BACKGROUND: Patients undergoing gastrectomy often experience postprandial hypoglycaemia, late dumping syndrome, and night-time hypoglycaemia. However, countermeasures for post-gastrectomy hypoglycaemia rely on the patients' own efforts. We sought to investigate how post-gastrectomy hypoglycaemia could be nutritionally improved in patients with gastric cancer. METHOD: Single-centre prospective, open-labelled, randomized crossover study including patients aged 20-80 years diagnosed with gastric adenocarcinoma, which have undergone total or distal gastrectomy 1-5 years before the study. The patients consumed 100 ml of a low-carbohydrate/high-monounsaturated fatty acid formula orally 30 min after meals and before sleep (400 kcal/day) during the first or second half of a 14-day glucose-monitoring period. The effects of the low-carbohydrate/high-monounsaturated fatty acid formula on the time below range, that is, the percentage of time during which the glucose concentration was <
70 mg/dl, and the coefficient of variation (CV) of the glucose concentration when the ideal time below range and CV were set at <
5% and ≤36% respectively were assessed. Dumping symptoms were investigated before and after the study. RESULTS: Thirty-eight patients were included in this study. In patients who had undergone total gastrectomy, the (median) daytime time below range, daytime CV, and night-time time below range remained high at 7.6% ((range) 0.0-45.0), 35.6% ((range) 9.5-50.5), and 10.8% ((range) 0.0-56.3) respectively, even after a long postoperative period. The (median) night-time time below range in patients who had undergone distal gastrectomy and total gastrectomy improved from 3.5% ((range) 0.0-47.9) to 1.4% ((range) 0.0-26.6) (P <
0.001, effect size 0.58) and 10.8% ((range) 0.0-56.3) to 9.4% ((range) 0.0-39.9) (P = 0.078, effect size 0.45) respectively. However, the daytime time below range and CV, as indicators of late dumping syndrome, did not change. CONCLUSION: The low-carbohydrate/high-monounsaturated fatty acid formula improved post-gastrectomy night-time hypoglycaemia, but not daytime glycaemic variability or hypoglycaemia. Thus, further investigation of nutritional optimization is required. CLINICAL TRIAL REGISTRATION: Japan Registry of Clinical Trials, jRCT https://jrct.niph.go.jp/, identifier jRCTs s051210200.