Protein and strength training have a long history. Those who hit the gym regularly have been pounding protein shakes for decades in order to build strength and muscle mass as quickly as possible.
But when it comes to weight lifting and protein intake, how much does it help? How much protein should I take? How much is too much?
Several studies have been published that investigate the role of protein intake on strength training. Some with conflicting results.
Therefore, some of the best approaches to take are looking at critical reviews and meta-analyses.
These studies attempt to summarize the state of the science and for meta-analyses, group several studies’ datasets together in order to increase the sample size and render more statistically relevant results.
One critical review published in the Journal of Nutrition reviewed the role that protein and/or amino acid intake plays in muscle growth during strength training. Here are some highlights.
Excess weight, particularly those with a large waist circumference, are at a higher risk of several health complications and chronic diseases. Thus, losing weight can be a positive goal for those who can stand to lose excess pounds.
But it is better to lose excess fat mass - not muscle mass.
Supplementing your diet with protein during weight loss, however, can help maintain lean muscle mass.
In addition to young and middle-aged individuals looking to shed pounds, this is particularly important for senior citizens who may or may not be intentionally trying to lose weight. Preserving lean muscle can help maintain mobility and prevent falls.
To build muscle, your body needs to replace and grow new cells. And growing new cells requires the production (synthesis) of new proteins. Taking a relatively simplified view, this process has two essential requirements:
The body is constantly experiencing “protein turnover.” This simply means that new proteins are being produced while old proteins are being broken down.
The act of exercising, and in particular weight training, stimulates protein synthesis regardless of your protein intake.
So why eat protein?
In the period just after resistance training (0 – 1 hour), muscle tissue becomes more sensitive to nutrition.
Dietary protein adds ingredients the body needs for protein synthesis and extends the duration the body spends building new protein.
When it comes to weight lifting, protein intake increases muscle mass. But only up to a point.
Another recent meta-analysis showed that increased muscle mass gains trend with increasing protein intake up to around 1.6 grams per kilogram of body weight. Protein intake above this plateau did not produce additional gains in muscle mass.
But in addition to quantity, protein quality matters too.
Protein quality refers to the composition of amino acids present in the protein source, as well as its bioavailability.
In other words, can you actually digest and absorb all of the essential amino acids required for muscle growth and a balanced diet?
Your cells undergo stress during exercise that trigger several metabolic pathways. Some create energy. Others synthesize muscle protein.
Leucine is one particularly important amino acid that happens to take part in pathway important for muscle protein synthesis.
Leucine is one particular amino acid that acts as a strong trigger for protein synthesis.
mTORC1 (mechanistic target of rapamycin complex (1) is a protein complex with a role in controlling protein synthesis. Leucine plays a role in activating mTORC1 signaling. Thus, leucine helps directly trigger a key mechanism in the MPS pathway. Adding leucine to post-exercise protein increases MPS in a dose-dependent manner. That means, increasing leucine content increases mTORC1 signaling and thus increases MPS activation.
But there appears to be a threshold for leucine too.
Meeting this threshold quantity, or trigger, for leucine (~1.8 g/day) appears to elicit the maximum muscle protein synthesis achievable. Adding more doesn’t appear to add any extra benefit.
This means, even if protein intake is high but leucine is low, your body won’t be maximizing muscle protein synthesis. Only when the leucine threshold is reached will your body fully stimulate mTORC1 signaling and maximize this process.
Interestingly, current reviews and meta-analyses show a minimal to non-existent improvement to strength for those who supplement with protein after strength training over the long-term.
Presumably, our bodies adapt. Over time, the rate of muscle protein synthesis declines and your muscle tissue’s sensitivity to amino acid absorption declines as well.
For those all-too-familiar with plateaus and stalled progress, understanding your body’s response to repeated exercises may help direct your future workout plans. But as we are learning in many aspects of nutrition and fitness, the results vary wildly per person.
Our response to dietary protein is highly individualized. Some of us respond well, others really well, but many seem to experience little or no response at all.
It turns out, there is significant variability between an individual’s response to protein post-exercise. Individual characteristics, such as genetics, gut flora, epigenetics, and environmental factors, may be producing responders and non-responders to dietary protein. In fact, their results suggested ~25% of the population may not respond at all to protein after acute exercise!
For those looking to maximize muscle growth, its important to measure your progress. As the old saying goes, “you can’t improve what you don’t measure.”
So track your growth, track your strength, track your protein intake, and analyze your findings to optimize your plan to meet your goals.
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