Protein is an important macronutrient in the diet of endurance exercise athletes and an essential dietary nutrient that promotes body growth and maintenance, but different protein sources differ in quality.
Providing all the essentials
After water, protein is the most abundant substance in the body – present in every cell and tissue including muscle. The body continually breaks down protein, so getting an adequate amount of protein in the diet is essential.
Soy protein is the only widely available vegetable protein that provides all the essential amino acids, in the proper amounts, making it a high quality protein comparable in quality to milk, meat and eggs.
A study published in the Journal of Agricultural and Food Chemistry evaluated the PDCAAS of four different processed soy ingredients, including three soy protein isolates and one soy protein concentrate. Isolated SUPRO® soy proteins achieved a PDCAAS value of 1.00 or 100%, which is the highest value possible to achieve. This information confirms that soy protein provides adequate amounts of all essential amino acids in appropriate amounts for children aged two years and older, as well as adults.
CLINICAL STUDIES CONFIRM THE BENEFITS OF SOYBEAN AND DAIRY PROTEIN FOR OPTIMIZED MUSCLE GAINS
Comparative studies between soy protein isolate and whey protein showed similar increases in muscle mass when given as supplements after resistance exercise. Many sports nutrition supplements primarily provide whey protein because it is quick to digest and can provide BCAAs quickly; however, this supply rapidly dwindles.
The idea of mixing soy and dairy proteins, first proposed by Paul, explored the potential benefits of combining different protein sources to support muscle recovery (Figure 5).
Soy, a protein that is digested at an intermediate rate, can be combined with fast-digesting whey protein and slow-digesting casein to maintain a steady supply of amino acids to the muscles to promote significant muscle growth. . 
Clinical studies evaluating soy and dairy protein blends show a potentially unique effect of prolonging amino acid supply to muscles to marked extents and suggest additional muscle growth during resistance training. This was first investigated in a preclinical study that tested different blends of high quality proteins and isolated protein sources in an animal model, comparing changes in fractional muscle protein synthesis rates. Both single protein sources and blends of soy and dairy proteins increase muscle protein synthesis (MPS); however, only the mixture of soy and dairy proteins prolonged the time that PMS remained activated.
DuPont collaborated with leading physiology and nutrition researchers at the University of Texas to conduct a series of clinical studies looking at the effect of various protein sources and protein blends on muscle health. The first study investigated whether ingestion of a protein blend containing 25% SUPRO® soy protein, 25% whey protein and 50% casein, with different digestion rates, could generate extended muscle protein syntheses compared to just whey protein in healthy young subjects  with a mean age of 23 years.  Study participants consumed a protein supplement (either a soy-dairy protein blend or whey protein containing a total of 1.9 grams of leucine from protein sources) one hour after completing a resistance training session. leg extension.
The researchers found that the protein blend increased amino acid supply four hours after consumption compared to whey protein alone. Whey protein amino acids reached their maximum supply within the first 30 minutes after consumption and then decreased to below the level provided by the milk soy protein blend. Both groups had fractional protein synthesis rates (TSF) two hours after consuming the protein supplements, but only the soy and dairy protein mix continued to show an elevated TSF four hours after supplementation, suggesting that the mix may increase the anabolic window increasing both recovery and promoting muscle growth. (Figure 6).
Well-designed cross-sectional studies can provide insight into the short-term mechanical response to a single intervention. Long-term support for muscle maintenance can be assessed through well-controlled, longitudinal studies comparing different interventions. To assess the impact of protein supplementation after long-term resistance exercise, Reidy and colleagues conducted a three-month study in young men with a mean age of 25 years to determine whether a daily supplement with 22 grams of protein is of a blend of SUPRO® soy and dairy proteins or just whey protein, provided some advantage for strength and muscle growth compared to a calorically equal carbohydrate supplement (22 g maltodextrin). For this type of resistance training, it was expected that all subjects would gain approximately 1.5 kg of lean mass in 12 weeks.  Although all groups showed gains in lean body mass, the group consuming the soy-dairy protein blend had the greatest muscle gain. Specifically, the control group gained about 2kg of lean body mass, the whey protein only group gained about 2.3kg, while the soy protein, whey and casein blend group gained 2.9 kg. Interestingly, most of the lean body mass gain in the whey group and the control group occurred during the first six weeks of training; however, during the last six weeks of the study, the soy-dairy protein blend group gained twice as much lean body mass (1.0 kg vs. 0.5 kg control and whey group). Serum testosterone levels did not differ between the three groups at baseline, six weeks, or 12 weeks of study. (Figure 7)
*Source: DuPont Nutrition & Health Study – SOYBEAN PROTEIN: A HIGH QUALITY VEGETABLE PROTEIN – A scientific review supporting its role in weight management, muscle and cardiovascular health.
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