Protein serves many vital roles, including forming muscles, bones, skin, hair, and nails, regulating the immune system, and aids brain functioning. As a result, protein deficiency may lead to many symptoms, such as brittle hair and nails, mood changes, muscle weakness, and getting sick more often.

Jump to Key Takeaways.

1. Feeling Unusually Tired or Lacking Energy

Protein is a crucial energy source, so when lacking, a person can feel weak and unusually exhausted—mentally, physically, or both. This weakness and fatigue can then lead to a poorer quality of life and a poor perception of physical abilities.

Muscle wasting (cachexia) from low protein levels occurs in protein (and calorie) deficiency cases, like starvation or prolonged fasting. Muscle wasting influenced by low protein in the body is also seen in the following health conditions:

2. Brittle nails, Thinning Hair, or Dry Skin

Dry, thin hair and brittle, poorly growing nails can be the first signs of low protein levels in the body.

With more severe protein deficiency, a person’s hair loses its pigment, and curly hair becomes straight. Also, the skin can become fragile and peel and flake off.

Lastly, with eating disorders like anorexia or bulimia nervosa, soft, light hair may grow on the face and body.

3. Increased Irritability or Mood Swings

Amino acids—the building blocks of proteins—are essential for producing mood-regulating neurotransmitters (brain chemicals) like serotonin and norepinephrine. Protein deficiency can lead to a reduction in these neurotransmitters, potentially contributing to the development of mood disorders, such as depression.

Besides depressive symptoms, anxiety has also been linked to protein deficiency, especially in teenagers. Depression is a common yet serious mental health disorder that can be mild or severe. Possible symptoms include:

• Feeling sad, irritable, or hopeless
• Losing interest in activities you once enjoyed
• Eating or sleeping way less or more than usual
• Feeling hopeless or excessively guilty
• Feeling agitated or unusually tired
• Having trouble focusing or making small decisions
• Thinking of death or making suicide attempts

4. Swelling in the Legs, Feet, or Hands

Swelling is a classic sign of kwashiorkor, a condition of severe protein deficiency that may occur in children living in countries with limited food resources and/or staple foods that are low in protein and high in carbohydrates. Kwashiorkor causes low albumin levels, which leads to fluid leaking out of blood vessels into surrounding tissues.

Children with kwashiorkor appear very thin except for significant swelling (edema) that manifests predominantly in their feet, ankles, and belly. Other symptoms of kwashiorkor include:

• Stunted growth
• Sparse and brittle hair that loses its pigment (blonde/rust-colored)
• Dry, peeling skin
• Apathy (lack of emotion) and listlessness

Swelling can also occur with a kidney disease called nephrotic syndrome, in which a person loses high albumin levels in their urine. With nephrotic syndrome, swelling is often prominent around the eyes before moving down the body into the legs and ankles.

5. Getting Sick More Oftent Due to a Weakend Immune System

Protein deficiency impairs the immune system, increasing a person’s chances of developing infections. Common infections include:

Research suggests that protein deficiency weakens the immune system by impairing the body’s ability to produce antibodies and cytokines. Antibodies mark and bind to foreign substances (such as germs) for destruction, whereas cytokines serve as messengers, informing and signaling the immune system to launch an attack against germs.

Cytokines are also involved in wound repair. As such, besides making people more vulnerable to illness, protein deficiency is associated with slowed wound healing.

6. Noticeable Decrease in Muscle Mass or Strength

Evidence suggests low protein intake can worsen the natural age-related decline in bone mineral density (BMD), a measurement of bone strength.

When BMD becomes too low, osteoporosis can develop. With osteoporosis, bones are weak, brittle, and prone to break as bone mass and bone mineral density decline.

In addition to advancing age and diets low in protein, other risk factors for osteoporosis include low calcium and vitamin D intake, hormone changes, a sedentary lifestyle, and certain health conditions (e.g., rheumatoid arthritis).

7. Stunted Growth in Children

Stunted growth is defined when a child’s height falls within the lower 2.5% of the median height of children of his or her same age.

Stunted growth is seen with kwashiorkor and another type of childhood malnutrition called marasmus. Marasmus is a protein and calorie deficiency condition that can occur in babies and young children, nearly always in countries with extremely limited food resources. The prolonged lack of calorie and protein intake leads to severe weight loss and stunted growth.

