Energy in the body can come directly from glucose in the blood stream from meals or from the depletion of energy stores in the body. In Jake's case, the glucose his body uses during the journey to the evening class will likely be drawn from the breakdown of fatty acid molecules to liberate the energy currrency of the human physiology, ATP....the carbon chain may then be used to produce glucose for more energy equivalents.
Low self-esteem is how you feel about yourself, feelings of low self-esteem include: feeling bad about yourself more than you feel good. lack of self-respect, low confidence