Understanding Undernutrition in Infants and Children: Causes, Symptoms, and Health Impacts

Every year, millions of children around the world fail to get the nutrition they need to grow, learn, and thrive. Undernutrition – a condition marked by insufficient intake of calories and essential nutrients – remains one of the most pressing global health challenges, particularly for infants and young children. Despite decades of progress, it continues to be a leading contributor to child mortality and long-term developmental setbacks. Understanding what undernutrition is, how it manifests, and why it disproportionately affects certain populations is the first step toward meaningful action.

What is undernutrition? 🔗

Undernutrition refers to a state in which the body does not receive enough energy or essential nutrients to maintain good health. While often used interchangeably with the broader term “malnutrition,” undernutrition specifically describes a deficiency in nutrient intake rather than an excess. According to the World Health Organization (WHO), malnutrition encompasses three broad groups of conditions: undernutrition, micronutrient-related deficiencies, and overweight or obesity. Undernutrition sits firmly on the deficiency end of this spectrum.

Undernutrition can develop when people are unable to obtain or prepare adequate food, when they have disorders that impair eating or nutrient absorption, or when their caloric needs are significantly increased due to illness or rapid growth. It progresses in stages – first, nutrient levels in the blood and tissues begin to drop, followed by changes at the cellular and biochemical level. Eventually, visible signs and symptoms appear.

Recognising the signs and symptoms 🔗

People suffering from undernutrition often show a range of physical symptoms. The most common include being visibly underweight, with protruding bones due to loss of body fat and muscle mass. The skin typically becomes dry, thin, and inelastic, and may appear pale or cold to the touch. Hair loss or thinning is another frequent indicator – hair may become dry, sparse, and fall out easily.

In severe cases, particularly in children, two clinical forms of protein-energy undernutrition may develop. Marasmus is characterised by extreme wasting of fat and muscle tissue, while kwashiorkor involves swelling (oedema), particularly in the abdomen, face, and limbs, along with skin changes and an enlarged liver. Both conditions are life-threatening and require immediate medical intervention. Affected children may also show signs of fatigue, irritability, weakened immunity, and developmental delays.

Why children and women are most vulnerable 🔗

While undernutrition can affect anyone at any age, infants, young children, and women – especially pregnant and breastfeeding women – face the greatest risk. Children are particularly susceptible because of their high demand for energy and essential nutrients during periods of rapid growth. According to the MSD Manual, protein-energy undernutrition is a significant cause of death among neonates and children aged one to four years, especially in low- and middle-income countries.

Women’s vulnerability stems from the increased nutritional demands of pregnancy and breastfeeding. Poor maternal nutrition not only harms the mother’s health but can also result in low birth weight babies, creating an intergenerational cycle of undernutrition. A malnourished mother is more likely to give birth to a stunted or underweight infant, who in turn faces a higher risk of health complications throughout life.

The scale of the crisis: global numbers 🔗

The statistics paint a sobering picture. According to the UNICEF-WHO-World Bank Joint Child Malnutrition Estimates, in 2024, approximately 150.2 million children under five were stunted (too short for their age), 42.8 million were wasted (too thin for their height), and 35.5 million were overweight. Nearly half of all deaths among children under five years of age are linked to undernutrition, and the vast majority of these deaths occur in low- and middle-income countries.

South Asia and Sub-Saharan Africa carry the heaviest burden. Roughly two-thirds of the world’s stunted children live in these two regions. The World Bank estimates that the economic costs of undernutrition amount to at least $1 trillion per year globally in lost productivity. Undernutrition doesn’t just claim lives – it limits the economic potential of entire nations.

Understanding the four sub-forms of undernutrition 🔗

Undernutrition manifests in four primary sub-forms, each measured using specific anthropometric indicators in children:

Stunting (low height-for-age) reflects chronic or recurrent undernutrition over time. It is usually linked to poor socioeconomic conditions, inadequate maternal nutrition, frequent illness, and inappropriate infant feeding practices. Stunted children often suffer from delayed mental development, poor school performance, and reduced cognitive potential. Critically, stunting is largely irreversible once it has occurred.

Wasting (low weight-for-height) typically indicates recent and severe weight loss, often caused by inadequate food intake or infectious diseases like diarrhoea. Wasted children face a significantly increased risk of death, though treatment is possible if intervention is timely.

Underweight (low weight-for-age) is a composite indicator that can reflect either stunting, wasting, or both. It is widely used in monitoring programmes but can be difficult to interpret in isolation because it does not distinguish between chronic and acute undernutrition.

Micronutrient deficiencies refer to a lack of essential vitamins and minerals – such as iron, iodine, zinc, and vitamin A – that the body needs in small quantities for critical functions. These deficiencies can impair immune function, cognitive development, and physical growth. The WHO notes that micronutrient deficiencies are among the most widespread forms of malnutrition globally.

Causes of undernutrition in infants and children 🔗

Undernutrition is rarely caused by a single factor. It results from a complex interplay of immediate, underlying, and structural causes.

