What are Essential and Non-Essential Amino Acids?
Amino acids are the fundamental building blocks of protein, vital for numerous bodily functions. Of the 20 amino acids the body uses, nine are considered essential because the body cannot produce them and they must be obtained through diet. These essential amino acids include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. The remaining 11 are non-essential, as the body can synthesize them internally.
The Meaning of "Incomplete Protein"
A food is classified as an 'incomplete protein' if it lacks adequate proportions of one or more essential amino acids. This classification doesn't diminish a food's nutritional value; many healthy plant foods fall into this category. While animal proteins are typically complete, a varied intake of plant proteins throughout the day can easily provide all essential amino acids.
Common Incomplete Protein Sources
- Legumes: Often low in methionine.
- Grains: Usually contain low amounts of lysine.
- Nuts and Seeds: Many are low in methionine, and some lack sufficient tryptophan.
- Vegetables: Provide some protein, generally in incomplete proportions.
Complementary Proteins: The Simple Solution
Combining different incomplete proteins to achieve a complete amino acid profile is known as protein complementing. For most healthy individuals with a varied diet, combining these foods in a single meal isn't necessary. The body maintains an amino acid pool, utilizing various plant proteins consumed over 24 hours to meet its needs. Traditional diets often naturally pair complementary proteins, such as rice and beans.
Combining Incomplete Proteins
Effective combinations include:
- Grains and Legumes: Rice and beans, hummus with pita.
- Nuts/Seeds and Legumes: Salads with chickpeas and sunflower seeds.
- Nut Butter and Grains: Peanut butter on whole-wheat bread.
- Legumes and Dairy (Lacto-vegetarians): Lentil soup with yogurt.
Complete vs. Incomplete Proteins: A Comparison
| Criteria | Complete Proteins | Incomplete Proteins |
|---|---|---|
| Definition | Contains all nine essential amino acids in adequate proportions. | Lacks sufficient amounts of one or more essential amino acids. |
| Primary Sources | Animal products, soy, quinoa, buckwheat, hemp seeds. | Most plant-based foods. |
| Dietary Strategy | Provides a complete amino acid profile in one food. | Requires combination with other plant proteins throughout the day. |
| Associated Nutrients | Often high in saturated fats and cholesterol. | High in fiber, vitamins, and minerals; low in saturated fats. |
The Health Implications of Amino Acid Deficiency
Consistent lack of essential amino acids can lead to health issues. The body may break down muscle tissue to obtain needed amino acids, potentially causing muscle wasting. Severe, long-term deficiency, particularly in children, can result in conditions like kwashiorkor. A balanced diet generally prevents these severe issues.
Deficiency Symptoms
- Muscle Wasting: Breakdown of muscle tissue.
- Weakened Immunity: Impaired immune function.
- Fatigue and Weakness: Low energy and general weakness.
- Brittle Hair and Nails: Due to protein being a key component.
- Skin Problems: Rashes or lesions in severe cases.
- Impaired Brain Function: Some amino acids are crucial for neurotransmitters.
A Note on Protein Quality
While animal proteins are complete sources, many plant foods are also excellent protein sources. Soy, quinoa, and buckwheat are examples of complete plant proteins. The focus should be on ensuring a complete intake of essential amino acids through a varied diet, not solely on whether individual foods are complete or incomplete. Soy, for instance, offers a high-quality plant protein comparable to animal protein.
Conclusion: Variety is Key
For those following a plant-based diet, the fact that a food does not contain all 9 essential amino acids is not a concern when eating a varied diet throughout the day. Combining different plant protein sources provides all necessary amino acids. A balanced and varied diet is the most effective approach for optimal protein and amino acid intake. For further information, the Cleveland Clinic offers reliable resources on dietary amino acids.
