Serum magnesium status after gastric bypass surgery in obesity

Roux-en-Y gastric bypass (RYGBP) has become a common surgical procedure to treat morbid obesity. Furthermore, it strongly reduces the incidence of type 2 diabetes and mortality. However, there is scant information on how magnesium status is affected by RYGBP surgery. Previous bariatric surgery methods, like jejunoileal bypass, are associated with hypomagnesemia.

Twenty-one non-diabetic morbidly obese patients who underwent RYGBP were evaluated before and 1 year after surgery and compared to a matched morbidly obese control group regarding serum magnesium. Groups were matched regarding weight, BMI, abdominal sagittal diameter and fasting glucose, blood pressure, and serum magnesium concentrations before surgery in the RYGBP group.

The serum magnesium concentrations increased by 6% from 0.80 to 0.85 mmol/l (p = 0.019) in the RYGBP group while a decrease by 4% (p = 0.132) was observed in the control group. The increase in magnesium concentration at the 1-year follow-up in the RYGBP group was accompanied by a decreased abdominal sagittal diameter (r (2) = 0.32, p = 0.009), a lowered BMI (r (2) = 0.28, p = 0.0214), a lowered glucose concentration (r (2) = 0.28, p = 0.027) but not by a lowered insulin concentration (p = 0.242), a lowered systolic (p = 0.789) or a lowered diastolic (p = 0.785) blood pressure.

RYGBP surgery in morbidly obese subjects is characterized by reduced visceral adiposity, lowered plasma glucose, and increased circulating magnesium concentrations. The inverse association between lowered central obesity, lowered plasma glucose and increased magnesium concentrations, needs further detailed studies to identify underlying mechanisms.