Why protein from animal-source should be reduced?

The requirement of daily intake of protein has been a subject of great debate with many unresolved questions. After reading Esselstyn's book "Prevent and Reverse Heart Disease", I learn certain bio-chemical process in our body that answer the question.


The internal surface of our blood vessels are lined with thin-layer of endothelium cells which  (one of its function) is responsible for vasodilation. It does that by making Nitric Oxide (NO) through Nitric Oxide Synthases (NOS3). To make NO, NOS3 require L-arginine which is a L-from alpha-amino-acid. Though Arginine is non-essential amino acid (that means our body can manufacture it), the biosynthetic pathway does not produce enough hence require supplementation through diet (either through animal-sources or plant-sources).

However there are other chemicals that compete/interfere with L-Arginine on the production of NO, for example Asymmetric dimethylarginine (ADMA) and MMA. ADMA is naturally found in blood-plasma as a metabolic by-product of protein methylation process. This is why too much protein is not good. As a general guideline, human breast-milk which is optimized for newborn baby unusually high protein requirement, contain only 5% calories from protein (compared to 20% in cow's milk). The Okinawan Diet, which have the world highest number of Centenarian and most healthy people, only have 10% calories from protein on their diet.

In healthy person (that is total cholesterol level less 150mg/dL and LDL cholesterol less than 80mg/dL), presence of ADMA and MMA are not a big issue since our body will also have Dimethylargininase (DDAH) enzyme which function is to degrades those methylarginines (ADMA and MMA). Unfortunately, DDAH itself is sensitive to oxidative stress, such as oxidized LDL-cholestrol. Hence the attenuation of DDAH level cause the elevation in ADMA, blocking the NO synthesis which lead to vasoconstriction. This is why when we try to fulfill our protein requirement, we should try to get it from plant (which have less fat) rather than animal (where even a lean meat, that is defined by USDA as 90% lean and 10% fat, actually calculated to be about 50% calories from fat). The actual correlation between high fat content and rise of LDL level is very complex, read more in the "Regulation of cholesterol synthesis" section of Wikipedia article.

Nitric Oxide aside, two more things to consider. First of all, animal-sourced protein have a high level of methionine amino-acid. One need to be careful here, methionine amino-acid is part of essential amino-acid that our body need, however high level of it can lead to increase of homocysteine level which is an artery-toxic substance that strongly linked to coronary heart disease and aging. Second is that meat protein have higher sulfur content that will increase uric-acid which will lead to medical condition such as kidney stones and gout.

In conclusion, the general dietary literature that recommend very high protein diet is false. One only need 10% of their calories from protein. Sourcing protein from animal-product unfortunately will bring in more unwanted stuff, hence the safer option to meet your protein requirement is through plant-based food. But remember, we still need protein. It helps with satiety (i.e. make us feel full) and preserving our muscle tissue.

If you have any comment on potential pitfall on my arguments, do drop me a comment.