The Ultimate Guide to Protein: Functions, Sources, and Health Impacts

By Jennifer Youngren, NDTR

Pumpkin seeds are a great source of plant-based protein to fuel your body and support your health goals. 🎃💪

Protein is one of the three essential macronutrients that our bodies rely on to function optimally. It plays a crucial role in a wide range of physiological processes, including tissue repair, immune defense, and the production of enzymes, hormones, and structural components such as muscles, skin, and hair. While carbohydrates are the body’s primary energy source and fats serve as long-term energy storage, protein is indispensable for maintaining and repairing tissues and supporting various metabolic functions.

However, not all proteins are the same. They come in different forms, including complete and incomplete proteins, as well as from diverse sources such as plant-based and animal-based foods. In recent years, protein powders have gained popularity due to their convenience, but the quality and effectiveness of these supplements can vary widely.

This article takes a comprehensive, science-driven approach to understanding protein—exploring its vital role in cellular function, the best food sources, the use of protein supplements, and how protein affects the health of various organs.

The Basics: What is Protein?

Proteins are large, complex molecules composed of amino acids, which are the fundamental units required for biological processes. There are 20 amino acids, and they are classified into three groups:

Essential amino acids (9): Must be obtained from the diet.

Non-essential amino acids (11): Can be synthesized by the body.

Conditionally essential amino acids: Usually non-essential but may become essential under stress, illness, or injury (e.g., glutamine during trauma recovery).

How Protein Works at the Cellular Level

Proteins are fundamental to nearly every biological process, acting as structural components, enzymes, hormones, and immune defenders. At the cellular level, protein production is a highly regulated process that ensures proper function and growth. This section breaks down how proteins are synthesized, their role in enzyme activity, hormone regulation, immune function, and structural integrity.

Protein Synthesis: DNA and RNA’s Role in Building Proteins

The process of protein synthesis is controlled by DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). It occurs in two main stages: transcription and translation.

Transcription (Copying the Code):
- Inside the nucleus, DNA provides the blueprint for making proteins.
- Messenger RNA (mRNA) transcribes (copies) the genetic code from DNA and carries it to the ribosome, the cell’s protein-making machinery.
Translation (Assembling the Protein):
- Transfer RNA (tRNA) brings specific amino acids to the ribosome, assembling them in the correct order based on the mRNA sequence.
- The ribosome links the amino acids together through peptide bonds, forming a polypeptide chain, which later folds into a functional protein.

This precise process ensures the production of structural proteins, enzymes, and hormones necessary for survival.

Enzyme Production: Catalyzing Chemical Reactions

Many proteins function as enzymes, which are biological catalysts that speed up chemical reactions essential for metabolism, digestion, and energy production.

Amylase: Breaks down carbohydrates into simpler sugars.
Lipase: Helps digest fats by breaking them into fatty acids and glycerol.
Protease (Pepsin, Trypsin): Breaks down proteins into amino acids for absorption.
DNA Polymerase: Assists in DNA replication and repair.

Without enzymes, chemical reactions would occur too slowly to sustain life.

Hormone Regulation: Proteins as Chemical Messengers

Proteins also play a major role in hormone production, helping regulate metabolism, growth, stress response, and reproductive functions.

Insulin: A protein hormone that regulates blood sugar levels by signaling cells to absorb glucose.
Glucagon: Works opposite to insulin by raising blood sugar levels when needed.
Thyroid Hormones (T3 & T4): Control metabolism, energy production, and growth.
Growth Hormone (GH): Stimulates cell growth and regeneration.

Protein-derived hormones ensure the body maintains balance (homeostasis) and responds effectively to internal and external changes.

Immune System Function: Proteins as Defenders

Proteins are essential for a strong immune system, helping the body recognize and fight off pathogens.

Antibodies (Immunoglobulins): Specialized proteins that recognize, bind to, and neutralize viruses and bacteria.
Cytokines: Proteins that regulate immune responses and inflammation.
Complement Proteins: Assist antibodies in destroying harmful invaders and clearing infections.

Without these protein-based defenses, the immune system would be ineffective at protecting the body from illness.

