The human body uses three main macronutrients: carbohydrates, proteins and fats.
All three are necessary, just in different amounts, and protein is the one that tends to get the most attention whenever people start talking about muscle, metabolism or “getting healthy.”
For most adults, the recommended range is that about 10% to 35% of daily calories come from protein, as noted in the Dietary Guidelines for Americans. Just keep in mind that many protein-rich foods also come packaged with fat, carbohydrates, fiber, vitamins and minerals, because food rarely shows up as just one nutrient.
In other words, chicken is not just protein, beans are not just carbs and nuts are not just fat. Nutrition loves to be less tidy than we want it to be.
How Do Our Bodies Use Protein?
Protein is needed for growth, repair, immune function, hormone production, fluid balance and the structure of almost every cell in the body.
There are many different types of proteins in human biology, but two big categories worth knowing are enzymes and structural proteins. And truly, nothing, absolutely nothing, in the human body happens without the involvement of protein.
Every single biochemical reaction, from the breakdown of glucose into carbon dioxide and water to the formation of new bone after a fracture, involves enzymes. Proteins also help move substances around the body, support the immune system and maintain tissues that are constantly being repaired and replaced.
Structural proteins include collagen in the skin and in connective tissues like tendons, ligaments and cartilage.
Cartilage is found in the larynx and respiratory tract and the external ear. It also lines the articulating surfaces of the knees, ankles and elbows.
The infant skeleton contains a higher percentage of cartilage than the adult skeleton and is gradually replaced by bone as a child grows. What kind of protein helps make this transition from cartilage to bone possible?
Enzymes.
Not very glamorous, I know, but enzymes are basically doing the behind-the-scenes work while the rest of us are just trying to remember where we put our water bottle.
What Is an Enzyme?
An enzyme is a type of catalyst, meaning it helps speed up a chemical reaction by lowering the activation energy needed for that reaction to get started, as explained in the NCBI Bookshelf.
Catalysts work by helping bring reactants close together and in the right positions for the reaction to take place. It is kind of like pinning two pieces of fabric together before running them through the sewing machine.
Without those pins, your material would be flopping around all over the place and you would have a hard time forming a straight seam. Enzymes do the biochemical version of that, only much faster and with no sewing kit required.
Scientists have estimated that an enormous number of chemical reactions take place in the human body every second.
Dr. Richard Wolfenden, a member of the National Academy of Sciences and an alumni professor of chemistry, biochemistry and biophysics at the University of North Carolina at Chapel Hill, helped show just how important enzymes really are.
In research reported by the University of North Carolina School of Medicine, a single step involved in creating nucleic acids, the building blocks of DNA and RNA, would take millions of years in water without enzymes. So yes, enzymes are not exactly optional.
Protein Structure
The function of a protein determines its structure. Proteins are made from building blocks called amino acids, and there are 20 amino acids that the body uses to build proteins.
Some amino acids are considered essential, which means the body cannot make enough of them on its own and they need to come from food. Sources such as the National Library of Medicine explain that proteins get their unique shapes from the specific order of these amino acids.
Using other enzymes, amino acids are linked together in a sequence determined by the gene that codes for that protein. Once the chain gets long enough, it begins to fold and twist until it forms its own distinct shape.
This is one reason there are so many different proteins in the body. Shape matters, especially when a protein has a very specific job to do.
Structural proteins are built in a similar way, but they tend to form longer, more fibrous shapes that help provide strength and support.
Collagen, for example, is the most abundant protein in the body and helps give structure to skin, bones, tendons and ligaments. Keratin is another structural protein, found in hair, nails and the outer layer of skin.
How Much Protein Do You Need?
The basic Recommended Dietary Allowance for protein is 0.8 grams per kilogram of body weight per day for most healthy adults, based on standards from the National Academies. For a 150-pound adult, that comes out to about 55 grams of protein per day.
But that number is not meant to be a perfect target for every single person. Protein needs can be higher for older adults, athletes, people recovering from surgery or illness, and those who are pregnant or breastfeeding.
It also depends on what the rest of the diet looks like. A person eating enough calories from a variety of foods will have a very different protein picture than someone undereating or relying mostly on ultra-processed snacks.
Good Food Sources of Protein
Protein comes from both animal and plant foods. Animal-based sources include eggs, fish, poultry, meat, yogurt, milk and cheese.
Plant-based sources include beans, lentils, tofu, tempeh, edamame, nuts, seeds and some whole grains. And yes, beans and lentils count even though the diet world loves to argue about whether they are a “protein” or a “carb.”
Personally, I think that is missing the point. Beans bring protein, fiber, carbohydrates, minerals and plant compounds to the table, which is exactly why they are so useful.
Many people do best when they spread protein throughout the day instead of eating most of it at dinner. That might look like Greek yogurt or eggs at breakfast, beans or tuna at lunch, and salmon, tofu or chicken at dinner.
Protein Turnover
Eventually, cells die and proteins and other large molecules break down. This is called protein turnover, and it is one reason the body needs a steady supply of dietary protein.
The amino acids from protein-rich foods help replace old proteins, build new cells and repair tissues. They also help the body make enzymes, antibodies and some hormones.
This does not mean more protein is always better. It simply means protein is important enough that we should include it regularly, ideally from a variety of nutrient-rich foods.
Bottom Line
Protein is essential for the body, but it does not need to be complicated. It helps build and repair tissues, supports immune function, forms enzymes and hormones, and keeps the body’s day-to-day chemistry moving along.
A healthy diet does not have to revolve around protein powders, giant steaks or tracking every gram. For most people, the better goal is to include a protein-rich food at meals while also making room for fruits, vegetables, whole grains, beans, nuts, seeds and healthy fats.
As with most things in nutrition, balance wins. Protein matters, but so does the rest of the plate.
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