Chipmunk cheeks are often caused by the prominence of buccal fat pads, masses of fat located along the sides of your face extending from your mouth to the temple. On each side of your face is a single buccal fat pad, and it is the middle and lower portion that contributes to excessive fullness in the cheeks. The problem can occur in adulthood because your body may naturally store too much fat in this area, something that occurs with excessive weight gain and/or genetics. While losing weight may slim down your cheeks a bit, you’ll most likely find that even the strictest diet and exercise regimen is not enough to make a significant improvement.