Identifying Causes and Consequences of Undernutrition in Infants and Young Children

Undernutrition remains one of the most pressing global health challenges, particularly for infants and young children. According to UNICEF, an estimated 149 million children under the age of five were stunted in 2022, and 45 million suffered from wasting. These numbers represent not just statistics, but real children whose growth, development, and survival are at stake. Understanding what causes undernutrition – and what it leads to – is the first step toward preventing it. In this post, we break down the immediate and underlying causes of undernutrition and explore its serious consequences during pregnancy, infancy, and early childhood.

What is undernutrition? 🔗

Before discussing the causes, it helps to define what undernutrition actually means. Undernutrition is a condition resulting from insufficient intake or poor absorption of essential nutrients. It manifests in several forms: stunting (low height for age, indicating chronic undernutrition), wasting (low weight for height, signalling acute undernutrition), underweight (low weight for age, a composite indicator), and micronutrient deficiencies – often called “hidden hunger” because visible signs may not always be present. The WHO notes that nearly half of all deaths among children under five are linked to undernutrition, with the majority occurring in low- and middle-income countries.

Immediate causes of undernutrition 🔗

The immediate causes of undernutrition are those that directly affect a child’s nutritional status at the individual level. These fall into two broad categories: inadequate dietary intake and disease.

Poor or inadequate diet 🔗

A diet that is lacking in quantity, quality, diversity, or feeding frequency is a primary driver of undernutrition. For infants, this often means receiving insufficient breastmilk – either because the mother herself is malnourished or because breastfeeding practices are suboptimal. When a mother’s own nutritional status is poor, both the quantity and quality of her breastmilk can be compromised, affecting the infant’s nutrient supply from the very start.

For older infants and toddlers, diets that are monotonous or based heavily on starchy staples, with few animal-source foods, fruits, or vegetables, fail to provide the range of vitamins and minerals children need. WHO’s complementary feeding guidelines highlight that the period from 6 to 23 months coincides with the peak risk for growth faltering and nutrient deficiencies, making dietary quality during this window especially critical.

Disease and infection 🔗

Infections are the other major immediate cause. Diseases like diarrhoea, respiratory tract infections, measles, and malaria reduce appetite, impair nutrient absorption, and increase the body’s metabolic demands. A child suffering from repeated bouts of diarrhoea, for instance, loses fluids and nutrients rapidly. Gut parasites such as hookworms also contribute by feeding on the child’s blood and nutrients. HIV/AIDS further compounds the problem by damaging immune function and increasing nutrient requirements. The relationship between undernutrition and infection is cyclical – malnourished children are more susceptible to infections, and infections in turn worsen their nutritional status.

Underlying causes of undernutrition 🔗

While diet and disease are the immediate triggers, undernutrition is rooted in deeper systemic and household-level factors. The UNICEF conceptual framework – widely used by global health organisations – categorises these into three underlying domains: household food insecurity, inadequate care, and unhealthy environments.

Household food insecurity 🔗

When families cannot consistently access or afford enough nutritious food, children suffer first. Household food insecurity is shaped by factors like income levels, food prices, agricultural productivity, and market access. In many communities, available food may be calorie-dense but nutrient-poor, meaning children fill their stomachs without meeting their micronutrient needs. The situation is worse during economic downturns, natural disasters, or armed conflicts, when food supply chains are disrupted.

Unfair food distribution and gender bias 🔗

Even within food-secure households, undernutrition can persist if food is distributed unequally. In many cultural contexts, men and older boys eat first, and women and young children – the most nutritionally vulnerable – receive whatever is left. Gender discrimination means girls may receive less food or lower-quality food than boys. The neglect of vulnerable household members, including children with disabilities, further compounds the problem.

Unhygienic living conditions 🔗

Poor water quality, inadequate sanitation, and lack of hygiene (collectively known as WASH) play a significant role. Children living in environments where clean water is unavailable and open defecation is common face repeated exposure to pathogens that cause diarrhoea and intestinal infections. These infections directly contribute to undernutrition through nutrient loss and reduced absorption. Research published in BMC Public Health confirms that household food insecurity, unhygienic environments, and lack of healthcare access are the three main underlying drivers identified by the UNICEF framework.

Inadequate health services 🔗

Limited access to healthcare – including immunisation, growth monitoring, deworming programmes, and treatment for common childhood illnesses – means many cases of undernutrition go undetected or untreated. In remote or conflict-affected areas, health infrastructure may be damaged or non-existent, leaving families without support.

Broader structural factors 🔗

Underlying all these factors is a web of poverty, political instability, economic insecurity, and lack of education. War and displacement disrupt food systems and healthcare. Natural calamities like floods and droughts destroy harvests. Low awareness about optimal infant feeding practices, lack of maternal education, and limited access to resources keep the cycle going. These are sometimes called the “basic causes” of undernutrition – the societal conditions that enable the underlying and immediate causes to persist.

Consequences of undernutrition during pregnancy 🔗

The effects of undernutrition begin even before a child is born. A malnourished pregnant woman faces serious risks, both for herself and her baby.

Slow fetal growth and low birth weight 🔗

Maternal undernutrition is the single most important cause of intrauterine growth restriction in low- and middle-income countries, according to a review published by the National Academies Press. When a mother does not receive adequate calories, protein, and micronutrients during pregnancy, the fetus cannot grow at its normal rate. This leads to low birth weight (LBW), defined as a weight below 2,500 grams at birth. Globally, an estimated 15-20% of all births – more than 20 million newborns each year – are affected by LBW.

The fetus depends entirely on the mother for its nutrient supply. Inadequate intake of protein and essential fats leads to reduced nutrient availability for the developing baby. A 2025 meta-analysis found a strong association between maternal undernutrition during pregnancy and the odds of delivering a low-birth-weight baby.

