The World Health Organization defines malnutrition as any deficiency, excess, or imbalance in a person’s intake of energy or nutrients. That definition is broader than most people expect: it covers not just hunger and wasting, but also obesity, vitamin deficiencies, and diet-related diseases like diabetes and heart disease. Globally, malnutrition in its various forms affects billions of people and remains one of the leading threats to human health.
The Three Categories of Malnutrition
WHO groups malnutrition into three broad categories. The first is undernutrition, which includes stunting (being too short for your age), wasting (being too thin for your height), and underweight (being too light for your age). These conditions primarily affect young children in low- and middle-income countries and reflect chronic or acute food deprivation.
The second category is micronutrient-related malnutrition, meaning a lack of essential vitamins and minerals or, less commonly, an excess of them. Iron, vitamin A, and iodine deficiencies are the most widespread worldwide, particularly in children and pregnant women.
The third category is overweight, obesity, and diet-related noncommunicable diseases, including heart disease, stroke, diabetes, and certain cancers. For adults, WHO classifies a BMI of 25 or above as overweight and 30 or above as obese.
Undernutrition in Children Under 5
WHO tracks child undernutrition using growth standards that compare a child’s measurements to a healthy reference population. A child whose height-for-age or weight-for-height falls more than two standard deviations below the median is classified as stunted or wasted, respectively. These thresholds help identify children at significantly elevated risk of illness and death.
The 2024 global estimates paint a stark picture. About 150.2 million children under five were stunted, representing 23.2% of all children in that age group. Another 42.8 million were wasted, with 12.2 million of those experiencing severe wasting. Meanwhile, 35.5 million children under five (5.5%) were overweight. These numbers illustrate how undernutrition and overweight can coexist as global problems simultaneously.
Severe acute malnutrition, the most dangerous form of undernutrition, is diagnosed when a child’s mid-upper arm circumference falls below 115 millimeters or when visible swelling (bilateral pitting edema) appears in the lower limbs. Children with severe acute malnutrition face a dramatically higher risk of death. The condition presents in two recognizable forms: marasmus, where the child has a skeletal appearance from extreme muscle and fat loss, and kwashiorkor, marked by swelling, discolored brittle hair, and cracked skin that can become infected.
Research published in Nature has shown that early wasting increases a child’s risk of later growth faltering, including stunting. This means the different forms of undernutrition are not independent problems. A child who experiences wasting is more likely to become stunted, compounding the health consequences.
Micronutrient Deficiencies and Their Effects
Micronutrients are vitamins and minerals that the body needs only in tiny amounts but that play critical roles in growth, immune function, and development. When they are missing, the consequences can be severe.
Iron deficiency is the most common nutritional deficiency worldwide. A lack of iron, along with deficiencies in folate, vitamin B12, or vitamin A, can cause anemia, a condition where the blood carries fewer red blood cells or less hemoglobin than normal. Anemia leads to fatigue, weakness, shortness of breath, and dizziness. It is especially dangerous during pregnancy and early childhood.
Vitamin A deficiency is the leading cause of preventable blindness in children. It also weakens the immune system, raising the risk of death from infections like diarrheal disease and measles. Iodine deficiency, meanwhile, can cause brain damage. During pregnancy, severe iodine deficiency is linked to stillbirth, spontaneous abortion, and congenital abnormalities. Even milder deficiency can reduce intellectual capacity in children.
The Double Burden of Malnutrition
One of the most important concepts in WHO’s framework is the “double burden” of malnutrition: the coexistence of undernutrition and overweight within the same individual, household, or population. This is not a theoretical concern. In many countries, a mother may be overweight or anemic while her child is underweight. A person can be obese yet deficient in several essential vitamins and minerals.
The connection runs deeper than simple coexistence. Undernutrition early in life, even in the womb, can predispose a person to overweight and diseases like diabetes and heart disease later on. And overweight in mothers is associated with overweight and obesity in their children. This means malnutrition can perpetuate itself across generations, with different forms appearing at different life stages within the same family.
Global Nutrition Targets Through 2030
In 2012, the World Health Assembly adopted six global nutrition targets aimed at reducing maternal and child malnutrition by 2025. As of 2025, the world is not on track to meet all of them. Recognizing this, WHO member states voted at the 78th World Health Assembly to extend four of the targets to 2030:
- Stunting: a 40% reduction in the number of stunted children under five
- Anemia: a 50% reduction in anemia among women of reproductive age
- Low birth weight: a 30% reduction
- Wasting: reducing and maintaining childhood wasting below 5%
Two targets that were closer to being met received more ambitious revisions. The childhood overweight target shifted from simply maintaining 2012 levels to reducing overweight among children under five to below 5% by 2030. The exclusive breastfeeding target increased from 50% of infants exclusively breastfed in the first six months to 60% by 2030.
These targets reflect a core reality of global malnutrition: progress has been uneven. Stunting rates have declined steadily in some regions while stalling in others. Wasting remains stubbornly persistent because it can develop quickly during food crises, infections, or seasonal shortages. And overweight is rising in nearly every region, including in countries that still struggle with hunger, making the double burden increasingly common.