Do you feel tired more often, notice that your muscles seem weaker, or find that your hair is shedding more than usual? These changes can happen for many reasons, but your diet is one factor worth considering.
Protein does much more than help build muscle. Your body needs it to repair tissues, maintain strength, support immune function, and produce important enzymes and hormones.
When protein intake is inadequate, especially when you’re not getting enough calories, your body may struggle to meet these needs.
So, what happens when you don’t get enough protein? Here are eight possible signs to watch for, keeping in mind that these symptoms can also have other causes.
1. You Are Losing Muscle Mass
Your body needs protein to maintain and repair muscle.
Consistently eating too little protein may cause your body to break down muscle tissue to supply amino acids for other essential functions. Not getting enough calories can make muscle loss worse.
You may notice smaller arms and legs, less-defined muscles, or difficulty with everyday activities.
Keep in mind muscle loss can also result from aging, inactivity, illness, or unintentional weight loss.
Older adults and muscle loss: Aging can make muscles less responsive to protein and exercise, increasing the risk of sarcopenia, or age-related muscle loss. Some research suggests that older adults may benefit from 1.0–1.3 grams of protein per kilogram of body weight daily, alongside regular resistance exercise, to help maintain muscle mass and function.
2. Your Hair, Skin, or Nails Change
Your hair, skin, and nails need protein and other nutrients to stay healthy. Severe protein deficiency, particularly when combined with inadequate calorie intake, can cause noticeable changes in all three.
- Skin: The skin may become unusually dry, dark, and flaky, sometimes cracking or peeling to reveal lighter patches. In severe cases, this pattern is known as flaky-paint dermatosis and is associated with kwashiorkor.
- Hair: Hair may become dry, brittle, sparse, or fall out easily. Its color may change from dark to reddish-yellow or grayish-white. Alternating light and dark bands, sometimes called the flag sign, may reflect periods of adequate and inadequate nutrition.
- Nails: Nails may become thin, soft, brittle, cracked, or ridged.
These changes can also result from iron deficiency or other nutrient deficiencies, hormonal changes, thyroid conditions, stress, and other health problems. If you notice persistent, sudden, or unexplained changes, consult a healthcare professional rather than assuming you need more protein.
3. Your Wounds Seem to Heal Slowly
Your body needs protein to repair damaged tissue and produce collagen, which helps your skin heal. Consistently eating too little protein, especially alongside inadequate calorie intake or other nutrient deficiencies, may interfere with wound healing.
In a study of 41 people with chronic leg ulcers and 43 controls, low blood albumin—a marker used to assess nutritional status—was found in 27% of patients compared with just 2% of controls. Protein deficiency was also associated with an increase in wound size over 12 weeks.
You may notice that cuts, sores, or other injuries take longer than expected to heal. Other possible causes include vitamin C deficiency, diabetes, poor circulation, infection, and other medical conditions.
If a wound isn’t healing, becomes increasingly painful, or shows signs of infection, seek medical care rather than relying on dietary changes alone.
4. You Feel Hungry Soon After Eating
If you often feel hungry shortly after meals, consider whether you’re getting enough protein.
Protein helps promote fullness after eating. When you consistently eat too little protein, your body may respond by increasing hunger and encouraging you to choose protein-rich foods to help meet its protein needs. This idea is known as the protein leverage hypothesis.
Research supports this possibility. In a controlled study of 37 adults, participants reported more hunger while following a low-protein diet for 14 days. When later allowed to choose their own foods, they consumed 13% more protein and showed a stronger preference for savory, protein-rich foods, although their total calorie intake remained similar.
5. You Keep Getting Sick
Protein helps your immune system function properly by supplying amino acids needed to support immune cells and produce antibodies and other protective substances.
When protein intake is inadequate, immune defenses may weaken, potentially increasing your susceptibility to infections.
A review of research on childhood malnutrition also found that malnutrition can impair both innate and adaptive immune defenses, increasing the risk and severity of infections.
However, protein deficiency often occurs alongside inadequate calorie intake and other nutrient deficiencies, making its individual effects difficult to isolate.
6. You Notice Swelling in Your Legs or Feet
Swelling, also called edema, can occur in severe protein deficiency, particularly in certain forms of malnutrition.
One reason is that very low blood levels of albumin, a protein made by the liver, can reduce the force that helps keep fluid inside blood vessels. Fluid may then accumulate in surrounding tissues.
You might notice swelling around your ankles, feet, or lower legs.
This is not a typical early sign of simply eating a little too little protein. Edema can also be caused by kidney disease, liver disease, heart conditions, and certain medications.
7. You Are Losing Weight Without Trying
Losing weight without changing your diet or activity levels may be a sign that your body isn’t getting enough nutrients or calories.
When you consistently consume too few calories and protein, your body may break down stored fat and muscle for energy, leading to weight loss and reduced strength.
You might notice your clothes becoming looser, your weight dropping unexpectedly, or everyday activities feeling more difficult.
However, unexplained weight loss can also result from digestive problems, thyroid conditions, diabetes, infections, and other illnesses.
If you’re losing weight without trying, especially if the loss continues, consult a healthcare professional to identify the underlying cause.
8. Stunted Growth in Children
Protein provides essential amino acids that children need to build tissues and grow. When protein and calorie intake remain inadequate, children may experience stunted growth, meaning they are shorter than expected for their age.
Severe protein-energy undernutrition can cause a condition called kwashiorkor, which is associated with stunted growth, swelling, and changes in hair and skin.
A 2023 review reported that children with inadequate protein intake may be four times more likely to experience stunting
How Much Protein Do You Need Per Day?
Your daily protein needs depend on factors such as your age, body weight, activity level, health, and nutritional status.
For healthy adults, the recommended dietary allowance (RDA) is approximately 0.8 grams of protein per kilogram of body weight per day. However, this amount is considered a minimum to meet basic protein requirements and help prevent muscle loss, rather than an optimal target for everyone.
Your activity level matters, too. People who exercise regularly may need around 1.4–2.0 grams per kilogram of body weight daily to support muscle growth and recovery.
What Causes Protein Deficiency?
Protein deficiency usually develops when you consistently consume less protein than your body needs. Several factors can contribute to inadequate protein intake, including:
- Low protein intake
- Insufficient food intake
- Digestive disorders
- Liver disease
- Kidney problems
- Increased nutritional needs due to illness, injury, or recovery from surgery
Protein deficiency often occurs alongside inadequate calorie intake or other nutrient deficiencies.
Final Thoughts
Muscle loss, weakness, poor wound healing, and certain changes in hair or nails can occur when protein intake is inadequate, particularly when overall nutrition is poor. However, none of these signs alone proves that you have a protein deficiency.
The best approach is to eat enough food, include protein-rich sources regularly, and maintain a varied, balanced diet.
If you experience unexplained weight loss, persistent weakness, swelling, or other ongoing symptoms, seek medical advice rather than trying to correct the problem with protein supplements alone.