Loose and frequent stools and PTH levels are positively correlated post–gastric bypass surgery due to less efficient intestinal calcium absorption

Abstract

BackgroundAfter Roux-en-Y gastric bypass, calcium and vitamin D deficiencies are frequently reported. In the presence of adequate vitamin D levels, calcium deficiency is caused by a lower efficacy of the intestinal calcium transport. ObjectiveTo investigate whether the use of a simple clinical score quantifying bowel habits (fecal score [FS]) correlates with the degree of secondary hyperparathyroidism that arises to compensate for calcium deficiency postsurgery. SettingLarge peripheral hospital. MethodsSeventy-five patients supplemented with calcium and vitamin D were prospectively studied before and 6 and 12 months after Roux-en-Y gastric bypass. FS, calcium (mmol/L), phosphate (mmol/L), magnesium (mmol/L), vitamin D (nmol/L), and parathyroid hormone (PTH; pmol/L) were measured in each patient. ResultsMean body mass index was 44.7±5.4 kg/m2 preoperatively and decreased to 34.3±5.0 kg/m2 at 6 months and 30.8±4.8 kg/m2 at 12 months, corresponding to a total weight loss of 23.2±5.9% and 30.9±8.3% respectively. There were no significant changes in serum calcium levels. Mean PTH levels rose from 3.5 pmol/L at baseline to 4.1 pmol/L at 6 months (P = .01) and to 4.9 pmol/L at 12 months (P<.001). Nine patients (12%) had increased PTH levels at 6 months, and 14 patients (19%) had increased PTH levels at 12 months. A significant positive correlation between FS and PTH at 12 months was found, which persisted after adjusting for vitamin D levels. ConclusionFS is positively correlated with secondary hyperparathyroidism using vitamin D–adjusted PTH levels as a biochemical marker. The present study in humans confirms the relation reported in animal studies. These results emphasize that managing stool habits are important after bariatric surgery.