The body’s natural response to acute illness is to prioritize the immune system, often at the expense of muscle tissue. When an infection is present, the body enters a catabolic state, accelerating the breakdown of muscle protein. This is triggered by systemic inflammation, where signaling molecules block muscle-building pathways and activate breakdown pathways. The amino acids liberated from this muscle breakdown are repurposed for essential functions, such as fueling immune cells and producing acute phase proteins to fight the infection. This metabolic shift explains why even a few days of sickness can lead to noticeable muscle loss.
Prioritizing Protein Intake
The primary defense against muscle catabolism during illness is increased protein consumption, even when appetite is suppressed. Protein needs during acute illness are elevated, often requiring an intake of 1.2 to 1.5 grams of protein per kilogram of body weight per day. This increased protein provides the necessary amino acid building blocks to fuel the immune response without excessively drawing them from existing muscle mass.
The challenge of meeting this target when feeling nauseated or lacking appetite can be overcome by focusing on liquid and easily digestible sources. Protein shakes (whey or casein) are highly bioavailable and require minimal digestive effort, making them ideal for an upset stomach. Dairy products like Greek yogurt and cottage cheese are also excellent sources of complete protein that can be consumed in small, frequent amounts.
Nutrient-dense liquids, such as bone broth, are helpful options for those who struggle with solid food. Eggs, especially soft-scrambled or hard-boiled, are a gold standard due to their high protein quality and ease of digestion. Shift the strategy from consuming large meals to small, frequent feedings every two to three hours. This continuously supplies the body with amino acids and helps maintain overall caloric intake.
Maintaining total calorie intake is nearly as important as protein consumption because calories spare protein from being used as energy. If the body lacks energy from carbohydrates and fats, it will burn dietary protein for fuel, leaving less available for muscle maintenance and immune function. Pairing protein with simple, bland carbohydrates like toast, rice, or crackers helps settle the stomach while providing needed energy.
Safe Movement and Activity Modification
While rest is necessary, complete immobility accelerates muscle atrophy and should be avoided. Muscle protein synthesis is stimulated by mechanical loading, and remaining sedentary signals the body that the muscle is not needed. The goal is to provide a low-level stimulus to the muscles to signal preservation without overstressing the body.
A helpful guideline for activity is the “neck check” rule. If symptoms are only above the neck, such as a runny nose or mild sore throat, light activity is safe. This activity should be low-intensity, such as a gentle walk, restorative yoga, or light stretching to promote blood flow. If symptoms include fever, body aches, chest congestion, or stomach issues, all exercise must be postponed until symptoms subside.
When symptoms are mild, incorporating very light resistance movements can be beneficial. Simple bodyweight exercises, such as wall push-ups, calf raises, or chair squats, performed briefly several times a day, help maintain nervous system signaling to the muscles. High-intensity or heavy resistance training must be avoided, as it increases metabolic stress and suppresses the immune system, diverting energy needed for recovery.
Hydration and Inflammation Management
Supporting the body’s internal environment is essential for reducing the catabolic drive of illness. Dehydration exacerbates muscle tissue breakdown and impairs metabolic function, which is already stressed by the immune response. Consistent fluid intake is necessary, including both plain water and electrolyte-rich beverages like oral rehydration solutions or broths, especially if fever, vomiting, or diarrhea are present.
Sleep is one of the most powerful tools for managing the inflammatory response and encouraging muscle preservation. During deep sleep, the body releases growth hormones that are essential for tissue repair and regeneration. Poor sleep quality or insufficient duration can elevate stress hormones like cortisol, which further promotes muscle protein breakdown.
Managing fever contributes to lowering the overall metabolic stress on the body. A high body temperature increases the rate of catabolism as the body works harder to regulate temperature. Using fever-reducing medications, such as non-steroidal anti-inflammatory drugs (NSAIDs), helps lower the temperature and reduce inflammation, minimizing muscle loss associated with the illness.