Protein in athlete diet – a current state of knowledge

 In Articles, Diet, Supplementation

Protein is a key building block in the assessment of the human body’s needs. This is due to the complicated protein metabolism, which is characterized by “protein turnover“, that is, the ratio of synthesis to the breakdown of body proteins. The transformation of proteins is closely related to the energy demand – with insufficient supply of carbohydrates and fats, proteins are used as an alternative source of energy. Proteins are the basic, functional structures of every cell of the human body. They form the structure of enzymes, hormones, antibodies, contractile myofibrillar proteins (eg actin and myosin, which allow muscle contraction), structural proteins (eg collagen), mitochondrial proteins as basic structures generating ATP and other biologically active compounds. (1)

The current recommendations in Poland for adult women and men at the RDA level are 0.9 g / kg (2), PRI according to EFSA is 0.83 g / kg (3), RDA in the United States is 0.8 g / kg BM (4) Demand is calculated based on calculations of the nitrogen balance for the majority of the population. Direct measurement of muscle protein synthesis has a clear advantage over nitrogen balance estimates, because it allows the evaluation of interventions in the target tissue, i.e. skeletal muscles. (1)

In physically active people and athletes, the need for protein is much higher due to the need to cover the needs related to the increase of lean body mass and repair of muscle damage caused by physical exercise. Resistance training induces increased protein turnover (synthesis and degradation) for hours or even days after completion of the training session (5), which results from the need to replace damaged old proteins with new ones. One of the most important aspects of post-workout regeneration is the consumption of wholesome proteins in order to ensure an adequate supply of free amino acids and a positive balance of muscle proteins. In the case of insufficient supply of protein, increased protein turnover caused by muscle damage intensifies the breakdown of other proteins to cover the demand. (5)

Based on the current literature and the current position of the International Society of Nutrition in Sport regarding protein intake in training people (6), I propose the following guidelines for protein intake in healthy, physically active people:

  • Training stimulus, in particular resistance exercise and protein intake, stimulate muscle protein synthesis (MPS) and act synergistically when protein intake occurs before or after training.
  • In order to build or maintain muscle mass through a positive balance of muscle proteins, the total daily intake of protein should oscillate within the limits of 1.4-2.0 g / kg BM / day. (6) Such value should be sufficient for most people.
  • Muscle protein synthesis occurs less efficiently during the energy deficit. (7, 8) To maintain maximum muscle retention during energy deficit, it is worth using a higher protein supply in the range of 2.3-3.1 / kg of lean body mass (FFM) / day (9) In addition, the protein and fiber exerts the greatest effect thermal food (TEF) and the most affect the level of satiety which is beneficial during the energy deficit.
  • There is new evidence suggesting that higher protein intake (> 3.0 g / kg m. C. / day) may have a positive effect on the body composition of trained individuals (ie, promote fat loss) (6)
  • Recommendations for athletes regarding optimal protein intake per serving to maximize MPS are mixed and depend on many factors. General recommendations are 0.25 g kg BM / high protein meal or absolute dose 20-40 g. In a review from 2018, Aragon and Schoenfeld suggested that in order to maximize anabolism, protein should be consumed at 0.4 g / kg mc / meal with a minimum of 4 meals a day to reach a minimum of 1.6 g / kg BM / day. (10)
  • Athletes should focus mainly on wholesome sources of protein (meat, fish, seafood, eggs, dairy products). Individual protein portions should contain 700-3000 or more mg of leucine and above all a full set of essential exogenous amino acids (EAA) for optimal stimulation of muscle protein synthesis (MPS). (6) Contrary to common theory, the energy balance should include all types of proteins, both animal and vegetable.
  • Different types and quality of the protein may affect the bioavailability of amino acids after ingesting a portion of protein. Fast digested proteins containing large amounts of essential amino acids (EAA) and the proper leucine content are the most effective at maximally stimulating MPS. (19, 20) Such proteins include mainly whey proteins: hydrolysates, isolates and concentrates. (23, 24, 25) Proteins derived from lean products will be digested faster than proteins derived from fatter products which will be associated with a more rapid increase in amino acids in the plasma. The absorption kinetics, however, will be affected by the entire meal composition.
  • According to the ISSN position in 2017, portions of protein should ideally be evenly distributed every 3-4 hours during the day. (6) On the other hand, in the 2016 study, Moro et al. Showed that the use of TRF (time-restricted feeding) diets, in this case 16/8, does not affect the loss of lean body mass, while increasing fat loss and improving certain metabolic markers compared to a diet with more meals (11) Therefore, the distribution of a portion of protein per day remains an individual matter. (10)
  • The optimal period of time for taking a portion of protein is an individual matter, because the benefits are recorded both from the supply of protein before and after training. The anabolic effect of the training lasts at least 24 hours (12), although it seems to weaken with time. Tang et al. In 2008 proved that in people trained post-workout intake of protein can stimulate MPS more efficiently 4 hours after training than 28 hours. after workout. (34)
  • People who are physically active can cover the daily need for protein by eating foods. Supplementation is a practical way to ensure the right quality and quantity of protein, while limiting the consumption of calories, especially for athletes with a busy training schedule. (6)
  • The effect of insulin on MPS depends on its ability to increase the availability of amino acids. (13) However, the effect of insulin reducing the breakdown of muscle protein occurs at moderate levels of insulin (~ 15-30 μIU / ml) (14), which can be achieved by ingesting a 45-gram dose of the whey protein isolate alone (15)
  • Endurance athletes should focus primarily on getting the right carbohydrate intake. The addition of protein can help balance muscle damage and promote post-workout regeneration. (16, 17, 18, 21, 22)
  • Branched chain amino acids (BCAAs) are leucine, valine and isoleucine. The multimillion industry of dietary supplements has been launching BCAA-containing products for years, informing consumers that they trigger an anabolic response in humans stimulated by the stimulation of muscle protein synthesis (MPS). The current literature proves, however, that BCAA supplementation without a full available pool of free exogenous amino acids (EAA) is not able to influence MPS favorably. (35)
  • Casein proteins are characterized by slow absorption kinetics. Their consumption results in slow but stable absorption of amino acids, which guarantees a stable MPS, without a sharp peak. Consumption of casein protein before bedtime (30-40 g) provides an increase in nocturnal MPS and metabolic rate without affecting lipolysis (6)

In general opinion, there are many concerns about high-protein diet. Among some “specialists” and representatives of learning the old date, you can hear that high protein diets cause damage to the kidneys and “acidification” of the body. Of course, people with kidney failure will benefit from introducing low protein diets. (26) However, it has never been found that the use of high-protein diets, even long-term, could harm healthy, well-trained individuals. Published reviews on this topic consistently show that increased protein intake by professional athletes and active people does not cause any signs of liver or kidney damage. (27, 28) The WHO issued a report that also found no relationship between high-protein diet and kidney disease. (29) Antonio et al. published a series of trials that used a high protein diet (~ 3.4-4.4 g / kg / day) and consistently reported no adverse effects, even if the trial lasted one year. (30, 31, 32, 33)

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