The Big Picture
Before reading this article, it is best to first read this short piece so that you understand the fundamentals of muscle growth.
If you decide not to read the linked article, the following is a very concise summary:
For muscle growth to occur, there are three requisites that must occur concurrently and consistently over time:
- An anabolic stimulus (i.e. strength training)
- An energy surplus (i.e. increased caloric intake to create a positive energy balance)
- The raw materials to build extra muscle tissue (i.e. increased protein intake to create a positive net protein balance)
This article focuses on the latter-most requisite – protein intake.
Protein: The Building Block of Muscle Tissue
Protein is the most essential macronutrient for muscle growth. Fat and carbohydrates, while less essential to the specific process of muscle growth, are also crucial because they contribute to a caloric surplus and provide fuel for other essential metabolic needs. However, protein is the only macronutrient that can be used as a “building block” for muscle tissue. Protein and carbohydrates can be transformed into stored fat tissue, and protein and fat can be transformed into carbohydrates for energy, but carbohydrates and fat cannot be transformed into protein. The exclusive nature of protein makes it a prime commodity in the business of muscle growth.
The anabolic journey of protein can be summarized as “Complex-to-Simple-to-Complex”. When dietary protein is ingested through the mouth, it exists as a collection of complex molecules. As protein undergoes digestion in the stomach and small intestine, it gets broken down into simpler amino acids, which are the constituents of complex protein molecules. The fun-sized amino acids are highly mobile and can easily cross the barrier between the small intestine and the blood stream. After crossing into the flow of the blood stream, the amino acids travel peripherally through the circulatory system and get delivered to muscle tissue where they are utilized in muscle protein synthesis – the most fundamental process of muscle growth that occurs on a cellular level. During muscle protein synthesis, amino acids undergo a process of accretion and get transformed back into complex protein molecules, but this time in the form of muscle tissue. Complex-to-Simple-to-Complex.
† Individual unmodified photo of circulatory system by Eric Villalba.
†† Individual unmodified micrograph of skeletal striated muscle (right fibularis longus), HPS stain, by Copyright © 2013 Michael Bonert.
You are free to share and adapt this image as per the CC BY-SA 3.0.
The Concept of Net Protein Balance
A positive net energy balance is necessary for muscle growth to occur. That is, you must consume enough food so that your daily caloric intake exceeds your daily energy expenditure. In addition to having an overall caloric requirement for muscle growth, the body has a specific protein requirement as well.
To understand why the body needs a certain amount of protein for muscle growth, we will use the same “net gain of the system” concept.
- Muscle Protein Synthesis (MPS) = The metabolic process of increasing muscle tissue
- Muscle Protein Breakdown (MPB) = The metabolic process of reducing muscle tissue
- Net Protein Balance (NPB) = MPS - MPB
- If MPS exceeds MPB, the NPB is positive (+), and anabolism occurs (i.e. net gain in muscle tissue)
- If MPB exceeds MPS, the NPB is negative (-), and catabolism occurs (i.e. net loss in muscle tissue)
MPS and MPB are continuous physiological processes, meaning that the body is simultaneously building up and breaking down muscle tissue at all times . The net result between these two opposing processes is what dictates muscle gain or muscle loss. It should be noted that MPB is not bad, as it is necessary to breakdown old, damaged muscle tissue in order to replace it with healthier, more resilient tissue . Muscle growth is optimized by increasing MPS and minimizing MPB.
By understanding the relationship between muscle protein synthesis, muscle protein breakdown, and net protein balance, we understand that the body requires a certain amount of protein to elicit a net gain in muscle tissue. The question now is, “What is the optimal amount of protein to eat in order to facilitate muscle growth?” The rest of this article attempts to answer that question by breaking down current scientific evidence on the matter.
Optimizing Protein Consumption for Muscle Growth
There is no hard and fast rule that dictates how much dietary protein is required to optimize muscle growth, and much debate surrounds this topic [2-5]. Optimal protein consumption is based on several factors that can vary considerably between individuals. Such factors include: goals, genetics, gender, age, bodyweight, body composition, overall physical activity, and mode of training (e.g. endurance-based or strength-based).
