Table of ContentsView AllTable of ContentsExamplesIncomplete vs. CompleteProtein Needs in Nonmeat Diets
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Table of Contents
Examples
Incomplete vs. Complete
Protein Needs in Nonmeat Diets
Foods containing protein are often categorized as complete or incomplete, depending on their amino acid composition. However, it’s a misconception that foods labeled as “incomplete proteins” lack amino acids or are inferior to complete proteins.
This article examines why the term “incomplete proteins” is misleading and what’s more important to focus on when choosing protein sources on a plant-based diet.
Cavan Images / Getty Images
What Is a Protein?
Incomplete Protein Examples
Many plant-derived protein sources are categorized as incomplete. However, most foods containing protein—from animal and plant sources—contain all nine essential amino acids.
Nine amino acids are considered “essential” because our bodies can’t produce them, so we have to get them through food. The remaining 11 amino acids are called “nonessential” or “conditional” (except during seasons like pregnancy, adolescence, or trauma) because our bodies can produce them.
The nine essential amino acids include:
The key difference between plant- and animal-based protein is that certain plant foods contain lower-than-needed amounts of specific essential amino acids than animal foods. These are often called “limiting amino acids.”
Limiting Amino AcidsThe key difference between plant- and animal-based protein is that certain plant foods contain limiting amino acids (lower-than-needed amounts of specific essential amino acids than animal foods).
Limiting Amino Acids
The key difference between plant- and animal-based protein is that certain plant foods contain limiting amino acids (lower-than-needed amounts of specific essential amino acids than animal foods).
Below are some plant protein sources that contain limiting amino acids and which ones.
Nuts
Nuts are an excellent source of protein, fiber, healthy unsaturated fats, and an array of vitamins and minerals. One ounce of unroasted raw cashews contains 4 grams of protein.
However, various nuts contain certain limiting essential amino acids:
If you’re concerned about the amino acid profile of nuts, note that chia seeds and hemp seeds contain adequate amounts of all nine essential amino acids. Incorporating a variety of nuts and seeds in a plant-based diet will ensure you get what you need.
Cereal Grains
Lysine is the most common limiting amino acid in cereal grains, such as oats, rice, barley, whole wheat, and millet.Lysine is a prominent limiting amino acid in the food supply, particularly in areas where cereal grains are a primary protein source.
A grain kernel’s bran (the outer multilayer of skin) contains 3 times more lysine than the endosperm (the innermost portion of the grain kernel). This means the more processed and refined a grain is, the less lysine it contains.
In other words, white rice and pasta will contain significantly less lysine than whole grain pasta and brown rice that haven’t had their bran removed.
Amaranth is an exception in this category, as it contains adequate amounts of all nine essential amino acids.
Understanding Amino Acids
Legumes
Certain legumes are typically limiting in the sulfur-containing amino acids methionine and cysteine but may also be low in lysine, valine, and threonine.
Legumes include beans, peas, and lentils, various types of which may be limiting in one or more of the amino acids above. The exceptions are soybeans and products made with soy, like tofu and tempeh, which are considered a complete protein as they don’t contain limiting amino acids.
Corn
What Foods Are High in Protein?
Comparing Incomplete vs. Complete Protein
Incomplete proteins are often said to lack one or more essential amino acids, whereas complete proteins contain all nine.
Our bodies use essential and nonessential amino acids to produce the combinations needed to make proteins in the body. Eating a variety of plant proteins ensures that your body receives the amino acids it needs to make proteins.
Composition
All protein foods contain the nine essential amino acids. The difference is that some protein sources, particularly certain plant-based ones, contain limiting amino acids.
While foods can have multiple limiting amino acids, there are four that are most likely to be limiting on a plant-forward diet, including:
Digestion
Plant proteins tend to be harder to digest than animal proteins. This may be because plants are rich in fiber, an essential nutrient for digestive, heart, and overall health.Only about 5% of Americans meet their daily fiber needs, suggesting that we could benefit from more plant proteins.
