Blog Post

Can You Only Absorb 30g of Protein in a Sitting?

Feature image for "Can you only absorb 30g of protein"

A common claim in the nutrition world is that you can only absorb X amount of protein in a sitting. Theoretically, going higher than that amount is “wasted.” The “X” number that is used often varies between 20g and 40g. In this article, I will systematically go through where this idea comes from, and how relevant it is.

Absorption vs “Used for Muscle”

As a quick note, we obviously “absorb” more than 30g of protein in a sitting. That aspect is not really up for debate.

If we did not “absorb it” the calories would just go missing and “wouldn’t count.” And we know that is not true.

Protein has more functions than just muscle growth. It can even be converted to glucose and used for energy.

Gluconeogensis Diagram

The part most people care about is whether going above that has any benefits for muscle growth. So that is what the rest of this post is about.

Where Does This Idea Come From?

The main place this idea comes from is research on muscle protein synthesis (MPS).

Muscle protein synthesis in response to different amounts of protein

One commonly cited example of this is a study that involved 80g of protein spread over 12 hours following resistance training.

They utilised a pattern of:

  • 8 servings of 10g of protein every 1.5 hours
  • 4 servings of 20g every 3 hours
  • 2 servings of 40g every 6 hours

MPS was greatest in those who consumed the 4 servings of 20g of protein. In that study, there was no further benefit of the 40g on MPS.

Other research has found similar findings that MPS peaks after around 20-40g of protein. This varies depending on the size of the individual and the training protocol used.

A Major Flaw in the Muscle Protein Synthesis Argument

Even solely looking at the acute MPS angle, this thinking has an often-overlooked flaw.

Net muscle gain is not just based on MPS. Muscle protein breakdown is the other side of the equation, although this is more difficult to measure.

More importantly, most of these studies looking at MPS involve the consumption of a protein supplement in isolation. Consuming a mixed meal that contains carbohydrates and fats, including whole foods, could change this a bit.

A study from 2020 fitting this description compared 40g of protein vs 70g of protein.

If you were of the understanding that we were limited to 20-40g of protein in a single sitting, you would assume there would be no difference in MPS.

Both meals in this study were calorie matched, containing roughly 1100kcal, 35-45g of fat and 115-150g of carbs.

Muscle Protein synthesis response to a high vs moderate protein intake

Muscle protein breakdown was significantly lower in the higher protein intake, and to a lesser degree, MPS was also higher.

So even if we looked at just MPS, there are situations where going above 40g of protein leads to further increases.

Longitudinal Data

We have quite a lot of research on MPS. And we usually use that as a proxy measure of muscle growth. But it also makes sense to look at research on the topic we actually care about – actual muscle growth.

While there is less research on this, the studies we do have though indicate that meal frequency matters far less than total protein intake. If you want to read a summary of that research, I encourage clicking on the link in the previous sentence.

This finding would not make sense if we were limited to only 30g of protein in a sitting.

Another Flaw – Research on Intermittent Fasting

16:8 Fasting

If we were limited to 30g of protein in a sitting, people who have low frequencies of protein intake should struggle to gain/retain muscle, even if total protein intake was high.

That is not what we see.

When calories and protein intake are similar, people in intermittent fasting studies retain muscle roughly as well as those with higher frequencies.

One area we do not have good research on is muscle growth (instead of just retention) in intermittent fasting.

This is large because almost all studies involving intermittent fasting also involve a calorie deficit, which makes muscle growth less common.

A Nuanced View

Total protein intake matters far more than protein timing and frequency. But those things still matter a bit.

If trying to optimise absolutely everything, it makes sense to focus on protein distribution still.

Narrowing it down to 3 key recommendations based on the research:

Protein Prioritisation Pyramid

Going above that total protein intake recommendation does not further increase muscle growth, outside of rare cases.

You might be wondering how it is possible for BOTH the acute MPS data to indicate that MPS peaks after 20-40g AND the longitudinal data to indicate that meal frequency matters less than total protein intake. The simplest factor, among many, could simply be that:

  1. Higher protein intakes in a sitting elevate MPS for longer, even if it peaks at a similar point.
  2. Mixed meals slow down absorption, which contributes to this longer elevation in MPS.

Summary

Summary of protein recommendations

MPS often does peak after 20-40g of protein in a sitting. But when you look at the big picture, that does not mean we are only limited to that amount. Instead of viewing that as a limit, it makes sense to view that as more of an amount that is required to maximise MPS in a single sitting.

Total protein intake is even more important too. In situations where you cannot spread protein intake out, it makes sense to go above that amount, to help meet your total protein target.

If you could only consume protein 1-3 times a day, and you had a high protein target, limiting yourself to a maximum of 30g of protein in a single sitting could mean you fall significantly short of that target.

In a perfect world, to optimise muscle growth, you should have 0.4-0.55g/kg of protein over 4-6 meals. But if that is unrealistic, switching the focus to total protein, and distributing the protein the best you can is the next best thing.

By Aidan Muir

Aidan is a Brisbane based dietitian who prides himself on staying up-to-date with evidence-based approaches to dietetic intervention. He has long been interested in all things nutrition, particularly the effects of different dietary approaches on body composition and sports performance. Due to this passion, he has built up an extensive knowledge base and experience in multiple areas of nutrition and is able to help clients with a variety of conditions. One of Aidan’s main strengths is his ability to adapt plans based on the client's desires. By having such a thorough understanding of optimal nutrition for different situations he is able to develop detailed meal plans and guidance for clients that can contribute to improving the clients overall quality of life and performance. He offers services both in-person and online.