What a BMI below 16 means
Learn why an adult BMI below 16 is classified as severe thinness and calls for timely professional assessment.
In adult WHO classification, a BMI below 16 is described as severe thinness. It is lower than the general underweight threshold of 18.5 and should not be managed solely through an online result.
First confirm the inputs: weigh without heavy clothing, measure height accurately and check the units. Even after correcting an error, however, a confirmed result below 16 merits prompt professional evaluation—especially when weight loss was unintentional.
BMI cannot identify the cause. Possibilities range from inadequate intake and digestive illness to medication effects, chronic disease or an eating disorder. A clinician can assess symptoms, weight history and medical risks; a dietitian can support safe nutritional rehabilitation where appropriate.
Seek urgent medical help for fainting, confusion, chest pain, severe weakness, dehydration or inability to eat or drink. Otherwise, arrange a timely appointment rather than making a large, unsupervised calorie change.
The BMI calculator can verify the arithmetic, but the result is a screening signal—not a diagnosis or treatment plan.