protein absorption

A common query I often get and is one of the most searched doubts on the net, in regards to protein absorption is, “how much protein can we eat in a go before it gets wasted?

Protein is one of the primary macronutrients and one of the most important ones, when it comes to sports performance, especially muscle hypertrophy & strength. But, it is also the most misunderstood, as there are tons of pervasive myths surrounding its consumption.

One of the top myths is that the body cannot absorb more than 30grams of protein in one go. Anything consumed beyond that in one sitting will go waste. This means a marathon runner, and a bodybuilder’s body will absorb protein at the same rate.

protein absorption

The origin of this myth can be dated back to a 1997 study in the journal Proceedings of the National Academy of Sciences, by a French & Swiss research team led by Y. Boirie, who examined the absorption of two different protein types, i.e. whey & casein, consumed in one meal. The study showed that approx 30grams of whey is absorbed in the body in 3-4hrs and 30grams of casein takes around 7hrs to get digested.

However, what was important to note here was that the subjects who were given whey & casein, did so after an overnight fast, and morning fast, that too without any other food. Protein when taken with foods, gets absorbed slowly. The results also got interpreted, that the athlete needs to consume protein every 3-4hrs to avoid getting into a catabolic state. But this conclusion was never made in any study.

In a 2009 study in the American Journal of Clinical Nutrition, a Canadian research team led by D.R. Moore determined the ingested protein dose response of muscle (MPS) and albumin protein synthesis (APS) after resistance exercise. For the study, six young men reported to the laboratory on 5 separate occasions to perform an intense bout of leg-based resistance exercise. After exercise, participants consumed, drinks containing 0, 5, 10, 20, or 40g whole egg protein. Protein synthesis and whole-body leucine oxidation were measured over 4h after exercise. MPS displayed a dose-response to dietary protein ingestion and was maximally stimulated at 20g. Researchers thus concluded that the Ingestion of 20g intact protein is sufficient to maximally stimulate MPS and APS after resistance exercise. 

A 2012 study in a British journal Nutrition & Metabolism, by a Swiss research team led by D.R. Moore, determined the effects of different protein feeding strategies on protein metabolism in resistance-trained young men. Participants were assigned to ingest either 80g of whey protein as 8x10g every 1.5h, 4x20g every 3h, or 2x40g every 6h, after an acute bout of bilateral knee extension exercise (4×10 repetitions at 80% maximal strength). Researchers concluded that the pattern of ingested protein, and not only the total daily amount, can impact whole-body protein metabolism. Individuals aiming to maximize net protein balance would likely benefit from repeated ingestion of moderate amounts of protein (~20g) at regular intervals (~3h) throughout the day.

A 2013 study in the Journal of Physiology, by an Australian research team led by J.L. Areta, determined how different distributions of protein feeding during 12h recovery after resistance exercise affects anabolic responses in skeletal muscle. Twenty-four trained males were assigned to three groups and undertook a bout of resistance exercise followed by ingestion of 80g of whey protein throughout 12h recovery in one of the following protocols: 8 × 10g every 1.5h; 4 × 20g every 3h; or 2 × 40g every 6h. Researchers found that 20g of whey protein consumed every 3h was superior to either 1.5h or 6h feeding patterns for stimulating MPS throughout the day. Researchers also found no additional benefit, and actually a lower rise in MPS when consuming the higher dosage (40g).

In a 2015 study in the journal Frontiers in Physiology, by a Canadian research team led by R.W. Morton, proposed that muscle protein synthesis (MPS) is maximized in young adults with an intake of approx 20–25 g of a high-quality protein, consistent with the “muscle full” concept; anything above this amount is believed to be oxidized for energy or transaminated to form alternative bodily compounds.

The human body is extremely adaptable and varies in anatomy & physiology. Every individual is different. Their requirement is different for nutrition, and their protein absorption capacity also varies with different conditions. In a 2018 study in the Journal of International Society of Sports Nutrition, researchers Brad Schoenfeld & Alan Aragaon suggested that a number of factors influence dietary protein metabolism including the composition of the given protein source, the composition of the meal, the amount of protein ingested, and the specifics of the exercise routine. In addition, individual variables such as age, training status, and the amount of lean body mass also impact muscle-building outcomes.

Therefore, it does not mean that 20g is a stipulated stamp on max protein intake. Schoenfeld & Aragon made the following glaring observation in the study by J.L. Areta & team, “that total protein intake over the 12h study period was only 80g, corresponding to less than 1g/kg of body mass. This is far below the amount necessary to maximize muscle protein balance in resistance-trained individuals who served as participants in the study. Furthermore, the ecological validity of this work is limited since habitual protein intakes of individuals focused on muscle gain or retention habitually consume approximately 2–4 times this amount per day.

It also should be noted that subjects in Areta et al. ingested nothing but whey protein throughout the post-exercise period. Whey is a “fast-acting” protein; its absorption rate has been estimated at ~ 10g per hour. At this rate, it would take just 2h to fully absorb a 20g dose of whey. While the rapid availability of amino acids will tend to spike MPS, earlier research examining whole-body protein kinetics showed that concomitant oxidation of some of the AA may result in a lower net protein balance when compared to a protein source that is absorbed in a slower rate. For example, cooked egg protein has an absorption rate of ~3g per hour, meaning complete absorption of an omelette containing the same 20g of protein would take approximately 7h, which may help attenuate oxidation of amino acids and thus promote greater whole-body net positive protein balance.”

