Amino acids are organic molecules that serve as the building blocks of proteins. They are vital for physiologic functions like tissue repair, neurotransmitter regulation, enzyme production, mood regulation, and metabolic processing.
This article describes the role of amino acids in body systems, explains essential and non-essential amino acids, presents food sources of the essential amino acids, and provides advice on ensuring dietary protein adequacy within plant-based diets.
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Understanding Amino Acids
There are 20 different amino acids, which are grouped into the categories of essential and non-essential. The body cannot make essential amino acids, so they must be obtained through the diet. The body produces non-essential amino acids through various compounds.
Essential amino acids include:
- Histidine
- Isoleucine
- Leucine
- Lysine
- Methionine
- Phenylalanine
- Threonine
- Tryptophan
- Valine
Non-essential amino acids include:
- Alanine
- Arginine
- Asparagine
- Aspartic acid
- Cysteine
- Glutamic acid
- Glutamine
- Glycine
- Proline
- Serine
- Tyrosine
Essential Amino Acids
Each of the nine essential amino acids serves different physiologic roles within the body.
Histidine
Histidine serves various bodily functions, specifically cellular repair and immune functions. It's a precursor to histamine, which is required for immune reactions, hemoglobin formation, and nerve conduction.
Isoleucine
Isoleucine is necessary for muscle remodeling and energy production. Particularly important during exercise, isoleucine is imperative in muscle growth and repair and also in wound healing after an injury.
Leucine
Leucine is a unique essential amino acid. It is necessary for muscle synthesis and growth, which it accomplishes by triggering growth hormone secretion. Because of its anabolic role, leucine stimulates pancreatic insulin release to help regulate blood glucose levels.
Lysine
Lysine is particularly important for bone health and immune function. It aids calcium absorption and is required for hormone and antibody production. Lysine is also involved in collagen formation, so it is important in the health of skin and connective tissues.
Methionine
Methionine is metabolically active, aiding in the breakdown of fats and removing toxic metabolites. It also helps form the antioxidants glutathione and cysteine.
Phenylalanine
Phenylalanine is a precursor for some of the main neurotransmitters, including epinephrine, norepinephrine, and dopamine. As a result, phenylalanine is important in mood regulation, memory, and learning.
Threonine
Threonine is particularly important for the health of skin and connective tissues, as it helps form collagen, elastin, and other proteins. It also promotes immunity by forming antibodies to help fight foreign pathogens.
Tryptophan
Tryptophan is well-known as a precursor to serotonin, an important neurotransmitter involved in appetite, sleep, and mood regulation. It is also necessary to make niacin (vitamin B3), which helps promote optimal immunity.
Valine
Valine is crucial for muscle repair, cell recovery, and energy production.
Amino Acids in Physiology
The physiologic functions of amino acids make them imperative in overall health, especially related to muscle functions, cellular metabolism, and cognition.
Roles in Physiology
Amino acids support various physiologic functions, such as tissue repair, neurotransmitter regulation, enzyme production, mood regulation, and metabolic processing.
Importantly, amino acids are vital in maintaining lean muscle mass (which may decline with age) and promoting healing during illnesses or injuries.
BCAAs (Branched-Chain Amino Acids)
Three amino acids are structured as branched-chain amino acids (BCAAs): leucine, isoleucine, and valine. BCAAs are particularly important for muscle metabolism, growth, and recovery. BCAAs are popular supplements in conjunction with exercise and for those with increased protein needs or dietary protein inadequacy.
Protein Structure and Function
Proteins are made up of amino acids held in different formations to support various functions.
Protein Structure
Amino acids are the building blocks of proteins. Peptide bonds hold amino acids together in structures of varying complexities.
Primary proteins consist of a linear chain of amino acids. Secondary proteins are structured in alpha helices and beta sheets. Tertiary proteins are in three-dimensional structures. Quaternary proteins are held in multiple polypeptides.
The specific amino acids and their sequence determine the protein's shape and function, essential for its physiologic activity.
