Malnutrition is present in a large minority of hospitalised adults on admission and worsens in many of them during the stay, yet it is one of the least reliably detected conditions in acute care because it hides behind the primary diagnosis. Its consequences are concrete and measurable: impaired wound healing, higher infection rates, muscle wasting that prevents mobilisation, pressure injury, longer stays, more readmissions, and higher mortality. Obesity does not exclude it — a patient can be simultaneously obese and severely protein-malnourished. Hydration failures cut both ways. Dehydration in older adults presents as confusion, falls, constipation, and acute kidney injury rather than as thirst, because the thirst response blunts with age. Fluid overload in heart failure and renal disease presents as breathlessness and oedema and is just as harmful. Meanwhile the interventions used to fix these problems carry their own serious hazards: aspiration during assisted feeding, refeeding syndrome when nutrition is restarted too fast in a starved patient, tube misplacement into the lung, and central line infection. Nutrition and hydration support is therefore not a hotel service delegated to the...