on September 03, 2026
Malnutrition represents one of the main alterations of nutritional and metabolic status and can manifest in apparently opposite forms. The World Health Organization defines malnutrition as a condition characterized by deficiencies, excesses, or imbalances in the intake of energy and nutrients. The concept therefore includes both undernutrition and malnutrition related to excess body weight, obesity, and chronic diseases associated with an unbalanced diet.
Undernutrition includes conditions such as involuntary weight loss, insufficient energy and protein intake, reduced muscle mass, and vitamin and mineral deficiencies. Historically, the most severe forms of protein-energy malnutrition were distinguished as marasmus, characterized primarily by a severe global energy deficiency, and kwashiorkor, associated with a profound alteration of protein metabolism in complex nutritional and clinical contexts. However, in modern clinical practice for adults and older adults, malnutrition is more frequently the result of the interaction between reduced food intake, acute or chronic illness, inflammation, and altered nutrient utilization.
The risk increases progressively with age. Older adults may experience a reduction in appetite, chewing ability, and sensory perception of taste and smell. These factors may be compounded by dysphagia, digestive disorders, reduced intestinal motility, malabsorption, economic or social difficulties, isolation, and depression. Oncological diseases, heart, kidney, or respiratory failure, neurological disorders, dementia, surgery, and prolonged bed rest can further increase the risk of deterioration of nutritional status.
Malnutrition should therefore not be considered simply as a consequence of a lack of food. In a sick patient, it can also develop in the presence of apparently sufficient intake, when systemic inflammation profoundly alters energy and protein metabolism. Proinflammatory cytokines can increase muscle catabolism, alter appetite, and change nutrient utilization. For this reason, the modern assessment of malnutrition considers both phenotypic changes, such as weight loss and reduced muscle mass, and etiological factors, including reduced intake, malabsorption, and inflammation.
Protein-energy malnutrition and loss of muscle mass
One of the most important consequences of undernutrition is the reduction of muscle mass. When energy and protein intake is insufficient, the body may use its own protein reserves to support essential metabolic needs. Skeletal muscle represents one of the main compartments involved in this process.
The loss of muscle mass does not only entail a reduction in strength. Muscle plays a fundamental role in glucose metabolism, mobility, postural stability, and response to metabolic stress. Its progressive reduction can promote sarcopenia, frailty, reduced autonomy, and an increased risk of falls.
In older adults, malnutrition and sarcopenia can mutually reinforce each other. Reduced physical activity decreases the anabolic stimulus on the muscle, while loss of strength can make it more difficult to prepare meals, shop, or eat independently. A progressive cycle can thus be established, characterized by reduced intake, muscle loss, and further reduction in functional capacity.
The clinical consequences of malnutrition can be numerous. Reduced availability of energy and amino acids can compromise the protein synthesis necessary for tissue maintenance and repair processes. This can result in delayed wound healing, greater vulnerability to pressure injuries, and worsening of recovery after surgery or acute illness.
Malnutrition can also compromise immune function. The immune response requires continuous cell renewal and an adequate supply of energy, amino acids, vitamins, and minerals. A compromised nutritional condition can therefore contribute to increased vulnerability to infections and worsening of recovery capacity.
In hospital and care settings, malnutrition is associated with a greater risk of complications and more difficult functional recovery. For this reason, nutritional status should be assessed early, especially in older, frail, or chronically ill individuals.
Causes of malnutrition in older adults
The causes of malnutrition in old age are frequently multifactorial.
Oral cavity problems can represent a primary obstacle. Compromised dentition, inadequate dentures, or pain during chewing can lead the individual to avoid protein- and fiber-rich foods, such as meat, legumes, nuts, raw vegetables, or whole grains. Over time, the diet can become increasingly monotonous and nutrient-poor.
Dysphagia can also have a significant impact. Difficulty swallowing can occur in various neurological diseases and can significantly reduce food and fluid intake. In these cases, the consistency of foods must be assessed and adapted individually.
Gastrointestinal diseases can compromise both the intake and absorption of nutrients. Inflammatory bowel diseases, pancreatic insufficiency, celiac disease, gastrointestinal surgery, and other conditions associated with malabsorption can cause weight loss and nutritional deficiencies even when food intake does not appear particularly reduced.
Psychological and social conditions are equally important. Depression, grief, isolation, and loss of autonomy can profoundly change eating behavior. An older adult living alone may reduce meal variety, skip main meals, or more frequently resort to ready-made foods, which are poor in essential nutrients.
