In order to answer the question as to when should protein be eaten, one must know how protein is digested. Protein is denatured (broken down) in stomach acid (1.5-3.5pH), and the bulk of protein is absorbed through the proximal jejunum, or the start of the small intestine, and even some protein is absorbed in the ileum (still in the small intestine but just below the jejunum). (Silk, Gimble, & Reese 1995). This part of the small intestine has a relatively small surface area which means that not all protein consumed will be digested. There is a limit to how much protein one can absorb within one meal. “Ingestion of more than 30 g of protein (10g of EAA) in a single meal does not further enhance the stimulation of muscle protein synthesis in young and elderly” (Symons, Moore, Wolfe, & Jones 2011). This means eating a large amount of protein all at once may not have the desired effect one might assume. Now that we know how much protein we should eat at one time, does it matter when in regards to our workout when we eat? Jager and Ralf found that “the optimal time period during which to ingest protein is likely a matter of individual tolerance, since benefits are derived from pre- or post-workout ingestion; however, the anabolic effect of exercise is long-lasting (at least 24 h), but likely diminishes with increasing time post-exercise” (Jager, Ralf et al. 2017). The idea of a maximum amount of absorbable protein being at 30g, leads to the question of when can I next eat protein that won’t be “wasted’ (it gets used as an energy source rather than amino acids, through a process called gluconeogenesis)? Jager and Ralf again lay out that “these protein doses should ideally be evenly distributed, every 3–4 h, across the day” (Jager, Ralf et al. 2017). We have, when and how much in a single meal, but how much does one need to eat for the whole day? Unsurprisingly the answer varies quite a based on activity levels and overall weight, height and muscle mass. That being said here are a few numbers you should know. How much to eat: Estimated Average Requirement is 0.66 g per kg body mass per day (g/kg/d). The RDA, however, is 0.8 g/kg/d, and reflects the minimum amount of dietary protein required to meet indispensable amino acid requirements, establish nitrogen balance, and prevent muscle mass loss for 97.5% of people (World Health Organization (0.83 g/kg/d)). These data are consistent with the contention that a protein source containing approximately 10 g of essential amino acids provides a maximal acute protein synthetic effect.  “The International Society for Sports Nutrition also recommends protein intake at levels higher than the RDA for physically active individuals (1.4–2.0 g/kg/d **)” which would look like a 100kg individual eating from 140-220g of protein a day. Protein supplementation beyond total protein intakes of 1.62 g/kg/day resulted in no further RET(resistance exercise training)-induced gains in FFM (fat free muscle mass) (Mortan, Murphy, Mckellar, et al., 2018). “Rapidly digested proteins that contain high proportions of essential amino acids (EAAs) and adequate leucine, are most effective in stimulating MPS.”  (Jager, Ralf et al. 2017.). It should be noted eating more protein is especially effective when calories are at a net deficit (cutting) higher protein will lead to higher muscle sparing effects (Carbone, McClung, & Pasiakos, 2019).

This brings into question the quality of protein sources, and the type of adsorption. High quality protein can be found in the following table.

Illustrating the data

Here’s an example of what this information would mean and how you would use it to inform your decisions about eating and protein intake.  Say you exercise a fair bit, but want to remain at a healthy weight, you’re not necessarily cutting or bulking, and you only want to eat as much protein as you can use, and you don’t want to eat excess protein (as to maintain your net calories), you are about 155 lbs, or 70kg. 

 You would need (from sports+nutrition numbers), approximately 100 – 140g of protein per day to be optimal.  You read the information above, and you know that eating multiple meals of protein gives you the best absorption, you also know that eating more than 30g of high quality protein in one meal is redundant. 

From this information, if you get from a 30g of protein from high quality  (say beef (but still go vegan)) and 10g of those are EAA, if you aim to eat 120g of protein or 4 servings of 10g of EAA, you are probably really close to optimum protein absorption. Say you are awake from 6AM to 10PM meaning 16 hours of being awake, ideally you would eat 30g of protein every 4 hours starting like: 8AM 12PM 4PM 8PM, or 6AM 10AM 2PM 6PM.    

Below is a specific table for those interested on the RDA for protein intake (again not necessarily optimum but meet requirements as to not lose nitrogen balance, and prevent muscle loss)

Sources: 

Carbone, John W, and Stefan M Pasiakos. “Dietary Protein and Muscle Mass: Translating Science to Application and Health Benefit.” Nutrients vol. 11,5 1136. 22 May. 2019, doi:10.3390/nu11051136 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6566799/#B6-nutrients-11-01136

Carbone J.W., McClung J.P., Pasiakos S.M. Recent Advances in the Characterization of Skeletal Muscle and Whole-Body Protein Responses to Dietary Protein and Exercise during Negative Energy Balance. Adv. Nutr. 2019;10:70–79. doi: 10.1093/advances/nmy087 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3197704/

Symons, T Brock et al. “A moderate serving of high-quality protein maximally stimulates skeletal muscle protein synthesis in young and elderly subjects.” Journal of the American Dietetic Association vol. 109,9 (2009): 1582-6. doi:10.1016/j.jada.2009.06.369 https://www.ncbi.nlm.nih.gov/pubmed/28698222

Morton RW, Murphy KT, McKellar SR, et alA systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adultsBritish Journal of Sports Medicine 2018;52:376-384. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5477153/

Jäger, Ralf et al. “International Society of Sports Nutrition Position Stand: protein and exercise.” Journal of the International Society of Sports Nutrition vol. 14 20. 20 Jun. 2017, doi:10.1186/s12970-017-0177-8

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/20043C98DF59B678E4A4F4AB7932A529/S0029665185000167a.pdf/protein_digestion_and_amino_acid_and_peptide_absorption.pdf

Silk, D., Grimble, G., & Rees, R. (1985). Protein digestion and amino acid and peptide absorption. Proceedings of the Nutrition Society, 44(1), 63-72. doi:10.1079/PNS19850011

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6245118/  

Image by: Photo by Kelly Sikkema on Unsplash