Overall Nutritional Value
There is a common misconception that nutritionally, plant proteins are inferior to animal proteins. However, some plant proteins can contain just as much (if not more) protein per serving than animal proteins. Plant proteins are rich in fiber and antioxidants, as well as certain vitamins and minerals that you won’t necessarily find in animal products.
Many studies show that plant-based diets are highly nutritious and offer countless health benefits.A 2020 study based on 16 years of research even suggests that replacing animal proteins with plant proteins is associated with a lower risk of chronic diseases and a longer life span.
Furthermore, there’s no need to intentionally combine certain plant proteins in the same meal in order to get all the essential amino acids. Researchers used to think that you had to combine foods like rice and beans or peanut butter and whole wheat toast at the same meal to ensure amino acid adequacy,but this was debunked years ago.
The best way to obtain all the amino acids and other nutrients you need in your diet is to include a wide variety of healthy foods. A plant-based diet that incorporates a balance of different types of fruits, vegetables, whole grains, legumes, nuts, and seeds will provide all of the amino acids needed.
Amino Acids
Confusion Around Protein Needs in Nonmeat Diets
Some excellent plant sources of protein include:
Even fruits and vegetables contain a small amount of protein. For instance, one cup of broccoli provides 2.5 g of protein.
The Vegan Diet: Everything You Need to Know About Plant-Based Foods
How Much Protein to Eat Daily
Western cultures like the United States focus on consuming significant amounts of protein, especially when working toward specific body composition goals like weight loss or muscle-building.
While protein is essential for health and wellness, most consume the recommended amount. Generally, if you’re eating enough overall calories, it’s unlikely that you’re protein deficient.
Daily recommendations for protein for adults are:
Daily protein needs vary depending on your body weight, weight goals, and activity level. Whether you consume animal products or not, you can meet your daily protein needs with various protein sources.
Protein Needs for ChildrenDaily protein needs for children and adolescents are as follows:Infants, 0–6 months: 9 gInfants, 7–12 months: 11 gChildren, 1–3 years: 13 gChildren, 4–8 years: 19 gMales and females, 9–13 years: 34 gMales, 14–18 years: 52 gFemales, 14–18 years: 46 g
Protein Needs for Children
Daily protein needs for children and adolescents are as follows:Infants, 0–6 months: 9 gInfants, 7–12 months: 11 gChildren, 1–3 years: 13 gChildren, 4–8 years: 19 gMales and females, 9–13 years: 34 gMales, 14–18 years: 52 gFemales, 14–18 years: 46 g
Daily protein needs for children and adolescents are as follows:
Summary
It’s a myth that most plant proteins are incomplete compared to animal proteins. While certain legumes, grains, corn, and nuts tend to be limited in one or more essential amino acids, they are not missing any.
Even if you don’t consume animal products, eating a variety of plant proteins will provide all the essential amino acids and protein you need, plus plenty of other vital nutrients. Experiment with new ways to use chickpeas, lentils, quinoa, cashews, and soy foods to ensure diversity in your diet.