Another factor is polypharmacy. Some medications can alter appetite, taste, gastrointestinal motility, or the absorption of specific nutrients. The assessment of nutritional status should therefore also consider possible interactions between medications and diet.
Malnutrition and obesity: two apparently opposite conditions
Malnutrition does not necessarily coincide with low body weight. A person with overweight or obesity may present a reduction in the nutritional quality of their diet, micronutrient deficiencies, and progressive loss of muscle mass.
WHO includes overweight, obesity, and diet-related chronic diseases in the broader concept of malnutrition. Obesity is characterized by an excess of adipose tissue capable of compromising health and is today considered a complex and relapsing chronic disease, influenced by biological, environmental, behavioral, and social factors.
In older adults, simply measuring body weight is not sufficient to assess nutritional status. With advancing age, an increase in adipose mass and loss of muscle mass can occur simultaneously. This condition is often described as sarcopenic obesity.
An individual can therefore present a high weight but have reduced functional muscle reserve. In these situations, an inadequately planned calorie restriction can further aggravate lean mass loss. Nutritional management must therefore consider not only weight, but also body composition, muscle strength, functional capacity, and the presence of associated pathologies.
Excess visceral adipose tissue is associated with a metabolic environment characterized by alterations in insulin sensitivity and a low-grade chronic inflammatory state. These mechanisms contribute to the risk of type 2 diabetes, dyslipidemia, hypertension, and cardiovascular diseases.
Nutritional screening as a primary prevention tool
Malnutrition prevention begins with the early recognition of risk. Nutritional screening should be particularly systematic in older adults, hospitalized patients, institutionalized individuals, and people with chronic diseases.
The assessment should include body weight trends, particularly involuntary weight loss, appetite, the amount of food consumed, the presence of difficulty chewing or swallowing, and the level of functional autonomy.
It is also important to assess muscle mass and strength. Body weight alone does not allow for distinguishing the loss of adipose tissue from the loss of lean mass. A reduction in muscle mass can be clinically relevant even when total weight appears relatively stable.
The assessment must also consider the presence of acute or chronic diseases, inflammatory processes, gastrointestinal alterations, and pharmacological treatments. The diagnosis of malnutrition should not be based on a single laboratory test, but on the integration of clinical, anthropometric, functional, and biochemical data.
Biochemical markers and their limitations
Albumin
Albumin is historically one of the most used parameters in the assessment of clinical and nutritional status. Low levels are associated with an increased risk of complications and mortality in various clinical populations.
However, albumin should not be considered a specific indicator of the amount of protein intake from food. Its concentration is influenced by inflammation, liver function, hydration, renal and gastrointestinal losses, and disease severity.
Its long half-life also makes albumin poorly sensitive to rapid nutritional changes. For this reason, it can provide useful information about overall clinical status, but it is not sufficient, on its own, to diagnose or monitor malnutrition.
Transferrin
Transferrin has a faster turnover than albumin and has been used as a possible indicator of changes in visceral protein status.
However, this parameter is also influenced by numerous factors independent of diet, including iron status, inflammation, and liver function. Therefore, its isolated interpretation can be misleading.
Retinol-binding protein
Retinol-binding protein, or retinol-binding protein, has a short half-life and can change rapidly in relation to metabolic conditions.
However, its interpretation is influenced by renal function, vitamin A availability, and other clinical conditions. For this reason, it can only be used in the context of a comprehensive clinical assessment.
IGF-1
Insulin-like Growth Factor 1 is involved in growth and anabolic processes and can decrease in conditions characterized by nutritional deficiency or increased catabolism.
However, its concentration can be altered by age, liver function, hormonal status, hypothyroidism, and other pathologies. IGF-1 therefore also does not represent a specific marker of malnutrition that can be used in isolation.
Creatininuria and muscle mass
24-hour urinary creatinine has historically been used to obtain an indirect estimate of muscle mass, since creatinine derives mainly from the metabolism of creatine present in the muscle.
However, its interpretation can be influenced by renal function, diet, preexisting muscle mass, and acute clinical conditions. Today, the assessment of muscle mass is preferably integrated with anthropometric, functional, and instrumental methods.
Immunological parameters
The total lymphocyte count has been used as an indirect indicator of nutritional status. A reduction in lymphocyte count can be present in malnutrition, but it is influenced by infections, medications, hematological diseases, and numerous other conditions.
Its value must therefore be interpreted in the clinical context and cannot represent an independent diagnostic criterion.
Cholesterol
A significant reduction in total cholesterol can be observed in some malnutrition conditions, especially when associated with involuntary weight loss and chronic illness.
