Protein 101: What Is Protein and What Does It Do for Our Bodies?

Protein 101: What Is Protein and What Does It Do for Our Bodies?

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Sheela Prakash
Apr 18, 2017
(Image credit: PHOTO: CHRISTINE HAN; DESIGN: SUSANNA HOPLER)

Protein is a word that carries a lot of weight. Packaged foods brag of their high-protein content; a whole aisle of the grocery store is filled with bars and powders that claim to be pumped full of it. We're told that we need to eat it — that protein is good for us and we need a lot of it — but what exactly is it? Why do we need it? And do we need as much as everyone seems to think?

Welcome to Nutrition 101, a new series where we step away from the health fads cluttering our news feeds, and get back to nutritional basics — starting with that most glamorous and high-profile of nutrients: protein.

Who I Am (and Why I'm Writing to You)

As a food editor who is also a Registered Dietitian, I know the confusion and clutter of our fractured landscape of nutrition and diet information. It seems that there's different advice every day!

But if you strip away the study-of-the-day and the fad diets, what do we really know about nutritional building blocks? Let's talk about the unsexy yet useful tools available to all cooks to make decisions that suit them — decisions they feel empowered to make with solid, science-driven information and resources.

This especially applies to protein, the first topic in our new Nutrition 101 series. I know the confusion that surrounds protein and want to help you, our reader, understand that it's actually not as complicated as you may think! That results in confident eating and a more wholesome diet — something we can all get behind.

So we're starting at the beginning with the most basic questions. What is protein? And what does it do for us? That's the first key to unravelling the confusion.

(Image credit: Christine Han)

What Is Protein?

Protein is a macronutrient, which is a nutrient that the body needs in large amounts to keep it functioning and to provide it with calories, which it uses for energy. Protein is one of three macronutrients — carbohydrate and fat are the other two.

What's Actually in Protein?

Protein is made up of small compounds called amino acids. There are hundreds of amino acids that exist in nature, but the body only needs 20 of them, in varying amounts, to be healthy and functioning. The body can actually produce 11 of the 20, but the remaining nine, called essential amino acids, must come from food, and therefore must come from foods that contain protein.


There are 20 amino acids. We can only produce 11. We need to eat the rest — in protein.


Why Is Protein Important?

Protein is considered to be a building block of life — without it, our bodies wouldn't exist! We are made of protein from our heart to our brain, our bones to our muscles, our lungs to our kidneys, and our arteries, veins, skin, hair, nails, and more. Protein's main job is to build, maintain, and restore all of these muscles, organs, and tissues.

The other reason protein is important is that it helps keep us full. That's probably what you hear most about the nutrient, and it's indeed true.

Why does food rich in protein keep you full for longer than say, a muffin, however? It's because protein takes longer to digest than carbohydrate. That means calories from protein tend to keep you full longer than calories from carbohydrate. (If you're wondering where fat stands, it actually takes even longer to digest than both, but Fat 101 is another topic for another month!)

(Image credit: Christine Han)

Which Foods Have Protein?

Almost all foods have some amount of protein in them, to varying extents. Protein in food can be divided into two categories: complete and incomplete.

Sources of Complete Protein (All 9 of Those Amino Acids!)

Foods that contain complete protein contain all nine essential amino acids that the body needs (well, it needs 20, but we can make the other 11, remember?).

These are the foods that are often touted as great protein sources, as they usually contain a lot of protein, and that protein is full of all nine required amino acids.

Some Sources of Complete Protein

  • Meat
  • Fish
  • Eggs
  • Dairy
  • Soy (tofu, tempeh, soy milk, etc.)
  • Quinoa
  • Buckwheat
  • Hemp & chia seeds

Sources of Incomplete Protein

Foods that contain incomplete protein contain some of the nine essential amino acids, but not all.

Myth Alert! It's a common myth that you must eat incomplete proteins together at a meal to make them a complete protein and get their nutritional benefit — that's not true.

Sure, rice and beans are great together, but as long as enough incomplete protein is consumed through the day (the body doesn't actually store amino acids for much longer than a day), they can be combined and used as complete protein, which means your body will get its nine essential amino acids for the day.

Some Sources of Incomplete Protein

  • Beans and legumes
  • Nuts and seeds (that includes nut butters and flours, along with seed butters)
  • All grains besides quinoa (oats, rice, pasta, wheat, cornmeal, bulgur, farro, rye, etc.)
  • Some vegetables (leafy greens, green peas, broccoli, mushrooms, Brussels sprouts, artichokes, asparagus, and others)
  • To a much lesser extent, some fruit (dried fruit, guava, avocado, and others)

And that is the most essential set of learning on protein that you need — complete, incomplete, and those very important amino acids.

What Do You Want to Know About Protein?

What's next in our Protein 101 course? Well, what are some more myths surrounding protein? We'll tackle these common myths, including what you really need to eat to stay healthy. And we'll show you some meals that give you a full daily serving of protein (they may surprise you!)

These and more coming up. Tell us if you have other questions as well!

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