Q. My children and I enjoy fast food restaurants. Is my wife correct when she warns us that eating there is not healthy?
A. It is certainly possible to get nutritious foods at a fast food restaurant, but you must make careful choices in order to avoid meals that are too high in calories, salt and fat.
Most nutritionists recommend the intake of fat should be less than 30 percent of total calories. The fat content exceeds 30 percent of calories in many popular fast foods: for example, it's about 43 percent in a cheeseburger, about 50 percent in a hot dog, taco or french fries, and from 24 to 38 percent in cheese pizzas.
Fast food restaurants do provide low-fat choices at the salad bar (watch the salad dressings) and are beginning to use vegetable oils instead of beef tallow to prepare food.
Q. We are constantly warned against eating eggs and other foods high in cholesterol. But last week a newspaper article described an 88-year-old man who has eaten 25 eggs a day for at least 15 years and still has a normal blood cholesterol level. How can you explain that?
A. The average American diet contains between 350 and 500 mg of cholesterol daily -- the equivalent of about 1 1/2 to 2 eggs a day since the cholesterol content of an egg is about 230 mg. Reducing the dietary cholesterol to less than 300 mg a day will lower the blood cholesterol level in almost all individuals.
However, when the amount of dietary cholesterol is increased to more than 500 mg a day, many studies have shown that the effect on the blood cholesterol level varies greatly from one individual to another. On average, the addition of three eggs a day to the usual diet will raise the cholesterol by 5 to 10 percent, more in men than in women. But the cholesterol level will increase much more in some people, while in a few others there'll be no change. Unfortunately, there is no way to tell.
Four factors determine the effect of dietary cholesterol on the level of blood cholesterol: the amount of cholesterol absorbed from the intestine, the conversion of cholesterol to bile acids in the liver, the effect of dietary cholesterol on the production of cholesterol in the body, and the excretion of cholesterol in the bile. Ordinarily, about half the cholesterol in the diet is absorbed from the intestine and enters the bloodstream.
If the report about the 88-year-old man is true, the man who ate 25 eggs a day absorbed only 18 percent of the cholesterol in his diet. In addition, he was able to convert more cholesterol to bile acids and to reduce his own production of cholesterol.
Dr. Margolis is professor of medicine and biological chemistry at the Johns Hopkins School of Medicine and associate dean for faculty affairs at the school.