Fatty Acid Profile

Early evidence demonstrated that diets relatively high in saturated fatty acids increased plasma total cholesterol levels. Subsequent work demonstrated that this elevation in total cholesterol levels is contributed to by increases in both LDL and HDL cholesterol levels. It also became clear that not all saturated fatty acids had identical effects on plasma lipoprotein levels. Very short-chain fatty acids (6:0 to 10:0) and stearic acid (18:0) produce little or no change in blood cholesterol levels, whereas saturated fatty acids with short- and intermediate-chain lengths—lauric (12:0), myristic (14:0), and palmitic (16:0) acids—appear to be the most potent in increasing blood cholesterol levels. Because a large proportion of stearic acid (18:0) is rapidly converted to oleic acid (18:1), it appears to have a relatively neutral effect. The underlying mechanism by which saturated fatty acids with 10 or fewer carbon atoms have different effects from those with 12-16 carbons is yet to be determined. The current dietary recommendation as defined in the NCEP Therapeutic Lifestyle Change diet to prevent and treat cardiovascular disease is to limit intakes of saturated fat to less than 7% of total energy. The major contributors of saturated fatty acids were discussed previously.

Compared to saturated fatty acids, unsaturated fatty acids, both monounsaturated and polyunsatu-rated fatty acids, lower both LDL and HDL cholesterol levels. The absolute magnitude of the change is greater for LDL cholesterol than HDL cholesterol. Most data suggest that monounsaturated fatty acids have a slightly smaller effect than polyunsaturated fatty acids in lowering both LDL and HDL cholesterol levels so that the total cholesterol:HDL cholesterol ratio is similar for both categories of fat.

Quantitatively, the major n-3 polyunsaturated fatty acid in the diet is alpha-linolenic acid (18:3n-3). Major dietary sources include soybean and canola oils (Figure 8). Two other n-3 polyunsaturated fatty acids, eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3), referred to as very long-chain n-3 fatty acids, are found predominantly in fish, specifically dark flesh fish such as salmon, tuna, and swordfish. Dietary intakes of very long-chain n-3 fatty acids are associated with decreased risk of heart disease and stroke. Intervention studies have substantiated these findings.

Cakes, cookies, crackers, pies, bread, etc. 40%

Animal products 21%

Candy 1%

Cakes, cookies, crackers, pies, bread, etc. 40%

Breakfast cereal ' 1% \ Salad dressing

Household shortening 4%

Potato chips, corn chips, popcorn

Fried p

Margarine 17%

Figure 9 Major food sources of trans fat for US adults. (Data from www.cfsan.fda.gov/~dms/qatrans2.)

Breakfast cereal ' 1% \ Salad dressing

Household shortening 4%

Potato chips, corn chips, popcorn

Fried p

Margarine 17%

Figure 9 Major food sources of trans fat for US adults. (Data from www.cfsan.fda.gov/~dms/qatrans2.)

The beneficial effects of EPA and DHA are attributed to decreased ventricular fibrillation resulting in decreased sudden death, and also decreased triglyceride levels, platelet aggregation, and blood pressure. Evidence suggests that very long-chain n-3 fatty acids may decrease atherosclerotic plaque progression.

Dietary trans fatty acids occur naturally in meat and dairy products as a result of anaerobic bacterial fermentation in ruminant animals. Trans fatty acids are also introduced into the diet as a result of the consumption of hydrogenated vegetable or fish oils. Hydrogenation results in a number of changes in the fatty acyl chain: conversion of cis to trans double bonds; saturation of double bonds; and migration of double bonds along the acyl chain, resulting in multiple positional isomers. Oils are primarily hydrogenated to increase viscosity (change a liquid oil into a semiliquid or solid) and extend shelf life (decrease susceptibility to oxidation). Major contributors of trans fatty acids are commercially baked products (40%), animal products (21%), margarine (17%), and fried potatoes and chips (13%) (Figure 9). In intervention and observational studies, trans fatty acid intake has been associated with less favorable total cholester-ol:HDL cholesterol ratios and increased risk of cardiovascular disease, respectively.

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