INTRODUCTION 

There is an abundance of nutritional information dispersed online by individuals with varying nutritional backgrounds and credentials. Unfortunately, the vast majority are not trained in disseminating and communicating nutritional science within the context it was intended. Therefore, the need for unbiased and evidence-based recommendations is essential. Here we aim to lay out an easy to follow breakdown of plant-based protein and some of the more important elements to consider and be aware of when designing a dietary strategy for muscle building, ENJOY 😃. 

Plant-based foods can and usually do contain all essential amino acids (EAA), although, some amino acids are in extremely low concentrations, meaning we do not have the adequate amount to stimulate muscle protein synthesis (muscle building). Therefore, some amino acids are seen as limiting in this regard, in which case would render the source incomplete if there was an insufficient amount of any EAA. In the real world, we rarely consume food in isolation, a varied and balanced diet should cover your bases and we will touch on this in more detail a little later. 

The quantity of food the body can absorb and the amino acid profile are the limiting factors for stimulating muscle protein synthesis, in the context of protein. Although we may be eating plenty of protein is it all digestible? Remember it's not what you eat, its what you can absorb and thereby use for biological processes such as muscle building that matters. Clearly, there are some inherent limitations to eating solely plant-based sources, however, with this in mind, we can plan around this to ensure we are where we need to be in terms of protein to maximise the muscle-building process. 

Strategies to increase overall protein consumption and co-ingest sources that are high in lysine, leucine and methionine (the main limiting EAA) in plant-based sources should be implemented, the next article will address this in more detail.

For now, remember leucine is mainly required for the stimulation of muscle building pathways, without this, we have not even started the machine to start building. As a quick refresher, shift your attention to Figure 1 below which categorises amino acids by essentiality. We need to ingest EAA via food as the body is incapable of producing them itself (lacks the enzymes), hence the term ESSENTIAL. 

Figure 1: Classification of Amino Acids by essentiality.

PLANT-BASED PROTEIN DIGESTIBILITY
 
The evidence is crystal clear with regard to plant-based protein sources having a lower quantity and available EAA for the body compared to animal sources. Therefore, both quantity and quality are two focal points for plant-based diets. Plant proteins are somewhere between 60-80% digestibility on average depending on the source, whereas animal-based sources have been consistently shown to have >90% digestibility.

This matters because it's not what's on the nutritional label that counts (20g protein per 100g serving), its what gets into circulation and ultimately incorporated into proteins and added to muscle tissue. The typical digestibility of some animal and plant sources are depicted in Figure 2 below. However, this is not something you should be overly worried about, although it should be known that this plays into how much protein you will absorb, it should be accounted for when setting protein targets. Meaning it may require a larger overall protein intake to account for the lower digestibility of plant-based sources. 
 

Figure 2: Protein digestibility of various protein sources. 
 
Plant protein powders are of great utility as the processing steps remove compounds called "anti-nutrients" which inhibit the aforementioned digestibility issues and accessibility of the protein. We see similar digestibility rates in plant-based powders when compared to animal-based powders due to the lower concentration of these compounds following production and also the protein is not tied or bound within a food matrix making it easier to access for the stomach enzymes.

PLANT-BASED PROTEIN & MUSCLE BUILDING 

Sufficient amounts of leucine (main amino acid responsible for stimulating the pathway) is needed to maximally stimulate muscle protein synthesis. If sufficient leucine is available and an inadequate amount of the remaining EAAs it's like shooting a gun without any bullets (we have stimulated the pathway but there is little to no essential amino acids available to start building protein structures and subsequent muscle tissue). Figure 3 below shows the varying essential amino acid content of protein sources, which provides a visual overview of why on plant-based diets it is more important to ingest a greater amount.  

The 9 EAA are the primary stimulatory agents which should highlight their importance. However, If we are interested in actually building the muscle all 20 amino acids are needed. Because our body can manufacture the other 11 amino acids we do not need to focus on these as intently. 

Figure 3: Essential amino acid content of different protein sources. 
 
There is one “uniquely important” amino acid as mentioned previously called Leucine. It is specifically needed to start the muscle-building process. 
 
Using a car to illustrate the concept - Leucine would be needed to start the engine (2.5-3g of leucine per meal) and the remaining AVAILABLE EAA (Figure 1, 8-10g per meal) will dictate the distance we can travel (muscle tissue we can build). 

