Front-of-package warning label (FOPWL) policies incentivize the food industry to reduce the content of regulated nutrients in products. We explored changes in the content of nutrients of concern (sugar, saturated fat, trans fat, and sodium) and the percentage of products in the Peruvian food supply that would carry a FOPWL before and after Peru's implementation of FOPWLs. Longitudinal data on the top-selling foods and beverages (n = 94) were collected at three time points: three months before the implementation of the policy, four months after, and two years after. Using the nutritional information declared on products' labels, we compared quantities of nutrients of concern and the percentage of foods that would carry a FOPWL at each time point. Between the first and the third data collection, a decrease in the median sugar content of beverages was observed (from 9.0 to 5.9 g/100 mL, p = 0.005), accompanied by an increase in the use of nonnutritive sweeteners. This change drove the reduction of the percentage of beverages that would carry a FOPWL (from 59 to 31%, p = 0.011). Among foods, decreases were observed in saturated fat (from 6.7 to 5.9 g/100 g, p = 0.002). The percentage of foods that would carry a FOPWL according to their nutritional profile declined from before to after implementation of the policy (from 82 to 62%, p < 0.001). The study shows that the industry reformulated products in Peru after implementation of its FOPWL policy.