Protein can be complicated. Are you having trouble wrapping your head around the concept of protein bioavailability?
In this article I will explain in understandable language what protein bioavailability means, and how it applies to your protein choices.
You will also learn some simple ways to make the protein in your food more available to your body.
Let’s get started.
Table of Contents
What is protein bioavailability?
First, an Important Fact About Your Gut
You probably already know your gut is a long, hollow tube that runs through the middle of your body. You might not realize it is actually outside of your body.
Anything that you swallow goes into your gut, but it doesn’t necessarily go into your body. Your gut has a very thin membrane lining its entire surface, and substances need to get through that membrane in order to enter your bloodstream.
Think of it as the customs and immigration room at an international airport. Everything you swallow is waiting around in that room, and your body has guards and procedures in place to decide what gets through.
Whatever doesn’t get through your gut membrane goes out the other end. It was never officially in your body.
What is bioavailability?
Now back to bioavailability. This is a measurement of what your body can absorb, or what gets through your gut membrane into your bloodstream. It becomes available to your biology.
Amino acids are the building blocks of protein. All the protein you eat is broken down into separate amino acids before it can be absorbed. These amino acids are reconstructed into different types of protein in your body.
The technical definition of protein bioavailability is the proportion of amino acids reaching systemic circulation, and that can be used for protein synthesis in your body (1).
Why is protein bioavailability important?
Protein bioavailability is important because there are so many different types of protein, and your body handles them all differently. You can choose foods and prepare them so that you get the biggest protein benefits.
Protein Bioavailability Vs. Protein Quality
Protein quality is the ability of a protein to supply the body with the essential amino acids and nitrogen that it needs to maintain bodily functions (2). We determine protein quality by looking at two things: the amino acid profile of a food, and how well that food is digested and absorbed.
So, protein bioavailability is just one part of the picture to determine protein quality. In this article we are focusing on bioavailability. We can delve into protein quality another time.
How do you measure protein bioavailability?
Protein bioavailability is measured at the level of the small intestine, because this is where amino acids are absorbed. It is a complicated process which can also be invasive, so not something you can do at home.
The most reliable method involves putting a tube down into your small intestine, not something most people would volunteer for (1).
Another less invasive method labels protein with an isotope, and analyzes how much of this shows up in the plasma after a meal. This method is complicated and not as reliable (1).
Another method measures bioavailability of just one limiting amino acid, with the assumption that if this one is not being absorbed, then the others are not either. A labeled amino acid, usually phenylalanine, is fed to the subject in a meal. The label is then measured in the subject’s breath to determine how much was absorbed (1).
Studies with animals like pigs and rats have provided much of the information about protein bioavailability (1).
Bioavailable Animal Protein
Protein from animal sources is generally absorbed better than plant protein. This makes animal protein more bioavailable. It is also higher quality than plant protein because it contains all the essential amino acids.
What is the most bioavailable form of animal protein?
We can use the Digestible Indispensable Amino Acid Score (DIAAS) to determine how much of a protein is digested and absorbed. DIAAS measures the amino acids that are absorbed at the level of the small intestine, which is the most accurate way to assess this, since amino acids that pass into the colon are generally not used by the body (3).
A DIAAS score can be higher than 100 to identify proteins that are extra high quality, or go above and beyond the basic protein requirements of humans. When you combine a higher DIAAS protein (over 100) with a lower DIAAS protein, you can increase the bioavailability of the lower one (3).
Whey protein concentrate and isolate have the highest DIAAS score of 125-135. Other milk proteins also score high, such as skim milk powder at 123, and casein at 117 (3).
Pork and beef are next in line, at 117 and 112 respectively. Chicken and egg have a DIAAS score between 100 and 110, so still a very high quality protein (3).
Surprisingly, insect protein has a score similar to a plant protein, with a DIAAS of 75 (3).
Bioavailable Plant Protein
Plant protein is generally less bioavailable than animal protein. On top of that, most plants don’t contain all the essential amino acids. This makes plant protein lower quality.
Plants are made up of fibers and polysaccharide structures that can interfere with digestion. They prevent your digestive enzymes from getting full access to the proteins and breaking them down. Substances like phytic acid, hemagglutinins, glucosinolates and tannins, can bind proteins and make them harder to digest (4).
What is the most bioavailable form of plant protein?
Soy is the most bioavailable plant protein with a DIAAS score hovering around 100. Potatoes also have a DIAAS of 100 (3).
Chickpeas, yellow split peas and pea protein concentrate have a DIAAS in the 70-90 range. Plant proteins in the 50-60 range for DIAAS include wheat, oats, fava beans, lupin, kidney beans and red lentils. Corn is lower on the scale with a DIAAS of 36 (3).
Can you increase protein bioavailability?
The bioavailability of animal protein depends on how it is prepared. Cooked protein is digested more easily than raw. Cooking meats at a lower temperature also increases bioavailability, while higher temperatures can actually make protein harder to digest (5).
High pressure cooking in a pressure cooker or instapot makes protein easier to digest (5).
When the protein is mechanically chopped up, such as hamburger vs steak, it is easier to digest. Any time you break up the cells and tissues of animal protein your body will digest it more easily.
You can increase the bioavailability of plant protein by soaking, sprouting, fermenting and cooking beans, legumes, grains, seeds and nuts (6).
Also, as I mentioned previously, if you combine a high quality protein (DIAAS score > 100) with a lower quality protein, the high scoring protein actually complements the lower one and increases its quality.
How does digestion affect protein bioavailability?
Your mother was right, you need to chew your food. Chewing breaks food apart into smaller pieces so that when it hits the stomach, it is easier to digest. The enzymes can surround those smaller food particles and break them down much more efficiently than they can a large chunk hitting your stomach.
Chewing is the only part of digestion where you can actively control your muscles. After you swallow your food, the autonomic nervous system takes over. You can give everything a head start by making sure that the food is thoroughly broken down before you send it to your stomach.
It is essential to have enough stomach acid to digest protein properly. Acid begins to unfold and break down the complex protein structure. It also helps to activate the enzymes that break down protein. If you are wondering whether you have good stomach acid, there is a simple test you can do at home.
Find out how to do the stomach acid baking soda test.
Final Thoughts
When you eat protein, your digestion breaks it down into a bunch of tiny, separate amino acids so that it can be absorbed into your body. Then, it gets rebuilt as muscle or organ tissue, blood, immune cells, enzymes, or whatever else your body needs it to be.
Protein bioavailability is the proportion of amino acids reaching your bloodstream that are available to be used to make protein in your body.
This depends mainly on how well you are able to digest that protein, or break it down into separate amino acids.
Animal protein is generally more bioavailable than plant protein. Plant protein contains substances like fiber, phytate, tannin and others that can interfere with digestion.
There is a lot you can do to improve the digestibility and bioavailability of protein. When you mechanically chop up animal proteins they are easier to digest. Chewing your food properly goes a long way towards better digestion.
You can soak, sprout, ferment and cook plant proteins to make them more bioavailable.