The metabolic effect of oncometabolic surgery (long limb Roux-en Y reconstruction) for early gastric cancer patients has been revealed in a few pilot studies. However, the nutritional safety has not been dealt with in previous literatures. This is a prospective pilot study for evaluating the nutritional safety and metabolic benefits of oncometabolic surgery for obese early gastric cancer patients.

We performed long limb uncut Roux-en Y gastrojejunostomy (uRYGJ) in 20 patients with clinical T1N0 stage and preoperative body mass index (BMI) ≥ 32.5 kg/m2 or ≥ 27.5 kg/m2 with co-morbidities between September 2015 and July 2016.

The primary endpoint was the incidence of micronutrients' deficiency (iron, folate, vitamin B12) at postoperative 1 year and secondary endpoints were anemia incidence, BMI change and remission rates of co-morbidities.

Inclusion Criteria:

• Lesion located on distal or mid stomach Lesion confined to submucosa (cT1b) : Early gastric cancer No evidence of metastatic enlarged lymph nodes Preoperative body mass index (BMI) ≥ 32.5 kg/m2 or ≥ 27.5 kg/m2 with co-morbidities

Exclusion Criteria:

• Being unable to understand the risks, benefits and compliance requirements of this trial Non- Korean speaker American society of anesthesiology (ASA) class IV or higher Other malignancy within 5 years.