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Differences in the type of bariatric surgery (or in the patients receiving it) meant different outcomes in metabolic profiles down the line, according to a study from Singapore.

In a comparison of Roux-en-Y gastric bypass and one-anastomosis gastric bypass procedures versus laparoscopic sleeve gastrectomy, gastric bypass patients saw significantly higher folate levels, yet lower serum magnesium and zinc levels 5 years after surgery, reported Nicholas Syn, of Singapore General Hospital, and colleagues in :

• Higher folate levels: mean difference 2.376 ng/mL (95% CI 1.716-3.036)
• Lower serum magnesium levels: -0.25 mg/dL (95% CI -0.35 to -0.16)
• Lower zinc levels: -7.58 μg/dL (95% CI -9.92 to -5.24)

Interestingly, hemoglobin levels were significantly higher -- on average a mean 0.63 g/dL (95% CI 0.41-0.85) higher -- after sleeve gastrectomy compared with gastric bypass surgeries. However, there weren't any significant differences between iron concentrations, total iron-binding capacity, or ferritin levels between the surgery types.

There also weren't any significant differences in intact parathyroid hormone levels, serum 25-hydroxyvitamin D levels, or phosphate levels between gastric bypass and sleeve gastrectomy procedures. After 5 years, sleeve gastrectomy patients did have significantly higher correct calcium levels versus gastric bypass patients (mean difference 0.12 mg/dL, 95% CI 0.07-0.16). And although gastric bypass patients saw "numerically" higher vitamin B12 levels, this difference wasn't significantly different than sleeve patients.

The prospective, longitudinal study looked at 499 adult patients who underwent laparoscopic sleeve gastrectomy and 189 who underwent Roux-en-Y gastric bypass or one-anastomosis gastric bypass at a single center in Singapore. The majority of patients in both groups were women.

Due to the differing nature of the procedure types, each are thought to have different nutritional deficiencies down the line. Specifically, "restrictive procedures" such as sleeve gastrectomy that achieves weight loss mainly through restricting the food accommodation capacity, are expected to be associated with "milder micronutrient deficiencies" due to reduced food intake.

On the other hand, "malabsorptive procedures" like gastric bypass that involves a malabsorptive component to the surgery, are expected to have more significant nutritional deficiencies associated with them since they "entail bypassing alimentary tract segments involved in the absorption of specific dietary nutrients," the researchers explained.

After surgery, all patients were prescribed nutrient supplements of elemental calcium (1,000-2,000 mg per day) and vitamin D2 (50,000 IU one to two times per week). The researchers pointed out that ergocalciferol (vitamin D2) was given instead of cholecalciferol (vitamin D3) because it was what was readily available at their institution. "The high dose vitamin D replacement regimen used at our institution is based on several endocrine society guidelines that have advocated aggressive vitamin D supplementation following a bariatric procedure," they said.

This was in addition to a daily multivitamin that contained vitamin A (3,000 IU), thiamine (10 mg), folic acid (10,00 μg), copper (100 μg), and iron (ferrous fumarate 30 mg). Additional iron, vitamin B12, and folic acid were only prescribed at the discretion of the healthcare provider.

All patients underwent fasting laboratory testing of the 13 biochemical parameters at 12 timepoints during the 5 years following surgery 1, 3, 6, 9, 12, 18, 24, 30, 36, 48, and 60 months postoperative.

Vitamin D concentrations were higher at all postoperative timepoints across all surgeries when compared with baseline levels. Because vitamin D2 and elemental calcium supplements "were stipulated as part of our postbariatric treatment protocol," Syn's group noted they were not surprised to see higher levels at all timepoints compared with baseline, as well as no real differences between the surgery types.

"Interestingly, intact parathyroid hormone levels were fairly stable in our study and stand in contrast with , who reported progressively increasing parathyroid hormone levels over time," the researchers pointed out. They explained that the "important difference" here could be "the aggressive vitamin D replacement regimen" they used at their center rather than the 800 IU of vitamin D used in the previous study.

The group also noted that gastric bypass patients saw a steeper decline in hemoglobin during the initial 3 months after surgery versus sleeve patients, which then remained lower throughout follow-up. As a result, "prophylactic efforts against anemia should commence earlier" for gastric bypass patients, even prior to the procedure, they advised.

Syn's group suggested future research look at how "prebariatric procedure energy restricted diets could entrench micronutrient deficiencies, scrutinizing whether race/ethnicity and cultural factors influence micronutrition, and more detailed longitudinal phenotyping of patients using biomarkers, such as bone mineral density and osteoclast activity."

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