Protein intake: guidelines
A recent revision of nutrient intake reference levels (LARN, 2014) reports an intake of 0.9 g/kg body weight for sedentary people aged 18 to 59 years and 1.1 g/kg for older people. These values may not be valid for athletes, because it is necessary to remember that, in addition to normal turnover, proteins are used to repair muscle damage after physical activity and to build new muscle mass.
Scientific evidence suggests that dietary protein is essential to support metabolic adaptation, repair, remodeling and turnover, and therefore daily amounts range from 1.2 to 2.0 g/kg body weight1.
- Higher amounts are only “allocated” for a short time and/or when the power supply is reduced.
- Recent guidelines state that protein intake is 1.2–1.4 g/kg/day in endurance events and team sports, 1.4–1.8 g/kg/day in strength events, and 1.4 g /kg/day in sports activities in which athletes must adhere to weight limits (combat sports, weightlifting) 2.
- Protein needs and training
Another aspect to consider is that it is not advisable to be too rigid in the division into “strength and/or strength activities” and “endurance activities”: the introduction of a protein diet must follow a training regimen that can change.
The need for protein varies according to the nature of the training.
An open question concerns the amount of protein needed to support the increase in muscle mass after strength activity or to cover oxidative losses in endurance subjects.
Actually, the protein quota of a subject performing strength activities must serve to cover the needs for the growth of muscle tissue and the repair of damage due to the physical activity itself, while for the subject performing endurance activities, proteins are known to serve to support part of the energy costs of the activity: expenditure is around 2-5% during light to moderate exercise (brisk walking, Nordic walking) and 5-8% during high-intensity resistance exercise (marathon training, cross-country skiing) 1.
We know that an exercised subject, compared to a sedentary subject or a subject who begins to perform physical activity, uses energy-providing substrates to support physical activity in a different way: for example, he uses more fats than carbohydrates, because adaptation phenomena occur that allow the shift of substrates.
The same is true for protein metabolism, as adaptation mechanisms are observed in the trained subject so that the metabolic utilization of amino acids is more efficient than in the sedentary subject.
The degree of training also affects the need for protein
Importance of protein intake timing
- Protein needs, as well as carbohydrate needs, in a sports subject must be assessed before, during and after physical activity.
- Given that muscle protein synthesis occurs only at the end of physical activity and protein digestion takes a relatively long time, it is evident that protein administration before and during activity is of little importance, with exceptions.
It is especially important to provide protein at the end of training.
So let’s take into account the intake of proteins at the end of physical activity, with the understanding that the introduction of these proteins will have all the already mentioned roles: increase in muscle mass, angiogenesis, repair of damaged fibers.
It has been shown that the timing of protein intake is very important, and at the end of physical activity, an “anabolic window” opens, i.e. a period when the metabolic pathways of synthesis are favored. At the end of training, it is advisable to take protein as soon as possible, because the possibility of protein synthesis is maximum in the first 7-8 hours, it decreases by 50% in the next 24 hours, but it can last up to 48 hours, even if it is of lower intensity2.
Protein synthesis requires that all twenty amino acids involved in synthesis be present and that they reach the blood as soon as possible.