You know that protein is the macronutrient responsible for helping you build muscle and look lean. But did you know that it's also needed for many other important bodily functions? So what is protein and how can it help you reach your health and weight-loss goals?
What Is Protein?
Simply put, proteins are the building blocks of life. The macro is found throughout the body — it's located in muscle, bone, ligaments, skin, hair, blood and virtually every tissue. Every living cell and all bodily fluids except bile and urine contain protein. Proteins are made up of chains of 20 amino acids, which are responsible for every metabolic function in your body from building muscle to regulating sleep to aiding in energy regulation, which we need for great workouts.
Amino acids are broken down into two categories, according to the FDA:
- Essential amino acids: Essential amino acids (EAAs) are not made by the body and need to be consumed via our diet — hence the name "essential." While you do not need to get all essential amino acids in one meal, having a balanced intake of these nutrients throughout the day is important. There are only nine EAAs: Histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.
- Non-essential amino acids: The body can create these amino acids by breaking down essential amino acids or other proteins in the body. There are 11 non-essential amino acids: Alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine and tyrosine.
Protein is needed in the body to repair cells and make new ones. This makes protein intake very important for pregnant women, children and teens as it is needed for healthy growth and development. Avoiding protein deficiency during these key stages of growth is very important.
Complete Protein Vs. Incomplete Protein
Protein sources can boast both essential and non-essential amino acids. When we choose foods for their protein content, it's important to have a balance of both essential and non-essential amino acids to ensure we are meeting our needs.
Proteins are classified into two groups based on the amino acids they provide:
- Complete proteins: Complete proteins contain adequate quantities of all the essential amino acids needed for protein synthesis in the body. "These proteins help with building and maintaining lean muscle mass as well as support immune function (immunoglobulins are made up of amino acids)," Christy Alexon, PhD, RD, associate professor at Arizona State University tells us.
- Incomplete proteins: Incomplete proteins are missing one or more of the essential amino acids, and this can result in sub-optimal protein synthesis since you won't have all the amino acids necessary to build certain proteins in the body, Alexon says. "Think of your proteins like a house — you need to have certain types of materials to build a house, and if one of those building materials is missing, your construction project is going to be incomplete!"
While animal sources of protein like meat, poultry, fish and dairy are considered complete proteins, there are also available sources of complete plant-based proteins — they're just harder to find. "Plant-based complete proteins include soy (as well as tofu products), hemp and quinoa," says Alexon. However, you can often mix plant-based sources of protein to create complete proteins and get a full amino acid profile.
Functions of Protein
Protein serves many functions in the body. Now that you know what protein is and what it's made out of, read on to find out how it supports daily life functions.
Protein Provides Helps Your Cells Maintain Their Structure
An important function of protein is to provide support in your body, which involves connective tissues, cartilage and bone. Contractual protein is responsible for muscle contraction and movement while structural protein is responsible for cells maintaining their shape and resisting deformity. Keratin is a structural protein found in your hair, nails and skin. And collagen is another structural protein that provides the framework for the ligaments that hold your bones together, in addition to the tendons that attach muscles to those bones.
Protein Strengthens Your Immune System
Antibodies are specialized proteins that travel through the bloodstream, defending the body from antigens such as bacteria, viruses, infections and disease. By binding to antigens, antibodies neutralize and immobilize foreign molecules so they can be destroyed by white blood cells. There are five different types of antibodies. Each type is found in different parts of the body, and each has a specific duty in maintaining the health of your body.
Protein Regulates Body Functions
Body processes are influenced by hormones — proteins that act as chemical messengers to help cells, tissues and organs communicate, according to Colorado State University. For example, they signal the uptake of glucose into a cell, stimulate the growth of tissue and bone, signal the kidneys to reabsorb water and aid in almost all facets of metabolism in your body.
So, How Much Protein Do I Need?
You should aim to include protein in every meal because your body doesn't store protein the way it stores fats or carbohydrates. How much protein you need depends on your age, sex, health and level of physical activity.
The Recommended Dietary Allowance (RDA) for both men and women is 0.8 grams per kilogram (2.2 pounds) of body weight but experts recommend more to sustain muscle mass. You should aim to get 1.2 to two daily grams of protein per kilogram of body weight, according to a March 2016 report in the Journal of the Academy of Nutrition and Dietetics. So if you weigh 150 pounds, aim to consume 82 to 136 grams of protein daily coming from both animal and plant-based sources.
For reference, protein provides four calories per gram.
Use the nutrition labels and an online nutrition tracker like MyPlate to easily determine the specific amount of protein in each food and track your intake for the day.
Quality High-Protein Foods
While it's ideal to get your protein from whole food sources — due to the ability to get additional vitamins and minerals into your diet — whey, casein or plant-based protein bars and shakes can aid in boosting your protein intake. Aim to get most of your protein from:
- Lean meat
- Low-fat dairy
- Nuts and seeds
- Whole grains
Signs of a Protein Deficiency
A protein deficiency occurs when your dietary intake of protein isn't enough to meet your body's requirements. While most Americans get enough protein in their diet, it's estimated that close to one billion of the world's population suffers from inadequate protein intake, according to an August 2014 report in the Annals of the New York Academy of Sciences.
Signs and symptoms of a protein deficiency include:
- Fatty liver
- Brittle nails
- Hair loss
- Loss of muscle mass
- Stunted growth in children
- Increased infections
- Increased appetite
- Increased risk for bone fractures
How Effective Is a High-Protein Diet For Weight Loss?
High-protein diets are very popular among dieters — and for good reason.
"High-protein diets improve satiety, weight management and help preserve lean body mass, slowing down the progression of sarcopenia or age-related muscle loss," Alexon says.
"A high-protein diet usually means you are eating about 1.6 to two grams of protein per kilogram body weight," Alexon says. To put that into perspective, a 150-pound person would eat anywhere between 109 and 136 grams of protein per day.
In fact, eating 1.2 to 1.6 grams of protein per kilogram of body weight, and ensuring each meal contains about 25 to 30 grams of protein, can lower your appetite and cardiometabolic risk factors as well as help manage body weight, an April 2015 review published in The American Journal of Clinical Nutrition found.
Alexon recommends high-protein diets that emphasize lean proteins, which provide 3.5 grams of fat or less per 10 grams of protein), to cut back on saturated fat.
Following a diet plan that focuses on increasing lean protein during weight loss also helps maintain lean muscle mass, regardless of age. A February 2016 meta-analysis published in Nutrition Reviews found that adults older than age 50 retained more lean muscle tissue and lost more fat while eating a higher protein diet.
Before starting any new diet program, including a high-protein diet, consult a physician or registered dietitian.
- USDA: "What Foods Are In The Protein Foods Group?"
- The American Journal of Clinical Nutrition: "The Role of Protein in Weight Loss and Maintenance"
- FDA: "Protein"
- Colorado State University: "Mechanism of Action: Hormones with Cell Surface Receptors"
- Journal of the Academy of Nutrition and Dietetics: "Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance"
- Annals of the New York Academy of Sciences: "Production and Supply of High-Quality Food Protein for Human Consumption: Sustainability, Challenges, and Innovations"
- Nutrition Reviews: "Effects of Dietary Protein Intake on Body Composition Changes After Weight Loss in Older Adults: A Systematic Review and Meta-Analysis"
- MedlinePlus: Enzyme
- MedlinePlus: Hormones
- MedlinePlus: Antibody