Laparoscopic Roux-en Y gastric bypass (RYGB) and sleeve gastrectomy (SG) are common and effective methods to treat severe obesity, but these procedures can adversely influence bone metabolism and areal bone mineral density (aBMD). This was a prospective 24 month single-center interventional two-arm study in 220 women and similarly aged men (median 40.7 years) with a body mass index (BMI) >38 kg/m(2) after RYGB and SG procedures. Patients were randomized into: (i) an intervention group receiving: 28,000 IU cholecalciferol/week for eight weeks prior to bariatric surgery, 16,000 IU/week and 1,000 mg calciummonocitrate/day after surgery, daily BMI adjusted protein supplementation and physical exercise (Nordic walking, strength perseverance and equipment training). (ii) A non-intervention group: no pre-operative loading, nutritional supplementation or obligatory physical exercise. At study endpoint, when comparing the intervention group to the non-intervention group, the relative percentage changes of serum levels of sclerostin (12.1% vs. 63.8%), Cross-linked C-telopeptide (CTX, 82.6% vs. 158.3%), 25-OH vitamin D (13.4% vs. 18.2%), phosphate (23.7% vs. 32%, p < 0.001 for all), procollagen type 1 amino-terminal propeptide (P1NP, 12% vs. 41.2%), intact parathyroid hormone (iPTH, -17.3% vs. -7.6%) and Dickkopf-1 (-3.9% vs. -8.9%, p < 0.05 for all) differed. The decline in lumbar spine, total hip and total body aBMD, changes in BMI, lean body mass (LBM) as well as changes in Trabecular Bone Score (TBS) values (p< 0.005 for all) were less, but significantly, pronounced in the intervention group. We conclude that vitamin D loading and ongoing vitamin D, calcium and BMI adjusted protein supplementation in combination with physical exercise decelerates the loss of aBMD and LBM after bariatric surgery. Moreover, the well-known increases of bone turnover markers are less pronounced. This article is protected by copyright. All rights reserved.