Proteins in Depth

Protein in a nutshell

Protein is a very important macronutrient that helps your body maintain cells and tissue, build muscle, maintain open blood vessels, and create enzymes and other substances needed to keep your body going. In order to perform these functions, your body breaks down the protein you eat into smaller units called amino acids. It uses these amino acids to rearrange and build different types of proteins, depending on which ones it needs. Certain proteins are used to repair muscle tissue, or maintain your heart and blood vessels, or help your blood clot when you get a cut.

Most of the proteins your body needs are made inside the body, but nine of the approximately 20 amino acids can only be obtained through food. These nine are called essential amino acids. Proteins can be either complete and incomplete, depending on which essential amino acids they contain. Complete proteins have all 9 essential amino acids while incomplete only carry some of the nine. But it’s okay to eat incomplete too because when you combine certain incomplete proteins in the same meal, these complementary proteins will give you the equivalent of a complete protein. For example, when you eat the complementary proteins wheat bread and peanut butter, or beans and rice, it is just like eating a complete protein!

Although getting enough protein is not a concern for most Americans, getting the right kind of protein is important. That means making sure your protein has mostly unsaturated fats and other nutrients such as vitamins and minerals so your body gets all the beneficial components it needs. When you eat healthy proteins bundled with other important nutrients, your body will have what it needs to stay fit, avoid diseases, and maintain cells while building strong muscles.

Drill Down

Back Up

Introduction

Protein is a macronutrient that plays a role in almost everything your body does. As your body performs its regular activities, cells are involved in a type of life-cycle of their own. As cells are used, leading to wear and tear, they need to be replaced or repaired…and protein is what helps make this happen! The body is actually full of proteins which are used to maintain your muscles, organs, and other tissues. Protein also helps with managing weight and reducing the risk of heart disease and diabetes. As you age, protein will help maintain muscle mass and healthy bone structure. Protein is an essential nutrient, or a nutrient that your body cannot create independently, helping your body restore itself while keeping it healthy and strong.

Amino acids

Proteins are not just a single nutrient. There are many different types of proteins found in the food you eat and within your body. When you eat something with protein, your body breaks it down into smaller components called amino acids. Amino acids are the building blocks of proteins. Your body can create new proteins from these units, taking them apart and rearranging them into whatever form of protein it needs. Your body needs to build a variety of proteins because they each perform different functions. Some are used to repair cells, maintain your skin (which is made of protein), or help keep blood vessels open. Others are used to make enzymes, special proteins which have specific jobs such as digesting food or making new substances that regulate body functions. Still others may be used to make neurotransmitters, the chemicals that help your brain send signals that control body processes. Protein and its smaller components, amino acids, play an important role in nearly every bodily function.

Though your body can make thousands of different types of proteins, there are about 20 amino acids that it uses to make new proteins. Nine of these 20 or so are called essential amino acids, that is, the body cannot make them itself and they must be obtained from food. Otherwise, your body is capable of making its own by breaking apart amino acids inside the body and reconstructing them into the new forms it needs. These other amino acids that your body can construct itself are called non-essential amino acids. As long as you eat enough foods with the essential and non-essential amino acids, your body will have all the building blocks it needs to make the necessary proteins.

Complete and incomplete proteins

Proteins also come in different “qualities”, high and low. This is more commonly referred to as complete protein and incomplete protein. How protein is categorized depends on which essential amino acids are present. High-quality, or complete protein has all nine essential amino acids, and in large enough amounts so the body can make whichever new proteins it needs. Complete protein can be found in animal based proteins, soy and quinoa (a whole grain). Incomplete protein also has amino acids, but does not include all nine essential amino acids. Incomplete protein can be found in plant-based proteins such as beans, peas, nuts and seeds. Although they are still very healthy foods to eat, you cannot get all nine essential amino acids from eating an incomplete protein. This is one reason variety is important in your diet: what one food lacks in essential amino acids, another may have. The good news is that if you eat two or more foods with incomplete protein at the same time, it can be just like eating a complete protein!