Amino Acid Supplements
Amino acid supplements can be helpful in certain situations, such as for athletes, individuals who cannot consume adequate complete proteins in their diet, or those who have increased protein needs.
Amino acid supplements are not without inherent risks, however. Protein molecules and individual amino acids are filtered through the kidneys, so patients with kidney diseases or dysfunctions may be unable to excrete excess amino acids.
Working with a knowledgeable professional to determine protein and amino acid needs is important to ensure adequacy and safety.
Complete Proteins in Plant-Based Diets
Ensuring amino acid and protein adequacy is crucial for those who follow a plant-based diet.
Challenges of Plant-Based Diets
Because plant proteins are usually incomplete proteins (they don't contain all nine essential amino acids), consuming complete proteins can be challenging for patients who follow plant-based diets.
Different plant foods contain various combinations of amino acids, so it is key to understand how to combine or pair plant-based foods to include all of the essential amino acids. Quinoa and buckwheat are plant foods that each contain all nine essential amino acids.
Combining Plant-Based Foods
Diligence in planning and balancing meals on plant-based diets is crucial to obtaining complete proteins. Specific plant food pairings can create complete proteins. Consider these examples:
- Hummus with whole-grain crackers or bread
- Chickpeas and quinoa
- Brown rice and beans
- Nut butter and whole grain crackers or bread
Many plant-based products are specifically formulated to include complete proteins in the modern food supply. While this can be helpful for some people, caution is still needed when consuming highly processed foods.
Whenever possible, it is most healthful to stick to whole, real foods, combined and paired in appropriate ways to ensure protein and amino acid adequacy.
Practical Applications and Recommendations
Establishing and implementing personalized protein recommendations is imperative for patients' overall health and nutrition status.
For Practitioners
Protein as a macronutrient has gained more attention over the last few years, and it is increasingly regarded as a priority within patient's diets. Evidence suggests that sufficient complete protein intake may offer these benefits:
- Healthy weight maintenance
- Increased metabolic energy burn
- Improved lean muscle mass
- Better functional strength
Protein needs vary by age, sex, activity level, functional status, other health conditions, medication use, fitness goals, and other factors. Establishing individualized protein targets is an essential component of a personalized nutrition plan.
For Patients
Implementing nutrition recommendations does not have to be daunting. With the wealth of information online, it can be difficult to understand what to trust. Having individualized protein targets set by a knowledgeable professional provides an excellent place to begin.
Maintaining regular contact with your physician and dietitian allows you to refine and change protein recommendations over time based on progress and other health factors.
It is usually safe for patients who consume animal proteins to aim for a total number of protein grams per day and assume amino acid adequacy since most animal proteins are complete proteins.
However, for those who follow plant-based diets, simply counting the total grams of protein per day may not be adequate. Protein intake can be adequate by working with a dietitian or using reliable, balanced plant-based meal plans.
For patients who may not have a dietitian or readily available guidance, consider the following pairings as a basis for meals:
- Whole grains with beans or legumes
- Whole grains with nuts or nut butter
- Beans or legumes with nuts or seeds
- Quinoa with other plant foods
- Buckwheat with other plant foods
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Key Takeaways
- Protein serves important functions for optimal health, including maintaining lean muscle mass, functional strength, a healthy weight, and a good immune system.
- Proteins comprise 20 amino acids, each with varying physiological functions.
- Amino acids are classified as either non-essential amino acids (which the body can make) or essential amino acids (which must be obtained in the diet).
- Animal proteins are complete proteins containing all nine essential amino acids within each food. Plant proteins are usually incomplete proteins, meaning they lack at least one essential amino acid within each food. Common exceptions include quinoa and buckwheat, which are plant-based complete proteins.
- Combining and pairing plant-based foods can form complete proteins to ensure protein adequacy within plant-based diets.
- Healthcare practitioners, including physicians and dietitians, should help patients understand the importance of sufficient protein with all the necessary amino acids.
- By providing patients with practical knowledge they can use for regular meal planning, patients can be empowered to optimize their protein intake and overall nutrition.
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