Undernutrition is a global health concern that disproportionately affects children, pregnant women, and individuals in low-income countries. It results from inadequate intake of calories, protein, and essential micronutrients, leading to poor growth, weakened immune systems, and increased susceptibility to infections. Undernutrition in children can cause stunting, wasting, and cognitive delays, while in adults, it can lead to fatigue, diminished work capacity, and poor overall health. Research in this area explores the causes of undernutrition, including food insecurity, lack of access to nutritious foods, and the impact of infectious diseases. Strategies to combat undernutrition involve improving food availability, enhancing nutritional education, and implementing government policies that support vulnerable populations.