Structural Proteins: Building and Maintaining Body Tissues

Proteins provide structural integrity to tissues, ensuring strength, elasticity, and durability.

Collagen: The most abundant protein in the body, supporting skin elasticity, joint health, and wound healing.
Keratin: A tough, fibrous protein that forms hair, nails, and skin.
Elastin: Gives tissues the ability to stretch and recoil, found in skin, blood vessels, and lungs.

These structural proteins maintain the body’s framework, supporting movement, protection, and cellular function.

The Bigger Picture: Why Protein is Essential for Life

Protein is more than just a macronutrient—it is involved in every cellular function, from DNA replication and tissue repair to immune defense and hormone balance. Ensuring adequate protein intake from diverse, whole food sources supports optimal health, longevity, and resilience.

Types of Proteins

Proteins can be classified in several ways, including their amino acid composition and their source. Understanding the differences between complete and incomplete proteins as well as animal-based and plant-based proteins can help optimize protein intake for overall health.

Complete vs. Incomplete Proteins

A complete protein contains all nine essential amino acids that the body cannot produce on its own. These proteins are typically found in:

Animal sources such as meat, fish, eggs, and dairy.
Plant-based sources including quinoa, soy, hemp seeds, chia seeds, and buckwheat.

In contrast, an incomplete protein lacks one or more essential amino acids. Most plant-based protein sources fall into this category, including legumes, grains, nuts, and seeds. However, incomplete proteins can still provide all essential amino acids when combined strategically. This is where complementary proteins come into play—pairing two or more incomplete proteins can create a complete amino acid profile. Examples include:

Rice and beans
Hummus with whole wheat pita
Peanut butter on whole grain bread

By combining different plant-based proteins throughout the day, individuals following a vegetarian or vegan diet can ensure they are meeting their essential amino acid needs.

Animal vs. Plant-Based Proteins

Protein sources can also be categorized based on whether they come from animals or plants.

Plant-Based Protein Highlights:

Legumes (beans, lentils, peas): High in lysine but lower in methionine.
Grains (rice, wheat, oats, corn): High in methionine but lower in lysine.
Nuts & seeds (almonds, walnuts, flaxseeds, sunflower seeds): Rich in protein and healthy fats, making them beneficial for heart health.

Since different plant proteins have varying amino acid profiles, incorporating a variety of plant-based protein sources can help ensure balanced nutrition.

Amino Acids and Their Functions

Amino acids are the building blocks of proteins and play a vital role in nearly every biological process in the body. There are 20 amino acids, nine of which are classified as essential amino acids, meaning they must be obtained through diet. The remaining 11 are non-essential, as the body can synthesize them. Each amino acid has unique functions, influencing everything from muscle growth and recovery to hormone production and immune support.

Below is a breakdown of key amino acids, their roles in the body, and the best food sources to obtain them naturally.

Key Amino Acids and Their Benefits

Lysine

Function: Essential for collagen production, wound healing, and immune support. Lysine plays a crucial role in calcium absorption, which contributes to bone health and muscle repair. Additionally, it has antiviral properties and may help prevent and reduce the severity of cold sores caused by the herpes simplex virus (HSV).
Food Sources: Found in high amounts in legumes (lentils, chickpeas, black beans), quinoa, eggs, fish, and dairy products.

Arginine

Function: Enhances blood circulation by boosting nitric oxide (NO) production, which relaxes blood vessels and improves oxygen and nutrient delivery to tissues. Arginine is often used to support cardiovascular health, reduce blood pressure, and enhance exercise performance. It also plays a role in wound healing and immune function.
Food Sources: Commonly found in nuts (walnuts, almonds, peanuts), seeds (pumpkin, sesame, sunflower), soybeans, chicken, and fish.

Leucine (A Branched-Chain Amino Acid – BCAA)

Function: One of the most important amino acids for muscle protein synthesis. Leucine activates the mTOR pathway, which signals the body to build muscle. It also plays a role in blood sugar regulation and energy production during exercise.
Food Sources: Rich sources include dairy products (cheese, milk, yogurt), eggs, soybeans, lean meats, fish, and pumpkin seeds.

