What Happens to Your Body When You Don't Eat a Lot of Protein?

December 17, 2025 •

4 min read

Protein is the most abundant compound in your body after water, playing a crucial role in nearly every bodily function, from building muscle to producing hormones. So, what happens to your body when you don't eat a lot of protein? The effects can be widespread and detrimental, impacting everything from your physical strength to your mood.

Quick Summary

Inadequate protein intake can trigger a cascade of negative health effects, including muscle wasting, weakened bones, brittle hair and nails, a compromised immune system, mood swings, and increased hunger. The body breaks down its own tissues to source the amino acids it needs for vital functions when dietary protein is low.

Key Points

Muscle Loss: Inadequate protein causes the body to break down muscle tissue for energy, leading to decreased muscle mass and strength, particularly in older adults.
Hair, Skin, and Nail Problems: Keratin and collagen-based structures suffer from a protein deficit, causing brittle hair and nails, skin dryness, and poor wound healing.
Weakened Immunity: Protein is vital for producing antibodies; low intake compromises the immune system, making you more susceptible to infections and illnesses.
Persistent Fatigue: A lack of protein and the resulting muscle breakdown can lead to chronic tiredness, low energy, and a general sense of weakness.
Increased Hunger and Cravings: Without the satiating effect of protein, the body may experience more hunger and cravings for high-calorie foods, potentially leading to weight gain.
Mood Changes: Amino acids from protein are needed to produce neurotransmitters like serotonin, and a deficiency can lead to mood swings, irritability, and brain fog.
Increased Fracture Risk: Bones require protein for strength and density; a deficiency can weaken bones and increase the risk of fractures, especially in older adults.
Fluid Retention (Edema): A severe lack of protein, specifically the blood protein albumin, can cause fluid to accumulate in tissues, leading to swelling in the limbs.

The Foundation of Health: Protein's Role

Protein is not just for bodybuilders; it's a fundamental macronutrient essential for life. Composed of amino acids, protein is the building block for muscles, bones, hair, skin, and enzymes. It's crucial for repairing tissues, regulating fluid balance, and producing hormones and antibodies. When your dietary intake of protein is consistently low, your body begins to prioritize, sacrificing less vital tissues—like muscle mass—to fuel more essential processes, leading to a host of health issues.

Impact on Muscle Mass and Strength

One of the most noticeable consequences of low protein intake is the loss of muscle mass, also known as sarcopenia. When your body doesn't get enough protein from your diet, it turns to its largest protein reserve: your skeletal muscles. It breaks down muscle tissue to liberate amino acids for critical functions, a process called muscle atrophy. This leads to a reduction in strength and can make physical activities more challenging.

Fatigue and Weakness: The breakdown of muscle tissue, combined with the body's reduced ability to produce energy, results in persistent weakness and overwhelming fatigue. This can lead to a lower quality of life and a reduced perception of physical abilities.
Increased Risk of Frailty: For older adults, low protein intake accelerates the natural age-related decline in muscle mass, increasing the risk of falls, disability, and frailty. Adequate protein consumption can help slow this process.

Effects on Hair, Skin, and Nails

Since skin, hair, and nails are primarily made of proteins like keratin, elastin, and collagen, a deficiency in protein has a direct and visible impact on their health and appearance.

Hair Problems: You may experience thinning hair, increased shedding, and strands that are brittle and weak. In severe cases, hair can lose its pigment.
Skin Issues: Skin may become dry, flaky, or develop rashes and sores, as the body struggles to repair and maintain skin tissue. Wound healing can also be significantly delayed.
Brittle Nails: A lack of protein can cause nails to become brittle, weak, and grow slowly, sometimes with the formation of deep ridges.

Weakened Immune System and Increased Hunger

Protein is essential for the production of antibodies, which are a critical part of your immune system. A deficiency leaves you more susceptible to infections and illnesses, as your body's ability to fight off bacteria and viruses is compromised. Furthermore, a lack of sufficient protein often leads to a constant feeling of hunger and increased cravings. Protein is more satiating than carbohydrates or fats, and without it, the body struggles to feel full, potentially leading to overeating and weight gain.

