AI generated image, created by Angela A Stanton©

My Take on Protein

Protein is discussed everywhere these days. One of the questions is whether the protein consumed will be usable as protein by our body. After all, eating an avocado won’t remain or be used as an avocado in our body. Foods change in our stomach to a mush (chyme), that is unrecognizable. What about protein? How is protein used by our body? And how much of it should we eat for health and strength?

I have frequently been criticized for the amount of protein consumption I support. I am a proponent of a high animal protein diet, not necessarily carnivore (an animal product only diet) but in large part animal based. I am also often challenged to explain why I believe that eating a lot of animal protein is the right thing to do since there is so much noise about how protein, specifically animal protein, is bad for us. How come I still recommend eating so much meat? There are plenty of blogs and academic articles claiming that meat causes various cancers.

Let me start by explaining what protein is, what it does, how much we need to eat and why, then I describe some of the misinformation around between animal and plant protein, the amount needed for health, and the cancer connection. Buckle up! This will be a bumpy ride!

Who Are We (You Included)?

It is very important for us to acknowledge and accept who we are. We are humans: Homo Sapiens Sapiens. 200-300k years ago some of our ancestors left Africa and set up camp in Europe, Asia, etc. You can check out the evolutionary timeline to update your knowledge. Throughout human evolution, our planet experienced a glacial period, frequently referred to as ice age, which started 2.6 million years ago. The last glacial period of this ice age, which started around 120,000 years ago and reached its peak around 20,000 years ago, saw glaciers covering most of North America, Europe, South America, Asia, parts of Australia, New Zealand, and Tasmania. Only the equatorial regions remained ice and snow free. Modern humans evolved during this last glacial period, the Pleistocene, and spread across the planet.

Now ask yourself the following question: what did our ancestors, apart from the ones in equatorial Africa, eat during the last ice age? Let me hazard an answer: our ancestors ate whatever they could find in the snow and ice. And that was not cherries or pineapples, tomatoes, avocados, or leafy vegetables. Just look at the cave paintings left behind. They depict what they ate. They hunted animals. Have they also consumed plants? Perhaps, some. We do know that plants were consumed as herbs for treatment of various diseases. There is some evidence that our ancestors,  before we started farming,  had eaten some grains, and there is even a surprise find of sorghum seed residue on 100,000 years old grinding tools in today’s Mozambique.

Most of our ancestors had to eat animals. There simply was nothing else in large-enough amount to feed them. Humans ate those animals that could scratch out a living from the grasses they dug up under the snow. Beyond the many cave paintings, archeological finds also attest to this.

It should also be clear to you that eating a lot of meat in the past didn’t cause us to go extinct as a result of cancer or cardiovascular disease.  If eating high levels of animal proteins got us to evolve into what we are today, why can’t we continue eating the same way?

Importantly, we have the wrong digestive enzymes and systems for lots of plant-eating. Furthermore, plants are insufficient in nutrients and vitamins and are full of antinutrients that block what little nutrients they have. Most of the plants during the Pleistocene were not edible. Most plants we eat today did not exist to the Pleistocene human! Modern plants were not part of our evolution.

Image created by Angela A Stanton© using AI

Because most plants didn’t exist during human evolution, we are not adapted to eating them nearly as much as we are adapted to eating animal products. Nevertheless, it is true that both animal and plant-based foods contain proteins. Let’s dive into the subject of proteins, and the differences between the animal and plant-based versions.

What Exactly is Protein?

Protein is a complex organic molecule made of long chains of amino acids, which are essential for various biological functions in the body.

An amino acid is a small molecule that contains a carbon atom attached to four “things”:

1. An amino group (–NH₂)
2. A carboxyl group (–COOH)
3. A hydrogen atom (-H)
4. A side chain (R group) that makes each amino acid unique

When amino acid molecules link together in a specific sequence, they form proteins, which the body uses to build and repair tissues, make enzymes and hormones, and perform countless other vital functions. There are between 80,000-400,000 different types of proteins made by our body—this varying number is the result of human variations in age, gender, activity, environment, health, and disease.

Whatever you eat, be it an animal or plant, there are proteins in that food. Each type of these proteins is  always made from the same amino acids. In other words, an amino acid in a human body is the same amino acid in a cow, snake, apple, broccoli, bacteria, and flower. Amino acids are preserved across life forms on Earth. There are 20 amino acids and they are the building blocks of all life on this planet. And these amino acids are so preserved between and across species, that if you obtain an amino acid, say glycine, by eating an oyster, not only is it used as glycine in your body as well but you can use this glycine the same way as glycine from eating any other animal or plant meal or if your body created its own glycine. It makes no difference where you get the amino acids from.

