Malnutrition

Introduction

Malnutrition is a condition caused by an imbalance between what the body needs and what it receives from food. It includes undernutrition (not enough calories, protein, or micronutrients) and overnutrition (excess energy intake leading to obesity and related metabolic problems).

Globally, malnutrition affects people of every age, income level, and region. Vulnerable groups include infants, pregnant women, older adults, and people with chronic illness, disability, or limited access to nutritious food.

Poor nutrition weakens immunity, slows wound healing, impairs growth and brain development in children, and increases the risk of infections, hospitalisation, and death. It also contributes to long-term conditions such as heart disease, diabetes, and osteoporosis when deficiencies or excess persist.

This page explains the types of malnutrition, how it develops, warning signs, evaluation, treatment, prevention, and when urgent medical care is needed.

Overview

Malnutrition is defined as a state resulting from insufficient, excessive, or imbalanced intake of nutrients that leads to measurable adverse effects on body composition, function, or clinical outcome. It is not limited to severe thinness—it also includes hidden hunger from vitamin and mineral deficiencies and diet-related overweight.

Assessment usually combines dietary history, anthropometry (weight, height, BMI, growth charts in children), physical examination, and laboratory tests. Treatment targets the underlying cause—food insecurity, illness, absorption problems, or eating disorders—alongside restoring nutritional balance.

With early recognition and appropriate feeding or supplementation, many people recover fully. Delayed treatment increases the risk of organ damage, developmental delay, frailty, and death, especially in infants and older adults.

• Includes undernutrition, micronutrient deficiencies, and diet-related overnutrition
• Affects growth, immunity, cognition, muscle strength, and wound healing
• Common in children, elderly people, and those with chronic disease or poverty
• May present as weight loss, stunting, oedema, fatigue, or obesity-related complications
• Diagnosis combines history, examination, growth/BMI data, and blood tests
• Treatment includes dietary rehabilitation, supplements, and treating underlying illness
• Prevention relies on food security, breastfeeding, screening, and infection control
• Can occur in both low-resource and high-income settings

What happens in the body

Undernutrition develops when energy or nutrient intake falls below requirements, or when illness increases metabolic demand while intake drops. The body breaks down fat and muscle for fuel, suppresses non-essential functions, and eventually compromises organ systems including the heart, liver, kidneys, and immune system.

Micronutrient deficiencies disrupt enzyme systems, bone formation, blood production, and nerve function even when total calories appear adequate. Overnutrition promotes insulin resistance, fatty liver, inflammation, and cardiovascular strain. Chronic infections such as diarrhoea worsen malnutrition through nutrient loss and malabsorption.

• Negative energy and protein balance leads to tissue breakdown and wasting
• Vitamin and mineral deficits impair immunity, haemoglobin synthesis, and bone health
• Inflammation and infection increase nutrient needs and reduce absorption
• Obesity-related malnutrition involves excess calories with poor nutrient quality

Signs and symptoms

Malnutrition symptoms depend on type and severity. Common features include:

• Unintentional weight loss or failure to gain weight in children
• Fatigue, weakness, and reduced exercise tolerance
• Poor concentration, irritability, or apathy
• Dry skin, brittle hair, or hair loss
• Muscle wasting and loss of subcutaneous fat
• Oedema (swelling) in some forms of severe protein deficiency
• Delayed growth, stunting, or developmental delay in children
• Frequent infections and slow recovery from illness
• Delayed wound healing after surgery or injury
• Anaemia symptoms: pallor, breathlessness, dizziness
• Constipation or diarrhoea related to poor intake or malabsorption
• In overnutrition: central obesity, breathlessness, joint pain, and metabolic signs
• In severe cases: confusion, heart failure, or organ dysfunction

Causes and risk factors

Malnutrition arises from inadequate intake, increased needs, or impaired utilisation:

• Insufficient food quantity or poor diet quality (low protein, fruits, vegetables)
• Poverty, food insecurity, and lack of clean water or sanitation
• Chronic illnesses: cancer, COPD, heart failure, liver or kidney disease
• Gastrointestinal disorders: coeliac disease, inflammatory bowel disease, short bowel
• Eating disorders, dementia, depression, or difficulty swallowing
• Repeated infections, especially diarrhoea and respiratory illness in children
• Excessive alcohol use interfering with intake and nutrient absorption
• Metabolic or genetic disorders affecting nutrient processing (e.g., PKU if untreated)
• Overconsumption of ultra-processed foods leading to obesity with micronutrient gaps
• Hospitalisation, surgery, or critical illness increasing catabolic demand

