Protein is essential for nearly every function in the human body, from maintaining muscle mass and healthy skin to regulating hormones and metabolism. Despite its importance, research suggests many adults—particularly women and older individuals—do not consume enough daily, leaving their bodies at risk of fatigue, slower recovery, and weakened immunity.
“Proteins are the body’s building and repair material,” said Dr. Glenn Jones, an internal medicine physician with Sentara Medical Group. “When we don’t get enough from food, the body begins breaking down muscle to create amino acids. Even with adequate calories, too little protein forces the body to pull from its own reserves.”
Experts say protein deficiencies, even mild ones, can present in subtle but noticeable ways. Persistent fatigue is a common early sign. Protein provides amino acids critical for cell repair and energy metabolism. Without it, people may feel drained or mentally foggy, even with sufficient sleep. Registered dietitian Leah Tsui of Ciba Health noted that low protein can also destabilize blood sugar, contributing to mid-afternoon energy crashes.
Muscle loss or difficulty building strength is another warning. Ashley Koff, a registered dietitian and founder of The Better Nutrition Program, explained that when protein intake falls, the body harvests amino acids from muscle tissue, reducing lean mass and slowing metabolism. Jones added that patients often report weaker grip strength or greater difficulty with routine activities like climbing stairs.
Protein also plays a role in appetite regulation. Meals low in protein can leave individuals hungry shortly after eating. “Protein triggers hormones that signal fullness,” said Dr. Gabrielle Lyon, a family physician. “Without it, cravings spike and blood sugar fluctuates, driving further hunger.” Experts recommend including 15–30 grams of protein per meal to improve satiety.
Deficiencies can affect hair, skin, and nails, which rely on proteins like keratin and collagen. Brittle nails, thinning hair, and dull skin can indicate that the body is diverting amino acids to maintain vital organs. Protein also supports immunity, forming the building blocks of antibodies and enzymes that fight infections. Low intake can lead to more frequent illness or slower recovery.
Cognitive function can also be impacted. Neurotransmitters such as dopamine and serotonin require amino acids, and shortages can cause brain fog, poor focus, and mood changes. Recovery after exercise may be delayed, with soreness lasting longer and progress plateauing without sufficient protein to repair muscle fibers.
In more severe cases, inadequate protein affects fluid balance, leading to mild swelling in the face, hands, or legs. Weight loss may also indicate muscle breakdown rather than fat loss, as the body cannibalizes lean tissue to meet essential amino acid needs.
Experts stress that protein is not just about muscle—it is a structural and functional nutrient critical to overall health. Tracking intake alongside daily activity can help ensure the body has the resources it needs to function optimally.
