The Building Blocks of Protein: Amino Acids
Proteins are large, complex molecules that play many critical roles in the body, from repairing tissues to producing hormones. Their structure is made up of smaller units known as amino acids. There are 20 different amino acids, which are classified into two groups based on whether the human body can produce them or not.
- Non-essential amino acids: The 11 amino acids that your body can produce on its own.
- Essential amino acids (EAAs): The 9 amino acids that your body cannot synthesize and must be obtained through your diet. These are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
The nutritional value of a protein source is determined by its ability to provide all nine essential amino acids in sufficient quantities. This distinction is what separates complete from incomplete proteins.
Complete Proteins: The Full Spectrum
A complete protein is a food source that contains all nine essential amino acids in adequate amounts. These are often referred to as high-quality proteins because they provide the full spectrum of amino acids needed for your body's functions.
Examples of Complete Proteins
Complete proteins include most animal products such as meat, fish, eggs, and dairy. Plant-based sources providing all essential amino acids include soybeans and soy products, quinoa, buckwheat, hemp, chia seeds, and spirulina.
Incomplete Proteins: The Missing Links
An incomplete protein is a food that lacks or is low in one or more of the nine essential amino acids. Most plant sources are in this category.
Examples of Incomplete Proteins
Examples of incomplete proteins include legumes (such as beans, peas, and lentils, which lack methionine), grains (like rice, wheat, and corn, often low in lysine and tryptophan), and most nuts and seeds (typically low in either lysine or methionine). Many vegetables also contain incomplete proteins. Collagen is also considered an incomplete animal protein due to low tryptophan.
Complementary Proteins: The Art of Combination
While it was once thought necessary to combine incomplete proteins in a single meal, consuming a variety of protein sources throughout the day is sufficient for the body to obtain all essential amino acids. The body can store amino acids and draw from this 'pool'. Combining foods can still be a practical way to ensure a complete amino acid profile.
Example Pairings
Classic complementary protein pairings include rice and beans, where the lysine from beans complements the methionine in rice. Peanut butter on whole wheat toast combines the grain (providing lysine) and the nuts/seeds (often low in lysine). Hummus (chickpeas/legume) with pita bread (grain) is another example, as is lentil soup with whole grain bread.
Complete vs. Incomplete Proteins: A Comparison
| Feature | Complete Proteins | Incomplete Proteins |
|---|---|---|
| Definition | Contains all 9 essential amino acids in adequate amounts. | Lacking or low in one or more essential amino acids. |
| Primary Sources | Animal products (meat, eggs, dairy) and a few plant sources (soy, quinoa). | Most plant-based foods (legumes, grains, nuts, seeds). |
| Amino Acid Profile | Balanced and contains all essential amino acids. | Contains an unbalanced profile with a 'limiting' amino acid. |
| Dietary Requirement | Can be consumed alone to meet needs. | Must be paired with other foods or varied throughout the day to meet needs. |
| Convenience | Often considered more convenient for ensuring complete amino acid intake, particularly for omnivores. | Requires more conscious effort to combine sources, particularly for strict vegans. |
Meeting Protein Needs on a Plant-Based Diet
A varied plant-based diet can easily provide all essential amino acids. Consuming a diverse range of these foods throughout the day ensures that the body receives a complete amino acid profile. This approach also offers the added benefit of providing a wider array of vitamins, minerals, and fiber. For example, a day's meals could include oatmeal with nuts, lentil soup, and rice and beans, allowing the body to draw amino acids from each to form complete proteins.
Conclusion
Both complete and incomplete proteins are valuable. While complete proteins offer all essential amino acids in one source, a diverse intake of various plant-based foods throughout the day is an effective way to obtain all necessary building blocks. Prioritizing dietary variety supports a balanced eating pattern.
