Effects of fish oil on serum lipids in men during a controlled feeding trial

Article Abstract:

It has been suggested that fish oils, in the form of supplements or fish itself, may alter the levels of lipids (fats) in the blood in a beneficial way. However, studies evaluating the effects of fish oils on blood cholesterol and triglycerides have yielded conflicting results. The most frequently reported effect of fish oils has been a reduction in blood triglycerides. Total cholesterol has not been altered by fish oil consumption in most studies, however, a few studies have reported decreases in cholesterol levels. The effects of fish oils on high-density-lipoprotein (HDL) cholesterol, the type of cholesterol that may protect against heart disease, have been very inconsistent; fish oils have been associated with increases, decreases, and no change in HDL cholesterol. Some of the disagreement between studies might be due to the common practice of allowing subjects to consume their usual diets while taking fish oils. This introduces error into a study because daily variations in an individual's diet can alter or mask the effect of the supplement. In the current study, this problem was averted by feeding 15 healthy male college students a controlled diet. For five weeks, three groups of five students each took no fish oil, 5 grams (g) fish oil per day, or 20 g fish oil per day; the groups that consumed fish oil took it in place of an equal amount of margarine. Blood tests revealed that both doses of fish oil led to changes in the fatty acid composition of the blood and blood cells, as the n-3 fatty acids (found in fish oils) were incorporated into these cells. In addition, the group taking 20 g of fish oil experienced a 30 percent decrease in triglycerides after two weeks of taking the supplements, with no additional decrease during the next three weeks. The lower dose of fish oils had no effect upon triglycerides, and neither dose altered the levels of total cholesterol, HDL cholesterol, or apolipoproteins A-I and B-100, substances that may be related to heart disease risk. It is concluded that the beneficial effects of low doses of fish oils appear to result from changes in the fatty acid composition of blood cells, rather than from changes in blood lipid levels. Higher doses of fish oils may, in addition, alter blood lipid levels, as they lowered triglycerides in this study. (Consumer Summary produced by Reliance Medical Information, Inc.)

Triglycerides, Fish oils in human nutrition, Fish oils

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Effect of diets high in butter, corn oil, or high-oleic acid sunflower oil on serum lipids and apolipoproteins in men

Article Abstract:

The risk of developing cardiovascular disease has been clearly linked to blood levels of total cholesterol and low-density-lipoprotein (LDL) cholesterol, one type of cholesterol. Reduction of cholesterol levels is thought to be best accomplished by reducing dietary intake of saturated fat. A second recommendation has been to reduce the total level of fat in the diet, to 30 percent of calories or less. Studies conflict as to the effects of replacing saturated fats with carbohydrates and monounsaturated or polyunsaturated fats. In particular, reductions in high-density-lipoprotein (HDL) cholesterol (an undesirable effect) were observed following intake of high levels of carbohydrate and polyunsaturated fats. In this study, the effects of polyunsaturated and monounsaturated fats on levels of cholesterol were reexamined. Each of the 20 male subjects followed three different diets. The diets were based on: corn oil as a source of polyunsaturated fats (Poly); high-oleic acid sunflower oil as a source of monounsaturated fats (Mono); and butter, a highly saturated fat. All the diets provided approximately 40 percent of calories from fat. As compared with the butter diet, the total level of cholesterol dropped quickly during the five-week vegetable oil diets (a 16 to 21 percent reduction), and remained significantly lower at the end of the diets. Levels of LDL-cholesterol dropped on both the Poly and Mono diets (21 to 26 percent), but more on the Poly diet than on the Mono diet. Similar effects on Apo B-100 (a protein component of LDL, and a possible predictor of disease risk) were observed. HDL-cholesterol did not differ significantly among the three diets. Blood levels of fat (triglyceride) dropped following either the Poly or Mono diet. The greatest changes in total and LDL-cholesterol were observed in subjects with a high initial level of total cholesterol. The results reinforce the importance of replacing saturated fats with polyunsaturated or monounsaturated fats, and also suggest that beneficial effects from these changes may occur without reducing the total level of fat in the diet. (Consumer Summary produced by Reliance Medical Information, Inc.)

Hyperlipidemia, Unsaturated fatty acids in human nutrition

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Serum lipid and apolipoprotein concentrations in healthy men on diets enriched in either canola oil or safflower oil

Article Abstract:

Over the last several decades it has become apparent that people who have high blood levels of cholesterol have an increased risk of developing heart disease. Many studies have examined the effects of various types of low-fat diets and diets supplemented with different types of oils (such as olive oil and sunflower oil). Diets high in monounsaturated fat have been shown to lower blood levels of low-density-lipoprotein (LDL) cholesterol, while some studies have reported that polyunsaturated fats reduce the amount of high-density-lipoprotein (HDL) cholesterol; it appears to be beneficial to lower LDL and raise HDL levels. Therefore, a study was performed to examine the effect of polyunsaturated fats on HDL levels, to determine if a diet low in saturated fats can lower LDL levels, and to determine if a diet containing canola oil or safflower oil can reduce blood cholesterol levels. Sixteen healthy men followed an eight-week diet containing 39 percent of total calories from fat, in the form of either safflower oil or canola oil (two different types of vegetable oil). Safflower oil is a polyunsaturated oil, and canola oil is a monounsaturated oil, thus both diets were low in saturated fat. Blood levels of cholesterol were measured before and after the diet period. The vegetable oil diets reduced blood levels of total cholesterol by 9 to 15 percent and reduced LDL (low-density-lipoprotein) cholesterol by 12 to 20 percent; reductions of these substances are thought to lower the risk of heart disease. The vegetable oil diets did not alter the levels of HDL (high-density-lipoprotein) cholesterol or triglycerides (fatty acids); it is not thought to be beneficial to lower HDL levels, since this form of cholesterol appears to protect against heart disease. It is concluded that a diet low in saturated fat can reduce the amount of LDL cholesterol in the blood, and that diets high in polyunsaturated fat do not necessarily reduce the amount of HDL cholesterol in the blood. (Consumer Summary produced by Reliance Medical Information, Inc.)

Physiological aspects, Lipoproteins, Hypercholesterolemia, Blood lipoproteins, Canola oil, Safflower oil

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