Postprandial effects of soy isoflavones on low-density lipoprotein oxidative resistance with a high carbohydrate meal

Abstract

Cardiovascular disease (CVD) encompasses a wide array of health problems including atherosclerosis which results in 50% of all cardiac deaths. Currently the American Heart Association developed the Step I guidelines for reducing the risk of CVD limits total fat to ≤30% of total energy, saturated fat to <10% of total energy, and cholesterol to < 300 mg/day. Reducing dietary fat generally decreases plasma cholesterol however carbohydrate (CHO) content typically rises accompanied by increasing plasma triacylglycerol (TC). Elevated TG may possibly be a risk factor for CVD, referred to as “CHO-induced hypertriacylglycerolemia” (HPTG). The disease process of atherogenesis has been hypothesized by Zilversmit as a postprandial phenomenon based on the formation of chylomicron remnants, low-density lipoproteins (LDL), and the uptake of these cholesterol and TG rich molecules by arterial cells. Oxidation of LDL and phagocytic immune system cells have been implicated in the mechanism involving fatty streaks and occlusion of the arterial lumen. The isoflavones diadzein and genistein in soy-protein have been associated with oxidative resistance of LDL due to their antioxidant activity. The purpose of this study was to determine if the oxidative resistance of postprandial LDL is enhanced with the consumption of a meal containing 39.0 g of soy protein (80 mg aglycone isoflavones) vs 39.9 g milk protein (0 mg aglycone isoflavones) in combination with a high carbohydrate meal. Fifteen healthy male subjects participated in a double-blind, crossover feeding study in the Nutrition Research Lab (NRL) at Montana State University. Subject’s height, weight, and baseline blood draw were completed before consuming the challenge meal consisting of 2 high carbohydrate muffins and a soy or milk protein shake (899 calories, 22% fat, 58.6% CHO, 19.4%). Blood samples were collected by venipuncture postprandially at hours 2, 4, and 6. Isolated LDL was subjected to ex vivo copper-induced oxidation. Initial absorbance, lag time, and propagation rate were calculated for each time point. Results indicated no significant difference (p>0.05) between the protein treatments or their interaction on LDL oxidation parameters. Additional research is needed to ascertain the function of soy in prevention of CVD, specifically in the postprandial state.