Protein plays a critical role in virtually every process in the human body, from metabolism and hormonal regulation to maintaining muscle mass and healthy skin. More research suggests that many people, especially women and older adults, are not consuming enough of it every day.
“Protein is the building block and repair material of the body,” says Dr. Glenn Jones, an internist at Sentara Medical Group. “When we don't get enough calories from food, the body begins to break down muscle to create amino acids, or the building blocks that make up proteins. Even if you eat enough calories, too little protein means your body has to use its own reserves, breaking down muscle.”
Experts say even mild protein deficiencies can occur unnoticed, affecting everything from energy levels to the strength of hair and nails. Here are nine common signs that you're eating too little protein.
You feel constantly tired
If you're getting enough sleep but still feel like you're stretching yourself, a lack of protein may be causing the problem. Protein contains amino acids that help the body repair cells and regulate energy metabolism. Without it, your system may struggle to generate consistent energy throughout the day, leaving you foggy or exhausted.
“Persistent fatigue is common because the body can't effectively repair cells or regulate energy metabolism without enough protein,” says Lia Tsui, a registered dietitian at Ciba Health in New York City. Protein also helps stabilize blood sugar levels, preventing the afternoon crash that many people experience after eating a high-carb meal.
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“Fatigue, low energy levels, and loss of muscle mass or strength are often the first signs of insufficient protein intake,” adds Taylor Fazio, registered dietitian and health consultant at The Lanby, a primary care practice in New York City. Over time, this low-grade fatigue can snowball, making workouts harder, slower recovery, and harder to concentrate, even if you think your diet is generally healthy.
You're losing muscle (or not gaining it as easily)
Muscle tissue depends on protein for repair and growth. Without enough, you may feel weaker, lose definition, or have difficulty building or maintaining muscle mass despite regular exercise.
“When your protein intake drops too low, your body begins to break down muscle tissue to gather amino acids for needed processes,” says Ashley Koff, a registered dietitian and founder of the Better Nutrition program who is director of the nutrition course at the University of California, Susan Samueli Institute of Integrative and Functional Medicine Fellowship in Irvine. “This loss of muscle mass has a negative impact on energy and metabolism.”
Because muscle is metabolically active, losing it can slow your metabolism and make it more difficult to control your weight.
Jones adds that loss of muscle mass is often the most common sign of protein deficiency that he sees in his patients. He says if walking up stairs feels harder, grip strength seems weak, or exercise causes unusual pain, it may not be age but a lack of protein.
You're always hungry
Protein is one of the most filling macronutrients, triggering the release of hormones that tell your brain you're full. Without it, even a meal that seems filling can leave you hungry an hour later.
“Food cravings or low blood sugar can occur when too little protein prevents carbohydrates from being balanced and blood sugar levels are stabilized,” says Dr. Gabriel Lyon, a family physician and author of the book Manual “Forever Strong”. When a meal is high in carbohydrates and low in protein, blood sugar levels rise and fall sharply, causing hunger and cravings for more food, especially sweets or starches.
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“Many people also notice increased hunger or poor feelings of fullness, since protein is critical for regulating appetite,” says Fazio. Simple solution: Make sure each meal contains at least 15 to 30 grams of protein, she says. research suggests it may significantly improve satiety and reduce overeating.
Your hair, skin or nails look dull or weak.
Because hair, skin and nails are made primarily of proteins such as keratin and collagen, they can be the first visual sign that you're not eating enough.
“The most common early signs of protein deficiency are fatigue, thinning hair, and brittle nails,” says Tsui. These tissues are constantly being repaired, so when protein is lacking, your body diverts amino acids from these aesthetic functions to more important ones, such as maintaining organ health and immunity.
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You may notice that your nails peel easily, your hair appears thinner or duller, and your skin loses its elasticity, all signs that your protein stores are becoming low, Lyon says.
“Many people think of protein only in the context of muscle, but in reality it is a structural and functional nutrient for almost every system in the body,” says Koff. “So when you don't get enough, the signs show up in surprising ways.”
You get sick more often
Protein not only builds muscle, but also supports immune defense. Antibodies that fight viruses and bacteria are made of protein, as are many enzymes involved in healing and fighting inflammation.
