AimsTo assess the impact of ‘Oishi Kenko’, a nutrition management application (app), on glycaemic control in patients with diabetes.Materials and MethodsA propensity‐score‐matched retrospective cohort study was performed using data from the KAMOGAWA‐DM cohort study conducted between January and June 2022 in Japan. We analysed data from patients with type 1 and type 2 diabetes, comparing users who used the Oishi Kenko app (app group) with non‐users (control group) over 3 months.ResultsAmong the 50 participants who actively used it, 47 participants in both the app and control cohorts were selected from the KAMOGAWA‐DM cohort according to propensity‐score matching. Within the app group, the median glycated haemoglobin (HbA1c) level was 51 mmol/mol (6.9%) at baseline, which slightly decreased to 50 mmol/mol (6.8%) at the 3‐month mark (median change 0.0%). Conversely, in the control group, the baseline HbA1c level of 51 mmol/mol (6.9%) exhibited a marginal increase of 52 mmol/mol (7.0%) after 3 months (median change 0.20%). The median HbA1c level change between the groups was statistically significant, with the app group showing a significant positive change compared with the control group (p = 0.012).ConclusionThe Oishi Kenko app effectively improved glycaemic control in patients with diabetes; hence, it may be a promising tool for patient‐driven dietary management.