Understanding Protein: Complete vs. Incomplete
Protein is a crucial macronutrient made up of amino acids, which are the building blocks of muscle, hormones, and enzymes. There are 20 different amino acids, but nine of these are considered 'essential.' This means the human body cannot produce them on its own, and they must be obtained through diet. The nine essential amino acids are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
Proteins that contain all nine essential amino acids in sufficient quantities are called 'complete proteins.' While animal products are classic examples, the notion that plant proteins are 'incomplete' is a long-debunked myth. The body is highly efficient at pooling amino acids from all the foods you consume throughout the day, not just within a single meal. As long as your diet includes a variety of plant-based foods, you will meet your essential amino acid requirements.
Leading Complete Plant Protein Sources
Numerous plant foods provide a complete amino acid profile, making them excellent staples for any diet. Here are some of the most notable examples:
Quinoa
Often mistaken for a grain, quinoa is actually a seed that is a true complete protein. It provides a higher amount of lysine than many other grains and is also an excellent source of fiber, magnesium, and iron. Its versatility allows it to be used in everything from breakfast bowls to side dishes and salads.
Soy and Its Derivatives
Soybeans are a primary source of high-quality, complete plant protein, with a protein profile that rivals that of animal products. As a complete protein, soy is used to create a wide range of popular vegan products:
- Edamame: These immature green soybeans are packed with protein and fiber and can be enjoyed steamed as a snack or added to salads.
- Tofu and Tempeh: Created from processed soybeans, these products serve as excellent meat substitutes. Tempeh, made from fermented soybeans, is particularly protein-dense.
Buckwheat
Another 'pseudocereal,' buckwheat is a seed that is entirely gluten-free and contains all nine essential amino acids. It is a nutritious source of fiber and can be consumed in the form of groats, flour, and noodles.
Hemp Seeds
Hemp seeds are considered one of the most nutritionally complete plant foods. They contain all nine essential amino acids and boast a healthy ratio of omega-3 and omega-6 fatty acids. While some sources indicate hemp protein is slightly lower in lysine compared to optimal levels, it still contains all essential amino acids and can be easily complemented by other foods.
Amaranth
This ancient, gluten-free grain is a complete protein with a balanced amino acid composition that surpasses many other grains, particularly its high content of lysine and tryptophan. Amaranth can be cooked like a cereal or used to make flour.
Spirulina
This blue-green algae is a potent superfood that is exceptionally high in protein (around 55-70% by dry weight) and provides all nine essential amino acids. Spirulina is often consumed in powdered form, mixed into smoothies or juices, and is also an excellent source of iron and B vitamins.
Achieving Balanced Nutrition with Incomplete Proteins
While complete plant proteins simplify meeting your amino acid needs, it is not necessary to rely solely on them. Most plant foods are technically 'incomplete,' meaning they are low in one or more essential amino acids, known as 'limiting amino acids.' However, by eating a varied diet, your body combines amino acids from different foods throughout the day to form complete proteins.
Combining Protein for a Balanced Diet
- Grains and Legumes: The classic combination of rice and beans is a textbook example of complementary proteins. Grains like rice are typically low in lysine but higher in methionine, while legumes like beans are rich in lysine but lower in methionine.
- Nuts/Seeds and Legumes: Pairing legumes with nuts or seeds, such as hummus (chickpeas) with a sprinkle of pine nuts or a salad with chickpeas and sunflower seeds, creates a complete protein profile.
- Peanut Butter on Whole Wheat Toast: The combination of a legume (peanut butter) with a grain (whole wheat bread) offers a full spectrum of amino acids.
Comparison of Complete and Incomplete Plant Protein Sources
| Feature | Complete Plant Proteins | Incomplete Plant Proteins |
|---|---|---|
| Definition | Contains all nine essential amino acids in sufficient amounts. | Contains some but not all nine essential amino acids in sufficient quantities. |
| Examples | Quinoa, Soy (Tofu, Edamame), Buckwheat, Hemp Seeds, Amaranth, Spirulina. | Lentils, Most Beans (excluding soy), Nuts (excluding hemp), Seeds (excluding hemp), Most Grains (e.g., rice). |
| Key Benefit | Offers a ready-made source of all essential amino acids in a single food item. | Contributes to a balanced amino acid intake when consumed in variety over the course of a day. |
| Dietary Strategy | Can be relied upon as a primary protein source for a meal or snack. | Best combined with other plant foods to create a full amino acid profile over time. |
Conclusion
Understanding what plant foods have all 9 amino acids is key for anyone following a plant-based diet. Quinoa, soy products, buckwheat, hemp seeds, amaranth, and spirulina all provide a complete protein profile, debunking the misconception that animal products are the only source of high-quality protein. Furthermore, remember that consuming a variety of different plant foods throughout the day is a natural and effective way to ensure your body receives all the essential amino acids it needs. Protein combining within a single meal is unnecessary, as the body can effectively pool amino acids to build the proteins it requires. By embracing a varied and nutrient-dense plant-based diet, you can easily meet all your protein requirements and support overall health.
For more information on protein combining and the myth surrounding it, see the resource from Forks Over Knives: The Myth of Complementary Protein.
