Sika deer (Cervus nippon) populations continue to survive at a relatively high density in heavily grazed habitats, where preferable plants have been decreased. To clarify the contradiction concerning the relation between food quality and carrying capacity, we compared the nutrition contents of original food and remaining available food, and experimentally tested the prediction that the low quality foods may increase carrying capacity through a reduction of food intake. High quality foods have been decreasing, and the remaining available foods were low quality foods with low crude protein. We quantified the amount of intake and digestibility of alfalfa as a high quality food and timothy as a low quality food, and measured the feeding activities. The dry matter intake and digestibility of timothy were lower than those of alfalfa. Additionally, the deer fed timothy ruminated a longer time than the deer fed alfalfa. Our results indicate that low quality food restricted the amount of intake. The low quality foods may increase carrying capacity through a reduction of the food intake, on the condition that the amount of the low quality food resource is similar to that of the high quality food resource.