The debate surrounding protein requirement is somewhat inane, as much of it is based on a confusion of concepts. Some scientists define protein requirement as the amount of protein necessary to prevent deficiency, and others define it as the amount of protein necessary to optimize function [2,5,6].
Definition of Preventing Deficiency
- The minimum amount of dietary protein necessary to maintain lean body mass and basic metabolic processes involving protein and amino acids.
Definition of Optimization (from Phillips et al., 2007)
The amount of dietary protein necessary to:
"1.) Support an athlete’s ability to repair and replace any damaged proteins (resulting potentially from oxidative stress or mechanical disruption);
2.) Adaptively “remodel” proteins in structures such as muscle, bone, tendon, and ligaments to better withstand the stress and strain imposed by training and competition;
3.) Maintain optimal function of all metabolic pathways in which amino acids are participatory intermediates (which includes being oxidative fuels);
4.) Support increments in lean mass, if desired;
5.) Support an optimally functioning immune system; and
6.) Support the optimal rate of production of all plasma proteins required for optimally physiological function, would the previous estimates of protein intake represent an optimal level?"
Clearly, if the goal is to optimize function, protein intake will be greater than the amount necessary to prevent deficiency. It’s also important to note that the comparatively low protein recommendations for deficiency prevention are largely based on a method called “nitrogen balance”, which has been shown to be an unreliable way of measuring protein needs [4-6]. Since this article investigates the relationship between protein consumption and muscle growth, we will focus on protein requirement for optimized function.
First, let’s start with the absolute basics. Individuals attempting to gain muscle mass through a combination of strength training and a hyper-caloric diet require more protein than endurance athletes and sedentary individuals [2-4,6-8].
Strength training challenges the musculoskeletal system more than any other form of exercise, resulting in increased protein needs for:
- Muscle fiber repair and maintenance (higher levels of muscle mass require more protein for maintenance) [2,3,7]
- Muscle fiber growth (muscle growth requires a positive net protein balance, which is created by increasing protein intake) [2,3,7]
- Connective tissue remodeling (i.e. tendon, ligament, and bone restructuring, resulting in increased stress-tolerance of said tissues) [2,7]
Based on the most recent scientific evidence, the recommended range of protein intake for adults wanting to optimize muscle growth is 1.2–2.0 grams of protein per kilogram of bodyweight [3,4,7], which approximately equates conveniently to 0.5–1.0 grams of protein per pound of bodyweight. The higher end of the range is recommended for individuals whose primary training goal is gaining muscle mass. For the sake of comparison, the recommended protein intake for preventing deficiency in adults is 0.8 grams of protein per kilogram of bodyweight, or approximately 0.35 grams of protein per pound of bodyweight . The upper end of the recommended range of protein intake for optimizing muscle growth is almost three times greater than the recommended intake for preventing deficiency.
There are claims that consuming large amounts of protein can be detrimental to health by excessively taxing the kidneys. However, for adults in good health with no pre-existing kidney problems, there is no evidence that a high protein diet is associated with adverse health outcomes [2,4]. High protein consumption may become a problem if other nutrients (e.g. fat, carbohydrates, fiber, and vitamin-dense foods like vegetables) are forgone to allow for excessive protein ingestion (i.e. 40% or more of total caloric intake). In other words, there is only so much food that can be eaten in a day, and overall nutritional balance should not be undermined in favor of eating extreme amounts of protein. For example, protein is the building block of muscle tissue, but carbohydrates are the primary fuel source for resistance training, and therefore both macronutrients must be consumed in sufficient amounts. As we know from the beginning of this article, resistance training and protein intake play equally important roles in the process of muscle growth.
Specific Protein Considerations for Optimizing Muscle Growth
Overall protein consumption (i.e. grams eaten per day) is a foundational consideration if your goal is to gain lean body mass, but there are several other factors to take into account if you truly want to optimize protein intake for muscle growth. This section breaks down such factors. The following information is intended for those seeking optimization; it may seem logistically intensive and perhaps challenging to practically implement on a daily basis. Please know that the following considerations are not necessary to achieve gains in lean body mass, but they are necessary if your goal is to take full advantage of your body’s capacity to build muscle.
