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Folate
Folate acts as a cofactor in the synthesis of methionine, thymidine, and purine nucleotides. Folate
deficiency, which occurs as a result of not eating a sufficient and balanced diet, is associated with anorexia,
weight loss, and weakness in individuals [20,24,25] . After bariatric surgery, an average of 38% of patients
[12]
are reported to have folate deficiency and this deficiency progresses asymptomatically . In the study
[14]
conducted by Gudzune et al. , vitamin D, iron, vitamin B12, and folate levels were evaluated in the first
year after RYGB. The prevalence of folate deficiency was reported to be 13% in the first year following
the operation in patients who underwent RYGB. In this study, it was emphasized that preoperative and
postoperative micronutrient levels of patients were not evaluated and micronutrient deficiencies were
common in the evaluated parameters.

Folate deficiency can be treated with 1-5 mg/day oral folic acid supplementation [20,23,24] .

An increase in serum folic acid levels after bariatric surgery is indicative of excessive bacterial growth in
the small intestine. This is because some bacteria present in the intestinal flora are capable of synthesizing
[25]
folic acid . Excess bacterial proliferation in the small intestine is a disorder observed frequently after the
[26]
bariatric surgery that changes the intestine structure . Therefore, patients should also be evaluated for the
[24]
intestinal malabsorptive disease after bariatric surgery .
Vitamin B12
Vitamin B12 deficiency is quite common in older individuals, vegetarians, pregnant women, and people
[27]
with kidney or intestinal disease . After bariatric surgery, vitamin B12 deficiency was observed in 4%-62%
of patients and it was argued that the deficiency occurred mostly due to duodenal bypass [12,24,28] . A selective
[29]
literature review was performed by Weng et al. , who reported that preoperative vitamin B12 prevalence
was 2.3% and postoperative prevalence in the 12th month after the operation was 6.5%. In another study,
75 patients with a mean age of 49 were studied; weight loss and nutrient deficiencies were evaluated.
According to the results of this study, prevalence of vitamin B12 deficiency increased to 61.8% five years
[28]
after RYGB operation .
Malabsorption and insufficient food intake were reported as the main reasons for vitamin B12
deficiency in patients who underwent bariatric surgery. Additionally, postoperative food intolerance and
bacterial overgrowth in the small intestine were also suggested as causes of the deficiency. Reduction
of B12 absorption in the distal ileum as a result of the loss of intrinsic factor-secreting cells, gastric
acid suppression therapy with H -receptor blockers, and the use of proton-pump inhibitors are other
2
[29]
pathophysiological mechanisms leading to the development of vitamin B12 deficiency in patients .
Vitamin B12 depots of the liver and kidney may delay postoperative deficiency for up to three years.
[28]
Therefore, vitamin B12 deficiency can also be observed several years after the operation .
In a study conducted on patients who underwent sleeve gastrectomy (SG), it was reported that, contrary
to the literature, serum B12 levels increased significantly in the third postoperative month compared to
preoperative data. In this study, 85% of patients reported that they received B12 supplementation and the
[30]
increase in serum B12 levels was associated with this condition .

Effective treatment methods of vitamin B12 deficiency was reported as orally 500-2000 µg/day B12 support,
1000-3000 μg intramuscular B12 support every six months, 500 μg nasal B12 support once a week, or 500 μg
sublingual B12 support once a day [20,23,28] .

Vitamin C
The deficiency of vitamin C was reported to be common in the first year following the RYGB, occurring in
[13]
34.6% of patients . The studies conducted on the subject reported that the deficiency increased in the first
year and continued for 2 years following the surgery [31,32] .