Two primary sources of energy for the body is fat and carbohydrates. The debate on whether low carbohydrates diets are superior to low fat diets are anecdotal. The data shows a reduction in calories from either source yields the same weight loss. In some models, a low fat diet lost a bit more weight the longer the diet was enforced. There’s the thermal affect of macronutrients and their contribution to weight gain.  Protein and carbohydrates contain 4 calories per-gram whereas fat contains 9 calories per-gram. Foods high in fat will naturally contain more calories than foods higher in protein and carbohydrates. The family of carbohydrates includes both simple and complex sugars. Glucose and fructose are simple sugars whereas starch, glycogen and cellulose are examples of complex sugars. 

The problem most people experience is high fats and high carbohydrates in combination can lead to more fat gain then adjusting or compensating for each source of energy. To further expand on this topic, a lot of processed foods contain high fat and carbohydrates, which leads to a calorie surplus. For example, foods like French fries are a starch fried in fat, and when you add more fat from cheese and meat in loaded fries, then you have a metabolic disaster. Of course, it tastes amazing because we’re naturally attracted to those types of foods. Fat metabolism is the oxidation of fatty acids to generate energy or form new fats from smaller molecules. Fat and carbohydrate metabolism are associated for products of glucose and can be converted into fat.