Lean people might be metabolically unhealthy.
According to the study, lean people who are metabolically unhealthy, but have normal weight, might be at a 300 per cent greater chance of dying.
This is in contrast to the small proportion of obese people who despite their high body mass index (BMI) are metabolically healthy, said Norbert Stefan, Professor at the University of Tubingen in Germany.
And for this group, the risk of death from all-cause mortality is only 25 per cent higher than that of healthy lean people, Stefan added.
The results showed that among lean people, skinny lower legs may prove to be the strongest predictor of poor metabolic health, while for obese people, abdominal fat levels and non-alcoholic fatty liver disease are strong predictors of cardiometabolic diseases such as Type 2 diabetes or cardiovascular disease.
In lean people, a gene-derived problem of storing fat in the lower limbs may be a crucial factor, placing them at an increased risk of cardiometabolic diseases, Stefan said.
For the study, detailed in the journal Cell Metabolism, the team analysed data from 981 subjects.
After having defined metabolic health as having less than two risk parameters of the metabolic syndrome, they found that 18 per cent of their lean subjects were metabolically unhealthy.
Using magnetic resonance imaging and magnetic resonance spectroscopy, they determined body fat mass, fat distribution and deposition of fat in the liver.
Further, they also determined insulin sensitivity, insulin secretion, thickness of the carotid vessel wall and fitness.
Such unhealthy lean but normal BMI phenotype — body-shape — also resembled people with certain rare diseases such as lipodystrophy in which the body is unable to sustain adequate fat reserves.
The findings provide evidence for the existence of a “lipodystrophy-like phenotype in the general population”, the researchers noted.
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