Diagnosis and evaluation

Diagnosis is clinical and supported by targeted tests:

• Detailed dietary history, weight trends, and growth chart review in children
• Physical exam for wasting, oedema, BMI, mid-upper arm circumference, and skin changes
• Blood tests: albumin, prealbumin, haemoglobin, iron studies, vitamins (B12, folate, D)
• Electrolytes, glucose, thyroid function, and liver/kidney panels when indicated
• Screening for malabsorption, infection, or malignancy in unexplained weight loss
• Nutrition risk tools in hospitals (e.g., MUST, NRS-2002) for at-risk adults
• Differentiate from eating disorders, depression, hyperthyroidism, and malignancy

Treatment and management

Treatment restores nutrition and addresses the root cause:

• Gradual refeeding with balanced meals or therapeutic feeds in severe cases
• Oral nutritional supplements, high-protein/high-calorie drinks when intake is low
• Micronutrient replacement: iron, folate, vitamin D, zinc, and others as needed
• Treatment of underlying disease, infection, or malabsorption
• Enteral tube feeding or parenteral nutrition when oral intake is impossible
• Dietitian-led meal planning for chronic conditions, dysphagia, or diabetes
• Medications for nausea, reflux, or appetite when clinically appropriate
• Community support: food assistance, home care, and caregiver education
• Monitoring weight, electrolytes, and refeeding syndrome risk during recovery

Prevention, self-care, and lifestyle

Not every condition is fully preventable, but the steps below may lower risk or recurrence:

• Promote breastfeeding and age-appropriate complementary feeding in infancy
• Ensure access to diverse, affordable foods including protein, fruits, and vegetables
• Routine growth monitoring and nutrition screening in children and older adults
• Vaccination, clean water, and hand hygiene to reduce infection-driven malnutrition
• Manage chronic disease, mental health, and swallowing problems early
• Limit ultra-processed foods; support healthy weight through balanced diet and activity

Possible complications

Delay, missed care, or unsafe self-medication can raise the chance of complications in some cases:

• Impaired immune function and higher infection and mortality risk
• Growth failure, cognitive impairment, and poor school performance in children
• Muscle weakness, falls, frailty, and pressure ulcers in older adults
• Delayed wound healing and poor surgical outcomes
• Heart failure, liver dysfunction, and electrolyte disturbances in severe refeeding
• Long-term osteoporosis, anaemia, and cardiovascular disease
• Refeeding syndrome if calories are restored too quickly without monitoring

When to see a doctor or seek emergency care

Seek prompt medical advice or emergency care if any of the following apply—it is safer not to wait and see:

• Unintentional loss of more than 5% body weight in one month
• Persistent diarrhoea, vomiting, or inability to eat or drink
• Signs of dehydration, confusion, severe weakness, or fainting
• Child not gaining weight, showing wasting, or failing to meet milestones
• Leg or abdominal swelling suggesting severe protein deficiency
• Any malnutrition concern in pregnancy, infancy, or frail elderly patients

Living with the condition

Work with a dietitian to build sustainable meal plans that meet medical and cultural needs rather than relying on fad diets.

Track weight and symptoms; attend follow-up for chronic illness, supplements, and swallowing or mental health support.

Caregivers of at-risk relatives should watch appetite, mobility, and food access—small, frequent nutrient-dense meals often help recovery.

Frequently asked questions

Is malnutrition only about being underweight?

No. Malnutrition includes undernutrition, micronutrient deficiencies, and overnutrition. A person can be overweight yet lack essential vitamins or protein.

Can malnutrition affect mental health?

Yes. Deficiencies in iron, B vitamins, and overall poor intake can worsen fatigue, depression, anxiety, and cognitive problems.

How is malnutrition treated?

Treatment combines correcting the diet, supplements or tube feeding when needed, and treating underlying illness or social barriers to food access.

Can malnutrition be reversed?

In many cases yes, especially with early intervention. Some effects on growth or cognition may persist if malnutrition was prolonged or severe.

Who is most at risk?

Infants, children, pregnant women, older adults, and people with chronic disease, disability, poverty, or repeated infections.

When is malnutrition an emergency?

Seek urgent care for rapid weight loss, severe dehydration, confusion, inability to eat, or signs of refeeding risk in severely malnourished patients.

Important caution

Malnutrition is a broad but treatable condition that affects physical health, immunity, and quality of life across the lifespan.

Early screening, adequate food, and treatment of underlying illness offer the best chance of recovery.

If you or someone you care for is losing weight, eating poorly, or failing to grow, ask a clinician for a nutrition assessment promptly.