Symptoms of protein deficiency include fatigue, weakness, thinning hair, brittle nails, and dry skin.

Protein deficiency is more likely to affect vegans, vegetarians, those over the age of 70, and anyone with a digestive issue like celiac or Crohn's disease.

To treat a protein deficiency, increase your intake of high-protein foods like eggs, salmon, and lentils.

Protein is an essential part of a healthy diet and not consuming enough can cause serious health problems. Here is what you need to know about the signs and symptoms of protein deficiency and how much protein you need each day.

What does protein do?
Protein is a complex macronutrient found in certain foods, such as animal products and legumes. In its most basic form, a protein is a string of amino acids that create the building blocks for the physical parts of your body, including muscles, bones, skin, hair, nails, and organs.

Protein deficiency, also called hypoproteinemia, is usually tied to overall low protein intake. The condition affects about 1 billion people worldwide but is rare in the US. Overall, Americans tend to eat the recommended amount of protein needed.

However, protein deficiency is more prevalent in Americans over the age of 70, according to a 2019 study. This is because older Americans tend to eat less, which can result in nutritional deficiencies, says Stacie Stephenson, a certified nutrition specialist and board member for the American Nutritional Association.

Signs and symptoms of protein deficiency
Protein deficiency can cause a range of symptoms, which can vary based on the severity of the deficiency, Stephenson says.

In mild cases of protein deficiency someone might experience:

An increased appetite for protein as the body tries to stimulate protein intake
Weakness
Fatigue
Signs of a moderate case of protein deficiency include:

Muscle wasting, also known as muscle atrophy
Thinning hair

Brittle nails
Flaky skin
Severe protein deficiency can cause serious health problems, like:

Stomach bloating
Liver failure
Skin that splits open
Stunted growth
Porous bones that are weak and thin
Causes of protein deficiency

Protein deficiency is most commonly associated with malnutrition and an inadequate protein intake, Stephenson says. A protein deficiency could also be linked to an underlying health condition, like celiac or Crohn's disease which can interfere with nutrient absorption.

The amount of protein you need depends on your age, health, and activity level. The recommended daily allowance (RDA) is a minimum of 0.36 grams per pound of body weight, so 54 grams of protein a day for someone who weighs 150 pounds.

Some people - like athletes - may need more protein, says Stephenson. A registered dietitian can help you determine the amount of protein you need based on your own unique lifestyle and health history.

According to Stephenson, those at a greater risk of protein deficiency include:

Adults over the age of 70
Vegetarians and vegans since animal products are rich sources of protein

However, people who do not consume animal products can still get enough protein from plant sources. A 2013 comparative study of nutrient profiles of vegetarians and meat-eaters found that plant-based eaters get plenty of protein from plant foods like lentils and beans. In that study, the vegetarians got as much protein as semi-vegetarians or vegetarians who eat eggs and dairy products.

"As long as you are consciously getting enough protein from plant sources, you won't be at any greater risk of protein deficiency, Stephenson says.

Protein deficiency diagnosis and treatment
If you are noticing signs of a protein deficiency, like unexplained fatigue or changes in your hair, skin, and nails, you should see a doctor who will run plasma protein tests to confirm protein deficiency and rule out other causes.

Protein deficiency is usually treated by either increasing daily protein intake (if the cause is related to poor intake) or treating an underlying disorder. The average healthy adult can generally consume up to 2 g/kg of protein per day.

If you have a protein deficiency your doctor might recommend increasing your intake of protein-containing foods, like:

Nuts and seeds such as almonds, pistachios, cashews, and flax seeds
Legumes, such as lentils and beans
Eggs
Seafood, like fish or shrimp
Whole grains like quinoa
Poultry, like chicken or turkey
Dairy products, like Greek yogurt or cottage cheese

Insider's takeaway
Protein deficiency is rare in the US, but people over the age of 70 and those who do not eat animal products are at a greater risk of low protein intake. Signs of protein deficiency include hair loss, brittle nails, weakness, and fatigue. Most people need at least 0.36 grams of protein per pound a day, but this can vary depending on the individual, so talk with your doctor about how much protein you need.