Protein is one of the three primary macronutrients, alongside carbohydrates and fats, that your body needs in large quantities to function properly.
It’s essential for building and repairing tissues, creating enzymes and hormones, supporting immune health, and even serving as a backup energy source.
Unlike carbohydrates and fats, protein is not stored in the body, which means you need to consume it regularly to meet your body’s demands.
The Structure of Protein: What is it Made Of?
At its core, protein is a complex molecule of amino acids, organic compounds composed of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur.
These amino acids are linked in chains to form proteins, which fold into specific shapes that determine their bodily function.
Types of Amino Acids
There are 20 amino acids that combine in different sequences to create proteins. These are categorized into three main types:
Essential Amino Acids
The body cannot produce these, so they must come from food.
There are 9 essential amino acids: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
Found in foods like meat, eggs, dairy, soy, and quinoa.
Non-Essential Amino Acids
The body can synthesize these, so they don’t need to come directly from your diet.
Examples include alanine, aspartic acid, and serine.
Conditionally Essential Amino Acids
These are usually non-essential but may become essential in times of stress, illness, or injury.
Examples include glutamine, arginine, and cysteine.
Functions of Protein in the Body
Proteins are versatile molecules with numerous roles, ranging from structural support to biochemical reactions. Here’s a deeper look at their functions:
Structural Support
Proteins like collagen and keratin provide strength and structure to tissues such as skin, hair, nails, and connective tissues.
Collagen, the most abundant protein in the body, supports bones, tendons, and ligaments.
Muscle Growth and Repair
Protein is critical for maintaining, repairing, and growing muscle tissue. This is why protein intake is emphasized after exercise or injury.
Enzymes and Catalysts
Enzymes are proteins that speed up chemical reactions in the body. For example, digestive enzymes like amylase and lipase break down food into absorbable nutrients.
Hormonal Regulation
Many hormones, such as insulin and growth hormone, are proteins. They help regulate processes like blood sugar levels, growth, and metabolism.
Immune Defense
Antibodies, that fight off infections, are specialized proteins. Without sufficient protein, your immune system may weaken.
Transport and Storage
Proteins like hemoglobin transport oxygen in the blood, while ferritin stores iron.
Energy Source
In the absence of sufficient carbohydrates or fats, the body can use protein for energy, although this is not its primary role.
Dietary Sources of Protein
Animal-Based Proteins
Animal products are considered complete proteins because they contain all nine essential amino acids in adequate amounts.
- Meat and Poultry: Beef, chicken, turkey, pork, and lamb.
- Fish and Seafood: Salmon, tuna, mackerel, shrimp, and shellfish.
- Dairy Products: Milk, cheese, yogurt, and cottage cheese.
- Eggs: A highly bioavailable source of complete protein.
Plant-Based Proteins
Most plant proteins are incomplete, meaning they lack one or more essential amino acids. However, by combining different plant-based foods, you can achieve a complete amino acid profile.
- Legumes: Lentils, chickpeas, black beans, and kidney beans.
- Nuts and Seeds: Almonds, walnuts, chia seeds, flaxseeds, and pumpkin seeds.
- Soy Products: Tofu, tempeh, edamame, and soy milk.
- Whole Grains: Quinoa, farro, amaranth, and buckwheat.
- Vegetables: Spinach, broccoli, and peas contain moderate amounts of protein.
How Much Protein Do You Need?
Your daily protein requirements depend on various factors like age, weight, activity level, and health goals. But beyond grams of protein, it’s also important to consider the calorie content of protein and how it contributes to your overall energy balance.
Calories in Protein
Protein provides 4 calories per gram, the same as carbohydrates.
Example: If you consume 56 grams of protein in a day, it contributes 224 calories to your total energy intake (56 g × 4 calories).
Daily Protein Recommendations
General population
0.83 grams of protein per kilogram of body weight per day.
For a 70-kg person (154 lbs), this equals 58 grams of protein, or 224 calories.
Active Individuals and Athletes
1.4–2.0 grams per kilogram of body weight per day.
For a 70-kg person, this would range from 84–140 grams of protein, contributing 336–560 calories.
Pregnant and Breastfeeding Women
0.83–1.3 grams per kilogram of body weight per day.
For a 70-kg person, this equals 77–91 grams of protein, or 308–364 calories.
Older Adults
0.83–1.2 grams per kilogram of body weight per day.
For a 70-kg individual, this means 70–84 grams, providing 280–336 calories.
How Many Calories Does Digesting Protein Burn?
Protein has a unique property: it requires more energy to digest and metabolize compared to fats and carbohydrates. This is called the Thermic Effect of Food (TEF).
Thermic Effect of Protein
Digesting protein burns 20–30% of the calories in the protein itself.
For example, if you consume 100 calories of protein, your body uses 20–30 calories just to process it.
In comparison, carbohydrates have a TEF of about 5–10% and fats have a TEF of about 0–3%. Therefore, consuming 100 calories of fat will require 5-10 calories to process it, and consuming carbohydrates will require only up to 3 percent to process it.
Why This Matters
The high TEF of protein means it supports a higher metabolic rate compared to other macronutrients. This makes protein particularly helpful for:
- Weight management, as it boosts calorie expenditure.
- Maintaining muscle mass during calorie deficits, as it spares muscle protein.
Complete vs. Incomplete Proteins: A Closer Look
Proteins are classified based on the amino acids they contain.
Complete Proteins
Contains all nine essential amino acids in sufficient amounts.
Found in animal products, soy, and quinoa.
Incomplete Proteins
Lack one or more essential amino acids.
Found in most plant-based foods like grains, legumes, and nuts.
By pairing incomplete proteins (e.g., rice and beans), you can create a complete protein.
The Role of Protein Timing
Protein timing—when and how you consume protein—can influence its effectiveness, particularly for muscle growth and recovery:
Protein Distribution
Spread protein intake evenly across meals to maximize absorption and muscle protein synthesis.
Post-Workout Window
Consuming protein within 30 minutes to 2 hours after exercise helps repair muscle tissue and stimulates growth.
Before Bedtime
A slow-digesting protein like casein (found in dairy) before bed can support overnight muscle repair.
Common Myths About Protein
High Protein Harms Kidneys
Research shows that high-protein diets are safe for healthy individuals. However, people with existing kidney conditions should consult a doctor.
Plant Proteins are Inferior
While individual plant proteins may lack one or more essential amino acids, a well-planned plant-based diet can meet all protein needs.
More Protein is Always Better
Excess protein is not stored as muscle; it’s either used for energy or stored as fat. Consuming beyond your needs offers no additional benefit.
You Need Protein Shakes to Build Muscle
While convenient, protein shakes are not essential. Whole foods can provide the protein you need.
Potential Risks of Low Protein Intake
- Muscle loss and weakness (sarcopenia).
- Poor wound healing and slower recovery from illness or injury.
- Weakened immune system.
- Increased risk of bone fractures.
What is Protein… In Short
Protein is an indispensable part of your diet, playing a crucial role in maintaining health, strength, and vitality.
Whether you’re aiming to build muscle, recover from injury, or simply support your overall health, consuming adequate, high-quality protein is essential.
By incorporating a variety of protein-rich foods—both animal and plant-based—you can meet your body’s needs and enjoy the full benefits of this powerhouse nutrient.