Glutamine

Function: A conditionally essential amino acid, meaning the body can usually produce it but may require more during periods of stress, illness, or injury. Glutamine is crucial for gut health, as it supports intestinal cell repair and reduces inflammation in the digestive tract. It also enhances immune function, making it beneficial for recovery after illness or intense exercise.
Food Sources: Naturally found in bone broth, spinach, cabbage, beets, tofu, and animal proteins such as beef and chicken.

Tryptophan

Function: A precursor to serotonin, the neurotransmitter responsible for mood regulation, sleep, and stress response. It also helps produce melatonin, the hormone that regulates sleep-wake cycles. Adequate tryptophan intake can support mental well-being and improve sleep quality.
Food Sources: Found in turkey, bananas, pumpkin seeds, oats, cheese, chocolate, and tofu.

Other Notable Amino Acids

Methionine: Essential for detoxification, metabolism, and antioxidant production. Found in meat, fish, eggs, and Brazil nuts.
Phenylalanine: A precursor to dopamine, norepinephrine, and epinephrine, making it crucial for mental alertness and cognitive function. Found in dairy, meat, and soy products.
Histidine: Supports red blood cell production, tissue repair, and immune function. Found in poultry, fish, nuts, and whole grains.
Threonine: Important for skin and connective tissue health, as it contributes to collagen and elastin formation. Found in cottage cheese, lentils, and leafy greens.

Balancing Amino Acid Intake for Optimal Health

Consuming a variety of whole foods ensures a balanced amino acid profile, especially for those following plant-based diets. While animal proteins naturally contain all essential amino acids, plant-based eaters can achieve the same benefits by incorporating diverse protein sources, such as legumes, grains, nuts, and seeds.

Protein, Carbohydrates, and Hormones: The Powerful Connection

It’s not just about protein alone—your body’s hormonal balance, including mood-regulating hormones like serotonin, relies on a synergy between protein and carbohydrates. Serotonin, often referred to as the "feel-good" hormone, is produced in the brain and plays a significant role in regulating mood, sleep, and even appetite. What many people don't realize is that serotonin is made from an amino acid called tryptophan, which comes from dietary protein. However, tryptophan needs to be transported across the blood-brain barrier to be converted into serotonin, and carbohydrates play a key role in this process.

When you consume carbohydrates, your body releases insulin, which helps to clear other amino acids from the bloodstream. This creates a more favorable environment for tryptophan to enter the brain. Essentially, the combination of protein (providing tryptophan) and carbohydrates (facilitating tryptophan's entry into the brain) works together to increase serotonin production. This is why balanced meals containing both protein and carbohydrates can help maintain better mood stability and energy levels.

For example, a meal that includes both lean protein (like chicken or tofu) and complex carbohydrates (such as whole grains or sweet potatoes) can promote a healthy production of serotonin, contributing to a positive mood and improved overall well-being. It’s a reminder that the nutrients we consume don’t just work in isolation; they interact to influence numerous bodily functions, including hormone regulation, in ways that are crucial for our health.

Protein Supplements: What You Need to Know

Protein powders are a convenient way to supplement your diet, especially for those with busy lifestyles or specific fitness goals. However, when choosing a protein supplement, it’s important to consider both the quality and the source of the protein. Here's a breakdown of some common protein powders, their benefits, and things to keep in mind when using them.