In a 2016 study in the journal Physiological Reports, by L.S. Macnaughton & team, assessed the influence of LBM, both total and the amount activated during exercise, on the maximal response of MPS to ingestion of 20 or 40g of whey protein following a bout of whole-body resistance exercise. The research indicated that the ingestion of 40g whey protein following whole-body resistance exercise stimulates a greater MPS response than 20g in young resistance-trained men. 

When you eat any food, the various nutrients get absorbed in a different manner, but they all go into the stomach, and then the small intestines, through who’s wall, the nutrients get absorbed into the bloodstream. The protein is broken down into amino acids by the acids and enzymes in the stomach. These amino acids are carried by special transporter cells in the small intestines to the bloodstream, and then to various parts of the body. The intestines have a limited number of these transporter cells, that’s why they are not able to send all the amino to blood. This is called ‘protein absorption’. This happens at different speeds for different types of protein.

According to a 2006 study in the International Journal of Sports Nutrition & Exercise Metabolism, by an Australian research team of S. Bilsborough & N. Mann, whey is absorbed in 8 to 10grams per hour, casein at ~6.1g/hr, soy at ~3.9g/hr, and cooked egg at ~2.9g/hr. These are not accurate numbers, but approximations, as absorption depends on multiple factors.

Of course, a smaller meal will take a shorter time to digest than a larger meal. Similarly, if you consume a larger portion of protein in the diet, then protein absorption will take a longer time. In a 2000 study in the Journal of Nutrition, by a French research team, led by M.A. Arnal, determine whether a pulse protein feeding pattern was more efficient than a spread pattern to improve protein anabolism in young women. 16 young women were given a 14-day diet providing 1.7g protein/kgbw/day, using either a pulse pattern (protein consumed mainly in one meal) or a spread pattern (spreading daily protein intake over four meals). No significant effects of the protein feeding pattern were detected on either whole-body protein turnover for spread and pulse pattern, respectively] or whole-body protein synthesis and protein breakdown. Thus, in young women, these protein feeding patterns did not have significantly different effects on protein retention.

Now, if the protein is not absorbed in the bloodstream, it simply gets excreted through the faeces.

protein absorption

A 1999 study in the Journal of Nutrition, by a French research team led by F. Mariotti, assessed the true digestibility, and the postprandial nutritional value of a soy protein isolate (SPI) in humans. To assess bioavailability and bio-utilization of SPI, 10 healthy volunteers ingested 30g of SPI, added with 100g of sucrose and water up to a final volume of 500ml. researchers found that the nutritional value of SPI is 92% of that in milk protein concentrate.

On the other hand, a 2005 study in the Journal of Nutrition, by a research team from Netherlands led by Y.C. Luiking assessed the quality of casein and soy protein by comparing their metabolic effects in healthy human subjects. In conclusion, the researchers saw that a significantly larger portion of soy protein is degraded to urea, whereas casein protein likely contributes to splanchnic utilization (probably protein synthesis) to a greater extent. The biological value of soy protein must be considered inferior to that of casein protein in humans.

Thus, the digestibility of proteins in most cases is over 90%, depending on the source (animal source gets absorbed better than plant source), and the dosage consumed (10-50gms in one go). owner & researcher Kamal Patel suggests that the small intestines are able to absorb and hold onto a large number of amino acids; waiting to release them until the body needs them, and can recycle some amino acids. Due to the aforementioned ability of the small intestines to ‘hold’ onto the protein, they are considered a ‘free amino acid pool’ that the body can draw amino acids from on an as-needed basis.

In a 1999 study in the American Journal of Clinical Nutrition, by M.A. Arnal & team, tested the hypothesis that an uneven protein feeding pattern was more efficient in improving protein anabolism than was an even pattern. 15 elderly women were fed for 14-days either a pulse diet, providing 80% of the daily protein intake at 1200, or a spread diet, in which the same daily protein intake was spread over 4 meals. Researchers saw that nitrogen balance was more positive with the pulse than with the spread diet. Protein turnover rates were also higher with the pulse than with the spread diet, mainly because of higher protein synthesis in the pulse group than in the spread group. It was thus concluded that a protein pulse-feeding pattern was more efficient than was a protein spread-feeding pattern.

Kamal Patel suggests that there really is no literature to indicate 30gm protein in a go, as a ‘holy grail’ of protein absorption. It may have arisen from assuming 10g/hour as a standard, and applying that to the typical mini-meal approach to bodybuilder nutrition (with a meal every three hours).

Schoenfeld & Aragon concluded by saying, “while consumption of higher protein doses (>20g) results in greater amino acid oxidation, this is not the fate for all the additional ingested amino acids, as some are utilized for tissue-building purposes. Based on the current evidence, we conclude that to maximize anabolism one should consume protein at a target intake of 0.4g/kg/meal across a minimum of four meals in order to reach a minimum of 1.6g/kg/day.”

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