29 SourcesVerywell 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.Lopez MJ, Mohiuddin SS.Biochemistry, essential amino acids. In: StatPearls. Treasure Island (FL): StatPearls Publishing; March 13, 2023.USDA FoodData Central.Cashews, unroasted.Lackey KA, Fleming SA.Brief research report: estimation of the protein digestibility-corrected amino acid score of defatted walnuts.Front Nutr. 2021;8:702857. doi:10.3389/fnut.2021.702857El-Sohaimy SA, Androsova NV, Toshev AD, El Enshasy HA.Nutritional quality, chemical, and functional characteristics of hemp (Cannabis sativa ssp. sativa) protein isolate.Plants (Basel). 2022;11(21):2825. doi:10.3390/plants11212825Grancieri M, Martino HSD, Gonzalez de Mejia E.Chia seed (Salvia hispanica L.) as a source of proteins and bioactive peptides with health benefits: a review.Compr Rev Food Sci Food Saf. 2019;18(2):480-499. doi:10.1111/1541-4337.12423Adhikari S, Schop M, de Boer IJM, Huppertz T.Protein quality in perspective: a review of protein quality metrics and their applications.Nutrients. 2022;14(5):947. doi:10.3390/nu14050947Poutanen KS, Kårlund AO, Gómez-Gallego C, et al.Grains - a major source of sustainable protein for health.Nutr Rev. 2022;80(6):1648-1663. doi:10.1093/nutrit/nuab084Procopet O, Oroian M.Amaranth seed polyphenol, fatty acid and amino acid profile.Applied Sciences. 2022; 12(4):2181. doi.org/10.3390/app12042181Hertzler SR, Lieblein-Boff JC, Weiler M, Allgeier C.Plant proteins: assessing their nutritional quality and effects on health and physical function.Nutrients. 2020;12(12):3704. doi:10.3390/nu12123704Han F, Moughan PJ, Li J, Stroebinger N, Pang S.The complementarity of amino acids in cooked pulse/cereal blends and effects on DIAAS.Plants (Basel). 2021;10(10):1999. doi:10.3390/plants10101999Berrazaga I, Micard V, Gueugneau M, Walrand S.The role of the anabolic properties of plant- versus animal-based protein sources in supporting muscle mass maintenance: a critical review.Nutrients. 2019;11(8):1825. doi:10.3390/nu11081825Barber TM, Kabisch S, Pfeiffer AFH, Weickert MO.The health benefits of dietary fibre. Nutrients. 2020;12(10):3209. Published 2020 Oct 21. doi:10.3390/nu12103209Frank SM, Jaacks LM, Adair LS, et al.Adherence to the Planetary Health Diet Index and correlation with nutrients of public health concern: an analysis of NHANES 2003-2018.Am J Clin Nutr.2024;119(2):384-392. doi:10.1016/j.ajcnut.2023.10.018Craig WJ, Mangels AR, Fresán U, et al.The safe and effective use of plant-based diets with guidelines for health professionals.Nutrients. 2021;13(11):4144. doi:10.3390/nu13114144Huang J, Liao LM, Weinstein SJ, Sinha R, Graubard BI, Albanes D.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.2020.2790Woolf PJ, Fu LL, Basu A.vProtein: identifying optimal amino acid complements from plant-based foods.PLoS One. 2011;6(4):e18836. doi:10.1371/journal.pone.0018836.American Heart Association.Vegetarian diets.Mariotti F, Gardner CD.Dietary protein and amino acids in vegetarian diets-A review. Nutrients. 2019;11(11):2661. Published 2019 Nov 4. doi:10.3390/nu11112661USDA FoodData Central.Meat substitute, cereal- and vegetable protein-based, fried.USDA FoodData Central.Chickpeas, from canned, no added fat.USDA FoodData Central.Lentils, from canned.USDA FoodData Central.Green peas, fresh, cooked with oil.USDA FoodData Central.Quinoa, no added fat.USDA FoodData Central.Premium firm tofu.USDA FoodData Central.Tempeh.USDA FoodData Central.Edamame, frozen, prepared.USDA FoodData Central.Soy milk.FoodData Central.Broccoli.Food and Nutrition Board, Institute of Medicine, National Academies.Dietary Reference Intakes (DRIs): recommended dietary allowances and adequate intakes, total water and macronutrients.