However, hypocholesterolemia can also be determined by liver diseases, hyperthyroidism, inflammatory processes, and pharmacological treatments. This parameter must also be interpreted within the overall picture.
Homocysteine
Increased homocysteine can be associated with reduced availability of folates, vitamin B12, or vitamin B6. However, hyperhomocysteinemia can also depend on age, renal function, medications, and genetic variants.
A high value can therefore suggest the need to further investigate vitamin status, but it does not constitute a general indicator of malnutrition on its own.
The role of diet in nutritional prevention and recovery
The first strategy to prevent or correct undernutrition consists in identifying and, when possible, treating the cause that led to the deterioration of nutritional status.
A balanced diet must provide sufficient energy, adequate protein, good-quality fats, complex carbohydrates, vitamins, minerals, and other bioactive components naturally present in foods.
In older or malnourished individuals, it is particularly important to avoid overly restrictive and monotonous dietary regimens. The choice of foods must be adapted to chewing and swallowing ability, digestion, and individual clinical conditions.
Whole grains and other cereals such as spelt, barley, oats, and buckwheat can contribute to the intake of complex carbohydrates, fiber, and micronutrients. Legumes are an important source of plant-based protein, fiber, and minerals. Fruit and vegetables contribute to the intake of vitamins, minerals, and bioactive compounds.
Nuts and oilseeds can provide energy in small volumes and may be particularly useful, when appropriate, for increasing the energy density of the diet. Extra virgin olive oil and other plant fats can contribute to energy and lipid intake.
The nutritional strategy must, however, be personalized. An individual with severe weight loss, sarcopenia, kidney failure, dysphagia, or cancer requires a different assessment than a healthy person who simply wishes to improve the quality of their diet.
Plant-based foods and brain health
Leafy green vegetables, nuts, berries, legumes, whole grains, and extra virgin olive oil are components of several dietary patterns associated with cardiometabolic benefits and, in observational studies, with better brain health.
The MIND diet combines elements of the Mediterranean and DASH dietary patterns and places particular emphasis on foods such as leafy green vegetables, nuts, berries, whole grains, fish, and olive oil, while limiting foods high in saturated fats and sugars.
Clinical studies have, however, provided results that require a balanced interpretation. A major randomized study conducted on older adults at risk of cognitive decline did not show, after three years, a statistically significant difference in cognitive decline between the MIND diet combined with moderate calorie restriction and a control diet with similar calorie restriction. The data therefore suggest that the benefit of individual dietary patterns on the prevention of dementia should not be presented as definitively proven, although the benefits of a diet rich in plant-based foods and favorable to cardiovascular health remain plausible.
Leafy green vegetables and berries contain numerous bioactive compounds. Carotenoids, folates, vitamin E, and polyphenols participate in different biological mechanisms, including protection against oxidative stress and the modulation of inflammatory pathways. However, the presence of these nutrients does not mean that a single food can independently prevent or cure neurodegenerative diseases.
Foods of animal origin and health: the need for a scientifically balanced approach
Scientific evidence does not support the idea that all foods of animal origin should be considered uniformly harmful or inevitably pro-inflammatory.
The nutritional profile and health effects depend on the quantity, frequency of consumption, type of food, and overall dietary pattern. Processed red meat, excessive saturated fats, and ultra-processed foods deserve a different assessment than fish, fermented foods, or other products included in moderate amounts within an overall balanced diet.
There is no solid clinical evidence demonstrating that the digestion of casein normally produces bacterial residues capable of forming pathological “mucus” responsible for mucosal obstruction, or that the consumption of milk is a general cause of increased intestinal permeability and autoimmune diseases.
Similarly, the concept that animal protein foods make the blood chronically “acidic,” inducing the body to draw calcium from the bones, is a simplification unsupported by the physiology of acid-base balance. Blood pH is regulated through complex respiratory and renal systems.
This does not mean that a plant-based diet cannot be beneficial for health. On the contrary, a diet rich in plant-based foods, legumes, whole grains, nuts, and seeds can offer important nutritional advantages. The key point is that dietary choices should be based on the quality and overall balance of the diet, rather than on the automatic demonization of entire food categories.
Reducing meat without increasing the risk of malnutrition
A properly planned vegetarian or vegan diet can be nutritionally adequate in adults. The position of the Academy of Nutrition and Dietetics published in 2025 states that appropriately planned vegetarian and vegan dietary patterns can be nutritionally adequate and offer benefits for certain cardiometabolic health outcomes.
This does not, however, mean that any plant-based diet is automatically complete. A diet composed mainly of refined products, sugars, and ultra-processed foods may be vegetarian or vegan but have insufficient nutritional quality.
