to the diet increases blood cholesterol levels only slightly and therefore might theoretically boost the risk of heart disease by about 10 percent. However, the focus on cholesterol has ignored the fact that eggs aren’t just packets of cholesterol. They are very low in saturated fat and contain many other nutrients that are good for you— protein, some polyunsaturated fats, folic acid and other B vitamins, and vitamin D. So their effect on heart disease risk can’t be predicted by considering only their cholesterol content. Also, people respond in different ways to cholesterol in their food. For some people, let’s call them responders, the amount of cholesterol in the diet has a direct effect on the amount of cholesterol in the bloodstream. Nonresponders, though, can eat and digest cholesterol with only small or immeasurable changes in the amount of cholesterol in the bloodstream. It also appears that eating eggs has relatively little effect on small, dense LDL, the class of bad cholesterol that poses the greatest risk to cardiovascular health.
No research has ever shown that people who eat more eggs have more heart attacks than people who eat few eggs. And recent research suggests you needn’t feel so guilty about eating them. The most comprehensive study to date looked at the egg-eating habits of almost 120,000 men and women. Healthy men and women who ate up to an egg a day were no more likely to have developed heart disease or to have had a stroke over many years of follow- up than those who ate less than one egg a week. For those with diabetes, though, there did seem to be some connection between eating an egg a day and the development of heart disease.
learn more: Fats in the Bloodstream
While this study, and others like it, don’t give the green light for daily three-egg omelets, they should be reassuring to people who enjoy eggs. If your breakfast Until the middle of the last century, when infectious diseases like tuberculosis and inﬂuenza were leading causes of death, calorie-rich diets laden with fat were thought to provide some protection against disease and aid in recovery. As late as the 1950s, a healthy diet meant eggs, bacon, and butter-slathered toast for breakfast, roast beef and mashed potatoes with gravy for dinner.
Our comfortable, almost thoughtless relationship with food was forever changed by separate threads of research that came together after World War II. Large studies in the late 1940s and early 1950s began to focus on diet as a cause of the skyrocketing rates of heart disease. In 1956, a midwestern scientist named Ancel Keys began an international survey called the Seven Countries Study. It showed a strong connection between saturated fat and heart disease—in general, the higher the amount of saturated fat in a country’s diet, the higher the rate of heart disease. Curiously, Keys and his colleagues didn’t ﬁnd any connection between the total amount of fat in the diet and heart disease. In fact, the area with the lowest rate of heart disease in the study, Crete, had the highest average total fat intake (about 40 percent of calories), mostly due to liberal use of olive oil. At around the same time, the Framingham Heart Study started tracking the health and habits of more than ﬁve thousand men and women living in the town of Framingham, Massachusetts. One of its early ﬁndings was that high levels of cholesterol in the bloodstream were often an early signal of impending heart disease. These important studies and others pointed to diet as a key element in the path to heart disease.
Without turning this into a textbook of nutritional epidemiology, I’ll brieﬂy describe the consistent evidence from several kinds of studies showing the harmful eﬀects of saturated and trans fats and the beneﬁts that can come from replacing these harmful fats with unsaturated fats.
CROSS-CULTURAL SURVEYS: THE MORE SATURATED FAT, THE MORE HEART DISEASE
The country-by-country surveys of Ancel Keys and others showed that heart disease rates varied more than tenfold between Crete and Finland, the country with the highest rates. And the more saturated fat in a country’s average diet, the more heart disease. Although the Seven Countries and Framingham studies pointed to something about diet and lifestyle as being a major cause of heart disease, other factors linked with saturated fat could have been responsible. Because the highest heart disease rates were seen in the richer Western countries, cigarette smoking, lack of activity, or other aspects of diet could have contributed to the large diﬀerence in rates.
learn more: Building a Better Pyramid
METABOLIC STUDIES: GOOD FATS CAN IMPROVE YOUR CHOLESTEROL PROFILE
In the 1950s and 1960s, dozens of carefully controlled feeding studies among small groups of volunteers showed conclusively that when saturated fat replaced carbohydrate in the diet, total cholesterol levels in the blood rose; and when polyunsaturated fat replaced carbohydrate, total cholesterol levels fell. Thus, for decades we have known that all fats should not be considered equal. Unfortunately, at that time the importance of other blood lipids—HDL in particular—was not appreciated. So those studies gave an incomplete picture at best. One of the most compelling pieces of evidence to challenge the emphasis on cutting back on all fat and eating more carbohydrates comes from an experiment by two Dutch scientists. They recruited forty-eight volunteers for an eight-week study. For the ﬁrst seventeen days, all of the volunteers ate a typical Western diet with about 40 percent of calories from fat. For the next thirty-six days, half of the volunteers were assigned to a diet rich in olive oil and lower in saturated fat, while the other half got a low-fat, high-carbohydrate diet. In both groups, total cholesterol levels plummeted. But in the high-carbohydrate group, levels of HDL (good) cholesterol also fell, while triglycerides rose—both changes that increase the chances of having a heart attack or developing some other form of heart disease. In the olive oil group, the same healthy trend was seen for total cholesterol without the unhealthy changes in HDL and triglycerides.