Protein 101 – The Basics

Protein is one of the most important nutrients for human health. It is one of three macronutrients, alongside carbohydrates and fats, that the body needs to function properly. Foods that provide these macronutrients also supply many vitamins and minerals (micronutrients), making them the foundation of a balanced dietary pattern.

The role of protein

Proteins are made of amino acids, which are organic molecules that your body needs to build, maintain, and repair tissues. It’s a major component of muscles, organs, skin, hair, nails, bones, tendons, and ligaments. Protein also plays essential roles in:

• Building and repairing cells and tissues
• Supporting muscle growth, maintenance, and contraction
• Producing enzymes, hormones, and other important body chemicals
• Carrying oxygen, vitamins, minerals, and other nutrients throughout the body
• Supporting immune system function and helping fight infection
• Promoting wound healing and blood clotting
• Maintaining fluid and acid-base balance in the body.^1,2,3,4

The body is constantly breaking down and rebuilding proteins through a process called protein turnover. Regular dietary supply of protein is needed to provide the amino acids required to support these vital functions.^1,4

The role of amino acids

To better understand protein, it helps to understand amino acids, the building blocks that make up proteins. Your body uses 20 different amino acids to build the different proteins it needs for growth, repair, immune function, and many other important jobs, much like using the same 20 Lego blocks to create different structures.

When you eat protein-rich foods, your digestive system breaks the proteins down into individual amino acids. The body then absorbs these amino acids and sends them where they’re needed. Inside your cells, special cellular “messengers” use instructions from your genes to link amino acids together in a specific order, creating new proteins for the body.

Like a LEGO creation that can be taken apart and rebuilt into something new, amino acids from food can be broken down and reassembled into many different proteins.

Of the 20 amino acids, the body can make 11, while 9 are essential amino acids that must be obtained from food sources. Different protein foods provide different types and amounts of amino acids, so not all protein sources are exactly the same. This is one reason scientists are increasingly interested in protein quality, which is determined by a food’s amino acid profile (the types and amounts of essential amino acids) and its digestibility (how efficiently the body can break down and absorb these amino acids). Based on these factors, proteins are classified as complete if they provide all 9 essential amino acids, or incomplete if they are limited in one or more of them. Protein quality therefore goes beyond total amount of protein and focuses on how well a food provides the amino acids your body needs.⁵

Most animal-based foods, such as meat, eggs, and dairy are complete proteins, while many plant-based foods are incomplete proteins. However, there are a few exceptions, including soy foods (e.g. tofu, tempeh, and edamame), quinoa, buckwheat, and amaranth, which provide all 9 essential amino acids. Including plant protein in your diet is also important because they provide fiber, vitamins, minerals, and beneficial plant compounds in addition to protein. By eating a variety of plant protein foods such as beans, lentils, nuts, seeds, and whole grains, the body can obtain all essential amino acids it needs over the course of the day.

A good place to start is by choosing whole food sources of protein, like

• lean meats
• eggs
• legumes (beans, peas, lentils)
• nuts
• seeds

You can make these protein foods part of your healthy eating pattern by balancing them with complex carbohydrates and healthy fats.

The role of dietary guidelines

The recent 2025-2030 Dietary Guidelines for Americans emphasize protein distribution across meals and suggest an intake range of approximately 1.2-1.6 grams per kilogram body weight per day, depending on individual needs.⁶ This is higher than the Recommended Dietary Allowance (RDA) of 0.8g/kg/day. The RDA represents the minimum amount of protein to prevent deficiency, while the Dietary Guidelines for Americans reflect evidence that higher protein intake may support optimal health outcomes.

Before adding more protein to your diet, it’s helpful to know how much you currently consume. Many Americans already have an adequate protein intake. One way to know your protein intake is by tracking your food for a few days without changing anything about your diet. Use an app that tracks macronutrients, such as Cronometer, MyFitnessPal or MyNetDiary, so you can see your protein intake, specifically.

Remember, simply adding protein to your diet is not the goal. Making these changes alone may lead to weight gain or crowd out other important nutrient sources.⁷ You need to be sure you’re meeting your protein and other nutrient needs within your daily calorie budget.

The role of exercise

Simply eating more protein does not automatically build muscle, speed up metabolism, or lead to major changes in body composition. Your body needs a signal to use that protein to build muscle strength and mass and/or preserve muscle during weight loss – that signal is exercise.^7,8

Think of protein as the building material and exercise as the signal to build. Without that signal, extra protein is more likely to be used for energy or stored as calories rather than turned into new muscle tissue. Research consistently shows that higher protein intake is most effective when combined with resistance training. Together, they help stimulate muscle protein synthesis, the process by which your body repairs and builds muscle after exercise.⁹

For weight loss, calories still matter most. However, getting enough protein while exercising regularly can help preserve lean muscle as you lose fat.¹⁰ Getting enough protein may also improve fullness and satisfaction after meals, and support recovery from workouts so you can stay active.

Creating a healthy goal

A healthy goal is to take a balanced approach. Include protein at each meal, spread it throughout the day, and pair it with regular movement and strength training. Aim for regular walking (or participating in other aerobic activity) plus 2-3 days of resistance training per week to help your body use dietary protein more effectively, improving muscle mass, and overall health.^8,11,12

More protein is not a shortcut to a leaner body. Instead, protein works best as part of a broader healthy lifestyle pattern that includes resistance training, regular physical activity, adequate sleep, and a balanced eating pattern.