Chrononutrition (i.e., circadian timing of food intake) offers promising opportunities to improve weight management strategies, but many fundamental aspects of chrononutrition are still unknown. While research to date has suggested that unhealthy chrononutrition behaviors are linked to weight gain, chrononutrition preferences are markedly understudied, and research has not yet determined whether chrononutrition preferences and behaviors are variable or stable over time in the natural environment. Potential mechanisms underlying chrononutrition’s impact on weight are still being explored. Recent evidence suggests that weight gain is the result of an imbalance of energy consumption and expenditure that is influenced by sleep duration. Though short sleep duration may undermine weight loss efforts, lead to increased preference for energy-dense foods, and even alter chrononutrition, chrononutrition’s role in energy balance has been less studied. The purpose of the present online study was therefore to examine chrononutrition, sleep duration, and body mass index (BMI) in the natural environment, over time, in a sample of healthy, non-shift working adults. Participants completed a series of measures online and self-reported their body weight and height three times, approximately every six months, for one year. This longitudinal study showed that chrononutrition preferences were largely stable over time, while chrononutrition behaviors were more variable over the study period. Results also showed that, contrary to our hypotheses, chrononutrition was not a significant predictor of later BMI, and chrononutrition did not mediate the relationship between sleep duration and later BMI. This study provided a novel examination of fundamental aspects of chrononutrition, knowledge of which may be vital for the development of obesity prevention and treatment strategies.