Thin-fat: when 'normal weight' is not metabolically normal

'Thin-fat', more formally, normal-weight metabolically unhealthy, describes people whose BMI falls in the normal range but whose body fat distribution, insulin sensitivity, and cardiovascular markers look like those of someone with obesity. In South Asian populations, this pattern is common from birth.

The biology is visceral fat, fat stored around organs, at higher proportions for a given weight, compared to European populations. The same jeans size, a very different internal story.

Insulin resistance at normal BMI can cause PMOS, irregular cycles, and lower IVF success rates. Because the woman in front of the doctor looks 'healthy', the investigation often stops before insulin is ever measured.

You cannot see-saw this with diet alone. Movement, particularly walking after meals and strength work, is what specifically reduces visceral fat and improves insulin sensitivity. Weight on the scale may not change. Waist measurement often does. The metabolic markers reliably improve.

This is also why PMOS management in lean South Asian women emphasises muscle-building and walking more than weight loss.