Increased body weight is a known risk factor for diabetes. In a new study, researchers evaluated five-year nutritional deficiencies in adolescents after metabolic bariatric surgery. Young patients who underwent either Roux-en-Y gastric bypass (RYGB, n = 161) or vertical sleeve gastrectomy (VSG, n = 65) from five tertiary-care centers between March 2007 and February 2012 were included in the study. Patients were evaluated for serum levels of ferritin; red blood cell folate; vitamins A, D, B1, B12; and parathyroid hormone at baseline and every year for five years. The researchers employed general linear mixed models to analyze changes over the study period and pinpoint predictors of nutritional deficiencies. The mean age of the 226 total patients included in the analysis (75% were female, and 72% were white) was 16.5 years; mean body mass index (BMI) at time of surgery was 52.7 kg/m2 and did not largely differ between the two surgery groups. BMI decreased 23% after five years. After RYGB, there was a significant decrease in serum concentrations of vitamin B12, while serum levels of transferrin and parathyroid hormone increased; neither of these observances occurred in the VSG group. Both groups presented decreased postoperative ferritin levels. Prior to RYGB, 2.5% of patients had hypo-ferritinemia, compared to 71% five years postoperatively; in the VSG group, pre- and five-year postoperative rates were 11% and 45%, respectively. Five-year changes in serum levels of folate or vitamins A, B1, and D were not significant. After five years, more RYGB patients than VSG patients had at least two nutritional deficiencies (59% vs. 27%). The following risk factors were correlated with specific deficiencies: surgery type, female sex, black race, supplementation intake, weight regain, and pregnancy.