In 8 of the pairs of twins, the obese twin was as 'metabolically healthy' as his or her lean co-twin, while in the other 8 pairs, the obese twin had a poorer blood fat profile, higher liver fat and increased insulin production and resistance, and higher blood pressure-all hallmarks of unhealthy obesity that can lead to diabetes, heart problems and other complications.
The study is by Dr Kirsi Pietilainen, Dr Jussi Naukkarinen and colleagues from the Obesity Research Unit, University of Helsinki, Helsinki, Finland, and is published in Diabetologia, the journal of the European Association for the Study of Diabetes (EASD).
In all 16 pairs, the average weight difference between the obese co-twin and the lean-co-twin was 17 kg. In half (8/16) of the pairs the obese co-twin had significantly higher liver fat (around 7 times higher), a 78 percent increase in insulin production during OGTT, increased CRP, significantly more disturbance in the blood fat profile and greater tendency for high blood pressure compared with the lean co-twin. In these obese co-twins, SAT expression of mitochondrial oxidative phosphorylation, branched-chain, amino acid catabolism, fatty acid oxidation and adipocyte differentiation pathways were downregulated and chronic inflammation upregulated, all of which are metabolic problems that can lead to complications and disease.
In the other eight pairs, the obese co-twin did not differ from the non-obese co-twin in liver fat, insulin sensitivity, CRP, lipids, blood pressure or SAT metabolic characteristics.