Ever wonder if that giant post-workout shake is really doing its job? Our bodies constantly break down and rebuild muscle tissue, and protein is essential for this process. In the fitness industry there is a common belief that there is a "protein ceiling," a limit on how much protein we can absorb at once. This article dives into the science behind protein absorption and explores the factors that influence how much protein your body can actually utilize.
First, let's get specific about what we mean by "absorbed." Almost all consumed protein is absorbed by healthy humans, however, the ceiling for how much protein your body can utilize towards muscle repair and/or growth in one sitting was previously hypothesized to be around 20g-30g of protein. Is this really the case though? It seems that a number of factors influence how much protein we can effectively use at any given time, including:
-
Bodyweight: A 2020 meta-analysis found that there were no additional benefits to consuming over 1.6 grams of protein per kilogram of bodyweight, with a 2018 study supporting these findings, suggesting that .4g per kg of bodyweight, spread across four meals per day, for a minimum of 1.6g per kg of bodyweight is optimal to maximise anabolism.
-
Muscle Mass Trained: Contrary to earlier studies, a 2016 paper shows 40g protein was better at increasing muscle protein synthesis than 20g. Unlike earlier studies, this study focused on full body workouts, whereas past studies primarily focused on lower body workouts. This could suggest that the more muscles being worked in a session, the higher your protein ceiling might be.
-
Age: As we age, anabolic resistance occurs. This means our muscles become less responsive to the muscle-building effects of exercise and protein intake. This translates to a higher protein need compared to younger individuals to maintain or build muscle mass, suggesting that older adults may need to inch closer to that protein ceiling, or even slightly exceed it, to achieve the same muscle-building benefits as their younger counterparts.
-
Fast vs. Slow-Digesting Protein: Protein sources digest at different rates. Whey protein is fast-acting, providing a quick burst of amino acids. Casein protein digests slowly, creating a sustained release of amino acids throughout the day, making it a good choice before bed. The extended protein availability of slow digesting proteins such as casein potentially keep amino acid levels within the MPS window for a longer duration, and may help reduce muscle protein breakdown to some extent.
How might this affect intermittent fasting? The short answer surprisingly appears to be- it doesn't! No significant differences in muscle mass were found in groups that ate their total protein intake within a four hour window when compared with those who ate more regular meals. In a 2007 study, participants who consumed 86g of protein in a sitting were actually found to have improved body composition when compared with participants that ate the same 86g of protein spread out over 3 meals. This might seem contradictory, but if we take a closer look, there does appear to be an explanation. Many of the studies surrounding this have limitations, such as focusing on a single meal, or in many cases, the protein consumed in these studies is not consumed as a concentrated protein source (such as a protein shake or steak). The fats, carbs, and fibre present in a full meal causes digestion to slow, which could account for these findings.
So, what's the verdict? How much protein can be utilized in a sitting? Unfortunately there is no completely clear answer yet. Muscle protein synthesis declines or plateaus after a certain amount of protein is consumed, though the exact amount remains unclear. The real takeaway here is that protein utilization isn't a one-size-fits-all concept. Factors like bodyweight, muscle mass trained, and even age play a role in how much protein your body can effectively use at once. The research seems to suggest that hitting your total daily protein goal is a more important factor than hitting your "protein ceiling" for each meal, but that if you are trying to optimise muscle synthesis, consuming .4g of protein per kg of bodyweight per meal, spread over four meals per day for a total of 1.6g per kg of bodyweight, seems to be a solid bet to maximise anabolism, although some might benefit from consuming up to 2.2g per kg per day.
Understanding these factors empowers you to optimize your protein intake for muscle growth or repair. Remember, everyone's needs are different. Consulting a registered dietitian or nutritionist can help you create a personalized plan to reach your specific health and fitness goals.