What Protein Really Does for Your Body—and How to Know If You're Getting Enough (2025)

Proteins are a fundamental part of life, woven into the very fabric of every living organism. They play countless roles, from driving essential biological processes to providing the structure that holds life together. But what exactly is protein, and why is it so vital to our existence? To understand this, we first need to unravel the mysteries surrounding this complex and fascinating molecule. Keep reading to learn exactly what protein is and why you need it.

What Is Protein?

Protein is one of the major components of a healthy, functional body. “Protein is a macronutrient that every cell in our body needs. Proteins are made up of building blocks called amino acids, and protein is found in every cell throughout our body, so an adequate amount of protein intake is important for keeping our muscles, bones and tissues healthy,” says Kristen Smith, M.S., RDN. Other macronutrients include carbohydrates and fat.

More than 500 amino acids have been identified in nature, and 20 of them make up the proteins found in the human body. Nine of these are considered “essential,” meaning that the body cannot make them by itself, so they need to come from food. These are isoleucine, leucine, valine, methionine, phenylalanine, tryptophan, threonine, histidine and lysine.

Why Do You Need Protein?

Protein is essential for countless bodily processes, playing a critical role in functions like bone health, digestion and energy production. Here are some reasons why we need protein.

Building Blocks of Enzymes

One of protein’s most important roles is serving as the foundation for enzymes—biological molecules that drive nearly every reaction within our cells. “Enzymes affect the rate of a physiological process, so they can speed up a reaction in the body,” explains Jessica Bihuniak, Ph.D, RDN. These proteins work by binding to specific molecules, called substrates, at a region known as the active site. Once bound, enzymes facilitate chemical reactions, allowing them to occur much faster. For example, some enzymes break down large food molecules into smaller components, making them easier for the body to absorb. Enzymes are also central to energy production, working collaboratively with substances like stomach acid and bile to support digestion. By enabling these vital processes, proteins and the enzymes they form ensure the body runs smoothly and efficiently.

Supports Bone Density

Bone density is a health consideration that has been linked to protein intake for decades. Both plant and animal proteins play a role in bone health support, and combining them with regular physical activity is key to keeping bones strong.

Supports Muscle Repair

Protein is vital for muscle growth and repair, especially after exercise. “Our body is in a constant state of turnover and growth when it comes to muscular tissue, and we need those individual amino acids to go in there and repair,” says Alex Caspero, M.A., RD. “When we have any break in our tissue from exercise, that’s when amino acids go in and not only make that muscle stronger, but more capable of increasing next time. That’s essentially how you build muscle.” However, Caspero adds that contrary to myths, eating protein, such as chicken, is not going to make bulk all on its own.

Additionally, protein helps strengthen your body on the outside in the form of keratin and collagen. Keratin is a protective protein in hair, skin and nails, and it has been shown to make hair smoother and easier to manage. Collagen, on the other hand, is considered the most abundant protein in the body, providing structure to your skin and aiding in blood clotting. You can encourage your body to produce collagen by consuming foods with vitamin C, copper (found in organ meats, sesame seeds, cashews and lentils) and proline (found in egg whites, dairy products, cabbage, asparagus and mushrooms).

Protein Sources

Dietary sources of protein include animal products, like meat and dairy, as well as some plant-based foods, including nuts, seeds, whole grains and legumes. Here’s a closer look at the differences between animal- and plant-based protein sources, along with examples of protein-containing foods.

Animal vs. Plant-based Protein

The biggest difference between animal- and plant-based sources of protein is the presence of “complete” proteins. Complete proteins contain all nine essential amino acids. Examples of complete protein sources include milk, pork, beef, eggs, poultry and fish. While the majority of these sources are animal products, soy foods, such as tofu, quinoa and pistachios, are plant-based alternatives that are complete as well. “Amino acid composition is the biggest thing,” Bihuniak says. “Some [animal-based protein sources] tend to be higher in certain amino acids like leucine, which is important for muscle protein synthesis, but you can meet your needs with plant protein sources if you eat a variety.”

For decades, a long-held myth asserted that vegetarians and vegans had to combine specific foods if they wanted to form a complete protein. “When the rise of vegetarianism came out in the ’60s and ’70s, it was very much commonplace to discuss the idea of combining certain foods. So you had to have a piece of whole-grain bread with peanut butter to get your ‘complete’ food; you had to eat beans and rice to make a complete protein. And that carried on for a long time,” Caspero says. “We recently found out that plant foods do contain all of the essential amino acids. They just contain limited amounts of some of them.” This means that it’s very possible to get sufficient amounts of essential amino acids on a plant-based diet. You just may need to eat a larger volume of food and be more intentional about enjoying a variety of protein sources.

Examples of High-Protein Foods

Looking to pack your plate with more protein? It can be found in a variety of sources that you can incorporate into any meal of the day. Here are some protein choices that can fit into a balanced and healthy diet:

• Chicken Breast (cooked, skinless): 26 grams per 3-ounce serving
• Eggs: 6 grams per large egg
• Greek Yogurt (plain, low-fat): 20 grams per 7-ounce serving
• Ground Beef (90% lean): 22 grams per 3-ounce serving
• Salmon (cooked): 19 grams per 3-ounce serving
• Shrimp (cooked): 20 grams per 3-ounce serving
• Tofu (firm, raw): 15 grams per 3-ounce serving
• Lentils (cooked): 18 grams per 1-cup serving
• Chickpeas (cooked): 15 grams per 1-cup serving
  

How to Know If You're Getting Enough

While many Americans are concerned about getting enough protein, they are more likely to consume too much. “If you’re including protein with most meals and with some snacks, you’re likely consuming an adequate amount,” Smith says. Bihuniak adds, “You really have to restrict your diet to not meet your body’s protein needs.” The daily amount of dietary protein recommended for adults is 0.8 grams per kilogram of body weight, or just over 7 grams for every 20 pounds of body weight. For a person with a 140-pound weight, for example, that equals about 50 grams of protein per day.

However, keep in mind that this recommendation is the minimum amount of protein you need, and your actual protein needs may be higher. Activity level, age and health status are just a few variables that influence protein needs. “[For] endurance athletes, that might pop up to about 1.2 [grams per kilogram]. Maybe the higher end is about 1.5 if you’re doing a lot of strength workouts. But I do think that the average person also overestimates how active they are,” says Bihuniak.

You may also need more protein if you’re trying to lose weight. “Eating dietary protein is what we consider to be protein-sparing, meaning the idea that when we lose weight, we don’t just lose fat,” Caspero says.

Consuming too much protein can have unintended consequences, even if it seems like a healthy choice. Excessive protein intake may put extra strain on your kidneys, leading to potential long-term issues. It can also result in dehydration if you’re not drinking enough water to balance it out. Additionally, diets high in protein may lack necessary nutrients like fiber, leading to digestive troubles. Finding the right balance is key to maintaining both physical health and overall well-being.

The Bottom Line

Incorporating a variety of healthful protein sources into each meal is key for optimal health. If you’re looking to increase intake, Smith recommends making sure at least a fourth of your plate includes a protein source, as well as substituting that midday bag of chips with protein-rich snacks, such as nuts, yogurt and cheese. While many meat sources are considered complete proteins, experts recommend being mindful of the saturated fat found in certain meats.

“We don’t just eat single nutrients. We eat food,” says Caspero. “If I’m eating black beans, yes, I’m getting protein. But I’m also getting a lot of insoluble fiber. I’m getting antioxidants. I’m getting other things that are in that food.” Many plant-based sources of protein also contain these healthful nutrients, such as fiber and antioxidants. “It’s important we consider what else is in the food,” she says.