Background Most studies on the dietary habits and overweight status of men aged 20–49 years have been cross‐sectional, with longitudinal studies being scarce. One‐quarter of Japanese men aged 20–49 years skip breakfast or have dinner within 2 h of bedtime (late dinner); therefore, the effects of these eating habits on men's increasing body weight need to be determined. Methods We conducted a retrospective cohort study using health check‐up data provided from several health insurance societies in Japan. Participants comprised 45 524 men employees aged 20–49 years who were followed up for 3 years. The primary outcome investigated was body mass index (BMI) ≥25 kg m−2. We conducted a multivariable logistic regression analysis and calculated the odds ratios for skipping breakfast and late dinner, as well as baseline age, body mass index, smoking status, eating speed, snack‐eating status, alcohol drinking frequency, physical activity, sleep habits, and the interaction between skipping breakfast and late dinner. Results Of the participants, 17 706 (38.8%) skipped breakfast and 25 987 (57.1%) had a late dinner. At the 3‐year follow‐up, 5093 (11.2%) had a BMI ≥25 kg m−2. The odds ratios of men skipping breakfast and having a late dinner were 1.18 (95% confidence interval = 1.04–1.33) and 0.92 (95% confidence interval = 0.84–1.01), respectively. The interaction between these factors was nonsignificant. Conclusions We suggest that skipping breakfast among men aged 20–49 years was one predictor of being overweight; however, having dinner within 2 h of bedtime was not a predictor.

Summary Context: International interest in the Japanese diet has grown in recent years. Objective: The aim of this systematic review was to evaluate and organize the Japanese diet and dietary characteristics from an epidemiological perspective, mainly focusing on the nutritional and dietary elements. Data Sources: PubMed, Web of Science, Japan Medical Abstracts Society, JDream III, and CiNii databases were searched. Study Selection: The eligibility criteria included research with an epidemiological study design that was either crosssectional, cohort, or case-control-based that defined the dietary patterns of the Japanese diet using dietary pattern analysis. A total of 39 research articles that described the Japanese diet were included. Data Extraction: The data that were extracted included the following: implementing country, location, study design, participant characteristics, key outcomes, methods used in the analysis of dietary patterns, and descriptions of the Japanese diet. Data Synthesis: As a result of the systematic review analyzing the descriptions of the Japanese diet from 39 selected articles, we were able to aggregate the descriptions into 16 categories from 33 factors. After performing a content analysis using a further aggregation of categories, we found that the top three applicable categories were soybeans/soybean-derived products, seafood, and vegetables; these were followed by rice and miso soup. Conclusion: The Japanese dietary content was found to be diverse based on an examination of epidemiological studies; however, we were able to aggregate the content into 16 categories. The Japanese diet is considered to be a dietary pattern that contains a combination of factors: the dietary staple, side dishes, and soup.

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