Correct Answer: A. < 12
A BMI of < 12 kg/m² is classified as the "lethal" threshold in men according to standard references used in Indian Preventive and Social Medicine, including Park's Textbook of Preventive and Social Medicine. At this extreme level of undernutrition, severe protein-energy malnutrition (PEM) becomes incompatible with survival without immediate and aggressive medical intervention. The body has exhausted all fat reserves and is catabolising essential lean body mass — including cardiac muscle, skeletal muscle, and visceral organs — to meet basic energy demands.
At BMI < 12 in men, the physiological consequences are catastrophic: cardiac arrhythmias (due to myocardial wasting), immune collapse (rendering the individual susceptible to overwhelming infection), renal and hepatic dysfunction, and profound electrolyte imbalances (particularly hypokalaemia and hypomagnesaemia) collectively drive mortality to near-certain levels without intervention. This threshold is particularly relevant in the Indian public health context — encountered in advanced tuberculosis, HIV/AIDS wasting syndrome, prolonged starvation, and famine triage settings.
The lethal BMI threshold is gender-specific: for men it is < 12 kg/m², while for women it is < 11 kg/m², reflecting differences in baseline body composition and fat reserves. This distinction is a high-yield fact frequently tested in NEET PG and NBE examinations.
Why other options are wrong
- B. < 15 — BMI < 15 kg/m² represents severe malnutrition but is well above the lethal threshold. Individuals at this level are at serious risk but can still survive and respond to nutritional rehabilitation. This cutoff is too high to be considered "lethal."
- C. < 14 — BMI < 14 kg/m² also falls in the severe malnutrition category. While it signals a critical nutritional emergency, it does not represent the precise lethal threshold recognised in standard PSM references. It is a common distractor due to its proximity to the correct value.
- D. < 13 — BMI < 13 kg/m² is a severely malnourished state and carries very high mortality risk, but it is not the defined lethal cutoff for men. This is the most common wrong answer chosen by students who misremember the threshold by one unit.
Reference: Park's Textbook of Preventive and Social Medicine — Nutrition and Health chapter.