Understanding Human Nutrition: Physiology Before Philosophy

“The body has nutritional requirements regardless of our personal food preferences. Understanding how the body is designed allows us to make informed choices that support our individual health.”

The Body Is Built From Amino Acids and Fatty Acids

Every day your body must repair tissues, build hormones, produce enzymes, manufacture neurotransmitters, support your immune system, detoxify harmful compounds, and maintain muscle.

To accomplish all of this, your body continually requires two fundamental building blocks:

Amino acids

• Build muscles, organs, skin, hair and connective tissue
• Produce enzymes that digest food
• Manufacture hormones and neurotransmitters
• Support immune function
• Create glutathione, the body’s master antioxidant
• Support detoxification and methylation

Fatty acids

• Form every cell membrane
• Build the brain and nervous system
• Produce hormones and signaling molecules
• Reduce inflammation
• Support healthy skin, eyes and cardiovascular health
• Provide long-lasting energy

While vitamins and minerals are essential, they often serve as helpers that allow the body to use these amino acids and fatty acids efficiently.

How Human Digestion Is Designed

Digestion begins long before food reaches the stomach.

1. Brain Phase

The sight, smell and even the thought of food begin preparing digestion by stimulating saliva, stomach acid, digestive enzymes and bile production.

2. The Stomach

The stomach creates a highly acidic environment.

This acid unfolds proteins so digestive enzymes can begin breaking them into smaller peptides. The stomach also helps protect against harmful microbes entering with food.

3. The Small Intestine

As food leaves the stomach, it mixes with pancreatic enzymes and bile.

Bile emulsifies fats so they can be absorbed, while pancreatic enzymes complete the digestion of proteins, carbohydrates and fats into forms that can be absorbed.

Most amino acids, fatty acids, vitamins and minerals are absorbed here.

4. The Colon

The colon contains the greatest concentration of beneficial bacteria in the body.

These microbes ferment fibers that escaped digestion, produce beneficial short-chain fatty acids, synthesize certain vitamins, and support immune function and overall gut health.

Although the colon contributes greatly to health, humans absorb most of their protein and fat before food ever reaches this stage.

Why Humans Differ From Ruminant Animals

Cows, sheep and other ruminants are often used as examples of animals thriving on plants alone.

Their digestive systems are fundamentally different from ours.

They possess specialized fermentation chambers filled with billions of microorganisms that convert plant fiber into usable nutrients.

Those microbes produce short-chain fatty acids that become the animal’s primary energy source, and the microbes themselves become an important source of amino acids and protein as they move through the digestive tract.

Humans are not built this way.

We have one stomach, a relatively short colon, and far less capacity to ferment plant fiber. Our digestive system is designed to digest and absorb dietary protein directly.

This doesn’t mean plants are unhealthy. It simply means humans and ruminants obtain nutrition through different digestive strategies.

Protein Quality Matters

Protein is more than a number on a nutrition label.

The body requires all nine essential amino acids in sufficient amounts and in forms that are easily digested and absorbed.

High-quality proteins generally provide:

• All essential amino acids
• Higher digestibility
• Greater amino acid density per calorie
• Less food volume required to meet daily needs

Animal foods naturally provide complete proteins with excellent digestibility.

Most plant proteins contain lower amounts of one or more essential amino acids and are often packaged with substantially more carbohydrate and fewer grams of protein per calorie.

For example:

• 1 cup cooked quinoa provides approximately 8 grams of protein.
• 1 cup cooked lentils provides approximately 18 grams of protein, along with nearly 40 grams of carbohydrate.
• One large egg provides approximately 6 grams of complete protein.
• Four ounces of chicken or fish provides roughly 30–35 grams of complete protein.

Meeting protein needs from plant foods alone is certainly possible for many people, but it generally requires greater planning, larger food volumes, and careful attention to total calorie intake.

Essential Amino Acids Deserve Special Attention

Some amino acids are particularly important because they are difficult for the body to manufacture in adequate amounts.

Examples include:

Methionine
Supports methylation, detoxification, glutathione production and liver function.

Leucine
Essential for maintaining muscle mass and stimulating muscle protein synthesis.

Lysine
Supports collagen formation, immune health and tissue repair.

Glycine
Supports collagen, connective tissue, sleep and glutathione production.

Taurine
Supports bile production, nervous system function and cardiovascular health.

Some of these nutrients are abundant in animal foods but occur in much smaller amounts—or not at all—in plant foods.

Essential Fatty Acids Matter Too

The body requires omega-3 and omega-6 fatty acids but cannot manufacture them from scratch.

DHA and EPA are the forms most readily used by the brain, eyes and nervous system.

Plant foods provide ALA, which the body must convert into DHA and EPA.

This conversion is highly variable and often limited, making it important for individuals following plant-based diets to pay close attention to their omega-3 status.

If You Choose a Plant-Based Diet

Many people choose vegetarian or vegan eating patterns for personal, cultural or ethical reasons.

If this is your preference, thoughtful planning becomes especially important.

Pay particular attention to:

• Total daily protein intake
• Protein quality
• Methionine and leucine intake
• Vitamin B12
• Iron
• Zinc
• Iodine
• Omega-3 fatty acids (DHA and EPA)
• Choline
• Vitamin A (retinol)
• Digestive health and nutrient absorption

The goal is not to change your values. The goal is to understand your body’s nutritional requirements so you can meet them as effectively as possible.

Individual Needs Matter

No single eating pattern is ideal for everyone.

Rather than asking which diet is “best,” a more helpful question is:

Is my body receiving the nutrients it needs to thrive?

Your symptoms, laboratory testing, body composition, energy, muscle mass, digestion and overall health provide valuable feedback about whether your current nutrition is meeting your body’s needs.

Understanding physiology empowers you to make informed decisions that align both with your values and with your health.