For decades, the weighing scale and the BMI chart have been treated as the final word on health. A doctor examining a patient with a trim waistline and a BMI of 22 would, in most cases, tick the 'healthy weight' box and move on. But a growing body of clinical evidence is forcing physicians across India to question that assumption. The condition now being described as Normal Weight Obesity, or the 'thin-fat' phenomenon, is revealing that a great many Indians who appear perfectly slim are quietly carrying dangerous levels of internal, or visceral, fat.

This is not a fringe observation. Studies from clinics in Gujarat, Kerala and northern India have found that between 14 and 31 per cent of individuals with a completely normal BMI actually meet the clinical criteria for excess body fat. In some urban Asian populations, that figure climbs closer to a third. These are not overweight people slipping through the cracks; they are patients who, by every conventional standard, look and weigh exactly as they should.

The myth of the visible fat

The most persistent myth doctors are now trying to dismantle is the idea that obesity must be visible to be dangerous. Fat accumulating around the abdomen, encasing organs such as the liver, pancreas and heart, does not always show up as a protruding belly or loose clothing. A person can weigh 56 kilograms, have a BMI comfortably in the "normal" range, and still be carrying the metabolic burden of someone who is clinically obese.

The reasons for this are partly biological. Indian and South Asian bodies tend to have a lower capacity to store fat safely under the skin. When calorie intake exceeds what this limited subcutaneous space can hold, the surplus fat does not simply disappear; it spills over into the abdominal cavity and organs.

Why it matters

Physicians treating this pattern are seeing its consequences arrive earlier than expected. Patients in their thirties, with no family history flagged and no obvious weight problem, are turning up with pre-diabetic blood sugar readings, abnormal lipid profiles and early fatty liver changes. The concern is not hypothetical; it explains, in part, why India carries one of the world's largest burdens of type 2 diabetes despite having comparatively low rates of visible obesity.

Lifestyle plays an equal role alongside genetics. Rapid urbanisation has stripped daily life of the physical labour that once built and preserved muscle, while diets rich in refined carbohydrates have become the norm. Low muscle mass compounds the problem, since muscle is what helps the body regulate blood sugar efficiently. The combination of high visceral fat and low lean mass is, in many respects, more concerning than a high BMI alone.

Looking beyond the scale

Doctors are increasingly urging a shift away from BMI as the sole measure of health, in favour of waist circumference, waist-to-hip ratio, and where possible, body composition analysis.

Looking slim is not the same as being metabolically healthy. A normal weight should prompt reassurance only after appropriate screening, not instead of it.

(Dr Paras Agarwal, Director - Diabetes, Obesity and Metabolic Clinic, CK Birla Hospital, Gurgaon)



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