am in my 70s, retired, supposedly enjoying life, and I'm not supposed to eat any of the things I like. No cheese. No milk. No prime rib. No chocolate ice cream. No fancy rich sauces. No butter. The hell with it."

Like my friend, most Americans know that a cholesterol-rich diet is bad for their health. But they are thoroughly confused about what foods should be avoided to lower their risk of heart disease. And many resent having to trim favorite foods from their diets.Welcome to the confusing world of cholesterol.

Physicians and scientists are similarly confused when it comes to suggesting low-cholesterol diets, anti-cholesterol therapies and treatments for the artery-blocking plaques that are formed by buildups of the fatty molecules.

Despite the lack of a clear consensus on preventing and treating hypercholesterolemia, elements of the medical community issue dietary bulletins to the public, the stock market sharply reflects investor interest in anti-cholesterol drugs, and the nation's dietary habits have changed so dramatically that the meat industry is now waging a major ad campaign aimed at wooing consumers back to steak and potatoes.

One thing is clear: Coronary heart disease is the No. 1 killer in the United States, claiming more than half a million lives every year. Cholesterol is one of the culprits responsible for this astonishing number of deaths.

Cholesterol is a thick, waxy substance formed from lipid, or fat, and special proteins. It comes in two forms: LDL, or low-density lipoprotein, and HDL, or high-density lipoprotein. Physicians popularly refer to LDL as "bad cholesterol" and HDL as "good cholesterol." The general dogma is that high levels of LDL, greater than 200 milligrams per deciliter of blood, constitute a serious threat for coronary heart disease. Individuals with blood counts over the 200 level usually are put on special diets and may be candidates for lifetime therapy with anti-cholesterol drugs.

The debates today center on a few key questions:

-Exactly how much LDL cholesterol in the blood is too much?

-What foods increase blood cholesterol levels?

-What foods lower blood cholesterol levels?

-How significant is HDL cholesterol's role in counteracting the negative effects of LDL?

-How efficiently does exercise lower blood cholesterol?

-Which anti-cholesterol drugs should be used, at what dosage, on which patients, and for how long?

The cholesterol saga began in 1951 when doctors from New York Hospital studied lipid levels in the blood of people suffering from atherosclerosis, or hardening of the arteries. Lacking sophisticated methods for testing cholesterol levels, the doctors were unable to prove that their patients suffered from heart disease because of high cholesterol consumption, but they concluded that "the data are most suggestive of a more-than-coincidental association."

In the following years hospitals throughout the world discovered the same thing: People with high levels of blood LDL were more likely to develop heart disease. Despite this virtually unanimous research, physicians weren't quick to suggest changes in the American diet. In general, the '50s and early '60s were marked by physician reluctance to accept the roles of nutrition and cultural habits in Americans' health. Few doctors even acknowledged the link between smoking and lung cancer.

It was the small community of Framingham, Mass., that did the most to change America's attitude toward cholesterol. In 1949 more than 5,000 Framingham residents agreed to participate in a lifetime health survey. Doctors analyzed their diets, exercise patterns, medical records and family health histories. They became the medical community's focus on the health and habits of the American people.

In the 1960s doctors started testing the Framingham volunteers for blood cholesterol levels, the strength of their hearts, blood pressure, stress performance, body weight and blood sugar levels. They found a clear relationship between LDL cholesterol levels and heart disease. Furthermore, Framingham residents who had high levels of HDL had markedly lower levels of heart disease, indicating that HDL somehow protected people from the ravages of arterial plaque buildup.

In both cases the relationship was linear. One could sit down, draw a graph placing coronary heart disease on one side and LDL or HDL on the other, and simply draw a straight diagonal line. The heart disease line would soar upward as LDL levels increased, and decline on a less steep gradient as HDL levels went up.

In the 1970s climate of New Age philosophy and wheat germ consumption, many Americans took the cholesterol message to heart, trading oleo for butter, exercise for the life of the couch potato, chicken for steak and granola bars for potato chips. The nation was deluged with cookbooks and health tips from would-be gurus advocating such practices as vegetarianism, periodic fasting, macrobiotics, massive vitamin consumption, and eating alfafa sprouts and tofu. Many things were said about cholesterol, but few were based on any scientific evidence.

By the end of the decade a public weary of chomping on granola and trail mix discovered the joys of freshly grated parmesan, milk-fed veal and balsamic vinegar. Based on very preliminary studies, running magazines told their readers that miles of rapid pavement pounding would mitigate the need to stay away from Brie and Camembert.

The American Medical Association stepped into the fray, warning Americans that polysaturated fats were key contributers to cholesterol. Major sources of polysaturated fats, it was said, were beef, pork, butter, eggs, cream, soft cheeses, coconut oil, cocoa butter and all animal fat. Consumers were urged to switch to foods with less saturated fat.

The AMA message has been modified, and in 1988 there are some new tenets:

-Americans currently get 40 percent of their daily calorie intake in the form of fats and cholesterol. That should be reduced to below 30 percent.

-Avoid coconut oil, palm oil, butter oil, highly fatty meats, egg yolks (whites are OK), lard, fried foods, luncheon meats, ice cream, hard margarine, whipped cream, and any foods prepared in either palm oil or animal fat.

-Beef and cocoa butter got a bum rap in the 1970s. Lean beef and chocolate probably don't contribute to heart disease and may actually help reduce LDL cholesterol buildup. The same may apply to pork. However, beef with more than 10 percent fat, such as typical hamburger meat, should be avoided.

-Some foods definitely help reduce LDL levels and should be consumed more often. These include vegetables, some types of fish, olive oil, soft vegetable oil-based margarine, peanut oil, avocados, fresh fruit and high-fiber foods.

One might be tempted to ask why we consumers should believe that these 1988 recommendations are any more reliable than those issued by the AMA and American Heart Association in the 1970s. Indeed, AHA and AMA guidelines are not the same; AHA still recommends reducing beef, pork and chocolate intake and says that these foods, combined, should never represent more than 10 percent of a person's total food consumption.

Ironically, this confusion is indicative of a rapidly growing and sophisticated body of knowledge about the molecular biology of cholesterol.

Much of the sophistication stems from Nobel Prize-winning work done by Drs. Michael Brown and Joseph Goldstein at University of Texas Southwestern Medical Center in Dallas.