Protein adequacy can be achieved through legumes, soy products, grains, nuts, seeds, and other protein-rich plant foods. It is not necessary to combine grains and legumes in the same dish for the proteins to be “complete”: the body can use amino acids from different foods throughout the day.
Soy, quinoa, amaranth, and buckwheat also have favorable amino acid profiles, but the fundamental principle remains dietary variety and the adequacy of overall protein and energy intake.
In older adults, children, adolescents, pregnant or breastfeeding women, and patients with chronic diseases, developing a vegetarian or vegan dietary regimen requires particular attention to specific nutritional needs.
Iron and plant-based nutrition
Iron found in plant foods is predominantly non-heme iron. Its absorption can be influenced by the composition of the meal.
Vitamin C can promote the absorption of non-heme iron. For this reason, combining legumes, grains, or plant foods rich in iron with foods containing vitamin C can help improve its bioavailability.
Conversely, certain compounds found in tea and coffee can reduce iron absorption if consumed close to meals. Phytates can also reduce the bioavailability of certain minerals, while techniques such as soaking, sprouting, and fermentation can help reduce their content.
However, the presence of a vegetarian diet should not automatically lead to the conclusion that the individual is anemic. The diagnosis of iron deficiency requires an appropriate clinical and laboratory assessment, considering the complete blood count, ferritin, and other parameters according to the clinical context.
Vitamin B12: an essential consideration in vegan diets
Vitamin B12 deserves specific consideration. It is incorrect to state that a vegan diet can safely rely on the presence of vitamin B12 in naturally grown plants or soil residues.
Unfortified plant foods do not constitute a reliable source of biologically active vitamin B12 in quantities sufficient to meet human requirements.
Vitamin B12 deficiency is a particularly relevant risk for individuals who follow a vegan diet without supplementation or fortified foods. Recent literature emphasizes that the use of vitamin B12 supplements is one of the most reliable strategies for maintaining adequate vitamin status in vegetarians and, especially, vegans.
However, deficiency can also occur in omnivores, particularly in older adults and individuals with reduced gastric or intestinal absorption. The assessment of vitamin B12 status should therefore be considered based on individual factors rather than solely on adherence to a specific dietary pattern.
A personalized nutritional strategy
Malnutrition requires a personalized clinical and nutritional approach. In individuals with involuntary weight loss, reduced muscle mass, or difficulty eating, it is not enough to generally advise them to “eat more.”
It is necessary to understand whether the problem stems from reduced appetite, swallowing difficulties, malabsorption, inflammation, pain, depression, medication, or increased metabolic needs.
Interventions may include modifying food consistency, increasing the energy and protein density of meals, distributing food intake throughout the day, and, when necessary, using specific nutritional interventions under professional supervision.
In preventing malnutrition, the quality of the diet remains fundamental. A dietary pattern rich in minimally processed plant foods, legumes, whole grains, fruit, vegetables, nuts, and seeds can help provide a wide variety of nutrients. At the same time, the diet must ensure sufficient energy and protein intake and pay attention to nutrients that may be critical in relation to individual dietary choices.
Malnutrition is therefore not a condition that can be identified solely by observing body weight. It can be present in underweight individuals, frail older adults, cancer patients, and even obese individuals. Early assessment of weight loss, muscle mass, food intake, functionality, and clinical conditions is one of the most important tools for preventing deterioration of nutritional status and preserving autonomy and quality of life.
Note: The information contained in this article is for informational and educational purposes only and does not replace the assessment of a physician, dietitian, or other qualified healthcare professional. In the presence of involuntary weight loss, reduced appetite, swallowing difficulties, or suspected malnutrition, a personalized clinical and nutritional assessment should be conducted.
Essential bibliographic references
World Health Organization. Malnutrition. WHO, 2025 update. Definition and classification of malnutrition.
World Health Organization. Obesity and overweight. WHO, 2025 update.
Raj S, Guest NS, Landry MJ, et al. Vegetarian Dietary Patterns for Adults: A Position Paper of the Academy of Nutrition and Dietetics. Journal of the Academy of Nutrition and Dietetics. 2025;125(6):831-846.e2. doi:10.1016/j.jand.2025.02.002.
Essel N, et al. Trial of the MIND Diet for Prevention of Cognitive Decline in Older Persons. New England Journal of Medicine. 2023;389:602-611. doi:10.1056/NEJMoa2302368.
Diagnostic and application guidelines for malnutrition in adult patients. 2025 edition. Contemporary approach to the assessment of malnutrition and the role of inflammation.
