To determine if a product contains added sugar, you can look for ingredients such as sugar, cane sugar, high fructose corn syrup, corn syrup, or any other form of added sweeteners on the nutrition label. Additionally, you can compare the total sugar content listed on the nutrition label with the sugar content from natural sources, such as fruits, to see if there is a significant difference. If the listed sugar content is much higher than what you would expect from the natural ingredients, it is likely that added sugar has been used.