Consideration I: Type of Protein
The majority of your daily protein intake should come from high-quality sources . The concentration of essential amino acids (EAAs) is what differentiates high-quality protein from low-quality. There are 20 total amino acids, 9 of which are deemed essential because the body cannot synthesize them. The only way the body has access to EAAs is through diet. If a protein source is made up of ~40% or more of EAAs, and contains all 9 EAAs, it is considered high-quality . EAAs are important because they play building block roles in the process of muscle protein synthesis (MPS). In addition to being the construction material for muscle tissue, EAAs also stimulate MPS , particularly the EAA leucine [2-4,7,8,10].
The following is a list of high-quality protein sources that are commonly recommended in scientific literature [2,3,6-8]:
- Lean Animal Meat
- Whey Protein Powder Supplement
- Casein Protein Powder Supplement
- Greek Yogurt
- Soy Beans
- Soy Protein Powder Supplement
*There is evidence suggesting that milk is a particularly effective source of protein for stimulating MPS because it gets efficiently delivered to muscle tissue once ingested, and it contains a relatively high concentration of the amino acid leucine [7,11].
The above list contains examples of high-quality protein sources; it is not meant to be comprehensive.
Consideration II: Timing
Protein should be consumed within 1 hour after a strength training session in order to provide fatigued muscles with the vital nutrients for anabolism/recovery [2-4,6,7,12,13]. Whey is a particularly effective form of protein for post-workout replenishment because it is fast-digesting and provides readily available nutrients for MPS [7,11].
Strength training and amino acid consumption stimulate MPS independently from each other. However, if consumed within 24 hours of strength training, amino acids deliver a more powerful stimulus to MPS than if strength training were not performed . This is a “whole is greater than the sum of its parts” kind of situation. Practically speaking, protein ingestion is a more vital consideration on training days compared to recovery days because the body is in a more anabolic state in the 24 hours after a training session. This is especially true for individuals who train in the morning. For example, if one trains at 7am every other day, their prime anabolic window is open until 7am the next morning after a training day. Therefore, care should be taken to ensure sufficient protein consumption on training days to capitalize on the synergistic anabolic effect of combining strength training with amino acid intake.
Considerations III & IV: Spacing Meals & Optimal Dose of Protein
Previously it was stated that the recommended range of protein intake for adults wanting to optimize muscle growth is approximately 0.5–1.0 grams of protein per pound of bodyweight [3,4,7]. This means that a 150 lb person wanting to gain muscle mass should consume between 75 and 150 grams of protein per day. It is intuitively obvious that one shouldn’t eat 150 grams of protein, equivalent to over a pound of cooked chicken breast, in one sitting. Clearly, one’s total daily protein intake should not be eaten in one fell swoop, but then the question is, “What is the best way to spread out one’s daily protein intake?”
Thankfully, science and common sense come together on the answer – protein intake should be spread out as evenly as possible through the day in order to frequently stimulate MPS . Simply eating protein stimulates MPS, regardless of resistance training , and the most effective protein dose for maximal stimulation appears to be 20-25 grams per meal [2,3,6,7]. Protein consumption beyond this recommended range does not appear to further stimulate MPS, although larger individuals will need to consume more than 20-25 grams of protein per meal due to their greater metabolic needs for muscle maintenance/growth.
By providing your body with evenly-spaced doses of protein that maximally stimulate MPS, you can achieve a greater positive net protein balance. Practically speaking, at least 20-25 grams of protein should be consumed with every meal, and meals should occur 3-6 times per day depending on lifestyle factors and total caloric & protein needs.
The following is a list that illustrates what 20-25 grams of high-quality protein looks like from different sources:
- A medium-sized chicken breast (cooked)
- A medium-sized hamburger patty (cooked)
- A medium-sized salmon filet (cooked)
- 1 large scoop of whey protein powder or soy protein powder
- 3-4 eggs
- 1 cup of fat-free Greek yogurt
- 3 cups of milk
Consideration V: Co-ingestion of Carbohydrates
From the information provided thus far, we know that a post-workout meal should occur within an hour after training and include at least 20-25 grams of protein, but there is another important consideration – co-ingestion of carbohydrates. When carbohydrates are consumed, insulin is released into the blood stream. One of insulin’s primary responsibilities is to travel through the circulatory system collecting glucose (i.e. blood sugar) and shuttling it into liver and muscle cells to be used for energy later on. However, insulin doesn’t just manage glucose levels in the blood; it is a complex hormone that causes many effects throughout the body, two of which are stimulation of MPS and suppression of MPB . When protein and carbohydrates are consumed together, they create a compounded anabolic effect that stimulates MPS more than consuming protein by itself.
