Correlation of serum triglyceride and its reduction by omega-3 fatty acids with lipid transfer activity and the neutral lipid compositions of high-density and low-density lipoproteins.

Serum triglyceride (TG) and high-density lipoprotein cholesterol (HDL-C) concentrations are inversely correlated and mechanistically linked by means of lipid transfer activities. Phospholipid transfer activity (PLTA) moves phospholipids among serum lipoproteins; cholesteryl ester transfer activity (CETA), which exchanges cholesteryl esters (CE) and TG among lipoproteins, is stimulated by nonesterified fatty acids (NEFA). The aims of this study were (a) to develop a quantitative model that correlates the neutral lipid (NL = CE + TG) compositions of HDL and LDL with serum TG concentration; (b) identify the serum lipid determinants of CETA and PLTA, and; (c) identify the effects of serum TG reductions on the neutral lipid compositions of HDL and LDL, serum NEFA concentrations, and on PLTA and CETA. These aims were addressed in 40 hypertriglyceridemic subjects before and after treatment with an 85% concentrate of omega-3 fatty acids (Omacor) and in 16 untreated normolipidemic subjects. In vivo, the NL compositions of LDL and HDL were described by a mathematical model having the form of adsorption isotherms: HDL - (TG/NL) = (0.90 +/- 0.07) serum TG/(7.0 +/- 1.2 mmol/l + serum TG) and LDL - (TG/NL) = (0.65 +/- 0.08) serum TG/(4.9 +/- 1.5 mmol/l + serum TG). Reduction of serum TG was associated with reductions in HDL - (TG/NL), serum NEFA concentration, and serum CETA but not PLTA. These data suggest that both hypertriglyceridemia and the attendant elevated serum CETA but not PLTA are determinants of HDL and LDL composition and structure and that serum TG concentrations are good predictors of the NL compositions of HDL and LDL.

Alterations in serum phosphatidylcholine fatty acyl species by eicosapentaenoic and docosahexaenoic ethyl esters in patients with severe hypertriglyceridemia.

A new and sensitive method has been developed to analyze the molecular species of glycerophospholipids. This method was used to examine the effects of hypolipidemic intervention with n-3 fatty acids on the serum phosphatidylcholine species in severely hypertriglyceridemic patients. The drug treated group (n = 19) received 4 g/day of an 85% concentrate of the ethyl esters of eicosapentenoic and docosahexaenoic acids for 6 weeks. Control patients (n = 21) received 4 g/day of ethyl esters of corn oil fatty acids. To evaluate the effects of n-3 fatty acids upon serum phosphatidylcholines (PCs), sera from treated and control patients were analyzed before and after 6 weeks of intervention. PCs isolated from sera were digested with phospholipase C to diglycerides, derivatized with 7-methoxycoumarin-3-carbonyl azide, and analyzed by reverse phase high performance liquid chromatography (HPLC) with fluorescence detection. Pre-intervention serum PC species were, in order of decreasing concentration C16:0,18:2, C16:0,18:1, C18:0,18:2, C16:0,20:1, C16:0,22:0, C18:0,20:4, C16:0,16:0, C18:0,18:1, C18:1,18:2, C16:0,20:5, and C18:1,20:5. In the treated patients, mean increases of 300% in C16:0,20:5 and of 160% in C16:0,22:6 species were observed. There were no significant changes in the molecular species of the serum phosphatidylcholines in the group receiving the corn oil ethyl esters. The cumulative relative percentages for each of the individual fatty acids measured by HPLC were comparable to those determined by gas-liquid chromatography (GLC). In the treated group plasma triglycerides were reduced 26%, while they were increased by 7% in the placebo group. Our data showed that incorporation of eicosapentaenoic and docosahexaenoic acid into the serum PCs occurred within 6 weeks primarily in the C16:0,20:5 and C16:0,22:6 species and were usually accompanied by a reduction in plasma triglyceride.

Effects of beef and chicken consumption on plasma lipid levels in hypercholesterolemic men.

BACKGROUND: The recommendation to lower saturated fat intake is often interpreted as requiring the elimination of beef to control or lower serum cholesterol levels. The study hypothesis was that the Step I Diet (8% to 10% of energy intake from saturated fatty acids) containing beef would have the same effect on plasma lipid levels of hypercholesterolemic men as a like diet containing chicken. METHODS: Thirty-eight free-living hypercholesterolemic (otherwise healthy) men completed a 13-week dietary intervention study. Subjects consumed their usual diets for 3 weeks, followed by a 5-week stabilization diet (18% of energy intake from saturated fatty acids), before randomization to one of two test diets for 5 weeks. The test diets contained either 85 g of cooked beef (8% fat) or 85 g of cooked chicken (7% fat) per 4184 kJ and had 7% to 8% of energy from saturated fatty acids. All food was supplied during the stabilization and test diets. RESULTS: The beef and chicken test diets both produced significant decreases in average plasma total cholesterol level (0.54 mmol/L [7.6%] for beef and 0.70 mmol/L [10.2%] for chicken) and low-density lipoprotein cholesterol level (0.46 mmol/L [9%] for beef and 0.55 mmol/L [11%] for chicken). Changes in average levels of plasma total cholesterol, high-density lipoprotein cholesterol, triglyceride, and low-density lipoprotein cholesterol were not statistically different (smallest P = .26) between the beef and chicken test diets. The average triglyceride level did not change for either test diet group. CONCLUSIONS: In this short-term study, comparably lean beef and chicken had similar effects on plasma levels of total, low-density lipoprotein, and high-density lipoprotein cholesterol and triglyceride. We concluded that lean beef and chicken are interchangeable in the Step I Diet.

Development and preparation of lean meat products.

When the effect of food on human lipoprotein levels is tested, or when human consumption of dietary lipids must be controlled or limited, all food needs to be provided under controlled conditions to achieve consistent composition and sensory traits. It is especially important to control the composition of foods, particularly fat and fatty acid content. Because of the inherent biologic variability in the chemical composition of animal tissues (beef in particular), raw materials must be selected carefully and prepared under strict guidelines. In addition, chemical composition should be verified initially and during the production of the product to ensure the accuracy necessary for controlled dietary intake. Furthermore, the meat provided must be easy for the study subject to prepare, be of consistent serving size, and yet be highly palatable to maintain the subject's interest and participation. This article outlines the protocol for developing lean meat products for use in nutrition studies in which fat content must be controlled, especially those studies designed to examine the effect of fat content on human lipoproteins. Preliminary studies, procurement of raw materials, procedures for recipe selection, product preparation, and sampling procedures for verification of chemical composition are described. Our findings indicate that fat intake from beef, chicken, and fish can be controlled for use in nutrition studies.