(2 of 8)
"The impression being given," admits Dr. Irwin Rosenberg, dean of nutrition sciences at Tufts University School of Nutrition, Science and Policy, "is that nutrition science doesn't know what it's doing." But despite appearances, the medical profession has not lost its collective mind. The bewildering flood of advice that assaults us week after week simply reflects the slow, laborious gathering of knowledge that defines science in action. Like most works in progress, it moves ahead in fits and starts--and occasionally goes down a blind alley.
Yet despite all the apparent confusion, scientists actually know a lot more today about what keeps the heart humming than they did a generation ago. The first glimmerings of understanding gathered 30 years ago were accurate as far as they went--but rudimentary. Today scientists have a much deeper understanding of what foods and activities are healthful or harmful--and why. The good news is that the path to a healthier heart is now pretty clear, once you master a few key concepts.
FAT AND CHOLESTEROL
Fat has been a staple of the human diet since our remote ancestors started eating meat more than 2 million years ago. In the 1960s, however, researchers began to notice that patients who had elevated blood levels of cholesterol--a fatty substance found in meat, poultry, eggs and dairy products--also tended to suffer from heart disease. Cholesterol by-products would form thick, tough deposits, called plaques, on the inner walls of arteries, stiffening them and then starving the heart of blood and creating choke points where a clot could stop the flow entirely.
At first blush, the solution seemed pretty obvious: consume low-cholesterol foods; switch from butter to vegetable-oil-based margarine; eat fewer eggs; eat less meat. Indeed, it was the best advice at the time, based on the limited knowledge available.
As scientists learned more about how the body works, however, that prescription proved too simplistic. Some people's cholesterol levels stayed high, no matter what they ate. And a lot of heart-disease patients had normal cholesterol levels. How could this be? Only recently have some of the reasons begun to emerge. For one thing, how much cholesterol you eat doesn't necessarily determine how much ends up in your blood. The body, it turns out, also manufactures its own cholesterol. And some people's bodies are just less efficient at vacuuming up excess cholesterol than others, for reasons that are largely genetic.
So, in the next phase of research, the object became keeping cholesterol levels in the blood under control and not necessarily keeping the cholesterol out of the diet. But how to do it? Again the key seemed to be eating less red meat, cream and butter, but it was based not so much on cholesterol as on saturated fat. Reason: saturated fat increases blood cholesterol. So eggs, high in cholesterol but not in saturated fat, were taken off the forbidden list, except for those people with the most serious cholesterol problems.