LAS VEGAS — Calcium absorption decreases about a third after Roux-en-Y gastric bypass surgery, placing patients in jeopardy of clinically significant bone loss, Claudia Riedt said at the annual meeting of the North American Association for the Study of Obesity.
A prospective study of 19 severely obese women found that average total calcium absorption was 137 mg/day in 17 patients who were examined 6 months after surgery. “This is about 40% below the estimated total amount of calcium required per day to maintain health and balance,” said Ms. Riedt, a doctoral candidate in nutritional sciences at Rutgers University, New Brunswick, N.J.
The investigators undertook the study because osteopenia had been seen in patients after Roux-en-Y gastric bypass. Although the procedure is believed to result in less malabsorption than other bypass procedures, Ms. Riedt and her colleagues theorized that inadequate calcium absorption was a factor along with decreased food intake and weight loss.
The women recruited for the study had a mean age of 45 years. They entered with an average body mass index (BMI) of 54 kg/m2, an average weight of 143 kg, and an average energy intake of 2,466 kcal/day. They consumed a mean of 1,123 mg calcium/day, of which they absorbed 36.6%: a total of 425 mg calcium/day.
By 6 months, the women had lost 104 kg on average and had a mean BMI of 39 kg/m2. Their energy intake had decreased to 840 kcal/day, and their calcium intake had dropped to 829 mg/day, Ms. Riedt said. Not only were they consuming less calcium, but the true fraction of calcium absorption had decreased by nearly 34%, becoming only 24.5% of their calcium intake.
The researchers also observed changes in bone turnover markers that are typical with weight loss and suggest that calcium was being mobilized from bone. Estradiol and parathyroid hormone levels were reported to correlate with the rate of calcium absorption. Vitamin D levels were relatively low and did not change during the study or predict calcium absorption.
Two women in the study followed recommendations that patients consume at least 1 g of calcium in daily supplements after the procedure. They increased their total intake by about 1200 mg, to 2400 mg and 2600 mg, respectively. As a result, the average amount of calcium absorbed by all 19 women reached 223 mg/day—closer to but still under the nutritional goal of 240 mg/day, Ms. Riedt said.
“Nutritional interventions must compensate for drastically reduced calcium absorption,” she said at the meeting, cosponsored by the American Diabetes Association. She recommended 1,500 mg/day above dietary intake but acknowledged that compliance can be a problem, especially in the first few months after the procedure. “All the women were always encouraged to take extra calcium. Whether they did was another matter,” she said in an interview.