Why does cancer cachexia cause unexplained weight loss?

Unexplained Weight Loss is a very common presentation of Cancer Cachexia. The condition is more than eating less. Signals released by the tumour and the body's immune response can alter how energy is used, increase the breakdown of muscle and fat, and reduce the body's ability to rebuild tissue. Pain, nausea, dry mouth, altered taste, constipation, low mood or treatment side effects can further reduce food intake. Weight may fall even when a person is trying to eat.

Loss of muscle can cause weakness, reduced mobility and difficulty with everyday activities. A falling weight or looser clothing should be recorded alongside appetite, symptoms and strength, because the pattern helps the care team distinguish causes and plan support.

Tell the oncology team about weight change, reduced appetite, early fullness, swallowing difficulty, vomiting, diarrhoea or mouth soreness. A dietitian can suggest energy- and protein-rich foods, suitable drinks and small frequent meals. The team may review medicines, pain control, constipation, nausea and mood. Gentle activity, when safe, can help preserve function; a physiotherapist can tailor it to current strength. Do not start supplements or restrictive diets without checking, because they may interact with treatment or worsen symptoms.

Contact the cancer team promptly if eating or drinking becomes difficult, weakness is worsening, urine becomes noticeably reduced or dark, repeated vomiting prevents fluids, or swallowing becomes unsafe. Seek urgent help for confusion, fainting, severe breathlessness, sudden inability to stand, or signs of dehydration. These problems may need same-day assessment rather than waiting for a routine visit.

Could treatment, pain, nausea or another problem be adding to the weight loss? Would a dietitian, physiotherapist or symptom-control clinician help? Which foods, drinks or supplements fit my treatment? What change in strength, intake or hydration should prompt a call?