BACKGROUND: Ramadan is a monthlong fast for healthy adolescents and adult Muslims. The quality of foods eaten and eating patterns in Ramadan may be different from other months of the year. Food intake of adolescents is a concern as energy and nutrient requirements are higher and needed to support the growth spurt of this stage. The objective of the present study was to describe the food patterns, dietary diversity and body weight changes among adolescents during Ramadan. METHODS: A prospective cohort study design with four measurement points (baseline, midline, endline and post endline) was conducted among 366 adolescents in Junior High Schools. Food pattern was assessed with a food frequency questionnaire, a 24-h dietary recall was used to assess dietary diversity and body weight was measured using an electronic scale. A repeated measures ANOVA was used to compare changes in dietary diversity scores (DDS) and weight of pupils. RESULTS: Half of the pupils (50.3%) were female and average age was 15.9 ± 1.8 years. Pupils fasted for an average of 28.3 ± 4.0 days and 14.3 ± 0.5 h a day (dawn to dusk) during Ramadan. The number and types of dishes taken at meal times differed substantially between Ramadan periods and outside Ramadan. Consumption of vitamin A-rich fruits, other fruits, and milk and milk products increased markedly during Ramadan. However, fasting came with a reduction in consumption of foods from roots and tubers, legumes and nuts, and dark green leafy vegetables while other food groups remained unchanged. Mean DDS increased significantly during Ramadan (F (2.933, 1070.573) = 7.152, p < 0.001) while mean daily meal frequency decreased (F (2.936, 1071.623) = 51.653, p < 0.001). There was significant body weight loss (-1.5 kg (95% CI: -1.1 kg to -1.6 kg)) among adolescents (F (2.656, 958.95) = 304.90, p < 0.001). Weight loss was short-lived; regained one month after Ramadan. CONCLUSION: In this prospective cohort study among schooling Ghanaian adolescents who fast during Ramadan, fasting was characterised by marked changes in usual food patterns, increased dietary diversity and significant body weight loss.