29 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.Lopez MJ, Mohiuddin SS.Biochemistry, essential amino acids. In: StatPearls. Treasure Island (FL): StatPearls Publishing; March 13, 2023.USDA FoodData Central.Cashews, unroasted.Lackey KA, Fleming SA.Brief research report: estimation of the protein digestibility-corrected amino acid score of defatted walnuts.Front Nutr. 2021;8:702857. doi:10.3389/fnut.2021.702857El-Sohaimy SA, Androsova NV, Toshev AD, El Enshasy HA.Nutritional quality, chemical, and functional characteristics of hemp (Cannabis sativa ssp. sativa) protein isolate.Plants (Basel). 2022;11(21):2825. doi:10.3390/plants11212825Grancieri M, Martino HSD, Gonzalez de Mejia E.Chia seed (Salvia hispanica L.) as a source of proteins and bioactive peptides with health benefits: a review.Compr Rev Food Sci Food Saf. 2019;18(2):480-499. doi:10.1111/1541-4337.12423Adhikari S, Schop M, de Boer IJM, Huppertz T.Protein quality in perspective: a review of protein quality metrics and their applications.Nutrients. 2022;14(5):947. doi:10.3390/nu14050947Poutanen KS, Kårlund AO, Gómez-Gallego C, et al.Grains - a major source of sustainable protein for health.Nutr Rev. 2022;80(6):1648-1663. doi:10.1093/nutrit/nuab084Procopet O, Oroian M.Amaranth seed polyphenol, fatty acid and amino acid profile.Applied Sciences. 2022; 12(4):2181. doi.org/10.3390/app12042181Hertzler SR, Lieblein-Boff JC, Weiler M, Allgeier C.Plant proteins: assessing their nutritional quality and effects on health and physical function.Nutrients. 2020;12(12):3704. doi:10.3390/nu12123704Han F, Moughan PJ, Li J, Stroebinger N, Pang S.The complementarity of amino acids in cooked pulse/cereal blends and effects on DIAAS.Plants (Basel). 2021;10(10):1999. doi:10.3390/plants10101999Berrazaga I, Micard V, Gueugneau M, Walrand S.The role of the anabolic properties of plant- versus animal-based protein sources in supporting muscle mass maintenance: a critical review.Nutrients. 2019;11(8):1825. doi:10.3390/nu11081825Barber TM, Kabisch S, Pfeiffer AFH, Weickert MO.The health benefits of dietary fibre. Nutrients. 2020;12(10):3209. Published 2020 Oct 21. doi:10.3390/nu12103209Frank SM, Jaacks LM, Adair LS, et al.Adherence to the Planetary Health Diet Index and correlation with nutrients of public health concern: an analysis of NHANES 2003-2018.Am J Clin Nutr.2024;119(2):384-392. doi:10.1016/j.ajcnut.2023.10.018Craig WJ, Mangels AR, Fresán U, et al.The safe and effective use of plant-based diets with guidelines for health professionals.Nutrients. 2021;13(11):4144. doi:10.3390/nu13114144Huang J, Liao LM, Weinstein SJ, Sinha R, Graubard BI, Albanes D.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.2020.2790Woolf PJ, Fu LL, Basu A.vProtein: identifying optimal amino acid complements from plant-based foods.PLoS One. 2011;6(4):e18836. doi:10.1371/journal.pone.0018836.American Heart Association.Vegetarian diets.Mariotti F, Gardner CD.Dietary protein and amino acids in vegetarian diets-A review. Nutrients. 2019;11(11):2661. Published 2019 Nov 4. doi:10.3390/nu11112661USDA FoodData Central.Meat substitute, cereal- and vegetable protein-based, fried.USDA FoodData Central.Chickpeas, from canned, no added fat.USDA FoodData Central.Lentils, from canned.USDA FoodData Central.Green peas, fresh, cooked with oil.USDA FoodData Central.Quinoa, no added fat.USDA FoodData Central.Premium firm tofu.USDA FoodData Central.Tempeh.USDA FoodData Central.Edamame, frozen, prepared.USDA FoodData Central.Soy milk.FoodData Central.Broccoli.Food and Nutrition Board, Institute of Medicine, National Academies.Dietary Reference Intakes (DRIs): recommended dietary allowances and adequate intakes, total water and macronutrients.
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.
