"Triglycerides aren't really bad guys. But they do keep bad company," says Dr. Scott Grundy, director of the Center for Human Nutrition. Triglycerides are simply the fats in foods -- like butter, corn oil, olive oil, the fat on meat or the fat in ice cream. When we talk about saturated, polyunsaturated or monounsaturated fats, those are triglycerides, too. Ninety-five percent of the fats we are triglycerides.

Fats are metabolized by the body for energy or stored in fat cells to supply future energy. Fat cells help to insulate the body from extremes of temperature, and they provide protective pads to guard vulnerable organs against shock. Triglycerides, in other words, are either used immediately or stored. They do not present a health problem unless they begin to build up in the blood in the form of very low density lipoproteins (VLDL). "You have to have something wrong with you before triglycerides begin to build up in the blood," says Dr. Grundy.

One cause of a high VLDL level is overproduction by the liver. VLDL is produced by the liver's wrapping the triglycerides in a protein coating to help them circulate through the blood. This occurs in the same way that cholesterol gets a protein coating and circulates in the blood as low density lipoprotein (LDL).

Obesity is the most common cause of the overproduction of VLDL. "If you are overweight, excess calories stimulate the liver to produce VLDL -- and that's calories from all sources, not just calories from fat," says Grundy. A high level of VLDL may be responsible in part for the increased cardiovascular risk associated with obesity. Obviously weight reduction is the appropriate treatment for high triglycerides of obesity, he says, but exercise also helps.

Diabetes is a second cause for overproduction of VLDL. High triglycerides may be one reason diabetic patients commonly have coronary heart disease. Proper treatment of diabetes will help to lower the VLDL triglycerides. Because obesity is a major contributor to adult-onset diabetes, the treatment should include reducing weight to a desirable level.

Other conditions causing overproduction of triglycerides include excessive alcohol intake and the use of a variety of drugs, including thiazide diuretics, oral contraceptives, estrogen hormones and some medications to lower blood pressure.

Finally, in some people, a genetic disease appears to cause a high production of VLDL by the liver. This disease accounts for 10 percent of all coronary heart disease. In these people, a drug called nicotinic acid may correct the condition.

Besides overproduction of VLDL, another major cause of high VLDL levels is a failure to break down the VLDL adequately. An important enzyme called lipoprotein lipase is needed for the breakdown of triglycerides. When this enzyme does not function properly, the VLDL will remain high. The Center for Human Nutrition is examining the value of a drug called gemfibrozil that appears to increase the activity of lipoprotein lipase.

As part of a complete measure of blood lipids, your physician may ask for a test of triglyceride levels after a 14-hour fast. A triglyceride level below 200 milligrams per deciliter is considered normal and desirable. Triglycerides between 200 and 250 mg/dL indicate potential trouble and call for a change in eating and drinking habits, including diet to bring body weight to a desirable level.

A person with triglyceride levels in the 250-500 mg/dL range frequently has a twofold risk for cardiovascular disease. This moderately high triglyceride level may indicate a genetic problem in clearing VLDL from the blood, and the cause should be investigated further. Above 500 md/gL, the elevation is serious and calls for lowering by diet and, if necessary, by drugs.

In analyzing the seriousness of elevated VLDL levels, your physician will take into account whether your high density lipoprotein (HDL) level is normal or low. HDL is the lipoprotein that indicates how effectively your triglycerides are being metabolized. For example, exercise burns up triglycerides and produces high HDL's. If you exercise a lot, you should have low VLDL and high HDL.

On the other hand, the combination of high VLDL and low HDL is a cause for concern because it suggests that VLDL is being overproduced at the same time it is not being cleared efficiently. "If you don't exercise and you're fat, then your triglycerides are often high and HDL is very low," says Grundy. "That is the problem for a man who sits in an office all day, goes home and watches TV at night, drinks beer and eats a lot of potato chips and other snacks. He gets fat and doesn't exercise. His VLDL is high and his HDL is low, and he is likely to have a heart attack even if his cholesterol isn't too high.

An HDL between 40 and 50 for a man is satisfactory; between 30 and 40, a cause for some concern; below 30, of considerable concern. For a woman 50-60 is satisfactory; below 40 is a cause for concern. The role of alcohol consumption in the VLDL-HDL linkage is interesting because alcohol raises the HDL level as well as the VLDL level. "It's my view that drinking messes up the thermostat," says Dr. Grundy. "It's like taking aspirin for a fever. The aspirin will lower the fever but not cure the infection that caused it. I think alcohol is the same way. It raises the HDL and makes you think you are all right, but you still have the triglyceride problem so you may get heart disease." A team of scientists at the CHN is conducting research on high triglycerides, as well as the diets and drugs to control them.

One important member of the Nutrition Center team is Dr. Gloria Lena Vega, who measures how much VLDL the liver makes and how fast VLDL is broken down. Recently, a physician from Japan, Dr. Shuchi Nosaki, has joined the group. He is an expert on the measure of the enzyme lipoprotein lipase. Dr. Cara East in the group recently completed a study of the use of two drugs together -- gemfibrozil and lovastatin (formerly called mevinolin) -- in the treatment of patients who have high levels of both triglycerides and cholesterol.

Her findings were presented at the National Scientific Meeting of the American Heart Association in Dallas in November.

Research on the cause and treatment of elevated triglycerides and cholesterol will continue to have high priority with the Center for Human Nutrition in the fight against coronary heart disease.