Some of the amino acids your body can generate from scratch but not all. Later I will discuss which amino acids must be consumed (essential) and which need not be (nonessential) because your body can create them from scratch.

Amino acids are connected end-to-end to create proteins that make up just about everything in our body. Most of us tend to think of muscle when we discuss protein. And it is correct, muscle is a major organ that needs a lot of protein, but there are other organs that need protein in our body as well.

I will explain protein-making via one of the smallest proteins in the human body: insulin.

The Smallest Human Protein: Insulin

A protein is a chain of amino acids in a particular sequence that is folded into a specific shape to function as intended. Insulin is a protein that is made up of 51 amino acids connected end to end forming a long linked amino-acid structure (polypeptide), like a long train. Once the chain of amino acids needed are all connected, it will fold in on itself in a specific way. Each protein type folds differently but what is critical is that each insulin protein is folded identically. It is often said in biology that “the form sets the function”. What  this means is that if the insulin ends up folding differently from what is expected, it is defective as insulin and cannot be used as such. Importantly, analogues can be created, which work similarly to the intended protein but are not made exactly of the above mentioned 51 amino acid molecules. In other words, we can find a different protein that has different amino acids but folds as if it were insulin, in which case it may act as an insulin analogue. Such analogues are: insulin lispro (Humalog), aspart (NovoLog), and glulisine (Apidra), as well as long-acting analogs like insulin detemir (Levemir), glargine (Lantus), and degludec (Tresiba). See the discussion on these analogues here.

Image from https://en.wikipedia.org/wiki/Insulin

On the above image you can see how the protein insulin is curved and looped. This form sets its function of what it can do, where in the body, and how. Protein is a functional element and if its amino acids change in amounts, composition, and folds, it will have vastly different functions in our body. Protein makes up the biggest part of our body other than water. About 60% is water, 16% protein, 15% lipids, minerals 5-6%, and carbohydrates and nucleic acids (our DNA/RNA) about 1% each.  

What is Protein Synthesis?

Protein synthesis is not limited to muscle repair or growth. It is essential for the regeneration of all tissues in the body as well as other substances, such as insulin. Just so you don’t get stuck on only insulin and muscles, here is a short list of some other common proteins our body (in almost every cell) makes continuously from amino acids: hemoglobin, collagen, albumin, keratin, enzymes such as lactase, amylase, pepsin, and also antibodies. So, when I recommend you eat protein, I am not thinking of your muscles… well a little… I am thinking of all your body functions!

Different cell types have distinct lifespans: gut cells renew every 2–4 days, platelets live about 10 days, red blood cells ~120 days, skin cells 3–4 months, liver cells ~6 months, and even heart muscle cells, once thought static, show slow turnover on the scale of years. Immune cells live variable length, depending on the type of immune cells: IgG 21-28 days, IgM 5 days, IgA 5-6 days, IgE 2 days, and IgD 3 days.

Meeting the body’s daily demands for cell renewal requires amino acid supply in excess of the minimum survival need! It is very hard to figure out how much protein a person needs because in addition to all of the constant cellular replacements in our body , there is also an age and activity associated factor. To demonstrate it I use a table that shows the relationship between kidney health and body weight and  also considers the body’s maximum ability to synthesize urea—a biproduct of protein synthesis, which is removed by the kidneys. We don’t want to exceed our kidneys’ ability to remove these metabolites from our blood.

In the table below the MRUS (Maximum Rate of Urea Synthesis) framework offers a practical range: for a 60 kg (132 lbs) person with an average MRUS of 65, the RDA is 48 g protein, which is too little for anyone; as you can see, the optimal intake is around 210 g, the ideal minimum is 178 gr, and the safe maximum is 258 g. Individuals with lower MRUS capacities will still have the same RDA, but their ideal minimum, optimal intake, and safe maximum values all scale down, but not to the RDA levels. This highlights the enormous variability in protein needs, far beyond the outdated RDA recommendations. Even the “1 gram per pound” rule is lower than ideal minimum for nearly everyone.

Image created by Angela A Stanton© based on data in an academic article cited above.

RDA, optimal, and maximum protein consumption recommendations per day table highlighting for a person with MRUS of 65, based on their weight what protein range they should be consuming a day. For example, if you weigh 60 kg (132 lbs) and you have healthy kidneys and liver, then your daily protein ideal is 178 gr, the RDA is 48 gr, and the maximum is 258 gr. The recommended daily protein should then be between 178gr and 258gr. Why the total daily protein of 48 gr is not sufficient will be discussed next.

