Table of ContentsView AllTable of ContentsComplete vs. Incomplete ProteinsCombining ProteinsDownsides of Too Much ProteinProtein Considerations
Table of ContentsView All
View All
Table of Contents
Complete vs. Incomplete Proteins
Combining Proteins
Downsides of Too Much Protein
Protein Considerations
Historically,protein-containing foods have been divided into two categories: incomplete and complete proteins. “Complete” and “incomplete” refer to the amino acids certain protein foods contain and how they contribute to your daily needs.
Generally, animal-based proteins are considered a higher-quality protein source than plant-based proteins in terms of their amino acid profiles. However, this isn’t necessarily the case.
This article examines what complete and incomplete proteins mean for your diet and meeting your protein needs.
Kilito Chan / Getty Images
What Are Complete and Incomplete Proteins?
Many have long assumed that protein-containing foods can be categorized as:
However, this is a widespread misconception that continues to circulate; the idea of complete and incomplete proteins is misleading.
All foods withproteincontain all nine essential amino acids (even those in the “incomplete proteins” list above). The difference is that amino acids are present in varying amounts in those types of foods. This doesn’t mean they’re incomplete, though.
The only truly incomplete protein in the food system is gelatin, which entirely lacks the amino acidtryptophan.
What Are Amino Acids?Amino acids are protein’s building blocks. Some amino acids are nonessential, meaning that your body makes them itself. Nine amino acids are essential, so you must get them through your diet because your body doesn’t make them. Your body combines the amino acids you make and those you consume in various ways to ensure adequate protein. The nine essential amino acids are:HistidineIsoleucineLeucineLysineMethioninePhenylalanineThreonineTryptophanValine
What Are Amino Acids?
Amino acids are protein’s building blocks. Some amino acids are nonessential, meaning that your body makes them itself. Nine amino acids are essential, so you must get them through your diet because your body doesn’t make them. Your body combines the amino acids you make and those you consume in various ways to ensure adequate protein. The nine essential amino acids are:HistidineIsoleucineLeucineLysineMethioninePhenylalanineThreonineTryptophanValine
Amino acids are protein’s building blocks. Some amino acids are nonessential, meaning that your body makes them itself. Nine amino acids are essential, so you must get them through your diet because your body doesn’t make them. Your body combines the amino acids you make and those you consume in various ways to ensure adequate protein. The nine essential amino acids are:
Do You Need to Combine Proteins?
You do not need to combine different proteins in the same meal to ensure amino acid adequacy. Some scientists have tried to develop tools, such as the protein digestibility corrected amino acid score (PDCAAS), to figure out how to combine multiple plant foods in specific ways to reproduce the amino acid profile of animal proteins in one meal. However, this hasn’t proved easy.
The PDCAAS is a measurement system for evaluating the quality of a protein based on its amino acid profile and digestibility. Animal proteins typically score higher on the PDCAAS scale than plant proteins due to their more even amino acid profiles and higher digestibility. However, researchers are calling for a better way, stating that PDCAAS has limitations in its ability to accurately evaluate plant protein quality and digestibility.
When Did the Idea of Combining Proteins Originate?
The idea that plant proteins are inferior to animal proteins stemmed from a study of rats from over 100 years ago.
For example, recommendations suggested pairing rice and beans, peanut butter on whole-grain bread, or oatmeal with chia seeds. These were called “complementary proteins” because they balanced out each other’s amino acid profiles.
However, the nutrition science community debunked the need for combining proteins over 20 years ago.Lappé changed her position and apologized for reinforcing the myth in the revised 1981 edition of her book.
Limiting Amino Acids
Instead of categorizing protein foods as complete or incomplete, it is more accurate to say that some contain limiting amounts of certain essential amino acids.For example, even though legumes contain all nine, they contain less of the amino acidmethioninecompared to other protein foods.
The only instance in which this would be problematic is if your diet was made solely of one food with limited amino acids. Most people eat many different foods, so as long as you incorporate various protein sources into your diet, your body will combine amino acids.
Potential Downsides of Too Much Protein
Despite all the frequent attention health influencers and convincing marketing give to getting enough protein, the truth is that most people get more than enough in their diet. True protein deficiency is rare in Western countries as long as you eat adequate calories.What’s more, there are potential downsides togetting too much protein.
Excessive protein intakeis associated with a higher risk of:
These health risks appear more likely when a high-protein diet is based on animal foods versus plant proteins. Recent studies have found that a higher plant protein intake has a more protective effect on heart health and lifespan than animal protein intake.
How Much Protein Do You Need in a Day?
Daily protein needs for adults depend on factors like age, sex, activity level, medical conditions, and health goals. However, baseline recommendations are as follows:
Protein is widely available in the U.S. food system, whether you consume animal sources, plant sources, or a mix of both. Most people in developed countries will have no trouble meeting their protein needs. Still, some individuals may need to pay extra attention to the protein sources in their diet.
Vegetarian or Vegan Diets
All plant foods contain all nine essential amino acids, but some contain limiting amounts of certain ones.On a plant-based diet, the following four essential amino acids may be limited:
This doesn’t mean a plant-based diet provides inadequate protein or nutrition. Instead, it means you should eat various plant foods regularly to ensure optimal amino acid intake.
