T, a 35 year old male, presents to your out-patient clinic for a consultation. He states that he has been experiencing constipation for the last three days. He has type I diabetes (well-controlled) and uses insulin therapy. He also takes vitamin D 1000 lU daily for bone health. He tries to drink up to 8 glasses of water a day to mitigate his constipation. However, he does have a sedentary lifestyle and works a desk job where he sits all day. Which of the following may be a contributing factor to T's constipation?