But That’s a Ton of Protein!

Our protein intake must be sufficient not just to prevent deficiency in cellular replacement but to optimize protein synthesis, the body’s process of generating and repairing tissues. In other words, when you need new insulin to be produced,  genetic instructions  detail the type and quantity of amino acids that need to be copied and the order they must be connected. This happens for the creation of every single insulin molecule in every single cell that is programmed to do this task! Imagine how many times the DNA must unravel each day to make just insulin by one cell! There are all kinds of other proteins to create as well, and for each protein that is made, the DNA must unravel, the section must be copied, and the selected protein must be created from scratch in every single cell in our body. Protein synthesis is the most energy demanding process in the body.

It follows that to start protein synthesis, everything must be in order for the process, and signals must arrive to start synthesizing. The signaling molecule is the amino acid leucine. Leucine is a “branch chain amino acid”, which refers to the unique chemical structure of 3 amino acids (leucine, isoleucine, and valine), where the side chains have a branching shape. In specific, muscle protein synthesis requires a minimum amount of leucine being present together with all other amino acids, fat and glucose. The actual protein synthesis steps are too advanced for this article, but if you are interested, read about it here.

For the protein synthesis to occur, the protein consumed must deliver a minimum amount of leucine per meal—this is known as the leucine threshold per bolus meal. For younger athletes of age 20-35, ~3 grams of leucine per meal is needed to trigger protein synthesis. This requirement increases with age (and for persons who have had reduced physical activity) to ~4 grams for middle-aged folks (36–45) and ~4.5 grams or more for people over 55. These leucine suggestions are based on my own experience and not on published clinical research.

Muscle protein synthesis becomes less responsive to leucine as people age, a phenomenon known as anabolic resistance. Older muscles require higher leucine concentrations to achieve the same stimulation as younger muscles (read some articles here, here, and here). The reduced leucine sensitivity is linked to impaired activation of the mTORC1 pathway, which is crucial for protein synthesis, and may be influenced by factors like decreased nutrient delivery and age-related changes in muscle signaling.

These minimum thresholds apply per meal, not per day, and cannot be compensated for by small leucine intakes spread across multiple meals. This makes bolus protein intake amount crucial—and it’s why many experts now recommend at the minimum 1 gram of protein per pound of body weight per meal, and even more in older adults or those aiming to build new muscle cells, as well as replace old ones.

Plant Protein vs Animal Protein

If the protein source is primarily plant-based, the protein target increases. Plant proteins typically have 50% lower bioavailability than animal proteins due to antinutrients, lower digestibility, and incomplete amino acid profiles. The table below demonstrates that, for example, eating black beans, long considered a high protein legume, while it provides 8.9 gr protein per 100gr cooked beans consumed, of the 8.9 gr protein only 4.36 gr can be actually absorbed by humans. The only plant-based protein that has high bioavailability is soy protein isolate, and that is because as an isolate, all of its “plantness” disappeared. Just to compare, even the bioavailable 80 gr per 100 gr soy protein isolate is still below the bioavailable 90 gr per 100 gr whey protein powder isolate, the most commonly used “quick fix” for athletes and people who work out.

Image created by Angela A Stanton using data with AI assistance.

Even when plant and animal foods are eaten together, plant compounds impair the absorption of amino acids from both plant and animal sources, diminishing the overall anabolic signal. Phytate and tannins are the most notable plant compounds that can reduce the bioavailability of minerals and proteins in both plant and co-intake animal sources.

Phytate: Binds minerals like iron, zinc, and calcium, reducing their absorption from both plant and animal sources. Phytate can also form complexes with proteins, decreasing protein digestibility and nutrient utilization (see here and here).

Tannins: Form complexes with proteins, making them less digestible and reducing their absorption. Tannins can also decrease feed intake and overall nutrient utilization (see here).

Saponins, Oxalates, and Others: Saponins may reduce nutrient absorption and affect metabolism, while oxalates bind calcium, limiting its absorption. (see here)

Anabolic signal is what initiates “build” and “increase” functions in the cells. Because of the importance of meeting the threshold on protein and leucine, vegetarians/vegans need to sometimes more than double their plant-based protein intake to reach the same leucine threshold and effective utilization as people eating animal proteins.

So, is it really “tons of protein” that you need to eat? As we have discussed, protein requirements vary greatly among people, but it is definitely higher than the majority is used to eating or is told to eat.

