Summary:
- Tofu has a relatively balanced essential amino acid profile
- While there’s no single definition of a complete protein, tofu is a complete protein by most standards
- Read the rest of this post to find out why…
The most common examples of complete protein sources are animal products like meat, eggs, or milk.
The majority of plants are not complete. That’s not a huge deal, it just means you need some variety to get enough of each essential amino acid.
Soy is an exception.
By most definitions, soy is considered a complete protein (1). Certain populations have lived off mostly soy and been very healthy.
The Definition of A Complete Protein
I’ll start off by saying that there’s no one definitive definition of a complete protein.
In general, it’s defined as:
A complete protein contains an adequate amount of each of the essential amino acids, and in a reasonable balance.
There’s a lot of vagueness in that statement.
Below is a table of the best current estimates of a human’s amino acid requirements according to the World Health Organization (WHO) (2).
There are 2 columns:
- mg/kg per day – Multiply this by your body weight in kilograms to find out how much of each essential amino acid you need per day (the minimum).
- mg/g of protein – In order to effectively utilize amino acids, there needs to be a certain amount of each amino acid.
The Amino Acid Profile of Soybeans and Tofu
Tofu is made by coagulating soy milk, so the protein in it has the same amino acid profile as soybeans.
The tricky thing is that the amino acid profile of a food varies based on strain. Soybeans from one farm do not necessarily have the same amino acids as from another farm.
A study looked at the essential amino acid profile of 44 strains of soybeans in Arkansas (3). The table below is the most important result from it:
There are some large ranges there.
Let’s compare those amounts to the minimum amount a complete protein should have (from the above section):
| Complete Protein (min %) | Soy protein (%) | |
|---|---|---|
| Histidine | 1.5 | 2.7-5.9 |
| Isoleucine | 3.0 | 1.5-4.0 |
| Leucine | 5.9 | 4.4-7.3 |
| Lysine | 4.5 | 4.7-13.8 |
| Methionine+Cysteine | 1.6 | 2.6-10.8 |
| Phenylalanine+Tyrosine | 3.0 | 2.5-5 |
| Threonine | 2.3 | 1.5-4.5 |
| Valine | 3.9 | 1.7-4.2 |
Soy has a high enough percent of most of the essential amino acids in all strains.
However, certain crops of soybeans may be a little shy of certain amino acids. For example, the valine percentage for a complete protein is 3.9%, which some soybeans have as low as 1.7% of valine.
The other thing we need to look at is if you can get a sufficient overall amount of each amino acid in a day.
I created the table below for the amount of each amino acid needed per day for a 65 kg adult (about 143 pounds).
| Needed per day (mg for 65 kg adult) | In 1 Block of Tofu (mg) | |
|---|---|---|
| Histidine | 650 | 1025 |
| Isoleucine | 1300 | 2020 |
| Leucine | 2535 | 3310 |
| Lysine | 1950 | 2145 |
| Methionine+Cysteine | 975 | 636.5 |
| Phenylalanine+Tyrosine | 1625 | 3660 |
| Threonine | 975 | 1870 |
| Valine | 1690 | 2070 |
In just one block of tofu, you exceed the daily amount needed for all but one essential amino acid. You can see why tofu and soy products in general are among the best vegan food sources of protein.
Even then, 1.5 blocks would just about hit them all, which really isn’t that much if tofu was your main protein source.
While the relative percentage of certain amino acids in tofu can be low in some cases, tofu has so much protein that it’s easy to high the quantity of each amino acid needed per day.
Verdict: Most Would Consider Tofu A Complete Protein
Based on all that, I think it’s fair to say that tofu is a complete protein.
It’s not a perfect protein source, but it’s extremely good, and one of the best plant sources of protein.
The one factor that we didn’t talk about is protein digestibility.
Research generally shows that plant proteins are not absorbed as well as animal proteins (anywhere from 60-90% depending on the plant).
That won’t affect the amino acid percentages in tofu, but it will affect the quantity by a bit. Still, I don’t think that really affects our overall answer here; a few blocks of protein alone would meet all your essential amino acid requirements.
Follow-up Questions
What plant-based sources of protein besides tofu have good amino acid profiles?
Several plant-based sources of protein, in addition to tofu, offer strong amino acid profiles. Quinoa, lentils, chickpeas, and beans are rich in protein and provide a well-rounded array of amino acids.
Combining different plant-based protein sources in a balanced diet can help ensure sufficient intake of essential amino acids.
Can eating too much tofu be harmful?
Consuming excessive amounts of tofu may have potential drawbacks. Tofu is a soy product, and while moderate consumption is generally considered safe and even beneficial, overconsumption can lead to an excessive intake of compounds called phytoestrogens.
These compounds may affect hormone levels and, in some cases, raise concerns about their impact on health. With that being said, you’d have to eat quite a lot. See our post on the science of tofu affecting estrogen and testosterone for more details.
Are complete proteins important to focus on in your diet?
While complete proteins, which contain all essential amino acids, are beneficial, it’s not necessary to obsessively focus on them in every meal. The concept of “protein combining” has been debunked, and a well-balanced, varied diet can still provide all the essential amino acids over the course of a day.
Many plant-based foods, such as legumes, grains, and nuts, complement each other in amino acid profiles. It’s essential to prioritize a diverse range of protein sources to ensure a comprehensive intake of amino acids, contributing to overall nutritional balance.
