What is the Difference Between a Complete and Incomplete Protein?

by Kristen Keen, MBA, RD, LDN

Last Updated: October 28, 2020

Protein is widely known for helping our bodies build muscle mass, but have you ever thought about what makes up protein, and why is it so important in our daily lives? Protein is one of the three main macronutrients we need daily. To understand the differences between complete and incomplete proteins, let’s start with the basics: What is a protein, and why do we need it?

Protein 101
Protein is one of the three key macronutrients we need each day. Protein helps build muscle mass and builds and repairs tissue and is a component of our bones, cartilage, skin, hair, nails, blood, muscles, hormones, and enzymes. Protein is needed for many of our body’s functions and cell structures. Proteins are literally the building blocks of life.

Proteins are compounds that consist of carbon, hydrogen, nitrogen, and amino acids. Proteins can consist of a single amino acid or multiple amino acids. Amino acids are categorized as essential and non-essential. Essential amino acids are amino acids your body cannot create, and you must get through food; non-essential amino acids are amino acids your body can create.

Protein sources can be considered a “complete” protein source or an “incomplete” protein source. Sources of protein can be found in both animal and plant foods. Now, let’s breakdown complete proteins, incomplete proteins, and their sources.

Complete Protein
A complete protein is a protein containing all nine essential amino acids. These complete proteins are also referred to as a “whole protein” source. Complete protein sources come mainly from animal-based proteins. These include eggs, dairy, fish, poultry, and meat. Plant-based complete proteins include quinoa, buckwheat, seitan, mycoprotein (Quorn), soy, and Ezekiel bread. Chia seeds and hemp seeds technically contain all nine essential amino acids, but they are not considered a complete protein due to their low levels of the amino acid lysine.

Incomplete Protein
An incomplete protein is a protein that does not contain all nine essential amino acids. These proteins can contain many essential amino acids, but if one amino acid is missing or the level is too low, it is an incomplete protein. Incomplete protein sources are most plant-based sources. These include nuts, seeds, beans, legumes, whole grains, tofu, rice, and vegetables (spinach, corn, peas, broccoli, mushrooms, asparagus, artichokes, and brussels sprouts, to name a few).

Incomplete proteins can be paired together at meals or throughout the day to make a complete protein. This is called complementary protein pairings, and for this pairing to work, they cannot be missing the same essential amino acid. Some examples of these pairings include the notorious peanut butter sandwich, rice and beans, hummus and pitas, beans and tortillas, and pasta and peas. Our bodies can also store essential amino acids, which gives even more flexibility. If we consume an incomplete protein without a complement, our body can supplement the missing amino acid from the body’s stores.

Protein Needs
One’s daily protein requirements are extremely individualized and variable. Age, gender, and activity level are a few things that play a role in how much protein our bodies need. The average protein recommendation is 0.8 grams of protein per kilogram of body weight. To calculate weight in kilograms, take your body weight in pounds and divide it by 2.2. Then take your body weight in kilograms and times it by 0.8. This will provide your body’s daily need for protein in grams. We need to incorporate a variety of protein sources into our diet. A good rule of thumb is to include something providing protein with each meal and with snacks. This ensures we get a nice balance of complete proteins, incomplete proteins, vitamins, and minerals. Wondering if you are consuming adequate protein amounts? Reach out to our Kroger Health Dietitian Team.

Disclaimer: This information is educational only and not providing healthcare recommendations. Please see a healthcare provider.


Kristen Keen, MBA, RD, LDN

Kristen Keen, MBA, RD, LDN

Kristen believes having a strong relationship with nutrition is key to having a healthy life and that relationship should center around the power of self-love!