Complementary foods

When you combine two or more foods with incomplete proteins to make a complete protein, you are eating complementary foods. One food may have some of the nine essential amino acids, while the other has the missing essential amino acids. For example, if you combine peanut butter and bread, rice and beans, pasta and cheese or milk and cereal, each pair will provide you with a complete protein. By eating them together, your body will have all the amino acids needed to produce a complete protein.

Getting the right amount of protein

Unlike carbs and fat, your body does not have a way to store excess protein. Therefore it is important to eat a steady diet of protein in order to get all the essential and non-essential proteins your body needs. The recommended daily allowance (RDA) of protein for children and adolescents up to age 18 is 10-30% of your total calories. For those 19 and older, the RDA is 10-35%. But getting enough protein is probably not as much of a concern as getting the right kinds of protein. The American diet is typically high in protein, so most Americans meet or exceed the RDA for this nutrient. Because your body does not store excess protein, there is no upper limit to the amount you can eat. However, a high protein diet is not necessarily healthy, depending on the source of protein. If you are eating a lot of red meat high in saturated fat, this may contribute to higher cholesterol levels. But if your high-protein diet is mostly made up of plant-based and low-fat animal proteins, then your overall cholesterol levels may actually be healthier.

Special protein needs

While most Americans get a sufficient amount of protein, there are some instances when more is needed. As you know, protein helps build and repair tissue. If you are trying to build muscle, eating a high-protein meal after working out will help your body build muscle mass. There are other instances when more protein is necessary. Women who are pregnant will need more protein as their body builds new cells for the fetus growing inside them. Likewise, someone with an injury will also need protein to help their body repair its tissue. Whether it is daily maintenance or some other instance where your body needs to make and repair cells, protein is essential.

Protein and your health

Protein not only takes an essential role in building and maintaining your body, it can also help maintain a healthy weight. Protein may help you feel full longer because it often takes longer to digest, and helps steady blood glucose levels, which signals your brain that you are full. Protein is also thermogenic, meaning that it requires more calories to digest compared with other macronutrients. Another way protein maintains good health is that it is bundled with other nutrients. Animal proteins such as meat, also have the minerals iron and zinc, among others. Fish has unsaturated fats such as Omega-3 fatty acids. Dairy products and almonds have a lot of calcium. Nuts and seeds have magnesium and Vitamin E. If you are only eating plant-based proteins, they will still have essential amino acids, as well as vitamins, minerals, fiber and unsaturated fats which are cholesterol-free. Depending on which proteins you choose, they can have many additional health benefits when they are bundled with other important nutrients.

Conclusion

Protein helps maintain your body by repairing cells, tissues and muscles. Many different proteins are needed for each of these processes. But your body knows how to break down proteins into amino acids (the building blocks of protein) and build whatever type of protein it needs. Your body can make most of these amino acids itself but there are nine essential amino acids it cannot make. Therefore, it is important to eat a variety of proteins so your body gets all the different components it needs. One way to do this is by eating complementary foods such as milk and cereal, or beans and rice. Combining these complementary foods will give your body the equivalent of a complete protein with all nine essential amino acids. Sometimes your body will need extra protein, if you are trying to build muscle or recovering from an injury. Just make sure those proteins have additional nutrients and healthy fats: plant based proteins like beans or nuts, lean meats that have mostly unsaturated fats, or fish. With your knowledge of proteins…how important it is for your body and which ones are the healthiest…you can make food choices that help your body get the kind of nutrients it needs!

Resources

Duyff, R., (2017). ADA Complete Food and Nutrition Guide, 5th Edition. Boston, MA /New York, NY: Houghton Mifflin Harcourt.
Rinzler, C., (2016). Nutrition for Dummies, 6th Ed. Hoboken, New Jersey: John Wiley & Sons, Inc.
Quick start guide to nuts and seeds, (September 2019). Harvard Health.
Thompson, J., Manore, M., Vaughan, L., (2014). The Science of Nutrition, 3rd Ed. Boston: Pearson Publishing, Inc.