“Goods” and “bads” of extra protein in sports
While Dietary Reference Intakes for protein are 0.8g protein per kg for adults, data suggest athletes may need more depending on their sport, particularly strength-training athletes (1). Research also indicates that even non-athletes who weight train may benefit from the added protein (2). Endurance exercise sports such as cycling and running increase protein turnover, including a lot more oxidation amino acids, so it is suggested that extra protein would also be wise (3;4).
However, many athletes often exceed intake required (5). While the positive balance may not affect competitiveness, excessiveness does not encourage further muscle growth or strength gain (5). It should also be noted that strength-training itself also encourages improved utilization of dietary protein possibly reducing need of added protein (5). When consumed with carbohydrate, net protein balance during and after endurance exercise is improved, but there is little evidence of actual improved performance due to the extra protein (3). There is also little evidence that the extra protein will stimulate muscle growth or strength (6).
Because daily requirements for protein are set by amount of protein lost, any extra protein should be added to make up for the loss and to maintain nitrogen balance (5). Protein intake that is excessive can lead to potential complications such as in the kidneys (if disease is onset) (7-10) and possible bone fracture if acidosis occurs (11).
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