What Happens If You Don't Get the 9 Essential Amino Acids?

November 15, 2025 •

5 min read

Amino acids are the building blocks of proteins, and an inadequate intake can have serious consequences. The human body requires 20 amino acids, but can only produce 11 of them, meaning the remaining nine must be obtained through food. So, what happens if you don't get the 9 essential amino acids, and how can it impact your overall health and well-being?

Quick Summary

A deficiency in essential amino acids can disrupt protein synthesis, leading to severe health problems. The body may break down muscle for necessary resources, resulting in muscle wasting, weakened immunity, impaired mood, and slow tissue repair.

Key Points

Muscle Atrophy: Without the nine essential amino acids, the body breaks down its own muscle tissue to obtain them, leading to loss of muscle mass.
Weakened Immune Function: An insufficient intake of essential amino acids compromises the body's ability to produce antibodies, making it more susceptible to infections and slower to heal.
Neurological Dysfunction: Deficiency can lead to mood swings, anxiety, depression, and poor concentration due to impaired neurotransmitter production.
Impaired Growth and Repair: The synthesis of new tissues is hindered, resulting in slowed wound healing, poor skin health, and stunted growth in the young.
General Fatigue and Weakness: Persistent lack of essential amino acids leads to decreased energy levels and a pervasive sense of weakness.
Metabolic Disturbances: Essential amino acids are involved in fat metabolism and other critical metabolic processes, which can be disrupted by deficiency.
Digestive Problems: The proteins needed for proper digestive function are compromised, potentially leading to gastrointestinal issues.

Understanding Essential Amino Acids

Amino acids are organic compounds that serve as the fundamental building blocks of proteins. The human body requires 20 different amino acids to function correctly. Of these, 11 are considered 'non-essential' because the body can synthesize them on its own. The other nine, however, cannot be produced internally and must be obtained from dietary sources. These are the nine 'essential' amino acids (EAAs).

The nine essential amino acids are:

Histidine: Precursor to histamine, which is involved in immune function, digestion, and sleep.
Isoleucine: Important for muscle metabolism, immune function, and energy regulation.
Leucine: Crucial for muscle repair, growth hormones, and blood sugar regulation.
Lysine: Plays a role in hormone production, energy, calcium absorption, and immune function.
Methionine: Aids in tissue growth, metabolism, and detoxification, as well as the absorption of zinc and selenium.
Phenylalanine: Precursor to neurotransmitters like dopamine and norepinephrine.
Threonine: Key for collagen and elastin production, blood clotting, and fat metabolism.
Tryptophan: Maintains proper nitrogen balance and helps produce serotonin, a mood regulator.
Valine: Vital for muscle growth, tissue regeneration, and energy production.

The Immediate Consequences of Inadequate Intake

When the diet lacks even one of these essential amino acids, the body's entire protein synthesis machinery can falter. Because the body does not store excess amino acids for later use, it has no reserve to pull from when intake is low. The immediate and most critical effect is a shift towards a 'negative nitrogen balance,' where protein breakdown outpaces protein synthesis. To compensate for the missing building blocks, the body begins breaking down its own muscle tissue. This process, known as muscle wasting or atrophy, begins with skeletal muscle but can eventually affect critical organs like the heart in severe cases. This initial depletion is often accompanied by noticeable fatigue and weakness.

Long-Term Health Consequences of Deficiency

Sustained deficiency of essential amino acids can trigger a cascade of severe, long-lasting health problems throughout the body.

Weakened Immune System

Since proteins are crucial for producing antibodies, a persistent amino acid shortage can cripple the immune system. This leaves the body vulnerable to infections, and recovery from illness can be significantly slower and more difficult. Some studies even suggest specific amino acid deficiencies can have a profound depressive effect on immune responses.

Neurological and Mental Health Issues

Several essential amino acids are precursors to vital neurotransmitters, chemical messengers for the brain. For instance, tryptophan is needed to make serotonin, which regulates mood, sleep, and appetite. Phenylalanine is necessary for dopamine and norepinephrine synthesis. A deficiency can lead to mood swings, anxiety, depression, difficulty concentrating, and memory loss.

Stunted Growth and Development

For children and adolescents, who are in periods of rapid growth, essential amino acid deficiency can be particularly devastating. It can lead to stunted growth, delayed development, and other long-term problems that affect overall health.

Digestive and Skin Problems

Amino acids are essential for maintaining healthy skin, hair, and nails. Deficiencies can cause hair loss, brittle nails, and various skin rashes or sores. They also impact the digestive system, potentially leading to digestive disturbances, bloating, and other gastrointestinal issues.

