Protein energy malnutrition, abbreviated PEM, is the clinical result of a diet chronically short of both protein and energy, or of disease that prevents the body absorbing them. It is most devastating in young children, where it appears as marasmus, severe wasting with loss of muscle and fat, or kwashiorkor, marked by oedema, skin and hair changes, and a swollen belly, with many cases blending the two. The underlying causes are poverty, famine, war, and repeated infection, which raises needs while depressing appetite. Treatment follows careful protocols: stabilise with therapeutic milks, treat infections, then rebuild weight with energy- and protein-dense feeds while correcting micronutrient deficiencies. Prevention rests on food security, breastfeeding, clean water, and growth monitoring.