Protein Requirements for Athletes
To first understand how much protein your athletes need daily, you must first understand the requirements of those that aren’t regularly active (sedentary). The current recommended dietary allowance (RDA) of protein is 0.8 g/kg (0.36g/lb) body weight for sedentary adults (American College of Sports Medicine (ACSM) et al., 2009).
However, a more recent analysis of the same data notes a value of 1.0g/kg (0.46g/lb) body weight for the average sedentary adult (Elango et al., 2010). Also, further analysis of daily requirements for sedentary adults using a more accurate amino acid analysis technique (Indicator Amino Acid Oxidation) found that a value of 1.2g/kg (0.55g/lb) body weight for sedentary adults.
So overall, there exists a range in the literature when it comes to sedentary adults (0.8-1.2g/kg [0.36-0.55g/lb] body mass). This should be the absolute bare minimum that your athletes ingest daily, but as athletes require more than the typical sedentary adult, read on to the next sections to determine their individual needs based upon various situations.
Sedentary Adults: (0.8-1.2g/kg [0.36-0.55g/lb] body mass)
When it comes to athletes, “cookie-cutter” recommendations aren’t the best ones to follow or consider. Endurance athletes are no different, protein requirements vary depending upon training status, exercise intensity, workout duration, and dietary intake (Kerksick, 2019). The best way to approach these variations is to classify athletes as recreational athletes (those predominantly performing low- to moderate-intensity endurance exercise), modestly trained athletes, and elite endurance athletes (Tarnopolsky, 2004).
Multiple studies have found that a recreational-level of endurance training does not alter the amount of protein needed for that athlete (Tarnopolsky, 2004; el-Khoury et al., 1997). One such study by el-Khoury et al. (1997), found that a protein intake of 1.0g/kg (0.46g/lb) was adequate for recreationally active young men.
Recreational Endurance Athletes: (1.0g/kg [0.46g/lb] body mass)
For modestly trained athletes, multiple studies have reported protein intakes of 0.94g/kg, 0.86g/kg, and 1.0g/kg as being inadequate (Meredith et al., 1989; Phillips et al., 1993; Lamont et al., 1990). These protein intakes resulted in net negative protein balances following exercise. Recommendations of 37.5% higher than the RDA of protein (1.1g/kg [0.5g/lb]) are made following analysis of the three mentioned studies (Tarnopolsky, 2004).
Modestly Trained Endurance Athletes: (1.1g/kg [0.5g/lb] body mass)
In terms of elite endurance athletes, a small collection of studies has examined their protein requirements. One found that 1.6g/kg (0.73g/lb) was needed in six elite male endurance athletes (Tarnopolsky et al., 1988). Another advised that 1.46g/kg (0.66g/lb) was optimal for 5 elite endurance runners. A further study by (Brouns et al., 1989) found a protein intake range of 1.5-1.8g/kg (0.68-0.82g/lb) was optimal within a Tour de France simulation (Brouns et al., 1989).
If an endurance athlete is interested in improving their endurance exercise performance, diets high in protein appear to offer no benefit. Still, they may help reduce psychological stress and declines in performance commonly seen during blocks on high-intensity training (Witard et al., 2011).
Elite Endurance Athletes: (1.46-1.8g/kg [0.66-0.82g/lb] body mass)
Strength & Power Athletes
Acute resistance exercise increases rates of both muscle protein synthesis and muscle protein breakdown (Biolo et al., 1995; Phillips et al., 1997). And ingestion of protein following resistance exercise is required for a positive protein balance (Miller et al., 2003). Regular resistance exercise along with adequate protein ingestion results in a positive protein balance which then leads to increases in lean body mass, something that strength/power athletes often prioritise (Tarnopolsky et al., 1988).
Regular resistance exercise is also a source of stress and trauma that requires greater protein availability to recover (Tarnopolsky et al., 1992). This theoretical framework suggests that strength/power athletes would have an increased requirement of dietary protein when compared to the needs of sedentary individuals (Tarnopolsky et al., 1988; Lemon et al., 1992; Tarnopolsky et al., 1992).