Micronutrient deficiencies and irreversible disabilities 🔗

Specific micronutrient deficiencies during pregnancy can cause severe and irreversible harm. Iodine deficiency can impair brain development, leading to intellectual disability and cretinism. Folic acid deficiency increases the risk of neural tube defects – serious birth defects of the brain and spine. Iron deficiency contributes to gestational anaemia, raising the risk of preterm delivery and maternal mortality. These outcomes are preventable with proper nutrition and supplementation, yet they continue to affect millions of pregnancies worldwide.

Long-term consequences of low birth weight 🔗

The consequences of being born underweight extend far beyond infancy. Research on fetal programming has shown that low birth weight is associated with a significantly increased risk of developing chronic diseases in adulthood, including type 2 diabetes, cardiovascular disease, and hypertension. This concept, known as the Developmental Origins of Health and Disease (DOHaD) hypothesis, suggests that fetal undernutrition permanently alters the structure and metabolism of the body. Low-birth-weight babies are also more likely to experience permanent stunting, reduced cognitive ability, and lower educational attainment. For girls, being born small can mean a smaller adult body size – which in turn increases obstetric risks in the next generation, creating an intergenerational cycle of undernutrition.

Impact of undernutrition on infants and young children 🔗

While undernutrition among infants under six months is relatively uncommon when breastfeeding is adequate, the risk rises sharply between the ages of 6 and 24 months. This is the period when breast milk alone can no longer meet a growing child’s nutritional requirements, and complementary foods must be introduced.

The critical complementary feeding window 🔗

WHO guidelines define complementary feeding as the process of providing foods in addition to milk starting at about six months. This period is critical: children are learning to accept solid foods, their nutritional demands are high relative to their small stomach capacity, and their immune systems are still developing. When complementary foods are introduced too late, too infrequently, or in insufficient variety, the child’s growth slows. Diets based mainly on thin porridges or starchy staples, without animal-source foods, fruits, or vegetables, fail to provide adequate energy and micronutrients.

Research on complementary feeding and micronutrients highlights that the 6-24 month period involves disproportionately high nutrient requirements relative to the child’s gastric capacity – making the quality and frequency of feeding critically important.

Growth faltering and susceptibility to infections 🔗

Children who do not receive adequate nutrition during this window experience growth faltering – a measurable slowing in their weight and height gain. Their weakened immune systems make them more vulnerable to common childhood infections such as pneumonia, diarrhoea, and measles. UNICEF reports that children with wasting have weakened immunity and face an increased risk of death, particularly when the wasting is severe. The combination of undernutrition and infection can quickly spiral into severe acute malnutrition (SAM), a life-threatening condition.

Micronutrient deficiencies in early childhood 🔗

Beyond overall calorie and protein shortfalls, deficiencies in specific micronutrients take a heavy toll on young children. Iron deficiency is the most common and leads to anaemia, which reduces oxygen delivery to tissues and impairs both physical and cognitive development. Vitamin A deficiency weakens the immune system and is a leading cause of preventable blindness in children. Iodine deficiency can cause hypothyroidism and impair brain development. Zinc deficiency increases susceptibility to diarrhoeal diseases. These deficiencies often coexist, compounding their negative effects on the child’s health and development.

Long-term developmental consequences 🔗

The effects of undernutrition during the first two years of life are not limited to childhood. Stunted children are more likely to perform poorly in school, earn less as adults, and face a higher burden of chronic disease. UNICEF estimates that the economic costs of undernutrition amount to roughly $3 trillion per year in lost productivity globally. Children deprived of proper nutrition in early life do less well in education and have reduced earning potential, trapping families in a cycle of poverty across generations.

The vicious cycle of undernutrition 🔗

One of the most important things to understand about undernutrition is that its causes and consequences form a vicious cycle. A malnourished mother gives birth to a low-birth-weight baby. That baby, if not adequately nourished, grows into a stunted child who is more susceptible to infections and performs poorly in school. As an adult, that individual earns less and is less able to provide nutritious food for their own children. Girls who were stunted in childhood face higher obstetric risks and are more likely to give birth to low-birth-weight babies, perpetuating the cycle into the next generation.

Breaking this cycle requires addressing not just the immediate causes – diet and disease – but also the deeper structural factors like poverty, lack of education, poor sanitation, and gender inequality. Nutrition interventions during the first 1,000 days (from conception through a child’s second birthday) offer the highest return, as this is when the foundations for lifelong health and development are laid.

What do you think? Given that undernutrition is driven by both individual-level and structural factors, which type of intervention do you believe would have the greatest impact – targeted nutrition programmes for mothers and children, or broader efforts to address poverty and inequality? How can communities play a more active role in breaking the intergenerational cycle of undernutrition?

References

1. https://data.unicef.org/topic/nutrition/malnutrition/
2. https://www.who.int/news-room/fact-sheets/detail/malnutrition
3. https://www.ncbi.nlm.nih.gov/books/NBK596430/
4. https://www.ncbi.nlm.nih.gov/books/NBK361900/
5. https://pmc.ncbi.nlm.nih.gov/articles/PMC4653928/
6. https://www.ncbi.nlm.nih.gov/books/NBK222095/
7. https://pmc.ncbi.nlm.nih.gov/articles/PMC12150135/
8. https://pmc.ncbi.nlm.nih.gov/articles/PMC5081104/
9. https://www.ncbi.nlm.nih.gov/books/NBK596431/
10. https://pubmed.ncbi.nlm.nih.gov/28315884/
11. https://www.unicef.org/nutrition/child-wasting
12. https://www.unicefusa.org/what-unicef-does/childrens-health/nutrition/fight-childhood-malnutrition