| | Soy Protein vs Milk Protein | | by: Coach Hale - Sat Dec 05 2009, 02:46PM | From Bos et. al. 2003, Postprandial Kinetics of Dietary Amino Acids Are the Main Determinant of Their Metabolism after Soy or Milk Protein Ingestion in Humans:
Soy proteins have been shown to result in lower postprandial nitrogen retention than milk proteins, but the mechanisms underlying these differences have not been elucidated. To investigate this question, we measured the postprandial kinetics of the appearance of individual 15N-amino acids in the serum of healthy adults after the ingestion of either 15N-soy (n =  or 15N-milk proteins (n = in a mixed single meal (46 kJ/kg). The kinetics of total and dietary amino acids (AA) in the peripheral circulation were characterized by an earlier and higher peak after soy protein ingestion. Dietary AA levels peaked at 2.5 h in the soy group vs. 3.9 h in the milk group (P < 0.02). This time interval difference between groups was associated with a faster transfer of dietary N into urea in the soy group (peak at 3 vs. 4.75 h in the milk group, P < 0.005) and a higher level of incorporation into the serum protein pool from 3 to 8 h after the soy meal. The dietary AA pattern in the peripheral blood closely reflected the dietary protein AA pattern. Postprandial glucose, insulin, and glucagon levels and profiles did not differ between groups. Soy AA were digested more rapidly and were directed toward both deamination pathways and liver protein synthesis more than milk AA. We conclude that differences in the metabolic postprandial fates of soy and milk proteins are due mainly to differences in digestion kinetics; however, the AA composition of dietary proteins may also play a role.
“Soy protein has been shown to increase protein breakdown in animal and human Experiments” (Tipton 2009). Therefore, a high protein diet consisting of animal proteins might be more effective than a diet consisting of soy proteins, when the objective is retention or gains in body proteins.
From Wilkinson et. al. 2007, Consumption of fluid skim milk promotes greater muscle protein accretion after resistance exercise than does consumption of an isonitrogenous and isoenergetic soy-protein beverage:
BACKGROUND: Resistance exercise leads to net muscle protein accretion through a synergistic interaction of exercise and feeding. Proteins from different sources may differ in their ability to support muscle protein accretion because of different patterns of postprandial hyperaminoacidemia. OBJECTIVE: We examined the effect of consuming isonitrogenous, isoenergetic, and macronutrient-matched soy or milk beverages (18 g protein, 750 kJ) on protein kinetics and net muscle protein balance after resistance exercise in healthy young men. Our hypothesis was that soy ingestion would result in larger but transient hyperaminoacidemia compared with milk and that milk would promote a greater net balance because of lower but prolonged hyperaminoacidemia. DESIGN: Arterial-venous amino acid balance and muscle fractional synthesis rates were measured in young men who consumed fluid milk or a soy-protein beverage in a crossover design after a bout of resistance exercise. RESULTS: Ingestion of both soy and milk resulted in a positive net protein balance. Analysis of area under the net balance curves indicated an overall greater net balance after milk ingestion (P < 0.05). The fractional synthesis rate in muscle was also greater after milk consumption (0.10 +/- 0.01%/h) than after soy consumption (0.07 +/- 0.01%/h; P = 0.05). CONCLUSIONS: Milk-based proteins promote muscle protein accretion to a greater extent than do soy-based proteins when consumed after resistance exercise. The consumption of either milk or soy protein with resistance training promotes muscle mass maintenance and gains, but chronic consumption of milk proteins after resistance exercise likely supports a more rapid lean mass accrual.
Milk protein is a better choice than soy if the objective is to maximize muscular gains.
Hartman et. al. 2007, concluded, “that chronic postexercise consumption of milk promotes greater hypertrophy during the early stages of resistance training in novice weightlifters when compared with isoenergetic soy or carbohydrate consumption.”
Why chose soy over milk, maybe because soy is healthier? Not according to tons of anecdotal evidence and scientific data.
The following quote is from the American Heart Association Science advisory (2006), “no benefit is evident on HDL cholesterol, triglycerides, lipoprotein (a), or blood pressure. Thus, the direct cardiovascular health benefit of soy protein or isoflavone supplements is minimal at best. Soy protein or isoflavones have not been shown to improve vasomotor symptoms of menopause, and results are mixed with regard to the slowing of postmenopausal bone loss. The efficacy and safety of soy isoflavones for preventing or treating cancer of the breast, endometrium, and prostate are not established; evidence from clinical trials is meager and cautionary with regard to a possible adverse effect. For this reason, use of isoflavone supplements in food or pills is not recommended.”
Consuming a moderate amount of Soy is probably not going to hurt most people, although high levels of intake might be harmful to health
thanks,
Coach Hale
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