Lopez MJ, Mohiuddin SS.Biochemistry, essential amino acids. In: StatPearls. Treasure Island (FL): StatPearls Publishing; March 13, 2023.USDA FoodData Central.Cashews, unroasted.Lackey KA, Fleming SA.Brief research report: estimation of the protein digestibility-corrected amino acid score of defatted walnuts.Front Nutr. 2021;8:702857. doi:10.3389/fnut.2021.702857El-Sohaimy SA, Androsova NV, Toshev AD, El Enshasy HA.Nutritional quality, chemical, and functional characteristics of hemp (Cannabis sativa ssp. sativa) protein isolate.Plants (Basel). 2022;11(21):2825. doi:10.3390/plants11212825Grancieri M, Martino HSD, Gonzalez de Mejia E.Chia seed (Salvia hispanica L.) as a source of proteins and bioactive peptides with health benefits: a review.Compr Rev Food Sci Food Saf. 2019;18(2):480-499. doi:10.1111/1541-4337.12423Adhikari S, Schop M, de Boer IJM, Huppertz T.Protein quality in perspective: a review of protein quality metrics and their applications.Nutrients. 2022;14(5):947. doi:10.3390/nu14050947Poutanen KS, Kårlund AO, Gómez-Gallego C, et al.Grains - a major source of sustainable protein for health.Nutr Rev. 2022;80(6):1648-1663. doi:10.1093/nutrit/nuab084Procopet O, Oroian M.Amaranth seed polyphenol, fatty acid and amino acid profile.Applied Sciences. 2022; 12(4):2181. doi.org/10.3390/app12042181Hertzler SR, Lieblein-Boff JC, Weiler M, Allgeier C.Plant proteins: assessing their nutritional quality and effects on health and physical function.Nutrients. 2020;12(12):3704. doi:10.3390/nu12123704Han F, Moughan PJ, Li J, Stroebinger N, Pang S.The complementarity of amino acids in cooked pulse/cereal blends and effects on DIAAS.Plants (Basel). 2021;10(10):1999. doi:10.3390/plants10101999Berrazaga I, Micard V, Gueugneau M, Walrand S.The role of the anabolic properties of plant- versus animal-based protein sources in supporting muscle mass maintenance: a critical review.Nutrients. 2019;11(8):1825. doi:10.3390/nu11081825Barber TM, Kabisch S, Pfeiffer AFH, Weickert MO.The health benefits of dietary fibre. Nutrients. 2020;12(10):3209. Published 2020 Oct 21. doi:10.3390/nu12103209Frank SM, Jaacks LM, Adair LS, et al.Adherence to the Planetary Health Diet Index and correlation with nutrients of public health concern: an analysis of NHANES 2003-2018.Am J Clin Nutr.2024;119(2):384-392. doi:10.1016/j.ajcnut.2023.10.018Craig WJ, Mangels AR, Fresán U, et al.The safe and effective use of plant-based diets with guidelines for health professionals.Nutrients. 2021;13(11):4144. doi:10.3390/nu13114144Huang J, Liao LM, Weinstein SJ, Sinha R, Graubard BI, Albanes D.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.2020.2790Woolf PJ, Fu LL, Basu A.vProtein: identifying optimal amino acid complements from plant-based foods.PLoS One. 2011;6(4):e18836. doi:10.1371/journal.pone.0018836.American Heart Association.Vegetarian diets.Mariotti F, Gardner CD.Dietary protein and amino acids in vegetarian diets-A review. Nutrients. 2019;11(11):2661. Published 2019 Nov 4. doi:10.3390/nu11112661USDA FoodData Central.Meat substitute, cereal- and vegetable protein-based, fried.USDA FoodData Central.Chickpeas, from canned, no added fat.USDA FoodData Central.Lentils, from canned.USDA FoodData Central.Green peas, fresh, cooked with oil.USDA FoodData Central.Quinoa, no added fat.USDA FoodData Central.Premium firm tofu.USDA FoodData Central.Tempeh.USDA FoodData Central.Edamame, frozen, prepared.USDA FoodData Central.Soy milk.FoodData Central.Broccoli.Food and Nutrition Board, Institute of Medicine, National Academies.Dietary Reference Intakes (DRIs): recommended dietary allowances and adequate intakes, total water and macronutrients.
Lopez MJ, Mohiuddin SS.Biochemistry, essential amino acids. In: StatPearls. Treasure Island (FL): StatPearls Publishing; March 13, 2023.
USDA FoodData Central.Cashews, unroasted.
