Abstract Background Laparoscopic sleeve gastrectomy (LSG) is increasingly popular due to its efficiency in reducing excess weight, however little is known about the nutritional status in patients after surgery. Purpose To investigate how LSG affects energy intake, nutritional status and body weight one year after surgery. Methods A total of 150 patients (116 women) were enrolled in the study. Data on body weight, waist circumference and blood samples were registered preoperatively and after surgery. Food intake was reported 3 and 12 months postoperatively. Results The preoperative median BMI was 44.3 (inter quartile range 41.4-47.1), and was significantly reduced to 35.4 (32.6-38.6) after 3 months and further reduced to 30.5 (27.4-33.8) 12 months after surgery (p < 0.05). The median post surgery daily energy intake was significantly increased from 2971 (1982–3687) kJ after three months to 3840 (3046–4625) kJ twelve months postoperatively. One year after surgery, serum levels of folate, cobalamin, PTH and HDL cholesterol were significantly increased, whereas calcium, albumin, haemoglobin, creatinine, uric acid, CRP, glucose, insulin, insulin c-peptide, HOMA-IR, HbA1c and triacylglycerol were significantly decreased. Serum levels of vitamins E and D were unchanged after one year. The prevalence of patients with medically regulated type 2 diabetes was significantly reduced one year post surgery however no changes were seen in the prevalence of patients taking lipid lowering drugs or thyroxin. Conclusion Based on the data obtained 12 months after surgery, LSG appears to be an effective treatment of morbid obesity without worsening the nutritional status despite the very low energy intake.