Children without marasmus or kwashiorkor can also experience stunted growth caused by an inadequate protein intake. Children with marasmus experience significant muscle wasting and loss of their fat stores. In addition to a very gaunt appearance, other symptoms include:

• Extreme weakness
• Thin, dry skin with excess skin folds due to loss of fat
• Sparse, brittle hair that can be easily plucked out

8. Fatty Liver

The liver is the biggest internal organ, weighing around 4 pounds. It’s located below the lungs on the upper right side of the abdomen. The liver serves several vital functions, such as filtering blood, converting food into energy, eliminating wastes, and producing various substances like bile, proteins, and cholesterol.

When a person has a fatty liver, fats called triglycerides abnormally accumulate inside liver cells, enlarging the liver. Many causes of fatty liver exist, such as high alcohol consumption and obesity. Protein deficiency is another contributor, albeit less common.

Fatty liver from protein deficiency develops when a person’s liver cannot produce unique proteins (lipoproteins) needed to help carry triglycerides out of the liver. Symptoms of fatty liver are usually absent but, if present, include mild stomach discomfort or fatigue.

9. Weight Loss or Gain

The body’s first response to severe protein deficiency is to lower its metabolic rate and break down fat tissue as an energy supply. Later, when fat tissues are all broken down, the body obtains protein for energy by breaking down muscles and internal organs, namely the liver and intestines, followed by the heart and kidneys.

The loss of fat, muscle, and organ weight causes significant weight loss. Starvation, in which there is a lack of protein and all other nutrients (e.g., during a famine), can cause weight loss of 50% or more in children.

Weight gain from protein deficiency is seen with nephrotic syndrome (discussed above) due to fluid retention. Limited scientific data suggest that weight gain may occur in individuals with a reduced (not deficient) protein diet due to increased hunger.

Common Risk Factors of Protein Deficiency

Poor nutritional intake may also occur as a result of alcohol use disorder or eating disorders like anorexia nervosa. Health problems that can cause protein deficiency as a secondary consequence include:

• Conditions associated with increased protein breakdown, as seen in individuals with severe burn injuries or after major surgery or trauma
• Diseases associated with reduced gut absorption or impaired digestion of protein (e.g., pancreatic insufficiency)
• Nephrotic syndrome (discussed above)

How to Get More Protein

Aim to incorporate protein into each meal and snack to ensure your body gets the essential amino acids it requires. Two types of dietary protein are:

• Animal-derived protein like meat (e.g., chicken, beef, pork, and turkey), fish (e.g., salmon, mackerel, and tuna), and dairy products (e.g., eggs, milk, cheese, and Greek yogurt)
• Plant-derived protein, like beans, peas, lentils, quinoa, nuts, seeds, and soy products (e.g., tofu, and tempeh)

Most animal protein sources are “complete” because they contain all nine essential amino acids in the amounts the body needs. Only some plant-based proteins are “complete,” such as buckwheat, hempseed, quinoa, and soy.

How Much Protein Do You Need Per Day?

Evidence suggests that about 75% of Americans meet or exceed the protein intake recommendation for meats, poultry, and eggs. However, almost 90% do not meet the recommendation for seafood, and more than 50% do not for nuts, seeds, and soy products.

For an average adult consuming 2,000 calories per day, the recommended ounces of protein foods that should be eaten per week include:

• 26 ounces of meats, poultry, and/or eggs per week
• 8 ounces of seafood per week
• 5 ounces of nuts, seeds, and soy products per week

When to Contact a Healthcare Provider

If you are worried you are experiencing symptoms or signs of protein deficiency or are concerned about the amount of protein in your daily eating patterns, contact your primary healthcare provider.

Along with the guidance of a primary care provider, consider seeing a registered dietitian nutritionist (RDN). An RDN can help you create an eating plan that ensures sufficient protein intake and considers your food tastes and meal routine.

Key Takeaways

• However, when protein deficiency does occur, symptoms and signs like muscle weakness, increased infections, mood changes, and brittle hair and nails can manifest.
• This is because proteins play several crucial roles in the body, including providing energy, helping the brain and immune system function, and serving as building blocks for muscle, bone, skin, hair, and nails.
• Speak with your healthcare provider if you are concerned about your or your child’s protein intake. The recommended protein intake depends on age, gender, activity level, height, and weight.