Humans, willingly or unwillingly, affect the lives of urban cats. Waste production is only one of the human effects on the urban cat ecosystem. The human-generated food waste provides a large portion of urban cat's food, and economic fluctuations change the quality, and content of waste bins. In this descriptive-estimation study with field monitoring, we tried to measure the weight of cats to find out how much the change in the volume of municipal food waste affects their physical condition? The results of a study conducted in Tehran from spring 2016 to winter 2020 showed that the average volume of food waste collected in this city had decreased by 26.9%. The reduction of food waste volume affected the weight of cats and caused an average of 18.71% reduction in the average weight of cats during the study. The weight loss rate intensified from autumn 2017 – to winter 2018 onwards. Male cats lost 18.68%, and female cats 18.40% of their weight from early spring 2016 to late winter 2020.