The following is a guest post on Exercise and Protein Requirements from CrossFit Sixth City member Maria Linda Burola. Originally created as a graduated project in Nutrition at Case Western Reserve University, Maria hopes that like her this post helps us better understand the protein requirements for the exercise-minded person.

Exercise and Protein Requirements

The athletic environment is a growing community filled with positive reinforcement, support, and motivation. Healthcare providers encourage adding at least 30 minutes of exercise a day as the benefits are ubiquitous. By introducing physical activity, a sedentary individual could decrease stress, increase lean muscle mass, and prevent the risk of developing a chronic disease. According to the American College of Sports Medicine and the Academy of Nutrition and Dietetics, anyone engaging in physical exercise will exhibit their best performance with adequate energy intake and optimal nutrition (Thomas, Erdman, & Burke 2016). Despite this statement, the definition of optimal nutrition in regards to protein is a debate. The recommended dietary allowance (RDA) of protein intake is set at 0.8g of protein per kg of body weight per day while the average macro nutrient distribution range (AMDR) is set at 10-35% of energy needs (Fukagawa 2014). The RDA may be appropriate for the average sedentary adult, however, since it does not take into account differences in physical activity. The literature provides controversial information for the disparity of protein in sedentary, active, and professional athletic individuals. Therefore, a nutritional assessment may be more appropriate for all individuals to evaluate goals in retrospect to dietary protein intake.

Redefining the protein requirements for individuals engaging in physical activity provides universal guidelines for practitioners to follow. Benefits of consuming dietary protein above the RDA included reduced skeletal muscle loss and increased muscle mass (Carbone, McClung, & Pasiakos, 2012). When questioned by sports medicine for changes to the RDA, the Institute of Medicine stated, “no additional dietary protein is suggested for healthy adults undertaking resistance or endurance exercise” (Rodriguez, Di Marco, & Langley, 2009), thus beginning an argument for customized dietary protein recommendations for active individuals to be above the standard requirement level. Dietary protein metabolically triggers the synthesis of contractile and metabolic proteins during exercise (Thomas et al., 2016). This suggests that athletes would need to consume enough dietary protein to maintain optimal physical performance as well as support metabolic adaptation, repair, and remodeling. Dietary protein comes from a variety of sources; however, whey, casein, egg, and soy, relative to other vegetarian protein sources, are the most effective sources of complete protein that increase muscle strength and body composition (Rodriguez et al., 2009; Stuart M Phillips, 2012; Thomas et al., 2016; Wolfe & Miller, 2008). Increasing protein intake using these complete sources and whole foods can improve adaptive response to training (Jager et al., 2017; Thomas et al., 2016; Wolfe & Miller, 2008). The use of protein supplements is a more accessible method to meeting dietary needs; however, all prospective athletes should receive adequate counseling prior to ingesting these types of protein, allowing them to understand the unique variations of consuming enough protein through diet alone.

In 2001, a review of studies from 1970-1999 investigated the relationship of protein nutrition and exercise training. Both aerobic and strength conditioning found that increasing dietary protein intake will increase muscle mass (Evans 2001). When examining the dietary protein with resistance exercise, researchers found that high protein consumption correlated with greater hypertrophic responses (Evan 2001). In addition, increasing the intensity of resistance training significantly enhanced muscle hypertrophy in all individuals when increasing dietary protein intake to 1.6g/kg/d, regardless of age (Evans 2001). These findings were brought into consideration when D’Lugos et al. found cyclists who measured increased muscle fiber cross-sectional areas after intensified training with carbohydrate and protein. Studies suggested that co-ingestion of carbohydrate and protein can enhance performance compared to carbohydrate-only intake (D’Lugos, Luden, Faller, Akers, McKenzie & Saunders, 2016). Carbohydrate and protein supplementation impacted skeletal muscle and heart rate responses during a period of heavy training and recovery (D’Lugos et al., 2016). In regards to building muscle mass, high protein intake proved to contribute to hypertrophy. If individuals who start exercise fail to increase their dietary protein intake, they will lose the added body composition benefits from their exercise.

Age related differences in protein metabolism are documented in the literature, yet the data supports no differences in dietary protein needs of the elderly compared to the young (Cardon-Thomas, Riviere, Tieges, & Greig, 2017 & Jager et al., 2017 & Liao et al., 2017). In fact, the evidence is copious when supporting protein and amino acids increasing the rate of protein synthesis following physical activity for all ages (Liao et al., 2017). In Denmark, 48 older adults, ages 72 years old +/-2, were recruited to play team sports with different protein intake after exercise (Vorup et al., 2017). The volunteers were split into high and low protein groups as well as a control group to measure muscle mass, strength, physical function as well as LDL, cholesterol, triglycerides, and CRP levels. The average intake of all participants was to be around 1.2g/kg in the high protein group versus 0.9g/kg in the low protein group (Vorup et al., 2017). After a 12-week exercise intervention, the high protein group found gains in leg muscle mass and an improved performance time (Vorup et al., 2017). Strength and physical functions were greater in the high protein group most likely due to increased muscle mass. The serum blood levels had significant decreases in cholesterol and LDL thus proving that higher protein intake in older individuals affects more than body composition. Since the low protein group consumed the protein RDA with fewer changes, higher protein is, as a result, recommended for active individuals regardless of age for maximum benefits.

Timing of protein intake may directly contribute to strength gains if ingested prior to sleep. In 2015, the Journal of Nutrition questioned if protein ingestion before sleep would increase muscle mass and strength gains for a group of healthy young men performing resistance training. The study recruited 44 young men, ages 21-23, and enrolled them in a 12-week resistance training program completed in the evenings (Snijders et al., 2015). One group consumed a beverage containing 27.5 grams of protein, 15 grams of carbohydrate, and 0.1 grams of fat, while the other group had a non-calorie placebo (Snijders et al., 2015).