Figure 4 below illustrates the leucine concentration in some typically consumed plant and animal food sources. However, it is important to note, muscle building is an expensive process, in one study where amino acids were continuously infused through the forearm and were readily available there was a drop off in protein synthesis. Meaning this process burns itself out even when the needed amino acids are available and then there is a  period where the muscle is unresponsive (due to depleted energy). Muscle protein synthesis slowly returns to baseline and energy stores are restored until it is stimulated again by another protein dose maybe 3 hours later.

This is where the concept of eating protein every 3-4 hours originates by the way. It is much more complex and nuanced than this oversimplification, however, for the purpose of this point, it works. 
 

Figure 4: Leucine content of plant and animal proteins. 
 
There are specific essential amino acids worth additional attention to ensure adequate amounts of each are consumed when following a plant-based diet. They are typically the limiting amino acids that inhibit the optimal synthesis of new proteins and muscle tissue. 

• Leucine:  Soybeans, oats, spinach, legumes (adzuki beans, lentils, mung beans, kidney beans, black beans), and peanuts
• Methionine: Peas, legumes, beans.
• Lysine: Wheat, rice and other cereal grains.

Combining sources such as rice and pea, as seen in Plantforce Synergy Protein, can be an effective strategy to complement limiting amino acids in both rice (lysine) and pea (methionine). Grain-legume combos work quite well as legumes contain the missing lysine and grains supply the methionine, then bumping up the overall quantity to reach the 2.5-3g leucine threshold would serve as optimal.

An example can be seen in Figure 5, where combining the same plant protein leads to an overload in the amino acids that are already in ample quantity. Using complementary protein sources (grain-legume) to supplement each other's inadequacies can provide an optimal balance of EAAs.

A protein is labelled complete when, proportionally to its overall amino-acid content, it has enough of each EAAs, this is based on the amino acid profile of muscle tissue. 

Figure 5: Example of combining protein sources and outcome. 

SPACE PROTEIN BETWEEN MEALS  

An even balance of protein intake at breakfast, lunch and dinner stimulates MPS more effective than eating the majority of daily protein during the evening meal which is typically observed in today's world.

Providing 20-40 g of high-quality protein every 3 hours stimulates MPS more than providing the same amount of protein in less regular doses (40 g every 6 hours), or more regular doses (10 g every 1.5 hours). Muscle protein synthesis rates are not only determined by total protein intake but also the pattern/distribution of protein intake, which is described in more detail - myth-busting article.

WHAT ARE THE ADVANTAGES OF PROTEIN POWDERS?

Obtaining all your protein from whole foods may be ideal, but it isn’t always practical:

1. Cost. Protein for protein, good protein powder is usually cheaper than whole foods.
2. Convenience. Cooking takes time. Eating whole foods takes time and you probably can’t do either in your office or at the gym. Protein powder is a quick, easy to carry, non-messy (mostly), portable solution.
3. Calories. In whole foods, protein comes with carbs and fat, you may reach your caloric intake before you reach your optimal protein intake, depending on diet, not atypical for plant-based diets.
4. Bioavailability. Protein powders bypass several issues of whole-food digestion and absorption that affect protein bioavailability.
5. Appetite. Protein is more filling than carbs or fat; some people have trouble hitting their quota because they get too full. These people will find it easier to chug a shake than eat a voluminous legume meal. This can especially benefit older people (who often have low appetite and problems to chew).

SUMMARY

Plant-based proteins are of lower quality than their animal-based counterpart, however, consuming a greater amount and eating a variety of sources can produce the same muscle growth as someone following an omnivorous diet. 
Look out for the next instalment where we show you the amino acid content of some typically consumed plant-based foods and some practical tips based on this.

• On a plant-based diet, we suggest increasing your protein intake up to 2.0-2.2g/kg to compensate for the lower bioavailability and essential amino acid content.
• Studies support eating 3-5 adequately dosed protein meals throughout the day will maximally stimulate muscle building pathways compared to larger infrequent meal patterns.
• Breakfast seems to be the mealtime that lacks protein, in comparison to lunch and dinner, it’s advised to distribute protein intake evenly over these meals times to optimize MPS. (Tip: Focus on Leucine being around 2.5-3g per meal to maximize the MPS response)
• Due to plant-based diets typically offering an incomplete spectrum of essential amino acids, it’s advised to compliment plant-protein sources to offset the limiting amino acids. Sources such as grains or beans can be combined. This is why we recommend protein powders that use more than one source (rice and pea). 
• Plant-based protein powders provide a convenient and high-quality option to achieve the full spectrum of essential amino acids. Great for those who may struggle to meet daily protein targets, specifically those who regularly engage in intense exercise as their needs are increased to support muscle recovery and their immune system.