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Can keratin supplementation improve body composition and cycling performance in endurance-trained men?

Getting your protein from feathers and hooves doesn't sound very tasty. Nor is it practical, since we can't digest them. However, sulfur-rich keratin can be extracted from these livestock-processing byproducts. Does it have any practical advantages over casein?

Study under review: The effect of chronic soluble keratin supplementation in physically active individuals on body composition, blood parameters and cycling performance

Introduction

Keratins are a class of fibrous proteins serving as the main structural constituent of feathers, horns, hooves, and hair. Historically, keratins have been considered a waste product[1] from processing livestock to meat due to their indigestibility[2]. However, a patented[3] highly digestible (83% digestibility in vivo) keratin protein supplement has recently been developed that overcomes this limitation.

The patented keratin product is rich in the sulphur-containing amino acid cysteine (primarily as cysteic acid), which is important for the synthesis of glutathione and taurine[4] in the body. One study[5] in rats found that replacing 50% of dietary casein protein with this patented keratin product increased blood hematocrit and hemoglobin content, tended to improve lean to fat mass ratio, and increased liver taurine content. However, glutathione levels were not affected.

Taurine is the most abundant free amino acid in the body, and plays important roles in numerous essential biological processes, including muscle contraction and relaxation[6], lipid metabolism[7], and, potentially, muscle protein synthesis[8]. Some research[9] has found taurine supplementation to improve time to exhaustion and maximum workload in recreationally trained men, and other research has observed a reduction in exercise-induced muscle damage[10] and exercise-induced oxidative stress[9].

Since keratin supplementation potentially has the ability to increase the glutathione and taurine levels in the body, it has been hypothesized[11] that supplementation may improve exercise performance and enhance training adaptations. Additionally, since blood concentrations of erythrocytes and hemoglobin are significant limiting factors[12] in oxygen transport during exercise, keratin’s ability to increase hematocrit and hemoglobin in rats[5] may benefit[13] endurance exercise performance as laid out in Figure 1. However, research examining the effects of keratin supplementation is scarce in animals and non-existent in humans.

If the above changes can be induced in humans, then keratin protein may be a cheap and effective protein source for people aiming to improve body composition and endurance performance. The study under review was the first to evaluate the effects of supplementation with the patented keratin product in endurance-trained men.

Keratins are fibrous proteins that make up hair, hooves, feathers, and horns. They have a low digestibility and are traditionally considered a waste product of animal processing plants. However, a patented and digestible keratin protein supplement has been made, which is rich in sulfur-containing amino acids that may benefit endurance exercise performance. The study under review was the first to evaluate the effects of keratin protein in humans, specifically endurance-trained men.

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