The effects of soy protein with and without isoflavones on fasting and post prandial lipemia in sedentary males
Santo, Antonio Saraiva
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Introduction . Cardiovascular disease (CVD) is the leading cause of death in the United States. Constituents of soy (i.e., isoflavones) have been associated with a decreased CVD risk. Hypothesis . We hypothesized that milk or soy protein without isoflavones would increase fasting total cholesterol (TC) and LDL-cholesterol, post-prandial triglycerides (TG), and hepatic lipase (HL) activity and decrease lipoprotein lipase (LPL) activity. Furthermore, the presence of isoflavones in soy would reduce this protein effect. Methods . Thirty sedentary males between the ages of 18 and 30 were randomly assigned to one of three groups: milk protein (Milk), isoflavone-poor soy (Soy-), or isoflavone-rich soy (Soy+). Participants supplemented their usual diet with 25 grams per day of protein for 28 days. Serum samples were collected before and after supplementation in a fasted state and after a high-fat, 1000 kcal shake. Post-prandial collections were at 30, 60, 120, 240 and 360 minutes. Glucose, TC, TG, non-esterified fatty acids, apolipoproteins B-100 and A-I and HDL-Cholesterol concentrations were determined. On a separate day, 30 U/kg of heparin was administered after a 12-hour fast and heparin samples were collected 15-minutes post administration for measurement of total, hepatic and lipoprotein lipase activities. Results . Fasting values for these variables were not different after any protein supplementation. Differences existed in post-prandial lipemia, calculated as total area under the incremental curve, with the post-prandial TG values being 435.5 and 484.7 for Milk, 326.3 and 597.3 far Soy-, and 564.4 and 417.3, for Soy+ (mg/dL for six hours, before and after supplementation, respectively). Hepatic lipase activity increased from 21.9 to 26.1 μmol FFA·ml -1 ·h -1 after Soy- supplementation. Conclusion . Results indicate that isoflavones reduced the hypertriglyceridemia and the HL activity associated with increased Soy- protein intake. These results suggest that the presence of 96.4 mg isoflavones is necessary for individuals to reap the purported benefits of soy with respect to CVD. Protein supplements were donated by The Solae Company (St. Louis, MO).