Background: Little information from prospective clinical trials is available on the influences of surgical approaches on postoperative body compositions and nutritional status. We designed a prospective non-randomized trial to compare postoperative chronological changes in body composition and nutritional status between laparoscopic and open distal gastrectomy for stage I gastric cancer (GC). Methods: Body compositions and nutritional indicators in blood tests were measured at the baseline and at the 1st, 3rd, 6th, and 12th postoperative months (POM). The primary end point was the decrease relative to the baseline in the body muscle mass at POM 6. Results: Ninety-six patients for the laparoscopic group and 52 for the open group were eligible for data analysis. No significant differences were found in any baseline demographics, body compositions, and nutritional indicators between the groups. The changes of body muscle mass at POM 6 were similar in both groups. Overall, no significant differences between the groups were observed in any of the body composition and nutritional indicators during the first year after surgery. Conclusions: Postoperative body compositions and nutritional status were not affected by surgical approaches during the first 12 months after surgery in patients who underwent distal gastrectomy for stage I GC.