The Building Blocks of Protein: Amino Acids
Protein is a critical macronutrient, playing a role in building and repairing tissues, creating enzymes and hormones, and supporting overall bodily function. It is composed of smaller organic compounds called amino acids. There are approximately 20 different amino acids important for human health, divided into essential and non-essential categories. The body can synthesize the 11 non-essential amino acids, but the nine essential amino acids must be obtained through food.
What is Considered a Complete Protein?
A complete protein is a food source containing adequate amounts of all nine essential amino acids. In contrast, an incomplete protein lacks one or more of these essential amino acids or contains them in insufficient quantities. The nine essential amino acids are: Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, and Valine.
Complete vs. Incomplete Proteins
Historically, it was believed that vegetarians and vegans needed to combine specific plant foods at each meal to get a full amino acid profile. However, modern nutritional science confirms that the body can combine amino acids from different foods eaten throughout the day. This means a varied diet with a range of protein sources will meet essential amino acid needs over the day.
Sources of Complete Protein
Complete protein sources include both animal and plant-based options.
Animal-Based Sources
Common animal-based complete proteins include meat (beef, pork, poultry), fish and seafood, dairy products (milk, cheese, yogurt), and eggs.
Plant-Based Sources
Several plant foods offer all nine essential amino acids, including soy products (tofu, tempeh, edamame, soy milk), quinoa, buckwheat, hempseed, spirulina, and mycoprotein. Chia seeds are also often cited, though some experts note they may be lower in certain essential amino acids.
Combining Incomplete Proteins for a Complete Profile
Consuming a variety of incomplete protein sources throughout the day ensures your body receives all necessary essential amino acids through a process called protein combining or complementarity. Examples of complementary pairings include rice and beans or peanut butter on whole-grain toast. A diverse intake of legumes, nuts, seeds, and whole grains is key for those on a plant-based diet.
Comparison of Complete vs. Incomplete Protein Sources
| Feature | Complete Proteins | Incomplete Proteins |
|---|---|---|
| Essential Amino Acids | Contain all nine essential amino acids in sufficient quantities. | Missing one or more essential amino acids or have them in low amounts. |
| Primary Sources | Animal products (meat, fish, eggs, dairy) and some plants (soy, quinoa, buckwheat). | Most plant-based foods, including grains (except quinoa/buckwheat), legumes (except soy), nuts, and seeds. |
| Dietary Importance | Easy to meet essential amino acid requirements in one food source. | Requires variety in diet to ensure all essential amino acids are consumed over the day. |
| Examples | Eggs, salmon, beef, chicken, milk, yogurt, soy, quinoa. | Rice, beans, nuts, most seeds, vegetables. |
Conclusion
Understanding what is considered a complete protein is important for a healthy diet, but achieving a complete amino acid profile is manageable with both animal and plant-based foods. While animal products typically offer all nine essential amino acids in one food, vegetarians and vegans can easily meet their needs by consuming a diverse array of protein-rich plant foods over the course of a day. Variety in your diet is key to ensuring your body gets the essential building blocks it needs. For further reading, consult resources like the National Institutes of Health.
