What is a complete protein?
Protein is a macronutrient composed of amino acids, which are its building blocks. There are 20 amino acids, but nine are classified as “essential” because the body cannot produce them and they must be obtained through diet. A food is a complete protein if it provides sufficient amounts of all nine essential amino acids. Complete proteins are vital for functions like muscle growth and tissue repair.
Many animal-based foods are complete proteins, including meat, poultry, fish, eggs, and dairy. Some plant-based sources, such as soybeans, quinoa, and buckwheat, are also complete proteins.
What are incomplete proteins?
Incomplete proteins are foods that do not contain adequate amounts of one or more essential amino acids. This doesn't mean they are lacking in nutritional value; they still offer beneficial nutrients. Most plant-based foods, like legumes, nuts, seeds, and grains, are incomplete proteins. For example, rice is low in lysine, while beans are high in lysine but low in methionine {Link: SimplyProtein https://simplyprotein.ca/blogs/news/what-s-the-difference-between-a-complete-and-incomplete-protein}. While it was once thought necessary to combine these foods in the same meal, current understanding is that consuming a variety of incomplete proteins throughout the day is sufficient, as the body can store and utilize amino acids from different sources.
The importance of complementary proteins
For those following vegetarian or vegan diets, consuming a diverse range of plant-based foods helps ensure all essential amino acids are acquired. Complementary proteins involve pairing different incomplete protein sources to achieve a complete amino acid profile over the course of the day.
Examples of complementary protein combinations include:
- Rice and beans
- Peanut butter on whole-grain toast
- Hummus with whole-wheat pita
- Corn with legumes {Link: SimplyProtein https://simplyprotein.ca/blogs/news/what-s-the-difference-between-a-complete-and-incomplete-protein}
- Lentil soup with whole-grain bread
Comparison table: Protein vs. Complete Protein
| Feature | Protein | Complete Protein |
|---|---|---|
| Definition | A macronutrient made of amino acids; found in all protein-containing foods. | A subset of protein containing all nine essential amino acids in adequate amounts. |
| Amino Acid Profile | Varies widely, can be a complete or incomplete source. | Contains all nine essential amino acids (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine) {Link: SimplyProtein https://simplyprotein.ca/blogs/news/what-s-the-difference-between-a-complete-and-incomplete-protein}. |
| Dietary Sources | Found in both animal and plant foods. | Primarily animal sources (meat, eggs, dairy) and some plant sources (soy, quinoa). |
| Functionality | Provides amino acids for building and repairing tissues. | Provides a full set of building blocks in one source, streamlining tissue repair and synthesis. |
| Dietary Requirement | The body needs a sufficient total intake of amino acids. | Necessary for a balanced diet, but can be achieved through combining incomplete sources throughout the day. |
Are complete proteins healthier than incomplete proteins?
It's a misconception that incomplete proteins are inferior. While complete proteins offer all essential amino acids in one food, incomplete proteins often provide additional beneficial nutrients like fiber, vitamins, and minerals. A balanced diet including a variety of both complete and incomplete protein sources is beneficial for overall health. The key is dietary diversity to ensure a wide range of nutrients.
How dietary choices affect protein intake
Omnivores typically consume complete proteins easily through animal products. Those on vegetarian or vegan diets need to be more strategic but can still meet essential amino acid needs through protein complementation and incorporating complete plant proteins like soy and quinoa.
Combining complementary proteins at every meal isn't necessary; a varied intake of plant-based foods throughout the day is sufficient. Focusing on the overall nutritional profile of foods, including fiber and micronutrients, is more important than just protein completeness. A diverse and balanced diet is key for wellness.
Conclusion
The main difference between protein and complete protein is their amino acid content: complete proteins contain all nine essential amino acids, while incomplete proteins do not. Protein is the general term, and complete protein is a specific type. While animal products are common sources of complete proteins, varied plant-based diets can also provide all essential amino acids through complementary pairings. For most individuals, consuming a variety of protein sources throughout the day is enough; focusing on a balanced and diverse diet is key for overall health.
References
- Cleveland Clinic. (2022). Complete vs. Incomplete Proteins and Examples. Health Essentials.
- Health.com. (2025). Complete vs. Incomplete Protein: Definition and Examples.
- Peloton. (2024). Incomplete vs. Complete Proteins & Top Food Sources of Each.
- Unjury. (2024). Complete vs. Incomplete Proteins: Whats the Difference?.
- East Valley Urology Center. (n.d.). Incomplete Vs. Complete Proteins.
- WebMD. (2025). {Link: WebMD https://www.webmd.com/diet/difference-between-complete-incomplete-proteins}
- Healthline. (2025). 16 Foods for High Protein Meals.
- Harvard T.H. Chan School of Public Health. (n.d.). Protein. The Nutrition Source.
- SimplyProtein. (2025). {Link: SimplyProtein https://simplyprotein.ca/blogs/news/what-s-the-difference-between-a-complete-and-incomplete-protein}