Women and Protein

Women often believe that eating too much protein will make them build large unsightly muscles. But the opposite is true. Getting loose skin and being too thin reflects eating too little protein and looks unappealing and frail. Our skin cells replace 4 times a year, giving women new healthy glow—if only they let that happen in a healthy way! And I see nothing wrong with my being able to pick up a case of 24 large drinking water bottles, carry it to my car, and toss it in the trunk. That is what I do at age 71! There is nothing wrong with having strong muscles in your old age. It is desirable and is to your benefit.

Protein Synthesis—the Big Foggy Concept

Protein synthesis is the fundamental biological process by which cells build new proteins based on the instructions encoded in DNA—this is done by every single one of our skeletal muscle cells. It begins in the cell nucleus (every skeletal muscle cell has more than one nuclei, while smooth muscle cells have only one nucleus), where a specific segment of DNA is transcribed into messenger RNA (mRNA). This mRNA carries the genetic blueprint out of the nucleus to ribosomes in the cytoplasm (cell body outside of the nucleus), where it undergoes “translation” (creating a mirror image). During translation, transfer RNA (tRNA) molecules bring amino acids one by one, matching them to the mRNA sequence through codons (for example, looking for the second amino acid that is connected to the first amino acid in the instruction manual (DNA code) and so forth, 51 times in the case of insulin, this copy-paste and matching the right amino acid to the blueprint is done one by one. Each amino acid is linked together by the ribosome to form a polypeptide (many amino acids, like in the case of insulin, the polypeptide contains 51 amino acids), which then folds into a specific 3D shape (see image earlier on the shape of insulin), thus becoming a functional protein.  

Insulin Protein Synthesis—in Detail

Using insulin as a model, I will demonstrate what it means to have amino acid selection and how these amino acids are connected based on the DNA code. This is what we refer to when we discuss protein synthesis. Protein synthesis literally means “make new protein”.   

Insulin:

The chemical formula for insulin is a monster: C₂₅₇H₃₈₃N₆₅O₇₇S₆

What the chemical formula tells us is that a single insulin molecule is made up of 257 carbon, 383 hydrogen, 65 nitrogen, 77 oxygen and 6 sulfur atoms—this is two chains, A and B chains together. But if you think that you can just grab 257 carbon, 383 hydrogen, 65 nitrogen, 77 oxygen and 6 sulfur atoms and mix them in a bowl, you are very wrong. Each of these atoms belongs to amino acids, 51 of them, that when connected into 2 polypeptide links, the A chain and the B chain, and these two chains roll up with each other, an insulin molecule is created. It is quite complex for something as common and simple as insulin. Here we will look at how the amino acids line up to form this monster compound, replicating the template in the DNA.  

Insulin is made of two chains, labeled A and B chains:

• A chain: 21 amino acids
• B chain: 30 amino acids

These are connected by two disulfide bonds, with an additional internal disulfide bond within the A chain. Here is the full amino acid sequence of human insulin (see list below for the full name of each amino acid, here labeled by a letter):

A Chain (21 amino acids):

G – I – V – E – Q – C – C – T – S – I – C – S – L – Y – Q – L – E – N – Y – C – N

B Chain (30 amino acids):

F – V – N – Q – H – L – C – G – S – H – L – V – E – A – L – Y – L – V – C – G – E – R – G – F – F – Y – T – P – K – A

F—Phenylalanine; V—Valine; N—Asparagine; Q—Glutamine; H—Histidine; L—Leucine; C—Cysteine; G—Glycine; S—Serine; H—Histidine; A—Alanine; E—Glutamic Acid; Y—Tyrosine; R—Arginine; T—Threonine; P—Proline; K—Lysine; I—Isoleucine

Two amino acid types, Aspartate and Methionine, are missing from these chains as they are not part of insulin.

What insulin as a key protein generated by protein synthesis demonstrates is how the amino acids we eat are components connected into long chains in various orders to create the proteins we use! The amino acids you eat in your protein are what make your insulin and, of course, other very important elements in your body.

Amino Acid Classification

There are three groups of amino acids: Essential, Conditionally Essential, and Nonessential. 

Essential amino acids: we must eat them because our body can’t create them:

Conditionally essential amino acids: we usually can make our own, but sometimes, dependent on what we have eaten versus what proteins we must be generating under certain conditions, we run out of some of the non-essential amino acids, so we must eat them. In these instances, they become essential. For example, glycine is a conditionally essential amino acid. Under normal circumstances we make enough. But if we eat a lot of chicken breast, egg whites, beef muscle meat, pork loin, and lamb, we should also eat chicken skin, pork skin, gelatin, ox tail or tendons with our meals. Alternatively, we have to supplement glycine.  

