Calories are provided by the nutrients carbohydrates, fats and proteins. Unlike these, water, vitamins and minerals don't give us calories but provide only the necessary nourishment.
After our body digests food, the nutrients get released and absorbed into the bloodstream after which are converted to glucose, or blood sugar. This blood sugar gives our body the energy needed to do things such as shiver, breathe,blink, remember, transport blood to various organs, run, and a lot more.
However if we don't use the energy provided by the three macro nutrients then it invariable gets converted to fats. So it holds true that excess carbohydrates are just as fattening as excess protein, and as excess fats, but all at slightly different levels.
|Nutrient / Food Item (1 gram)||Calorie provided per gram|
Fat provides the maximum calories, which is good when food is scarce, but otherwise for people trying to lose weight, or not gain it can be pretty bad. Vitamins, minerals and indigestible fiber have no calories.