Unfortunately, nutrition is complex, and it requires understanding physiology which is a tough subject. There is so much misinformation out there, without at least a primitive understanding of physiology it is tough to discern good information from bad information.
A calorie is a unit, based on the measurement of energy provided by food. While we all need a certain number of calories per day, it is certain that all calories were not created equal.
In studying neurobiology, we learn that our behavior and perception stem from neurotransmitters, hormones, receptors, and synapses that constantly create senses and perceptions from information in our environment.