Efficacy and consequences of very-high-protein diets for athletes and exercisers

Abstract

Athletes and exercisers have utilised high-protein diets for centuries. The objective of this review is to examine the evidence for the efficacy and potential dangers of high-protein diets. One important factor to consider is the definition of a 'high-protein diet'. There are several ways to consider protein content of a diet. The composition of the diet can be determined as the absolute amount of the protein (or other nutrient of interest), the % of total energy (calories) as protein and the amount of protein ingested per kg of body weight. Many athletes consume very high amounts of protein. High-protein diets most often are associated with muscle hypertrophy and strength, but now also are advocated for weight loss and recovery from intense exercise or injuries. Prolonged intake of a large amount of protein has been associated with potential dangers, such as bone mineral loss and kidney damage. In otherwise healthy individuals, there is little evidence that high protein intake is dangerous. However, kidney damage may be an issue for individuals with already existing kidney dysfunction. Increased protein intake necessarily means that overall energy intake must increase or consumption of either carbohydrate or fat must decrease. In conclusion, high protein intake may be appropriate for some athletes, but there are potential negative consequences that must be carefully considered before adopting such a diet. In particular, care must be taken to ensure that there is sufficient intake of other nutrients to support the training load

Optimal Protein Intake in Athletes

“…However, muscle hypertrophy can occur at protein levels as low as 1.2 g/kg/ day [25]. The beneficial effects of increased protein consumption seem to plateau well below the level consumed by many athletes [9].…”

“…However, the extent to which this excess is beneficial is minimal as even 2.4 g/kg/day may be excessive [9,21,26]. Additionally, research shows that subjects who strength train regularly adapt to decrease protein turnover, increase retention, and increase the efficiency of amino acid utilization [25,27]. This further emphasizes the point that protein needs will be initially much higher, but as the body's efficiency for protein utilization increases, required protein may decrease [27].…”

“…The National Athletic Trainers' Association's recommendations adopt a "food first" philosophy in which it is stressed that trainers and other professionals should assess an athlete's nutrition status and assess for any required changes in diet before any other adjustments are made [46]. Additionally, Tipton [25] has pointed out that if an athlete is to increase protein intake but maintain constant calories, he or she must decrease intake of fat or carbohydrates. Tipton stresses the importance of carbohydrates for fueling exercise and notes that decreasing them may inhibit optimal performance [25].…”

Effectiveness of Whey Protein Supplement in Resistance Trained Individuals

“…These differences in digestive properties are likely to contribute to the different patterns of AA concentrations that have been observed after ingestion of whey or casein protein [24,38]. Therefore, casein has been termed as "slow", and whey has been termed as "fast" protein [39,40].…”

“…Although, each protein source has unique attributes that may convey specific nutritional advantages compared to the others (general health benefits, body weight management, gaining lean body mass, enhancing muscle recovery after exercise or stimulating muscular protein synthesis) the degree by which each source of protein can stimulate these process are related to different factors involving digestion rates, divergent AA profiles, pattern of ingestion and the metabolic state (rest or exercise) related to the timing of ingestion [39,40].…”