Immediate causes 🔗

At the most direct level, undernutrition is caused by inadequate dietary intake and disease. When a child does not receive enough calories, protein, or micronutrients – or when illness prevents the body from absorbing nutrients properly – undernutrition follows. Infectious diseases such as diarrhoea and respiratory infections are particularly damaging because they increase nutrient needs while simultaneously reducing appetite and absorption.

Underlying causes 🔗

Beneath the immediate triggers lie deeper issues: household food insecurity (the inability to access sufficient, nutritious food), inadequate caregiving and feeding practices, lack of access to clean water and sanitation, and limited healthcare. Poor knowledge about appropriate infant and young child feeding – including the importance of exclusive breastfeeding for the first six months – is a major contributing factor. According to the World Food Programme, if children don’t receive proper nutrients during the first 1,000 days of life (from conception to age two), the damage to their development can be permanent.

Structural causes 🔗

At the broadest level, poverty remains the single most important driver of undernutrition. Conflict, climate extremes, economic shocks, gender inequality, and poorly functioning food systems all limit access to nutritious food. These structural factors explain why undernutrition is concentrated in specific regions and communities – particularly in low-income countries experiencing political instability or environmental degradation.

Health impacts: short-term and long-term consequences 🔗

The effects of undernutrition on children’s health are both immediate and far-reaching, often extending well into adulthood.

Short-term health impacts 🔗

In the short term, undernourished children have weakened immune systems, making them highly susceptible to infections such as pneumonia, diarrhoeal diseases, and measles. These infections, in turn, worsen nutritional status – creating a dangerous cycle where illness and undernutrition reinforce each other. Severely malnourished children may also develop life-threatening complications like hypoglycaemia (dangerously low blood sugar), hypothermia, and severe dehydration.

Long-term health impacts 🔗

The long-term consequences of undernutrition are equally devastating. Chronic undernutrition during the early years can result in permanent cognitive impairment, reduced educational attainment, and lower lifetime earning potential. The World Bank highlights that stunting early in life causes irreversible damage to cognitive development, with educational, income, and productivity consequences that persist into adulthood.

Adults who were undernourished as children also face a higher risk of chronic diseases later in life, including cardiovascular disease and diabetes. For women, being stunted increases the risk of obstetric complications and the likelihood of delivering a low birth weight baby – perpetuating the cycle into the next generation.

The disease burden: India’s challenge 🔗

India carries a particularly large share of the global undernutrition burden. According to the India State-Level Disease Burden Initiative (published in The Lancet, analysing data up to 2017), child and maternal malnutrition was the predominant risk factor for death in children under five in every state of India, contributing to 68.2% of under-five deaths.

The study found that in 2017, the prevalence of child stunting in India stood at 39.3%, child wasting at 15.7%, and child underweight at 32.7%. Anaemia affected nearly 60% of Indian children. The disease burden attributable to child and maternal malnutrition includes increased risk of neonatal disorders, nutritional deficiencies, diarrhoeal diseases, lower respiratory infections, and other common infections. States such as Uttar Pradesh, Bihar, Assam, and Rajasthan bore the heaviest burden.

India contributes roughly a third of the global burden of undernutrition, as noted by the WHO India office. Addressing this challenge is not only critical for India’s population but also essential for meeting global nutrition targets under the Sustainable Development Goals (SDGs).

The critical window: first 1,000 days 🔗

Nutrition scientists emphasise the period from conception to a child’s second birthday – the first 1,000 days – as the most critical window for nutritional intervention. During this period, the brain and body undergo rapid development, and nutritional deficiencies can cause irreversible harm. Optimising nutrition during these 1,000 days is considered the single most effective strategy for improving long-term health outcomes, cognitive development, and economic productivity.

This means that interventions must begin even before birth, with adequate maternal nutrition during pregnancy, followed by exclusive breastfeeding for the first six months and appropriate complementary feeding thereafter. Delays in addressing undernutrition during this window are difficult – and sometimes impossible – to compensate for later in life.

Moving forward: why awareness matters 🔗

Undernutrition is not an inevitable consequence of poverty. It is a preventable condition that responds to well-designed interventions – from promoting breastfeeding and improving dietary diversity to strengthening healthcare systems and social safety nets. But effective action begins with understanding the problem clearly: its causes, its manifestations, and its consequences.

When we recognise that undernutrition is not just about hunger but about the quality and adequacy of diets, access to healthcare, and the broader social and economic environment, we can begin to design responses that address root causes rather than just symptoms.

What do you think? Given that the first 1,000 days of life are so critical, how can communities and local health systems better support mothers and infants during this window – especially in resource-limited settings? And what role should nutrition education play in addressing the underlying causes of undernutrition?

References

1. https://www.who.int/news-room/fact-sheets/detail/malnutrition
2. https://www.msdmanuals.com/home/disorders-of-nutrition/undernutrition/undernutrition
3. https://www.msdmanuals.com/professional/nutritional-disorders/undernutrition/overview-of-undernutrition
4. https://data.unicef.org/topic/nutrition/malnutrition/
5. https://www.worldbank.org/en/topic/nutrition/overview
6. https://www.who.int/health-topics/malnutrition
7. https://www.wfp.org/ending-malnutrition
8. https://pmc.ncbi.nlm.nih.gov/articles/PMC6839043/
9. https://www.who.int/india/health-topics/nutrition