Lackey KA, Fleming SA.Brief research report: estimation of the protein digestibility-corrected amino acid score of defatted walnuts.Front Nutr. 2021;8:702857. doi:10.3389/fnut.2021.702857
El-Sohaimy SA, Androsova NV, Toshev AD, El Enshasy HA.Nutritional quality, chemical, and functional characteristics of hemp (Cannabis sativa ssp. sativa) protein isolate.Plants (Basel). 2022;11(21):2825. doi:10.3390/plants11212825
Grancieri M, Martino HSD, Gonzalez de Mejia E.Chia seed (Salvia hispanica L.) as a source of proteins and bioactive peptides with health benefits: a review.Compr Rev Food Sci Food Saf. 2019;18(2):480-499. doi:10.1111/1541-4337.12423
Adhikari S, Schop M, de Boer IJM, Huppertz T.Protein quality in perspective: a review of protein quality metrics and their applications.Nutrients. 2022;14(5):947. doi:10.3390/nu14050947
Poutanen KS, Kårlund AO, Gómez-Gallego C, et al.Grains - a major source of sustainable protein for health.Nutr Rev. 2022;80(6):1648-1663. doi:10.1093/nutrit/nuab084
Procopet O, Oroian M.Amaranth seed polyphenol, fatty acid and amino acid profile.Applied Sciences. 2022; 12(4):2181. doi.org/10.3390/app12042181
Hertzler SR, Lieblein-Boff JC, Weiler M, Allgeier C.Plant proteins: assessing their nutritional quality and effects on health and physical function.Nutrients. 2020;12(12):3704. doi:10.3390/nu12123704
Han F, Moughan PJ, Li J, Stroebinger N, Pang S.The complementarity of amino acids in cooked pulse/cereal blends and effects on DIAAS.Plants (Basel). 2021;10(10):1999. doi:10.3390/plants10101999
Berrazaga I, Micard V, Gueugneau M, Walrand S.The role of the anabolic properties of plant- versus animal-based protein sources in supporting muscle mass maintenance: a critical review.Nutrients. 2019;11(8):1825. doi:10.3390/nu11081825
Barber TM, Kabisch S, Pfeiffer AFH, Weickert MO.The health benefits of dietary fibre. Nutrients. 2020;12(10):3209. Published 2020 Oct 21. doi:10.3390/nu12103209
Frank SM, Jaacks LM, Adair LS, et al.Adherence to the Planetary Health Diet Index and correlation with nutrients of public health concern: an analysis of NHANES 2003-2018.Am J Clin Nutr.2024;119(2):384-392. doi:10.1016/j.ajcnut.2023.10.018
Craig WJ, Mangels AR, Fresán U, et al.The safe and effective use of plant-based diets with guidelines for health professionals.Nutrients. 2021;13(11):4144. doi:10.3390/nu13114144
Huang J, Liao LM, Weinstein SJ, Sinha R, Graubard BI, Albanes D.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
Woolf PJ, Fu LL, Basu A.vProtein: identifying optimal amino acid complements from plant-based foods.PLoS One. 2011;6(4):e18836. doi:10.1371/journal.pone.0018836.
American Heart Association.Vegetarian diets.
Mariotti F, Gardner CD.Dietary protein and amino acids in vegetarian diets-A review. Nutrients. 2019;11(11):2661. Published 2019 Nov 4. doi:10.3390/nu11112661
USDA FoodData Central.Meat substitute, cereal- and vegetable protein-based, fried.
USDA FoodData Central.Chickpeas, from canned, no added fat.
USDA FoodData Central.Lentils, from canned.
USDA FoodData Central.Green peas, fresh, cooked with oil.
USDA FoodData Central.Quinoa, no added fat.
USDA FoodData Central.Premium firm tofu.
USDA FoodData Central.Tempeh.
USDA FoodData Central.Edamame, frozen, prepared.
USDA FoodData Central.Soy milk.
FoodData Central.Broccoli.
Food and Nutrition Board, Institute of Medicine, National Academies.Dietary Reference Intakes (DRIs): recommended dietary allowances and adequate intakes, total water and macronutrients.
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