In addition, post-workout carbohydrate consumption is critical for replenishing glycogen, a complex aggregation of glucose molecules that is stored in liver and muscle tissue. During intense strength training, glycogen stores are used as a primary energy source and consequently become depleted. Therefore, carbohydrate ingestion fulfills two important purposes – replenishment of energy stores and stimulation of MPS.
Consideration VI: Optimized Post-Workout Drink
- Consumed within 1 hour of strength training [2-4,6,7,12,13]
- Consuming protein right after training provides much needed nutrients for MPS, and it also helps prevent MPB
- Contains high-quality and fast-digesting protein, such as whey [7,11]
- High-quality proteins contain all the essential amino acids used in MPS, and fast-digestion means speedy delivery of amino acids to muscle cells
- Contains at least 20-25 grams of protein [2,3,6,7]
- This is the dose of protein that maximizes MPS
- Contains simple carbohydrates to cause a release of insulin
- Insulin further stimulates MPS and suppresses MPB 
The combination of the above factors creates a synergistic intensification of MPS, which optimizes muscle growth.
This article provides a comprehensive, evidence-based explanation of how to manipulate protein consumption to elicit optimal gains in muscle mass, assuming that one concurrently engages in a strength training program and eats enough calories to create a positive energy balance. If your primary goal is to increase muscle mass, don’t let your hard work in the gym go to waste by not consuming protein in an optimal way.
When it comes to muscle growth, no macronutrient gets as much attention as protein. This is with good reason, as protein provides the molecular building blocks for muscle tissue. Since protein is put at a premium in muscle growth, its consumption gets much attention. Resultantly, there are many opinions on what the optimal range of protein intake is. The U.S. recommended daily allowance (RDA) of protein is quite low (~0.35 grams per pound of bodyweight) because it is meant to prevent deficiency . Conversely, parts of the bodybuilding community promote a protein intake that is quite high (as much as 3.0 grams of protein per pound of bodyweight), likely due to an obsessive concern about gaining as much muscle mass as possible. However, as with many things, the answer appears to lie somewhere in the middle. Current scientific evidence suggests that the optimal range of protein intake for muscle growth in adults is approximately 0.5 – 1.0 grams of protein per pound of bodyweight [3,4,7].
- Muscle growth requires a combination of strength training + caloric surplus + positive net protein balance.
- Strength training is the most effective form of exercise for stimulating muscle growth.
- Individuals seeking to gain muscle mass by engaging in a strength training program require more protein than endurance athletes and sedentary individuals [2-4,6-8].
- Those wanting to gain muscle should follow protein recommendations based on optimization of function, not prevention of deficiency.
- The recommended range of protein intake for optimizing muscle growth is 0.5 – 1.0 grams of protein per pound of bodyweight [3,4,7].
- Those whose primary training goal is gaining muscle mass should consume protein according to the higher end of the recommended range.
- There is no evidence suggesting that a high protein diet increases the risk of adverse health outcomes, except perhaps in those with pre-existing kidney dysfunction [2,4].
- The majority of protein intake should consist of high-quality sources such as dairy, lean animal meat, eggs, and soy [2,3,6-8].
- Each meal should contain at least 20-25 grams of high-quality protein [2,3,6,7].
- Protein and simple carbohydrates should be consumed within an hour after a training session to maximize muscle growth and recovery [2-4,6,7,12,13].
- Protein and calorie intake is particularly important in the 24 hours following a training session, as the body is in a heightened anabolic state during that time .
- Meals should be spaced evenly throughout the day to provide the body with frequent stimulation of muscle protein synthesis .
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Retrieved from https://www.nal.usda.gov/sites/default/files/fnic_uploads/energy_full_report.pdf
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