Each cell, tissue, muscle, all have different power or energy values.
power to produce relative energy for hosts body to pull, push or do any work. though one can definitely manage more work than capacity by adding required energy value providing diet to stay fit. sometimes it is advised to workout on demanding existing cells or tissues to achieve more energy* to perform greater work as desired.
all these energy* values are written at back of eatables box. perhaps one can manage to measure his diet with some analytical practice as per their taste and preferences.
being fat/unfit we always lack full workable energy to perform daily work. lack of energy leads our preferences to ignore the damage to avoid some or other work on priority basis. in most of american states people are suffering with hypertension due to being over-weight/unfit.
you must be thinking how to deal with all those numbers.
an expert dietitian can help you go along with those numbers initially, if followed carefully one can learn and slowly master his own dietary self.
then it is a cakewalk to achieve daily and long term fitness objectives.