While carbohydrates may be the most popular macronutrient, the one with the most important role in our bodies is held by protein. It is probably a given that protein is important for our training recovery and lean muscle mass, but in this newsletter, we will be reviewing protein metabolism a bit further in order to better understand it’s a critical role in our physiological processes.

 

The protein we consume is comprised of 20 amino acids. 8 of these are essential amino acids (EAAs) and the remaining 12 are considered non-essential. EAAs are called ‘essential’ because we cannot synthesize them in our bodies and must get them through our diets. The overall purpose of protein digestion is to free these amino acids from the foods we eat. There is a constant flow and exchange of amino acids in the blood, liver, and bodily tissues – the liver being an important center for amino acid metabolism.

 

The primary end goal of protein digestion includes:

  1. Forming structural proteins (skeletal muscle)

  2. Forming functional proteins (enzymes)

  3. Forming signaling proteins (hormones)

 

A multitude of cells in our body will use only the amount of amino acids they need to meet their protein requirements, and no more. The rest of the amino acids that are not utilized for protein synthesis or any other metabolic pathways will be broken down (deaminated), and their carbon skeletons are oxidized, reconstructed into another amino acid, or used for other important pathways such as glucose (gluconeogenesis) or fatty acid synthesis.


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Training Adaptations

The major role of protein is different than that of carbs and fat in that its consumption serves to promote training and muscular adaptations that come from our diet and exercise programs. If we are aiming to maximize both our diet and training, we must be in a positive net muscle protein balance.

 

Net muscle protein balance = muscle protein synthesis – muscle protein breakdown (aka protein consumed > protein excreted)

 

How do we do this? By getting enough protein each day! Surprisingly (but not really haha), the RDA’s recommendation for daily protein is pretty low for athletic populations (0.8 g/kg/day). For active individuals, a good guideline for protein is a range of 1.5-2.0 g/kg/day. For those looking to maximize muscle hypertrophy, the range of 1.8-2.5g/kg/day has been studied recently with great success. This alone is not the only consideration to have on protein since many more factors are important such as protein quality, overall energy intake, types and intensity of training, or the timing of protein intake. These are things that are unique to the individual and worth looking into as well.
 

Protein Quality

Just getting protein alone doesn’t guarantee stimulation of our pathways to muscle protein synthesis. The most important variable to consider is our protein quality. By high protein quality, I am referring to protein sources that contain enough of the EAA leucine in order to stimulate muscle protein synthesis. Based on the available research, having a leucine content of ~20-45 mg/kg body mass per meal maximizes muscle protein synthesis. This is because leucine is able to specifically activate key regulatory factors in our muscle protein synthesis pathways (Akt/mTOR pathway), thus enhancing the process of muscle protein synthesis. Leucine is an important consideration to keep in mind when choosing protein sources and structuring meals.

 

To dive a bit further for a moment, the Akt/mTOR pathway is the main regulatory pathway responsible for our increased rates of muscle protein synthesis. Major compounds that regulate translation initiation (the process of muscle protein synthesis) have the same upstream regulator found in this pathway, known as the mammalian target of rapamycin (mTOR). Through the activation of mTOR, mTOR then phosphorylates the major compounds contributing to translation initiation, thus increasing protein translation (muscle protein synthesis). Evidence supports that leucine is able to phosphorylate these regulatory compounds, causing a rise in muscle protein synthesis rates.

 

Beef, casein, poultry, egg, and fish are about 8-9% leucine. Whey protein isolate is about 12%


Guidelines

Generally, we recommend anywhere from 20-30 grams of high quality protein per meal. For larger individuals with higher protein intakes, they will need more protein per meal to adequately hit their targets. Excess protein has not been shown yet to have any additional direct benefits on performance adaptations but there is preliminary research showing higher protein intakes promoted more muscle growth and no additional fat gain, even with 400+ extra calories coming from protein (1). Protein is also the most satiating macronutrient, so if adherence is a problem due to hunger, higher daily protein targets will assist you with sticking to your diet.

 

As for the timing of protein throughout the day, small amounts of protein (less than 20g) spread out is not optimal for maximizing muscle protein synthesis. According to the current research, dividing high-quality protein evenly among 4-5 meals/day is considered an optimal method for maximizing rates of muscle protein synthesis.

 

Protein plays so many major roles in our recovery, training, and muscular adaptations. If you have any questions on protein recommendations or trustworthy products, please let us know! We are happy to help. In the final part 3 of this series, we’ll get into fat metabolism, how we process it, and its role in the physiology of an active population.