Nutrient deficiency after bariatric surgery varies by procedure

Nutrient deficiencies that occur after bariatric surgery appear to differ by surgery type, showed a prospective, observational study from Singapore.

Participants were 688 consecutive patients who underwent either laparoscopic sleeve gastrectomy (LSG; n=499, mean age 41.5 years, 63.7 percent female), one-anastomosis gastric bypass (OAGB), or laparoscopic Roux-en-Y gastric bypass (RYGB; n=189, mean age 48.6 years, 59.3 percent female) at Singapore General Hospital. Patients were given standard dietary advice and prescribed multivitamins, elemental calcium (1,000–2,000 mg/day), and vitamin D₂ (50,000 IU once or twice/week), with doses tapered over follow-up. Thirteen biochemical parameters* at 12 time points were assessed for up to 5 years of follow-up.

Intact parathyroid hormone levels did not significantly differ between patients who underwent LSG and OAGB/RYGB (mean difference, 7.05 pg/mL; p=0.70). [JAMA Netw Open 2020;3:e205123]

While serum 25-hydroxyvitamin D levels were higher than baseline at all post-surgery assessments and significantly differed between the LSG and OAGB/RYGB groups at several follow-up points, overall, there was no significant between-group difference (mean difference, -0.72 ng/mL; p=0.09).

Calcium levels were higher among LSG than OAGB/RYGB recipients (mean difference, 0.12 mg/dL; p<0.001), but phosphate levels comparable between groups (mean difference, 0.006 mg/dL; p=0.83).

Iron concentration levels were also comparable between groups (mean difference, 1.50 μg/dL; p=0.31), as was total iron-binding capacity (mean difference, 4.36 μg/dL; p=0.37), and ferritin levels (mean difference, 3.0 ng/mL; p=0.71). However, LSG recipients had higher haemoglobin (Hb) levels than OAGB/RYGB recipients (mean difference, 0.63 g/dL; p<0.001).

“[W]e surmise that the comparatively lower Hb levels among [OAGB/RYGB recipients] could potentially be associated with their lower serum zinc concentrations or perhaps deficiencies in other micronutrients, such as copper and vitamins A and E, that were not collected in our study,” said the researchers.

They also noted a monotonic decrease in Hb levels in women but not men, while ferritin levels were consistently higher in women that underwent OAGB/RYGB vs LSG (mean difference, 31.1 ng/mL; p=0.002).

This suggests inadequate nutritional support for women who underwent bariatric procedures, said the researchers. The similar Hb levels despite higher ferritin levels in female recipients of OAGB/RYGB than LSG may also suggest “an unsuccessful attempt … to counteract the declining Hb levels by prescribing iron supplements more aggressively in women undergoing OAGB or RYGB,” they said.

OAGB/RYGB recipients had higher folate levels vs LSG recipients (mean difference, 2.376 ng/mL), and lower serum magnesium (mean difference, -0.25 mg/dL) and zinc levels (mean difference, -7.58 μg/dL; p<0.001 for all). Vitamin B₁₂ levels were numerically higher among OAGB/RYGB vs LSG recipients (mean difference, 39.85 pg/mL; p=0.06). Serum albumin levels (mean difference, 0.06 g/dL; p=0.09) and total weight loss (mean difference, 0 percent) did not differ between groups.

Deficiencies are procedure-dependent

“The findings of this study suggest that choice of bariatric procedure may be associated with differences in trajectories of micronutrient levels related to erythropoiesis and bone metabolism,” said the researchers.

The increase in vitamin D levels from baseline and stable parathyroid hormone levels may be attributed to high-dose vitamin D supplementation post-surgery, they said. Additionally, OAGB/RYGB recipients had a steeper decrease in Hb levels in the first 3 months post-surgery than LSG recipients. As such, the researchers advocated initiating anaemia prophylaxis earlier in patients undergoing OAGB/RYGB than those undergoing LSG, perhaps even prior to surgery.

The researchers noted that while the procedures were classified as restrictive (ie, LSG) or malabsorptive (ie, OAGB/RYGB) in this study, bariatric procedure-induced weight loss is often a combination of both mechanisms.

Given the fluctuating levels of micronutrients throughout follow-up, prior research that investigated post-bariatric surgery effects through single assessments should be interpreted cautiously. Avenues for future research include the effect of pre-surgery diets on micronutrient deficiencies and the use of biomarkers in examining the outcomes, they said.