We all know that protein is a critical macronutrient, but what exactly does protein do for us and how much should we consume? Protein helps regulate our hormones and takes on building, repairing, and oxygenating the body. It also plays a key role in making enzymes that digest our food.

Protein needs vary based on age, activity level, gender, and health—we generally need more during periods of growth like adolescence and pregnancy—but a good rule of thumb for daily intake is 0.36 grams of protein multiplied by pounds of body weight. If you’re unsure if you’re reaching your recommended intake, these 11 signs are indicators that you could be protein deficient.

Slow healing

When our protein intake is low, our collagen formation is impaired, which can lead wounds to take longer to heal. If you have a pesky cut or bruise that just won’t go away, it could be a sign of protein deficiency!

Weak immune system

Because amino acids have a role in forming antibodies, low protein intake could result in poor immune function. To learn more about immune health, check out this article.

Muscle loss

There are many factors behind muscle loss, or sarcopenia, including age, malnutrition, eating disorders, disease, and more, but ensuring that you’re getting enough protein will help maintain muscle strength. Remember that regular exercise is also a factor here and protein intake needs to increase after age 70 to protect muscle as we age.

Weak bones

Collagen malfunction can also affect bone health, leading to weaker bones as we age.

Hair loss

This iron-linked symptom can be caused by a lack of protein, especially from meat and legumes.

Brittle nails or dry skin

This symptom is not uncommon as we age, but it can be protein-linked as well.

Increased hunger or cravings

When we’re not consuming enough protein, our body signals hunger in an attempt to get the nutrients we need. Increased hunger can be caused by numerous factors, but lack of protein is a good starting point.

Fatigue

As a macronutrient, protein is critical for fueling the body. Protein deficiency and calorie restriction can both take a toll on daily energy levels.

Mood changes

Amino acid tryptophan is a precursor to the neurotransmitter, serotonin, so when we’re protein deprived we can see a negative impact on brain function and mood.

Slow growth (in children)

Protein is especially critical for supporting growing bodies and forming collagen, bones, teeth, and more. If a child is experiencing slow growth, your pediatrician will likely examine their macronutrient intake.

Poor sleep

Sleep is also influenced by tryptophan, so inadequate protein can result in poor or disrupted rest.