Yes. A serious infection can lead to protein deficiency or broader malnutrition, especially when a person eats very little or is critically ill. During infection, the body may break down muscle protein while inflammation can lower blood proteins such as albumin. However, a low albumin result does not automatically mean someone has not eaten enough protein; illness itself can affect the level.
How can a serious infection affect protein needs?
Protein helps maintain muscles, repair tissues, and support many normal body functions. During a serious infection, the body's response to illness can change how it uses nutrients. Inflammation may reduce appetite and contribute to muscle breakdown, while the physical stress of illness can increase the body's energy and protein needs. These changes can make it harder to maintain muscle and nutritional health, particularly when the illness is prolonged or requires intensive care.
The Merck Manual Professional Edition explains that infections can increase the body's metabolic demands and that infection-related inflammatory signals can contribute to reduced appetite and muscle wasting. The effect depends partly on a person's nutritional condition before the infection and how much nutrition they can take in during the illness.
Protein deficiency may develop as part of protein-energy malnutrition, a condition in which the body does not receive or effectively use enough energy and nutrients to meet its needs. A person may also lose muscle during serious illness even when the problem is not simply a lack of protein in the diet. This distinction matters because eating more protein alone may not address every cause of muscle loss.
When is the risk of protein deficiency higher?
Not everyone with a serious infection develops protein deficiency. The risk is greater when the illness reduces food intake or increases nutritional demands, especially if a person already has limited nutritional reserves. Factors that may contribute include:
- Reduced food intake: A poor appetite, nausea, vomiting, or other illness-related problems can make it difficult to eat enough food and protein.
- Prolonged or critical illness: A person who is seriously ill may have greater nutritional needs while being unable to eat normally.
- Existing malnutrition or unintended weight loss: Someone who was already undernourished before an infection may be less able to meet the added demands of illness.
- Older age or frailty: Older adults, particularly those who are hospitalized or have been eating poorly, may need closer nutritional assessment.
- Problems with digestion or absorption: Certain digestive conditions can make it harder for the body to obtain enough nutrients from food, even when a person is trying to eat adequately.
The risk can be especially important in intensive care. A 2025 consensus paper published in the Journal of Parenteral and Enteral Nutrition explains that critically ill adults may already have malnutrition when admitted to intensive care and can develop or experience worsening malnutrition because of inflammation, changes in metabolism, and difficulties with feeding.
What changes may occur when protein intake is inadequate?
When protein-energy malnutrition develops, a person may experience changes that affect strength, body weight, and recovery. Examples can include:
- Loss of muscle size or strength.
- Unintended weight loss during or after the illness.
- Weakness or reduced ability to carry out usual activities.
- Slower healing of wounds or other damaged tissues.
- Swelling in some cases of significant malnutrition.
These changes can also occur for reasons other than insufficient protein, and some may overlap with the effects of infection or hospitalization. Their significance depends on the person's nutritional history, examination, fluid balance, and progress during recovery. For someone being treated for a serious infection, new or increasing weakness, ongoing poor food intake, or unexpected weight loss should be discussed with the healthcare team.
Does a low albumin level mean there is protein deficiency?
Not necessarily. Albumin is a protein made by the liver and measured in a blood test. A lower-than-expected albumin level can occur with malnutrition, but it may also occur because of infection, liver disease, kidney disease, or other medical conditions. In a seriously ill person, the result cannot reliably show whether the main problem is inadequate protein intake.
MedlinePlus explains that low blood albumin can be associated with both infection and malnutrition, among other conditions, and that an albumin test alone cannot diagnose a condition. Healthcare professionals interpret the result alongside the person's overall health, other test findings, and clinical examination rather than treating it as a direct measure of how much protein they have eaten.
Prealbumin is another blood protein that may sometimes be measured during nutritional assessment. However, its level can also decrease with inflammation, serious infection, injury, and malnutrition. According to MedlinePlus, a low prealbumin result in someone who is ill may have several possible explanations, so additional clinical information may be needed to understand it.
How do healthcare professionals assess nutrition during a serious infection?
Assessment usually combines information about what a person was eating before becoming ill, how much they have eaten during the illness, changes in weight, and any loss of muscle or physical strength. The healthcare team may also review swallowing or digestive difficulties, existing medical conditions, current treatments, and whether fluid changes could affect body weight or the appearance of swelling.
Blood tests can help identify associated problems and provide information about conditions affecting the liver, kidneys, or other organs. However, results must be interpreted in the context of active inflammation and the person's clinical condition. A single blood protein measurement does not establish the cause of malnutrition or reliably describe the person's entire nutritional status.
In hospital, assessment may be repeated as the illness progresses because a person's ability to eat, nutritional needs, muscle condition, and response to feeding can change. When the risk of malnutrition is significant, a registered dietitian or another clinician with nutrition expertise can help the team assess intake and plan appropriate support.
How is protein deficiency managed during recovery from infection?
Care generally involves treating the infection and addressing any nutritional problems at the same time. When a person can eat safely, the team may encourage regular meals and suitable protein-containing foods, with portions and food choices adapted to appetite, tolerance, and individual needs. Depending on the situation, oral nutritional supplements may be considered when ordinary food does not provide enough nutrition.
The amount of protein and energy needed is not the same for everyone. Serious illness may increase nutritional requirements, but age, body size, kidney function, other medical conditions, and the nature of the illness can affect the plan. The Merck Manual Professional Edition's overview of nutritional support notes that protein needs may be higher during metabolic stress and that nutritional requirements should be estimated for the individual.
If a person cannot eat enough by mouth, the healthcare team may consider tube feeding when appropriate. Nutrition given through a vein may be considered when adequate nutrition cannot be provided through the digestive system. These approaches require individual assessment and monitoring, particularly in people who are critically ill or have conditions that affect fluid, electrolyte, or nutrient handling.
People with kidney disease or other conditions that require dietary restrictions should not automatically increase protein intake or start protein supplements without discussing it with their healthcare professional. The appropriate approach depends on the person's medical condition, nutritional status, and treatment plan.
When should nutrition concerns be raised with the care team?
Tell the treating healthcare professional if someone with a serious infection is eating very little, cannot keep food down, is losing weight unexpectedly, or appears to be losing strength. These concerns are particularly important when the person was already undernourished, is frail, or has been hospitalized for an extended period. Prompt nutritional assessment can help identify whether additional support is needed while the infection is treated.
Recovery of strength and muscle may take longer than improvement in the infection itself. The care team can monitor food intake, weight trends, physical function, and relevant medical findings to decide whether the nutrition plan needs to change. A low albumin result should be considered alongside this broader picture, rather than used on its own to determine protein needs.