Table: Complete vs. Incomplete Protein Sources


Feature	Complete Protein Sources	Incomplete Protein Sources
EAA Profile	Contain all nine essential amino acids in sufficient quantities.	Lack one or more essential amino acids, making them deficient in a full EAA profile.
Common Examples	Meat, poultry, fish, eggs, dairy, soy products (tofu, edamame), quinoa, buckwheat.	Legumes (beans, lentils), most grains (except quinoa, buckwheat), nuts, seeds, and most vegetables.
Dietary Strategy	For omnivores, these are easily integrated into the diet.	For vegetarians and vegans, combining different incomplete proteins (e.g., rice and beans) is necessary to form a complete profile.
Benefit	Simplifies dietary planning to ensure EAA intake.	Requires careful meal planning to combine sources, but can provide a nutrient-dense diet.

Who is at Risk for Amino Acid Deficiency?

While severe amino acid deficiencies are uncommon in developed nations with a diverse food supply, certain populations face a higher risk. This includes:

Individuals on Restrictive Diets: Vegans and vegetarians who do not plan their meals carefully to combine complementary proteins may be at risk.
Older Adults: The elderly often experience reduced appetite and may have difficulty absorbing nutrients, increasing their susceptibility to deficiency.
Individuals with Chronic Illnesses: Certain diseases can increase the body's need for amino acids or interfere with their absorption and metabolism.
People Experiencing Stress or Sickness: Physical or psychological stress and periods of illness increase the body's demand for amino acids, making adequate intake even more critical.
Athletes: Intense training requires increased protein for muscle repair and growth, and a lack of essential amino acids can hinder recovery and performance.

How to Ensure Adequate Essential Amino Acid Intake

Fortunately, it is relatively straightforward to ensure you get all nine essential amino acids. The key is a varied and balanced diet.

For Meat Eaters: Incorporating a variety of high-quality animal proteins, such as beef, poultry, fish, eggs, and dairy, will provide all nine EAAs in sufficient amounts.
For Vegans and Vegetarians: Plant-based diets can also provide all essential amino acids with proper planning. Foods like quinoa, soy products (tofu, tempeh), chia seeds, and buckwheat are considered complete proteins. Additionally, combining different incomplete protein sources throughout the day, such as legumes with grains (e.g., rice and beans), ensures all essential amino acids are consumed.
Diversify Your Diet: The best approach for anyone is to eat a wide variety of protein sources to cover all nutritional bases.

Conclusion

Failing to get the nine essential amino acids has significant, wide-ranging health consequences, from immediate muscle wasting to long-term issues affecting immunity, mental health, and physical development. The body is a complex system reliant on a steady supply of these building blocks, which it cannot produce itself. The good news is that for most people with access to a diverse diet, a deficiency is easily avoidable by consuming a variety of protein-rich foods, including both animal and plant-based sources. For those on restricted diets or with other risk factors, understanding the importance of protein combining or seeking guidance from a healthcare professional can help maintain optimal health and well-being. Ensuring adequate essential amino acid intake is a cornerstone of overall health and vitality.

For more detailed information on specific health conditions related to amino acid metabolism, you can visit the NCBI StatPearls article on Biochemistry, Essential Amino Acids.

Frequently Asked Questions

The nine essential amino acids are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. They are called 'essential' because the human body cannot produce them and they must be obtained from dietary sources.

Yes, it is possible to get all nine essential amino acids from a well-planned plant-based diet. While many plant-based protein sources are 'incomplete,' combining a variety of them throughout the day, such as legumes with grains, ensures a complete amino acid profile.

The body doesn't store amino acids for long, so if your dietary intake drops significantly, the body will begin to break down muscle tissue to compensate within a relatively short period, though visible symptoms may take longer to appear.

Early signs often include increased fatigue, muscle weakness, and a decreased sense of mental alertness. As the deficiency progresses, more severe symptoms like muscle loss and mood changes can occur.

Yes, older adults are at a higher risk due to factors like reduced appetite, potential malabsorption issues, and the natural process of muscle loss with aging. This makes consistent and adequate intake especially important for this demographic.

For most people with a balanced diet, supplements are unnecessary. However, in cases of confirmed deficiency or for certain athletic or health needs, supplements can help. It's crucial to speak with a healthcare provider before starting any supplement regimen.

Complete protein sources, which contain all nine essential amino acids, include meat, poultry, fish, eggs, dairy products, soy products (like tofu and edamame), quinoa, and buckwheat.