**4.7 Nutritional deficiencies**

Although LSG is viewed as a restrictive procedure, some degree of malabsorption is also expected. After recovering from surgery, patients are at risk of macronutrient deficiencies in the long term due to reduced dietary intake, decreased gastric secretion of hydrochloric acid and intrinsic factor, and poor food choices. The most common micronutrient deficiencies are of vitamins B12 and D, iron, and calcium [85]. Other micronutrient deficiencies that can lead to severe complications include thiamine, folate, and fat-soluble vitamins [85]. Daily micronutrient supplements are necessary, including multivitamin concentrate (with iron, copper, and zinc), calcium citrate with vitamin D, vitamin B12, and elemental iron [82]. However, multivitamins or nutritional supplements are typically not initiated in the immediate postoperative period [82]. It is necessary to clinically monitor the bariatric patient during the first five years. Some evidence suggests that patients experienced fewer nutrient deficiencies after LSG than after RYGB [86].