Comparison of Symptoms


Symptom	Cause of Symptom	Impact	Reversibility
Muscle Wasting	Body breaking down muscle tissue for energy.	Reduces strength and physical performance, especially in older adults.	Reversible with increased protein intake and exercise.
Edema (Swelling)	Low albumin levels cause fluid to leak into tissues.	Puffiness in hands, feet, legs, and abdomen.	Reversible, typically with severe protein deficiency.
Brittle Hair & Nails	Lack of amino acids needed to build keratin, collagen, and elastin.	Thinning hair, slow-growing and weak nails.	Reversible with sufficient protein intake over several months.
Weakened Immunity	Impaired production of antibodies and immune cells.	Frequent infections and slow wound healing.	Reversible with improved nutrition.
Mood Swings	Disrupted synthesis of mood-regulating neurotransmitters.	Irritability, fatigue, and even depression.	Improved with balanced nutrition.
Increased Hunger	Body's attempt to restore protein status; lower satiety.	Leads to cravings for carbs and high-calorie foods, potentially causing weight gain.	Addressable by increasing protein at meals and snacks.

Addressing Low Protein Intake

For most individuals, the solution is to increase dietary protein through a variety of sources. Animal proteins (meat, fish, eggs, dairy) are considered "complete" as they contain all nine essential amino acids. Plant-based proteins (legumes, nuts, seeds, some grains) can be combined throughout the day to achieve a complete amino acid profile. The Recommended Dietary Allowance (RDA) for protein is 0.8 grams per kilogram of body weight for the average adult, but this may be higher for physically active individuals or older adults.

For some, underlying health conditions like certain diseases or eating disorders may cause or exacerbate a protein deficiency. It is crucial to consult a healthcare professional or registered dietitian to determine your specific protein needs and create a personalized nutrition plan. Ignoring a protein deficiency can have serious, long-term health consequences. To learn more about how protein is broken down and used by the body, visit MedlinePlus on the National Institutes of Health website.

Conclusion

Failing to consume adequate protein can have far-reaching negative effects on your health, from tangible signs like muscle weakness and brittle hair to more subtle internal issues like a compromised immune system and hormonal imbalances. Recognizing the symptoms of a low-protein diet is the first step toward correcting the issue. By prioritizing high-quality protein sources and ensuring consistent intake throughout the day, you can help protect your body's essential functions and maintain your overall well-being. If you suspect a serious deficiency, medical advice should always be sought to rule out any underlying health conditions.

Frequently Asked Questions

The most common and immediate symptom is often muscle wasting and a feeling of persistent fatigue and weakness, as the body begins to break down its own muscle tissue for energy.

Symptoms can vary in how quickly they appear. More subtle signs like fatigue may start within a week, while noticeable issues with hair, skin, and nails may take several months to manifest.

Yes, it can. Proteins provide the amino acids needed to create mood-regulating neurotransmitters like serotonin and dopamine. A deficiency can disrupt their production, leading to irritability, anxiety, or depression.

Yes, a protein deficiency can cause hair loss. Hair is primarily made of the protein keratin, and when intake is insufficient, hair growth slows, and existing strands may become weak, leading to shedding.

Vegetarians and vegans can get sufficient protein by eating a variety of plant-based protein sources, such as lentils, beans, nuts, seeds, and certain grains like quinoa and soy products. Eating different sources throughout the day ensures all essential amino acids are consumed.

Yes, edema (swelling) is a classic sign of severe protein deficiency, as low levels of the blood protein albumin cause fluid to leak into body tissues.

The Recommended Dietary Allowance (RDA) for a sedentary adult is 0.8 grams per kilogram of body weight. However, individual needs vary based on age, health, and activity level; active individuals may require more.

This hypothesis suggests that if you are not getting enough protein, your body increases your appetite to drive you to find and eat more food, potentially leading to overeating and weight gain.