A dietary calorie, also known as a kilocalorie in scientific terms, is the amount of energy necessary to raise a kilogram (2.2 lbs) of water a degree Celsius (1.8 degrees Fahrenheit). This measure is arbitrary in that it describes combustion of food and not nutrition. As an example, calories from eating an avocado are equivalent to calories from lard. While the caloric value could be made equivalent, it is clear that the nutritional value and digestibility are substantially different. I realize the effect this has on those of you who count calories, and consider only energy combustion in diet.
It is important to note that utilizability of food is equally if not more important to diet. If you eat a food that cannot be digested or used effectively by the body, it becomes stored as fat. When we select food to eat, we need to consider more than calories. We need to consider nutrition.
The time of the day or night is another important factor to consider when selecting food or abstaining. The biological clock starts up upon awakening, and our digestive tract is ready to consume food shortly thereafter. Approximately 9 hours later, it begins to shut down. Essentially, about 5pm or so, the body shuts down complex digestive processes and begins to store food as fat. This means that complex digestion is better performed at breakfast and lunch, with dinners including complex fats and proteins generally acting as a weight gaining act that contributes little to true nutrition.
Certain fats and oils degrade dramatically with the addition of heat, to the point of altering them significantly. Sometimes these fats and oils are ingredients in food, or come prepared in food already assembled to be heated or reheated. Sometimes they are a means to cooking by frying. Often, they are a part of the basic food itself. In all cases, increasing the temperature has an effect on chemical bonds, often rendering the fats and oils into an unhealthy, indigestible, or even toxic state. Microwaving is even more dramatic than simple heat, as it shakes the molecules intensely, thus biochemically altering them.
Essentially, counting empty calories such as white flour, refined sugar, and bad oils and fats as nutrition of any sort is absurd. I was taught years ago in Chiropractic school that all food is composed of nutrients, toxins, or a combination of both. The human body can utilize nutrients, but must dispose of toxins or store them. We really need a new evaluation unit to determine if the food you eat is utilizable as a cellular building block. While we currently lack an empirical unit to determine this, it is necessary to use logic and reasoning to understand how to be healthy regarding food selection.