Whey Protein (Animal-Based)Whey protein is derived from milk and is a fast-digesting protein that is rich in leucine, an essential amino acid that plays a key role in stimulating muscle protein synthesis and promoting muscle growth. Its rapid absorption makes it an excellent option for post-workout recovery, as it quickly replenishes muscle proteins. However, since whey is dairy-based, it can cause digestive issues for individuals who are lactose intolerant due to its lactose content, potentially leading to bloating, cramps, or gas.
Casein Protein (Animal-Based)Casein protein is also derived from milk but digests more slowly than whey, providing a steady release of amino acids into the bloodstream over several hours. This makes it ideal for providing sustained muscle repair and preventing muscle breakdown during long periods without food, such as overnight. Like whey, however, casein is dairy-based, which may cause digestive issues for those with lactose intolerance.
Vegan Protein Powders
- Pea Protein: Pea protein is rich in branched-chain amino acids (BCAAs), particularly leucine, isoleucine, and valine, which are essential for muscle recovery and the repair of muscle tissue. It is also highly digestible, making it a good choice for individuals looking for plant-based protein options.
- Hemp Protein: Hemp protein contains essential omega-3 fatty acids, particularly alpha-linolenic acid (ALA), which support cardiovascular health, as well as high amounts of fiber that aid digestion. It is also a good source of plant-based protein, though it is lower in certain amino acids compared to other protein sources.
- Brown Rice Protein: Brown rice protein is hypoallergenic, making it a safe option for those with food allergies. It is often combined with pea protein to improve its amino acid profile, as rice protein is low in lysine, an essential amino acid, while pea protein is high in lysine. Together, they create a more complete protein.
- Soy Protein: Soy protein is one of the few plant-based proteins that is considered a complete protein, meaning it contains all nine essential amino acids that the body cannot produce on its own. It is particularly rich in leucine, making it beneficial for muscle growth and recovery. Additionally, soy protein contains isoflavones, a type of phytoestrogen, which have been shown to potentially lower the risk of breast cancer by influencing estrogen receptors in the body. Research suggests that these phytoestrogens may help protect against the development of breast cancer cells, making soy protein a valuable choice for overall health. Soy protein is also a good source of antioxidants, vitamins, and minerals, including calcium and iron. However, some individuals may have soy allergies, and while phytoestrogens are generally considered safe, there has been some debate about their effects on hormone levels. Still, the body of evidence supporting soy’s health benefits continues to grow.
- Pumpkin Seed Protein: Pumpkin seed protein is high in magnesium, zinc, and iron, and is rich in essential amino acids, including tryptophan. It has a slightly nutty flavor and is highly digestible. It is also beneficial for supporting immune function and promoting heart health due to its high levels of healthy fats and antioxidants. This protein is hypoallergenic, making it a great choice for those with allergies to other plant proteins like soy or gluten.
- Chia Protein: Chia protein is made from the seeds of the chia plant, which are packed with fiber, omega-3 fatty acids, and antioxidants. Chia protein is a complete protein, offering all nine essential amino acids. It also has the added benefits of being high in fiber, which supports digestion and helps with satiety. It may be slightly lower in protein content compared to other sources, but it is still a valuable plant-based protein source.
- Almond Protein: Almond protein is made from the byproduct of almond milk production and is rich in vitamin E, magnesium, and heart-healthy fats. While it is not a complete protein (lacking in some essential amino acids), it still provides a good balance of amino acids and can be combined with other plant proteins like pea or rice protein to create a complete profile. Almond protein is also a good source of fiber, which aids digestion and promotes fullness.
- Sunflower Seed Protein: Sunflower seed protein is another hypoallergenic option that is rich in vitamins and minerals, including magnesium, selenium, and vitamin E. It contains a decent amount of essential amino acids but is particularly high in arginine, which supports muscle health and recovery. It is often used in plant-based protein blends to improve amino acid profiles.

Concerns with Protein Powders

While protein powders can be a convenient and beneficial supplement for those looking to meet their protein needs, it’s important to approach them mindfully. There are a few considerations to keep in mind to ensure you're making the healthiest and most informed choices.

Heavy Metal Contamination: Some protein powders, particularly cheaper or lower-quality brands, have been found to contain high levels of heavy metals like lead and arsenic. These contaminants are concerning because they can accumulate in the body over time, potentially leading to long-term health issues, particularly in the kidneys, liver, and nervous system. To minimize risk, it’s advisable to choose protein powders from reputable brands that test for heavy metals and provide transparency about their sourcing and testing practices.

Additives & Fillers: Many protein powders contain additives like artificial sweeteners, flavors, and thickeners to improve taste and texture. While these ingredients may not pose an immediate health risk, they can detract from the overall nutritional value and may not align with a balanced, mindful eating approach. For example, some sweeteners can cause digestive discomfort in sensitive individuals or may contribute to cravings for sweeter foods, which can affect your relationship with food. It’s best to look for protein powders with simple ingredient lists, free from unnecessary additives, or opt for those that use natural sweeteners like stevia or monk fruit if you prefer a sweeter taste.

