Complete Protein vs. Incomplete Protein Explained

Understanding the concept of complete vs incomplete protein can help you make informed choices about your daily protein sources. By knowing the importance of protein quality, the amount and balance of amino acids that dietary protein provides, you can choose a variety of foods in your diet. Whether you choose complete protein or incomplete protein foods, you can still meet your requirements for essential amino acids, as long as you are eating a balanced diet including protein rich foods. In this blog, let’s try and understand complete protein vs incomplete protein by taking a close look at protein and related aspects. This includes how combining different foods creates a complete protein which contributes to protein nutrition.

What Is a Protein?

Proteins are macronutrients made up of many smaller units called amino acids, which are attached to one another in long chains.[1] Twenty different types of amino acids constitute protein. Dietary protein is classified into two types: complete protein and incomplete protein based on its essential amino acid profile. Here are a few important functions of protein in your body:

  • It provides the amino acids needed for the growth, muscle maintenance and repair of body tissues.
  • It is required for the production of enzymes and hormones that regulate various bodily functions. The enzyme-dependent bodily functions include digestion, energy production, blood clotting and muscle contraction.[2] Some proteins are hormones, which act as chemical messengers that aid communication between your cells, tissues and organs.
  • It helps form immunoglobulins, or antibodies to fight infections and strengthen the immune system.  

The dietary protein requirement of a person depends on age, gender, activity level, physiological status and medical conditions, if any. Sources of dietary protein include milk, curd, low-fat paneer, pulses, legumes, eggs, chicken and fish.

What Are Amino Acids?

They are the building blocks of protein and are classified as essential amino acids (indispensable) and non-essential (dispensable) amino acids. Out of the 20, nine are classified as nutritionally essential amino acids.[3] These are histidine, isoleucine, leucine, lysine, methionine, phenyl alanine, threonine, tryptophan and valine.[4]

Why protein quality matters?

The protein quality mainly depends upon the composition of amino acids, digestibility and the availability of the indispensable amino acids after digestion. Indispensable amino acids (IAAs) or essential amino acids are those which the body cannot make on its own and must be obtained from food. A high quality protein provides these amino acids in adequate proportions and is efficiently digested and absorbed. The dietary protein quality is evaluated using the Digestible Indispensable Amino acid Score (DIAAS), which measures how well the human body digests and absorbs its essential amino acids.[5]

What Is a Complete Protein?

If the dietary protein sources contain all the nine essential amino acids in sufficient amounts, it is called a complete protein.[6] Animal protein sources like dairy products, eggs, chicken and fish are complete protein foods.  These foods are widely known for their high protein quality as they provide all the essential amino acids in the right proportions. Animal protein sources also provide other nutrients such as vitamin D, B12 and highly bioavailable haeme iron. Plant-based protein sources such as soy and products and grains like quinoa are also complete protein foods.[7]

What Is an Incomplete Protein?

If the dietary protein sources lack one or more of the nine essential amino acids, it is called an incomplete protein.4 Incomplete protein foods include cereals, lentils, and pulses. Plant-based protein sources are considered incomplete protein as they lack some essential amino acids like lysine, threonine and sulfur containing amino acids such as cysteine and methionine that humans need for proper growth.7 If you are a vegetarian or a vegan, eating a variety of different plant-based protein sources can help you meet your protein requirements. Besides, these foods also provide other nutritional benefits as they contain fiber, vitamins and minerals.

Can You Combine Foods to Create Complete Proteins?

Yes, combining different foods can help transform incomplete protein into complete protein and improve the overall nutritional quality of the diet. Here are some ways in which you can do so by using the different protein sources:

  • Grains tend to be lower in lysine, whereas pulses and legumes are lower in methionine. Hence, combining cereals or millets with pulses can provide all the essential amino acids.[8] For example, dal khichdi, chapati/rice with dal, idli and dosa are complete protein foods.
  • Pairing incomplete protein foods like plant protein with animal protein sources can also help create a high quality complete protein combination. For example, milk + cereal/ millets OR curd + any legume+ rice OR egg + rice /chapati.
  • Mixing up different high protein foods such as soy and its products with other plant protein sources upgrades them into complete protein, making them more protein rich. This can especially benefit vegans and vegetarians. For example, soya chunks pulao OR soya flour added to wheat flour for chapati OR tofu bhurjee with millet chapati.

Complete Protein Vs. Incomplete Protein: Understanding the difference

When comparing complete vs. incomplete protein, the primary difference lies in the amino acid profile, digestibility and overall protein quality. Most animal proteins are highly digestible, while digestibility for plant proteins may vary due to the presence of anti-nutritional factors like phytates and tannins.[9] However, what matters most is that this criteria alone should not be used to choose one over the other or label foods as simply good or bad. Food variety, dietary intake, and individual requirements when taken into consideration, contribute to protein nutrition.

Thus, instead of focusing solely on complete vs incomplete protein, aim to include a variety of healthy protein sources to help you meet both your protein and overall nutritional needs.

Author: Nurture Health Solutions

Reference:

 

[1] What are proteins and what do they do? Available at https://medlineplus.gov/genetics/understanding/howgeneswork/protein/. Last accessed on 26th August 2026

[2] 9 Important Functions of Protein in Your Body. Available at

https://www.healthline.com/nutrition/functions-of-protein#TOC_TITLE_HDR_. Last accessed on 26th August 2026

[3] Calvez, J., Azzout-Marniche, D., & Tomé, D. (2024). Protein quality, nutrition and health. Frontiers in Nutrition, 11, 1406618. https://doi.org/10.3389/fnut.2024.1406618

[4] The Difference between Complete and Incomplete Proteins. Available at https://www.webmd.com/diet/difference-between-complete-and-incomplete-proteins. Last accessed on 26th August 2026

[5] Have You Heard Of A Diaas Score? What It Is And What It Means To You. Available at https://medspecialtyclinic.com/have-you-heard-of-a-diaas-score/. Last accessed on 26th August 2026

[6] What Are Complete Proteins? Available at https://health.clevelandclinic.org/do-i-need-to-worry-about-eating-complete-proteins. Last accessed on 26th August 2026

[7] Shanthakumar, P., Klepacka, J., Bains, A., Chawla, P., Dhull, S. B., & Najda, A. (2022). The current situation of pea protein and its application in the food industry. Molecules, 27(16), 5354. https://doi.org/10.3390/molecules27165354

[8] Bouchard, J., Malalgoda, M., Storsley, J., Malunga, L., Netticadan, T., & Thandapilly, S. (2022b). Health benefits of cereal grain- and Pulse-Derived proteins. Molecules, 27(12), 3746. https://doi.org/10.3390/molecules27123746

[9] Kaur, L., Mao, B., Beniwal, A. S., Abhilasha, Kaur, R., Chian, F. M., & Singh, J. (2022b). Alternative proteins vs animal proteins: The influence of structure and processing on their gastro-small intestinal digestion. Trends in Food Science & Technology, 122, 275–286. https://doi.org/10.1016/j.tifs.2022.02.021