Effects of the nature of dietary proteins, lecithin and methionine on rat plasma lipids

In order to study the complex interrelationships between on the one hand, dietary proteins, lecithin and methionine and, on the other, blood cholesterol and triglyceride levels, groups of 10 rats were fed for six weeks with diets only differing by the nature of proteins which comprised 10% of the diet. These diets were composed of egg white, heated soybean flour, casein, heated soybean flour supplemented with 1% methionine, or with 4% of the lipids replaced by soybean lecithin, heated 5-day germinated soybean supplemented or not with 1% methionine and casein with 4% of the lipids replaced by lecithin.Egg white caused no change in blood cholesterol compared to heated soybean meal (0.955 ±0.18 vs 0.83 ± 0.14), but caused a significant increase in blood cholesterol levels compared to casein (0.955 ± 0.18 vs 0.81 ± 0.11 g/1). No effect was found on blood triglycerides levels. Lecithin caused no change when it partially replaced lipids in the soybean or casein diets though it increased triglycerides with the casein diet (1.16 ± 0.31 vs 0.84 ± 0.24 g/1). Supplementation of the heated soybean diet with 1% methionine led to an increase in blood triglycerides (0.85 ± 0.26 vs 1.18 ± 0.34 g/1). After germination, this effect disappeared. The effects of the type of protein, partial replacement of dietary lipids by lecithin and supplementation with methionine are discussed.