FDA Regulation: Protein powders are not strictly regulated by the FDA, meaning that the quality and safety of these products can vary widely. To ensure that you're consuming a product that is both safe and effective, look for third-party certifications such as NSF Certified for Sport or Informed Choice. These labels indicate that the product has been tested for safety, quality, and compliance with certain standards. This is particularly important for athletes or those with specific health concerns, as some protein powders may contain banned substances or impurities that aren’t immediately obvious from the label.

How Much Protein Do You Need?

Protein is a vital macronutrient that supports muscle growth, immune function, and overall health. However, the amount of protein your body requires depends on several factors, including your activity level, age, and health status. For example, athletes and individuals recovering from illness may have higher protein needs compared to someone who is less active.

Too Much Protein?

While protein is essential, consuming too much can lead to several health issues. For individuals with pre-existing kidney disease, excessive protein intake can be particularly harmful. High protein consumption increases the glomerular filtration rate (GFR), which can put strain on the kidneys and potentially lead to kidney damage over time.

In addition to kidney concerns, overconsumption of protein, especially from processed meats, may contribute to the development of heart disease. Processed meats are often high in saturated fats and sodium, both of which can negatively impact cardiovascular health. Moreover, when protein intake is excessive, it can lead to dehydration. This happens because your body excretes more nitrogen in urine as it processes the protein, which can result in a loss of fluids.

A Balanced Approach

Instead of focusing solely on protein supplements, it is important to prioritize whole-food sources of protein such as lean meats, fish, beans, and legumes. Whole foods provide a variety of nutrients that your body needs to function optimally, including fiber, vitamins, and minerals. Protein supplements should be used when necessary, particularly for individuals with higher protein requirements, such as athletes or those recovering from illness or surgery. When used appropriately, supplements can help fill gaps in your diet but should not replace balanced, nutrient-dense meals.

Protein and Organ Health

Protein is essential for a variety of bodily functions, but excessive intake can have an impact on different organs:

Kidneys: Consuming too much protein can stress the kidneys by increasing the GFR, which may lead to kidney damage over time.
Heart: High-protein diets that include lean sources like poultry and fish may support heart health. However, consuming excessive red meat has been linked to an increased risk of heart disease due to its higher content of saturated fats.
Liver: The liver is responsible for processing amino acids from the protein you consume. Too much protein can overload the liver and potentially impair its ability to function effectively.
Lungs: Protein plays a role in supporting immune function, which can help maintain respiratory health.
Skin & Hair: Collagen and keratin are both proteins that help maintain the elasticity of your skin and the strength of your hair. Adequate protein intake is essential for healthy skin and hair growth.

The Key is Balance

Protein is a vital component of a healthy diet, playing an essential role in muscle repair, immune function, and overall bodily health. However, the key to achieving optimal health is not just about meeting your protein requirements but also ensuring that the protein sources you consume are diverse and of high quality. Whole foods such as lean meats, fish, beans, lentils, and whole grains provide a wide range of essential nutrients that work together to support your health. These foods offer not only protein but also fiber, vitamins, minerals, and antioxidants that help keep your body functioning at its best. Additionally, plant-based proteins, such as those from legumes, soy, quinoa, and hemp, offer a great alternative to animal-based proteins, providing nutritional benefits while supporting those who prefer or require a plant-based diet.

When protein supplementation becomes necessary—whether due to higher protein needs or convenience—it’s crucial to choose clean, high-quality products. Opt for supplements free from artificial fillers, additives, and excessive sweeteners. It’s also important to select well-tested, safe products, such as those with third-party certifications like NSF Certified for Sport. The balance in your protein intake is about finding the right amount for your body’s needs, while also ensuring that your choices align with your health goals. Remember, protein is just one piece of the puzzle when it comes to nutrition. By incorporating a variety of food sources, you will create a sustainable and nourishing approach to supporting your health for the long term.

Disclaimer: This article is for educational purposes only and is not intended to diagnose or treat any medical condition. It is recommended to consult with a healthcare professional before making any changes to your diet or protein intake.