TRPM6 and Osteopenia: Given that osteopenia develops after bariatric surgery in animal models and humans together with lower serum Ghrelin levels, we hypothesized that the reduction in serum Ghrelin secretion post-surgery may impair tubular Ca2+ or Mg2+ absorption via TRPV5 or TRPM6/7 which subsequently leads to reduced Ca2+ and Mg2+ bone content and osteopenia.