Cholesterol ester transfer protein (CETP) plays a key role in remodeling triglyceride-rich particles and high-density lipoproteins (HDL). We investigated CETP sequence variants in response to long-term overfeeding (100 days) in 12 pairs of male monozygotic twins (mean age+/-S.D.: 21+/-2 years). Body fat mass (FM), abdominal subcutaneous (ASF) and visceral fat (AVF), and plasma lipoproteins were determined. The CETP variants C>T/In9 (rs289714) and G>A/Ex14 (rs5882, or I405V) were investigated by RFLP-PCR methodologies. Before overfeeding, the CETP CC/In9 (n=18) genotype was associated with lower FM compared to the C>T/In9 heterozygotes. Overfeeding induced more FM and ASF accretion in C>T/In9 carriers (P<or=0.05). CETP V405V homozygotes (n=8) had lower BMI, FM, and ASF before overfeeding than those with the I405I (n=6) or I405V (n=10) genotypes. However, V405V subjects had the largest gain in AVF with overfeeding (P=0.02). Decreases from baseline were significantly different across the I405V genotypes for HDL-C, HDL-Apo AI, HDL(2), and HDL(3) (P<or=0.05). Our data suggests that CETP sequence variation contributes to the undesirable changes in adiposity and HDL-C levels when exposed to excessive calorie consumption and may be potentially helpful to identify individuals with the metabolic syndrome who are at higher risk of cardiovascular disease.