Many myths exist about the impact of increased soy protein intake. Knowing the truth about soy protein is important to making the right sports nutrition choices.
FALSE. Multiple research studies following professional male athletes with high levels of soy protein intake show no changes in testosterone levels. Hormone levels and fertility rates also were unaffected.
Similar studies were conducted with female gymnasts, male and female rowers and world-class swimmers. No negative effects were seen, blood hormone levels were normal, yet subjects gained lean body mass and athletic performance.
FALSE. Soy does not contain the hormone estrogen, but it does contain isoflavones, also known as phytoestrogens which function differently from estrogen in the body. Phytoestrogens are not the same as estrogen, but their chemical structure is somewhat similar. There is no scientific evidence that typical use of soy protein exerts any unwanted effects on hormone levels, muscle development, strength training or physical characteristics of the body. Numerous studies with healthy, young men show that soy protein does not increase estrogen concentrations in the blood.
Soy protein has proven health benefits for both men and women. Research linking a diet low in saturated fat and cholesterol and high in soy protein with
heart health was significant enough that the Food & Drug Administration approved a health claim in 1999. Additional studies link soy protein consumption to reduced rate of prostate cancer. A meta-analysis of these studies indicates that consumption of foods containing soy protein may reduce the risk of prostate cancer by up to 26 percent.
FALSE. Isolated soy protein is highly digestible. Its digestibility value of 95 to 98 percent is higher than many commonly consumed animal proteins. Certain soy forms, such as soy flour, contain both protein and carbohydrates, which can be more difficult to digest. However, most sports nutrition products use isolated soy protein, which is easily digestible.
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