Malnutrition is a broad clinical and public-health term describing deficiencies, excesses or imbalances in a person's intake of energy and nutrients. It is therefore not synonymous with starvation, underweight or nutrient deficiency. WHO divides the concept broadly into undernutrition, micronutrient-related malnutrition, and overweight, obesity and associated diet-related noncommunicable diseases. Undernutrition includes wasting, stunting and underweight as well as deficiencies of vitamins and minerals.
This broad definition is important because a person can be malnourished while consuming excessive energy if the diet is nutritionally inadequate or produces obesity and diet-related disease. Malnutrition is consequently a problem of nutritional adequacy and balance across the life course rather than simply a measure of how much food a person eats.
Undernutrition has several distinct manifestations. Wasting refers to low weight-for-height and commonly indicates recent and severe weight loss, often associated with inadequate food intake and acute illness such as diarrhoeal disease. Stunting refers to low height-for-age and generally reflects chronic or recurrent undernutrition, often beginning during early development. Underweight is defined relative to weight-for-age in children and can reflect wasting, stunting or both. These measures describe different dimensions of nutritional status and should not be treated as interchangeable. A child may be stunted without being wasted, wasted without being stunted, or affected by both. The distinctions are clinically and epidemiologically important because they reflect different patterns and timing of nutritional stress.
Micronutrient-related Malnutrition occurs when the body receives inadequate or excessive amounts of essential vitamins and minerals. Iron, vitamin A and iodine deficiencies are among the major global public-health concerns identified by WHO, although many other micronutrients can also become deficient. Micronutrients are required for processes including enzyme activity, hormone production, oxygen transport, immune function, tissue development and neurological development. Deficiency may occur even when total energy intake is sufficient, particularly when diets are monotonous or dominated by nutrient-poor foods. Conversely, excessive intake of particular micronutrients can also be harmful. This demonstrates why nutritional adequacy cannot be evaluated simply from calories or body weight; nutrient composition and physiological requirements must also be considered.
Malnutrition is influenced by biological, social, economic and environmental factors. Poverty can limit access to sufficient quantities of nutritious food, while conflict, displacement, disease, climate extremes and economic disruption can undermine food systems and household purchasing power. Infection and malnutrition can reinforce one another: illness can reduce appetite and nutrient absorption while increasing physiological requirements, whereas undernutrition can weaken immune function and increase susceptibility to infection.
Maternal nutrition and infant feeding practices also influence later outcomes, particularly during the early developmental period from conception through early childhood. Consequently, malnutrition cannot be understood solely as an individual failure to choose appropriate foods. Food availability, affordability, healthcare, sanitation, education, social protection and living conditions all contribute to nutritional status.
Malnutrition also includes excess nutrition, particularly overweight and obesity and the diet-related noncommunicable diseases associated with unhealthy dietary patterns. WHO reported that in 2022 approximately 2.5 billion adults worldwide were overweight, including 890 million living with obesity, while approximately 390 million adults were underweight. Among children under five, WHO estimated 149 million were stunted, 45 million were wasted and 37 million were overweight or living with obesity in 2022.
These figures demonstrate that different forms of malnutrition can coexist within the same country, community or household. A population may simultaneously experience child undernutrition, micronutrient deficiencies and rising obesity. Nutrition policy therefore increasingly addresses malnutrition “in all its forms” rather than focusing exclusively on hunger.
The consequences of Malnutrition can be immediate, developmental and long-term. Severe undernutrition increases vulnerability to infection and death, particularly among young children. Chronic undernutrition during development can impair physical growth and cognitive potential. Micronutrient deficiencies can produce specific functional disorders, such as impaired oxygen transport in iron deficiency or developmental consequences associated with iodine deficiency. Excess nutrition and obesity increase the risk of several noncommunicable diseases, including cardiovascular disease and type 2 diabetes.
The consequences also extend beyond the individual: malnutrition can increase healthcare costs, reduce educational and economic productivity and reinforce cycles of poverty. WHO notes that nearly half of deaths among children under five are linked to undernutrition, illustrating the major population-level significance of inadequate nutrition.
Diagnosis and management depend on the form, severity, age and clinical circumstances. Assessment can involve body measurements such as weight, height or length, body-mass indices appropriate to age, biochemical tests, dietary assessment, physical examination and evaluation of underlying disease. Treatment of severe acute undernutrition may require specialised therapeutic foods and carefully managed medical care, particularly when infection or metabolic complications are present.
Micronutrient deficiencies may require targeted dietary changes, fortified foods or supplements, while excess weight may require interventions addressing diet, physical activity, behaviour and the wider environment. Treating a symptom without addressing its cause can be insufficient. For example, recurrent gastrointestinal disease, malabsorption, food insecurity or inappropriate feeding practices may need to be addressed alongside the immediate nutritional deficit.
A common misconception is that Malnutrition simply means being visibly thin or not eating enough. Nutritional status can be abnormal at any body size, and obesity can coexist with micronutrient deficiencies. Another misconception is that one food or supplement can correct malnutrition regardless of its cause. Nutritional rehabilitation depends on identifying which nutrients are deficient or excessive, how severe the problem is and what factors caused it. Prevention similarly requires more than increasing food quantity.
WHO emphasises sustainable food systems, social protection, nutrition education, nutrition-sensitive health services, supportive environments and effective governance as components of addressing malnutrition globally. The most accurate conceptualisation is therefore multidimensional: Malnutrition encompasses inadequate, excessive and imbalanced nutrition and reflects interactions among diet, disease, development, socioeconomic conditions and the wider food system.
