The body’s need for protein
The influence of physical activity on the conservation of proteins in the body can be regarded as probable, based on the results of three studies using the stable isotope technique.
The need for protein during aerobic training
In the experiment, young untrained participants underwent aerobic training for 4 weeks, with a protein intake of 0.88 g per kg of body weight per day. As a result, an increase in nitrogen balance, a decrease in the level of leucine oxidation, and a tendency to leucine accumulation were noted. In general, the authors noted an improvement in the utilization of proteins by the body, as well as an increase in nitrogen levels as a response to aerobic exercise by participants with a stable body weight level.
The need for protein during strength training
In another long-term experiment, young untrained participants underwent strength training for 12 weeks. At the same time, the proportion of consumed protein in them was 15% of the daily diet in energy equivalent. Assessment of the total protein cycle was carried out for 5 days during controlled diets (1.2 g per kg of body weight per day), before the training period, and after it. As a result of training, a decrease in the rate of synthesis and breakdown of proteins was noted, while the total protein balance and the level of nitrogen in the urine increased.
In the third study, no correlation was found between regular intake of proteins (as well as the intake of other macronutrients) and the hypertrophic response exhibited by the muscles of the legs of the participants after 16 weeks of strength training. Moreover, in general, the difference in the individual hypertrophic response reached 60%.
The average protein intake ranged from 0.97 to 1.07 g per kg of body weight per day, and did not differ among the groups that showed an increased, moderate or reduced response. Thus, this amount of protein consumed was sufficient to provide a wide range of muscle response, and as a result, insufficient muscle response cannot be explained only by a non-optimal diet. Nevertheless, data analysis suggests that the level of total calorie intake in all three clusters indicated in the study could differ significantly from the real one.
Thus, the data of this study confirm the fact that physical exercises have a beneficial effect on the integrity of proteins within the body, and also that after a long period of training, the need for protein decreases rather than grow. However, different individuals may exhibit different responses to exercise.
Evidence regarding the effect of exercise on the body’s need for proteins is worth categorizing as inconclusive. In all three studies reviewed, protein intake was equal to or higher than the recommended daily value for healthy adults (RDA). Similar results would be obtained if the level of protein intake was below the recommended norm, it remains unclear. Most studies of the relationship between physical activity and protein metabolism are short-term in nature or concern the use of specific amino acid or protein supplements. For this reason, they were not included in this review. Today, there is a lack of long-term studies of the effect of (moderate) physical activity on protein metabolism.
In general, despite the fact that physical exercise can positively affect the safety of proteins, the body’s response in one case or another may differ, which cannot be explained by the intake of proteins alone. Our assessment is consistent with the position of the American Dietetic Association, the Dietetic Association of Canada, and the American College of Sports Medicine, which states that the body’s need for proteins (including the body of athletes) can be fully covered from traditional food sources without resorting to the use of various protein or amino acid supplements. This applies to healthy adults who lead an active lifestyle. However, the above organizations recommend increased protein intake for strength athletes, as well as endurance athletes (from 1.2 to 1.7 g per kg of body weight per day).
Most of the findings from large North American studies can be attributed to the following points:
· The actual need of the body for proteins is determined by the minimum amount necessary to balance the loss of nitrogen in the body;
· The amount of protein needed, calculated on the basis of nitrogen balance, does not necessarily reflect the optimal value for an individual’s health, since this factor should be evaluated not only from a quantitative point of view;
· Protein intake beyond the recommended range can reduce the risk of coronary heart disease, improve bone health, and help lower blood pressure. Further studies are required to verify the validity of this assumption, to study the possible mechanisms of the relationship, and also to establish the necessary doses;
· The main task remains to determine the optimal long-term doses of consumed proteins in the context of maintaining the health of the body.
As a result, we were not able to find high-quality studies, the results of which would help to revise the existing classical criterion for calculating the optimal amount of protein – namely: the recommended value is the amount of protein that is necessary to balance the loss of nitrogen in the body.
Calculation of Daily Protein Requirement
Remember that in all cases it is ideal to get 50% protein from sports nutrition, the remaining 50% – from food.
· When gaining muscle mass:
Low in body fat: 250 – 300 g;
Fat and prone to overweight: 150 – 200 g.
Low in body fat: 250 – 300 g;
Fat and prone to overweight: 180 – 250 g.
· When losing weight:
For men: 130 – 160 g;
For women: 100 – 140 g.
· When working for cutting (relief):
Low in body fat: 200 – 250 g;
Fat and prone to overweight: 180 – 220 g.
Low in body fat: 150-200 g;
Fat and prone to overweight: 140 – 180 g.