Sources of these limiting amino acids on a plant-based diet include:
Amino Acid Metabolic Disorders
Amino acid metabolic disorders are a group of genetic conditions wherein your body can’t break down amino acids properly. These disorders often result from deficiencies in specific enzymes involved in amino acid metabolism.
Early detection and management are important because amino acid metabolism disorders can disrupt the balance of amino acids necessary for making protein. This can lead to a deficiency in proteins that are essential for various bodily functions.
Treatment for amino acid metabolic disorders often includes a specialized diet pattern and supplements to help ensure adequate amino acid intake. If you have an amino acid metabolic disorder, work closely with a healthcare provider to determine the best plan for you.
8 Fruits and Vegetables That Can Help You Get More Protein
Summary
24 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Mariotti F, Gardner CD.Dietary protein and amino acids in vegetarian diets—a review.Nutrients. 2019;11(11):2661. doi:10.3390/nu11112661
Young SN.Acute tryptophan depletion in humans: a review of theoretical, practical and ethical aspects.J Psychiatry Neurosci. 2013;38(5):294-305. doi:10.1503/jpn.120209
Lopez MJ, Mohiuddin SS.Biochemistry, essential amino acids. In:StatPearls. Treasure Island (FL): StatPearls Publishing; March 13, 2023.
Dimina L, Rémond D, Huneau JF, Mariotti F.Combining plant proteins to achieve amino acid profiles adapted to various nutritional objectives—an exploratory analysis using linear programming.Front Nutr. 2022;8:809685. doi:10.3389/fnut.2021.809685
Monsonego Ornan E, Reifen R.Revisiting protein quality assessment to include alternative proteins. Foods. 2022;11(22):3740. Published 2022 Nov 21. doi:10.3390/foods11223740
American Heart Association.Vegetarian diets.
Osborne TB, Mendel LB.Amino-acids in nutrition and growth. Abtlerhdden: Zeitschr. f. phvsiol. Chem., Ixxvii, p. 27, 1912.
Lappé, FM. Diet for a Small Planet. Ballantine Books, 2021.
McDougall J.Plant foods have a complete amino acid composition.Circulation. 2002;105(25):e197. doi:10.1161/01.cir.0000018905.97677.1f
Young VR, Pellett PL.Plant proteins in relation to human protein and amino acid nutrition.Am J Clin Nutr. 1994;59(5 Suppl):1203S-1212S. doi:10.1093/ajcn/59.5.1203S
Watford M, Wu G.Protein. Adv Nutr. 2018;9(5):651-653. doi:10.1093/advances/nmy027
Ferraro PM, Bargagli M, Trinchieri A, Gambaro G.Risk of kidney stones: influence of dietary factors, dietary patterns, and vegetarian-vegan diets.Nutrients. 2020;12(3):779. doi:10.3390/nu12030779
Ko GJ, Rhee CM, Kalantar-Zadeh K, Joshi S.The effects of high-protein diets on kidney health and longevity.J Am Soc Nephrol. 2020;31(8):1667-1679. doi:10.1681/ASN.2020010028
Vallis J, Wang PP.The role of diet and lifestyle in colorectal cancer incidence and survival. In: Morgado-Diaz JA, ed. Gastrointestinal Cancers. Brisbane (AU): Exon Publications; September 30, 2022.
Ferrari L, Panaite SA, Bertazzo A, Visioli F.Animal- and plant-based protein sources: a scoping review of human health outcomes and environmental impact.Nutrients. 2022;14(23):5115. doi:10.3390/nu14235115
Huang J, Liao LM, Weinstein SJ, et al.Association between plant and animal protein intake and overall and cause-specific mortality.JAMA Intern Med. 2020;180(9):1173-1184. doi:10.1001/jamainternmed.2020.2790
Naghshi S, Sadeghi O, Willett WC, Esmaillzadeh A.Dietary intake of total, animal, and plant proteins and risk of all cause, cardiovascular, and cancer mortality: systematic review and dose-response meta-analysis of prospective cohort studies.BMJ. 2020;370:m2412. doi:10.1136/bmj.m2412
Food and Nutrition Board, Institute of Medicine, National Academies.Dietary Deference Intakes (DRIs): recommended dietary allowances and adequate intakes, total water and macronutrients.
Richter M, Baerlocher K, Bauer JM, et al.Revised reference values for the intake of protein. Ann Nutr Metab. 2019;74(3):242-250. doi:10.1159/000499374
Neufingerl N, Eilander A.Nutrient intake and status in adults consuming plant-based diets compared to meat-eaters: a systematic review.Nutrients. 2021;14(1):29. doi:10.3390/nu14010029
Stanford Report.Embracing a plant-based diet.
Aliu E, Kanungo S, Arnold GL.Amino acid disorders.Ann Transl Med. 2018;6(24):471. doi:10.21037/atm.2018.12.12
Ling ZN, Jiang YF, Ru JN, et al.Amino acid metabolism in health and disease.Signal Transduct Target Ther. 2023;8(1):345. doi:10.1038/s41392-023-01569-3
Meet Our Medical Expert Board
Share Feedback
Was this page helpful?Thanks for your feedback!What is your feedback?OtherHelpfulReport an ErrorSubmit
Was this page helpful?
Thanks for your feedback!
What is your feedback?OtherHelpfulReport an ErrorSubmit
What is your feedback?
