Lean diabetes is one end of the spectrum of type 2 diabetes and not a separate entity.

Aims: Lean diabetes mellitus is non-type 1 diabetes with BMI < 18.5 kg/m and is now proposed to be a unique form of diabetes. We report on prevalence, clinical and microvascular complication profile in lean diabetes to see whether it stands out as a distinct entity or is a continuum of type 2 diabetes (T2D).

Methods: Using electronic records of a tertiary care diabetes centre in South India, individuals with T2D(n = 398,258) were classified using BMI, as lean(<18.5 kg/m), normal weight(18.5-22.9 kg/m),overweight(23.0-24.9 kg/m),mildly obese(25.0-29.9 kg/m), and markedly obese(≥30.0 kg/m) T2D. Clinical and biochemical features as well as frequency of microvascular complications of lean diabetes were compared with other T2D groups.

Results: The prevalence of lean diabetes was 1.5 %(n = 5865). Lean diabetes were younger with male preponderance, had higher fasting, postprandial plasma glucose, HbA1c levels, lower C-peptide and serum cholesterol compared to normal weight, overweight and obese T2D. Lean T2D had higher prevalence of retinopathy (42%), nephropathy (39 %), and neuropathy (73 %) compared to other groups(p < 0.001). Additionally, lean T2D were more likely to be treated with insulin (55.6 %, p < 0.001) compared with other groups.

Conclusions: Lean diabetes is one end of the spectrum of T2D and is characterized by an earlier age of onset, more severe insulin deficiency and increased risk of microvascular complications.