The Islamic month of Ramadan is marked by fasting, when Muslims refrain from eating and drinking from dawn to sunset, which has an impact on their dietary habits. The study aimed to assess Nigerian Muslims’ dietary modifications during Ramadan and their related changes in body weight and health status. A web-based cross-sectional study was conducted among Nigerian adult Muslims. The survey assessed sociodemographic, dietary habits, eating behaviors, food choices, perceived weight changes, and health status. The logistic regression model was used to assess the predictors of weight change and perceived health status. There were 770 participants, 62.9% of whom were women, ranging in age from 18 to 60 years with a mean age of 27.7 ± 6.4 years. Fruits, palm dates, homemade foods, milk products, and vegetables were more frequently consumed. There were fewer energy drinks, pastries, salty snacks, and carbonated or sugared drinks consumed during Ramadan than before. Over half (54.6%, 95% CI: 51.0–58.9%) of the respondents lost weight during Ramadan, 37.0% (95% CI: 17.4–38.6%) maintained their weight and 8.4% (95% CI: 6.6–10.6%) gained weight during the month. Nearly all (97.3%, 95% CI: 95.8–98.3%) reported having good health during Ramadan, and 2.7% (95% CI: 1.7–4.1%) reported having a poorer health state during Ramadan. There was a significant weight loss and healthy dietary change associated with Ramadan fasting in Nigeria. Public health measures must be in place to impart such positive health behaviors so that such healthy habits continue throughout the year.