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Cardiologists at the University of Maryland, who used special milkshakes to measure spikes in blood fat levels, conclude that triglyceride levels need to be reduced in order to lower the risk of heart disease. Their study found that fats consumed from meals throughout the day may cause a person's triglyceride levels to soar to dangerous levels, even though their doctor may have found a normal reading when their triglyceride was measured following a fast. The study, published in the current issue of the Journal of Investigative Medicine, provides a potential rationale for advocating much lower fasting triglyceride levels than those currently considered desirable.
"The results give us more reason to believe that lower triglyceride levels are better for you," says Michael Miller, M.D., director of preventive cardiology at the University of Maryland Medical Center and associate professor of medicine at the University of Maryland School of Medicine.
New understanding about the role of triglycerides in heart disease in recent years has prompted a redefinition of the optimal target level. The National Cholesterol Education Program now recommends having a fasting triglyceride of less than 150 milligrams per deciliter (mg/dL). But that may not be low enough to protect us from the peaking levels throughout the day. Dr. Miller says his study suggests that less than 100 mg/dL is a more appropriate fasting benchmark, to provide a wider margin of safety.
"Our study shows that even when people have acceptable fasting levels, after a high fat meal their triglyceride shoots up to levels that could put them at higher risk of heart disease. In other words, if the fasting triglyceride level is 140 mg/dL, then chances are likely that throughout the day triglyceride levels will double and will be in the range between 200 and 300 mg/dL. These levels may be dangerously high and over time may lead to heart attacks and stroke," says Dr. Miller. "Unfortunately, physicians have often discounted triglyceride levels in a blood test performed after a meal and it has been common practice to tell patients to ignore such high post-meal triglycerides. If we can help patients lower their baseline triglyceride levels with diet changes and exercise, their heart disease risk may drop throughout the day, even after high fat meals."
The study evaluated the implications of optimal fasting triglyceride in 50 healthy, non-obese men and women with normal cholesterol levels, whose average age was 35. After their fasting triglyceride level was measured, each volunteer was given a milkshake, standardized at 70 grams of fat per square meter of body surface, approximating the fat in a fast food extra large double hamburger and a large shake. Triglyceride levels following the shake were measured at intervals of two, four, six, eight and ten hours.
Four hours after consuming the milkshake, the triglyceride levels in volunteers who began with a fasting triglyceride between 101 and 149, now defined as acceptable, had risen to an average of 200 mg/dL. However, in volunteers with a fasting triglyceride of less than 100, the four-hour peak triglyceride level after the milkshake was only 124 mg/dL on average.
"The average triglyceride level in the United States is 134 mg/dL, considerably higher than triglyceride levels below 100 mg/dL commonly observed in countries where heart disease rates are low," says Dr. Miller. "The higher triglyceride levels are associated with both increases
in body weight and the disturbing increase in diabetes. It's a two-sided problem, because people with high triglycerides often develop insulin resistance, a major factor in the most common type of diabetes. In some cases, high triglycerides are identified years before the onset of diabetes."
Triglyceride is a fat that always circulates in the blood, especially after a meal high in saturated fat. Enzymes normally break down these fat particles, but when the process is not working efficiently, triglycerides that are only partially broken down can cause fatty deposits in blood vessels, leading to atherosclerosis, also known as hardening of the arteries. Triglycerides can increase the risk of blood clots, which combine with fatty deposits in the coronary vessels to cause heart attacks. The present study extends previous research by Dr. Miller's group which showed that compared to lower levels, triglycerides above 100 mg/dL were associated with a 50 percent increased risk of heart attacks and death.
Dr. Miller says a combination of diet changes and exercise can reduce triglyceride levels by as much as 30 percent. These fats respond to regular exercise, weight loss, and a diet low in saturated fat and high in omega 3 fatty acids. Sources of omega 3 fatty acids include fish, such as salmon, herring, mackerel, sardines and tuna. Niacin, and certain prescription medications, including gemfibrozil, fenofibrate and some statins, can lower triglyceride levels significantly.
Angeliki Georgopoulos, M.D., of the Veterans Affairs Medical Center at the University of Minnesota co-authored the study with Dr. Miller. The research was supported with funding from the American Heart Association, the Veterans Affairs Medical Center and the National Institutes of Health.
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