How far is your commute? If I do my 20 miler on just a cup of tea I find the ride fine but I get snoozy at about 10am, having a small bowl of cereal half an hour before leaving the house seems to solve that, but I don't notice any difference in the ride.
Not far, only about 7 miles each way. However I do tend to go at a steady 18mph on a fixed.

