A Comparison of Body Fat Distribution in HIV-1 Infected Patients Receiving, Since the Beginning and for at Least Two Years, an Antiretroviral Therapy Based on Efavirenz or Lopinavir/Ritonavir Combined With Tenofovir + Emtricitabine or Lamivudine

Inclusion Criteria * Men and women aged ≥ 18 years with HIV-1 infection who are clinically stable and who were invited to participate in the study at a routine follow-up visit. * HIV-1 infected patients receiving since the beginning and continuously, for at least two years, initial antiretroviral therapy (ART) based on efavirenz (EFV) and a combination of tenofovir (TDF) + emtricitabine (FTC) \[or lamivudine (3TC)\] or HIV-1 infected patients receiving since the beginning and continuously, for at least two years, initial ART based on lopinavir/ritonavir (LPV/r) and a combination of TDF +FTC (or 3TC). * Patients with an undetectable viral load, in response to the detection limit of each participating hospital defined in the last 6 months. * Patients who have given written informed consent to participate in this study \[personal data collection and performance of dual energy X-ray absorptiometry (DEXA)\]. Exclusion Criteria * Patients who have received at some point both efavirenz (EFV) and lopinavir/ritonavir (LPV/r) in combination regimen or thereafter. * Patients who have had structured treatment interruptions (therapeutic holidays). * Patients with a body mass index \<16 kg/m\^2. * Patients with metallic prostheses or prosthetic material that could interfere with the measurement of dual energy X-ray absorptiometry (DEXA). * Patients with a history of plastic or repair surgery in the buttocks and breasts. * Patients with a diagnostic test with barium or radionucleotides, performed during the last month. * Pregnant women. * Patients treated with other agents under investigational phase. * Patients on current treatment with systemic corticosteroids or chemotherapy. * Diabetes mellitus and hypoglycaemic treatment. * Transsexualism (though implicit in prostheses and drugs). * Any drug taken chronically, which may alter the distribution of fat or adipocyte biology (insulin, non-steroidal anti-inflammatory drugs, etc). * Patient has undergone liposuction.