Nonessential amino acids: are amino acids that are so important that our body always makes enough of them. These we never need to eat.  

What makes protein synthesis so remarkably complex is the precision, coordination, and regulation required at every stage. The body must choose the right gene segments at the right time, avoid mutations, splice mRNA correctly, assemble amino acids in exact order, ensure proper folding, and sometimes chemically modify the protein for full function, all while monitoring feedback signals and conserving energy. Errors can lead to nonfunctional or harmful proteins, so multiple checkpoints exist to correct mistakes. In essence, protein synthesis is not just cell maintenance; it’s the molecular execution of life’s blueprint, performed trillions of times a day with astonishing accuracy and speed.

[1] Serine may become conditionally essential in some disease states, so I listed it under both nonessential and conditionally essential.

Protein for the Elderly

You likely see lots of very frail elderly people in your life. Frailty is the symbol of old age. But it need not be so. There are some examples perhaps in your life as well of 80-year-olds looking quite healthy, lifting weights, some run half-marathons. The most well-known of these elderly is Ernestine Shepherd, who at age 85 created this YouTube video.  One can get old while feeling and looking their best. Eating lots of protein is not optional but essential!

The best thing you can do is to increase the protein you eat as you age, especially animal protein.

…wait… animal protein??? But what about mTOR and cancer and all that jazz?

mTOR, Everyone’s Fear! Cancer Connection?… Not!…

This last section is for the expert curious:

The fear largely comes from overactivation in chronic disease conditions rather than from protein intake in general:

1. Constant mTOR activation is trouble: true but under healthy, normal conditions, mTOR shuts off after synthesis, unless it is overridden by disease states, like insulin resistance.

2. Cancer: Constant mTORC1 activation promotes uncontrolled cell growth. But protein synthesis is not constant. The system needs to be dysfunctional for mTOR to be on for longer than necessary. This will happen with insulin resistance, inflammatory conditions, autoimmune diseases, or excess growth signals.
3. Aging (“Hyperfunction Theory”): Some researchers argue that persistent mTOR activity accelerates cellular aging. However, mTOR is vital for repair and regeneration, and pulsatile activation via meals or workouts is beneficial, not harmful. The key here too: pulsatile vs constant. Eating protein won’t cause constant and persistent mTOR activation.
4. Metabolic disease: Chronically elevated insulin and glucose, from a high-carb/high-fat diet, keep mTOR activated longer than ideal, especially in insulin-resistant individuals. But again, this is not due to protein, but rather to chronic disease conditions.
5. Fasting, AMPK activation, exercise, and nutrient cycling (feeding/fasting) ensure that mTOR stays in healthy balance.

When You Should Ask You Doctor About Protein

There are some conditions under which you may want to evaluate your health before eating a ton of protein. For example, if your kidney function is poor and you find high metabolites in your blood, such as albumin, globulin, protein, creatinine, and BUN, you may want to focus on improving your kidneys first by proper hydration (with salt and water) before you increase your protein consumption.

Another condition is gout. While gout is not caused by high protein initially(it is caused by overconsumption of fructose and alcohol), once you have gout you will always have gout, and high protein in your blood will make uric acid removal more difficult, increasing your chances for gout from high protein consumption as well.

Avoid a high-protein diet if you have a genetic condition affecting protein metabolism or the excretion of its metabolites. Examples: urea cycle disorders, cirrhosis of the liver or some other liver diseases, Phenylketonuria (PKU). Maple Syrup Urine Disease (MSUD), or homocystinuria, metabolic acidosis, and others.

As always, it is best to consult with your doctor about how high protein consumption may affect you.

When Should You Eat The Most Protein?

Type 2 Diabetes Protein balances glucose and insulin levels and normalizes both over time (see here and here). Eating meals with high protein also reduces your carbs cravings.

Osteoporosis Higher protein intake improves bone density when calcium and minerals are adequate. Over 35% of our bones are made of protein (collagen), which forms a scaffolding to which calcium can attach (see here and here).

Cancer Unless cachexia is present, protein is necessary to maintain tissue and immunity (see here and here).

There are a host of other health conditions that benefit from eating high amounts of protein. The list is as long as the list of diseases. What you need to know is that protein and fat are two essential macronutrients that we must eat, while carbs are not essential at all. So, plan your meals around high amounts of protein and fat and eat small amounts of carbs if you enjoy them. Learn to enjoy eating high amounts of protein!

Comments are welcomed, as always, and are moderated for appropriateness.

Angela