Protein for Vegans and Vegetarians

[Tenet Nosce]

A lot of these people you are referring to that talk about how much protein greens have or how much protein babies supposedly don't need, are misinformed.

How about source vs assimilable? Does the percentage mean as much if a body can't assimilate it as well?

There are a few different ways to measure protein digestibility, each with its own advantages and drawbacks.

The oldest and simplest method is called Protein Efficiency Ratio (PER) which takes into account the weight gain of an animal as compared to its protein intake. It is now considered obsolete as it is in many ways oversimplistic and we have better methodologies. Plus, it was originally based in rat research, and there are several differences in protein metabolism between rats and humans.

There is the Biological Value (BV) which is still fairly simple to calculate. Basically you take the nitrogen content of the food input and compare it to how much nitrogen is coming out in the urine and the stool to determine how much was absorbed into the blood. Drawbacks are that it doesn't differentiate between the varying levels of digestibility among different amino acids. Also, it doesn't account for protein that was actually fermented by gut bacteria instead of being absorbed.

The current standard is called Protein Digestibility Corrected Amino Acid Score (PDCAAS). It is much more complex of a formula. You can read about it in more detail here:

Criteria and Significance of Dietary Protein Sources in Humans

Here is a basic listing of protein digestibility according to PDCAAS:

1.00 casein (milk protein)
1.00 egg white
1.00 soy protein
1.00 whey (milk protein)
0.92 beef
0.91 soybeans
0.78 chickpeas
0.76 fruits
0.75 black beans
0.73 vegetables
0.70 Other legumes
0.59 cereals and derivatives
0.52 peanuts
0.42 whole wheat

As you can clearly see- animal sources of protein actually have a HIGHER digestibility ranking than plant sources across the board.

Still, this methodology has many limitations and oversights. It does attempt to somewhat account for fermentation by gut bacteria, but still doesn't account for differences in the digestive function from human to human.

None of the methods do.

Protein digestion is dependent on the presence of stomach acid and other factors, as well as proteolytic (protein-digesting) enzymes produced by the pancreas. All of these can vary widely from person to person, and even in the same person at different times under different circumstances.

Stomach acid can be measured using something called a Heidelberg Test where the recipient actually swallows a pH meter that sends out a radio signal that can be picked up by a receiver. However, this test is not really used all that much as it is expensive and time consuming.

People can also do what is called a "Gastric Acid Function Test" by taking HCl capsules before meals and recording symptoms. But this kind of "test" doesn't produce any objective data, and so it cannot be used for research purposes.

Pancreatic enzyme function can be estimated by measuring the amount of an enzyme called pancreatic elastase present in a stool sample. Now, elastase actually digests fats, not protein. But unfortunately, the proteolytic enzymes are easily degraded in the bowels, and so measuring the amount in the stool wouldn't really tell us anything. Elastase holds up well in the bowel, and so this is the one we use in order to generalize about digestive enzyme production in general.

In addition, I highly suspect that different gut bacteria enterotypes digest and absorb different kinds of protein with varying efficiencies. Research has shown that human gut bacteria can be categorized into three different clusters with significant differences in metabolism. One type is dominated by iron metabolism, another by thiamin, and the third by biotin. My intuitive sense is that these three types have evolved along with the three dominant protein sources of human populations: sea animals, land animals, or plant-based proteins.

So my guess is that certain people digest vegetable protein better than others. Even perhaps in those people they digest vegetable protein better than animal protein. But I don't have any evidence to back that up. We will just have to wait and see.

In the meantime, I think that the body is a pretty good communicator of what it needs IF we are listening to it. It is turning out that gut microbes can even influence our cravings in order to induce us to feed them what they need in order to thrive. Now if we have a healthy gut flora, this is a good thing. But if we have "nasties" in there, such as opportunistic bacteria or yeast which feed primarily on sugar, this could work against us.

Also both the rational mind and the emotions can get in the way of correctly reading the body's signals.