Apolipoprotein A-IV concentration did not differ between both control groups (lean 1.06±0.06 vs. obese 1.04±0.06 A.U., p = 0.90), however, the level for T2DM patients was significantly higher (1.33±0.08 A.U.)compared to both control groups (p = 0.01 for lean and p = 0.04 for obese) before the diet, whereas the level for T2DM patients was significantly lower to those of the controls (p = 0.002 for lean and p = 0.003 for obese) after the diet. The gene discussed is APOA4; the disease is type 2 diabetes mellitus.