A meta-analysis involving 680 participants across 22 published studies has also demonstrated a positive impact of protein supplementation on improvements in fat-free mass and leg strength when compared to a placebo in both young and old populations (Cermak et al., 2012).
As with endurance athletes, multiple factors impact protein balance and protein requirements for strength/power athletes; however, training history and training status appear to significantly impact the efficiency with which the body processes protein (Phillips et al., 1997; Phillips et al., 2002).
An example of this is the near-universal finding of untrained or unaccustomed individuals needing increased amounts of dietary protein. But when resistance training becomes habitual (>4 days/week for at least 2 months), the body processes protein more efficiently which has led some studies to report that more trained individuals have lesser protein requirements (1.4g/kg [0.64g/lb] (Phillips et al., 1997; Phillips et al., 2002).
Novice Strength Athletes (0-6 months training): (1.4g/kg [0.64g/lb] body mass)
Tarnopolsky et al. (1992) analysed the protein requirements for American football and rugby players by comparing low (0.86g/kg [0.39g/lb]), moderate (1.4 g/kg [0.64g/lb]), and high (2.4 g/kg [1.1g/lb] amounts of dietary protein intakes.
They concluded that the lowest intake compromised protein synthesis when compared to the moderate and high intakes and that while the moderate protein intake amounted to neutral protein balance, they recommended one standard deviation above at 1.76g/kg [0.8g/lb]. Other studies have also suggested that protein intakes ranging from 1.4-1.7g/kg [0.64-0.77g/lb] may be required for strength/power athletes (Lemon et al., 1992; Tarnopolsky et al., 1992).
American Football/Rugby Players: (1.4-1.76g/kg [0.64-0.8g/lb] body mass)
The International Society of Sports Nutrition (ISSN) has also published position statements on the protein requirements of athletes, and they note 1.4-2.0g/kg [0.64-0.91g/lb] for resistance-trained athletes (Campbell et al., 2007). And a consensus statement from ACSM et al. (2009) recommended protein intakes ranging from 1.2-1.7g/kg [0.55-0.77g/lb].
International Consensus Statements: (1.2-2.0g/kg [0.55-0.91g/lb] body mass)
A fascinating and recent study was a systematic review, meta-analysis, and meta-regression by Morton et al. (2018) on the effects of protein supplementation on resistance training adaptations. Data from the review, including 49 previous studies and 1863 participants, showed that protein supplementation significantly improved fat-free mass gains, maximal strength, muscle fibre diameter, and cross-sectional area of femur thigh mass (Morton et al., 2018). The authors also noted that a protein intake higher than 1.62g/kg [0.74g/lb] showed no further improvements in fat-free mass gain.
Two other studies by Antonio et al. (2014, 2015) explored the impact of high-protein diets (at a caloric surplus) on body mass and composition. Their first intervention had 30 resistance-trained individuals continue following their typical exercise training program alongside either a control or high-protein diet (4.4g/kg [2g/lb]) (Antonio et al., 2014). While the 30 participants were at a caloric surplus for 8 weeks, no changes in body mass, fat mass, fat-free mass, or per cent body fat were found when compared to the control group.
Their follow-up intervention one year later dealt with 48 resistance-trained men and women and had them follow a prescribed split-body, 5 days/week resistance training program for 8 weeks (Antonio et al., 2015). The participants followed either their normal diet of 2.3g/kg [1.05g/lb] of protein or a high-protein diet of 3.4g/kg [1.55g/lb]. Ultimately, the researchers found similar changes in strength, and the control group saw a significant increase in body mass.
In contrast, the high-protein group saw a greater decrease in fat mass and per cent body fat (Antonio et al., 2015). They theorised that those changes in fat-free mass they saw in both of the groups were the result of a different training stimulus. They call back to their previous 2014 intervention and note that merely increasing protein intake to over 4g/kg [1.82g/lb] did not see equal increases in fat-free mass as their 2015 intervention which included resistance-training.
Intermediate Strength Athletes (6 months – 2 years training): (1.62-1.76g/kg [0.64-0.8g/lb] body mass)