Muscle fiber and protein recovery

The protein group increased muscle strength with a greater percentage of type II muscle fiber size (Snijders et al., 2015). Table A and B present the differences with Type I and II muscle fibers before and after the 12 weeks. Table C and D show the tremendous difference from placebo to protein supplementation groups. The science behind this phenomena is simple. Protein ingestion after exercise stimulated protein synthesis and inhibited muscle protein breakdown leading to net muscle protein accretion during the acute stages of post exercise recovery (Arentson-Lantz, Clairmont, Paddon-Jones, Tremblay, & Elango, 2015; Fielding & Parkington, 2002; Verdijk et al., 2009). Both groups found that after three months of resistance-type exercise, there are increases in skeletal muscle mass, strength, and muscle fiber size (Snijders et al., 2015). However, the data supports ingesting protein prior to sleep as it will increase muscle protein accretion throughout overnight rest. Athletes looking to maximize their strength gains may choose to modify their protein timing.

Protein intake has been measured with nitrogen balance studies; however, a re-evaluation of the pre-existing data may be performed by a study using indicator amino acid oxidation technique. The indicator amino acid oxidation technique study from 2007 suggested a reanalysis of the preexisting nitrogen balance data to reassess dietary protein requirements (Humayun, Elango, Ball, & Pencharz, 2007). Following this initial study, Bandegan et al. evaluated the dietary protein requirements in bodybuilders during a non-training day. Since bodybuilders prioritize increasing fat-free mass, researchers hypothesized using the IAAO would give a different value than the nitrogen balance study results (Bandegan et al., 2017). Eight young men were observed on rest days, their normal intake of dietary protein ranging from 1.8-3.2g/kg/d, three times the RDA (Bandegan et al., 2017). After using the IAAO technique, the mean dietary requirement for the bodybuilders with the upper 95% CI break point was at 2.2g/kg/d (Bandegan et al., 2017). This suggested that the RDA for protein of male bodybuilders should be near 2.2g/kg/d, which is two and a half times the current RDA for dietary protein (Bandegan et al., 2017). Table 4 compared the individuals from this study to sedentary males only to find the bodybuilders to have higher protein requirements (Bandegan et al., 2017). Following suit, additional studies using the IAAO method estimated protein requirements up to 1.4-1.7 in female athletes performing variable-intensity intermittent exercise (Wooding et al., 2017). These increases suggests our testing mechanism may be giving incorrect information.

Bodybuilders versus sedentary men

Before higher ranges of protein recommendations can be released, studies began to evaluate what percentage of the athletic population is consuming this amount. In 2017, the Netherlands released a study that recruited 553 athletes who provided 24 hour dietary recalls to analyze the differences between dietary intakes in sports (Wardenaar et al., 2017). Since many speculations are made that strength athletes have higher protein intake than endurance or team athletes, researchers began to evaluate the nutritional intake in all sport disciplines for accurate evidence to support these claims. From 2012-2015, elite and sub-elite athletes were asked to complete 24-hour recalls and questionnaires about nutritional supplement use. The findings revealed that almost all athletes met the estimated average requirement for protein (0.8g/kg); however, the prevalence of intake below the sports nutrition recommendation (1.2g/kg) was seen in all disciplines (Wardenaar et al., 2017). In women, team athletes consumed less protein per kg body weight than endurance and strength athletes, while in men, no significant differences were detected (Wardenaar et al., 2017). The absolute protein intake seems sufficient in most athletes; however, a substantial population of athletes did not meet this recommendation. There was no difference with protein intake found in any of the male groups, whereas individual females had an increased protein intake with endurance and strength but not with the team athletes (Wardenaar et al., 2017). Even with these increases in protein for certain athletic groups, females were found to be 20% lower in dietary protein intake as recommended by the sports nutrition recommendations.

The International Society of Sports Nutrition took a stand on the protein and exercise topic to lay down guidelines for their athletic readers. Based on the current literature, they confirmed that a majority of exercising individuals should consume at minimum 1.4-2.0 grams of protein per kg of body weight to achieve benefits with body composition and performance (Jager et al., 2017). If the individual is healthy and exercising, they should not be concerned with consuming this amount of protein; however, preference is choosing whole foods with high levels of complete protein over protein supplements (Thomas et al., 2016). Research demonstrates that protein supplements can increase rate of muscle protein synthesis, decrease muscle protein degradation, and aid in recovery from exercise; yet, the essential amino acids that promote this response can be found in whole foods (Jager et al., 2017). These findings support the Journal of The Academy of Nutrition and Dietetics article that promote daily protein intake goals with a regular spread of moderate amounts of high quality protein across the day (Jager et al., 2017 & Thomas et al., 2016). The range differs slightly from 1.2-2.0g/kg/day; however, it encompasses all types of physical activity, athletic goals, and energy considerations.

Recent studies have redefined the protein recommendations to include all active individuals regardless of athletic status or age. There is now solid rationale for recommending daily protein intakes that are well above the RDA to maximize metabolic adaptation to training. Quality of protein is important to achieve hypertrophy of muscle for individuals participating in physical activity. The range of 1.2-2.0 grams of protein per kilogram per day offers clinicians variability to customize their suggestions with different physical activity groups. Although the discrepancy still exists for the new dietary protein range for exercise fanatics, the future meta-analysis of studies can help pull common themes to amend the current RDA. Exercise enthusiasts should continue to consult with their practitioners to identify the most appropriate amount of protein in relation to the physical activity goals. In addition, practitioners should review the literature prior to consulting with a patient who is about to commence exercising. Awareness of the current updated guidelines and literature is key to providing excellent care for any patient.


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