“Proteins are the building blocks and repair materials of the body,” says Jones. “When we don't get enough food, the body begins to break down muscle to create the amino acids needed to support essential systems such as organ repair, immune support, and wound healing.” Over time, this may mean you get sick more often or take longer to recover from a cold.
You have trouble concentrating
Brain fog, poor concentration, and even mood changes can be linked to low protein. This is because your brain depends on amino acids, which produce neurotransmitters such as dopamine and serotonin, chemical messengers that regulate mood, motivation and alertness.
“Amino acids from protein are essential for the production of neurotransmitters such as dopamine and serotonin,” says Lyon. “When these are lacking, concentration and mood can suffer.” You may notice that your thoughts slow, your patience dwindles, or your motivation decreases when you skimp on protein.
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Cui adds that “when there is not enough protein, the body does not receive the amino acids needed to build and maintain tissues such as muscles, bones, enzymes and red blood cells. If there is not enough protein to create red blood cells, the delivery of energy to all parts of the body is impaired.” This means less oxygen reaches your brain and increases lethargy.
Recovery after exercise takes longer
If you notice that post-workout soreness persists for several days, protein may be the missing link. During exercise, small tears form in muscle fibers, and protein provides the raw material to repair them, making you stronger over time.
“If someone doesn't have enough protein, their body won't have enough amino acids to effectively repair muscle fibers,” says Lyon. “You will notice that your workouts will become harder and your progress will slow down.” This can make training frustrating, especially if you're eating healthy but not meeting your recovery needs.
“People often describe feeling weaker, recovering more slowly, or noticing subtle changes in body composition even when sleep and stress are normal,” Fazio adds. Anyone who is regularly active should watch their protein intake as closely as they watch their workouts, she says.
Do you notice swelling or puffiness?
In more extreme cases of low protein, the body's fluid balance may be disrupted, leading to puffiness or swelling of the face, arms, or legs.
Protein helps maintain proper pressure balance in blood vessels, so “when protein is in short supply, the body diverts amino acids to critical organ functions at the expense of muscle tissue and fluid balance,” Fazio says. This swelling, called edema, is often more noticeable at the end of the day or after sitting for a long time.
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“Other signs of long-term insufficient protein intake include swollen legs, anemia and poor wound healing,” Jones adds.
Although severe edema due to protein deficiency is rare in developed countries, mild fluid retention combined with fatigue or weakness can be an early warning sign.
You're losing weight for the wrong reasons
If you're losing weight but feel weaker, softer, or more tired, you may be losing muscle rather than fat. When there is not enough protein, the body breaks down muscle tissue to provide amino acids for vital processes, even if this means slowing metabolism.
“When muscle mass begins to decrease, metabolism can slow down as muscle helps burn more calories at rest,” says Tsui. That's why sudden weight loss combined with these symptoms should be a red flag.
How much protein do you really need?
So how long is enough? “The average adult needs about 1 gram of protein per kilogram of body weight per day, says Jones. “If you are recovering from an illness or surgery, your body needs more—about 1.2 to 1.5 grams per kilogram.”
Fazio recommends a slightly higher range for optimal health. “Current research suggests that 1.2 to 2.0 grams per kilogram is better for supporting muscle mass, metabolic health, and satiety.” For a 150-pound person, that's about 80-135 grams per day, divided evenly between meals.
Lyon says a good starting point for adults is 15 to 30 grams per meal or snack, about every three hours. This could be two eggs and Greek yogurt for breakfast, chicken or tofu for lunch, and salmon or lentils for dinner.
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Koff and other experts agree that for most healthy adults, not eating enough protein poses a greater risk than getting too much protein.
“Many people consume just enough protein to avoid overt deficiency, but not enough to maintain optimal muscle mass, immunity, or metabolic function,” she says. “This gray area of low but not deficient protein intake often goes undetected because the signs are subtle and progressive rather than acute.”
Whether it's lean meats, eggs, legumes, tofu, fish or dairy, prioritizing protein at every meal can restore energy, improve focus and strengthen muscles, all while helping you feel like yourself again.
“The biggest misconception is that protein is only for athletes or bodybuilders,” says Koff. “None of this can be said for healthy people. In fact, research consistently shows that a high-protein diet improves body composition, blood sugar control and overall longevity.”
