This is why all carbs/calories are not created equal.

Now, look at another hypothetical diet, consisting again of 30% protein but 70% fat with no carbohydrates. The proteins are used in the same way as the first diet, so even without consuming any carbohydrates, as much as 58% of the protein consumed is converted to glucose. This will not be enough to satisfy the energy needs of the body, so in the absence of carbohydrates, the body begins to burn the fat it consumes. This causes the body to "convert" to a fat-burning engine instead of primarily being a glucose-burning engine.

Fats, unlike carbohydrates, have a high satiety factor. Whereas carbohydrates make you hungry a couple of hours after eating, fats make you full, and the satiety lasts for hours. Therefore, you tend to consume fewer calories on a high-fat diet than on a high-carbohydrate diet. Also, remember, without carbs, your body does not produce much insulin. Therefore, the fat you eat cannot be stored. Thus a high-fat diet, in the absence of carbohydrates, typically results in weight loss. Yet your blood glucose does not drop too low, because your liver continues to convert some of the dietary protein into glucose. Any excess dietary fat is not stored but broken down by a process known as lipolysis (the opposite of dehydration synthesis) and excreted.

The products of fat metabolism are fatty acids and glycerin. The glycerin is used as a fuel source or can be eliminated in the urine and the fatty acids are broken down further into ketone bodies, which become the primary fuel of the body in the absence of glucose. Any excess ketones are not stored but are excreted in the urine. The production of ketones during fat metabolism is called ketosis.

The upshot of these different metabolic processes is that a calorie of carbohydrates will tend to make you fatter than a calorie of fat that is eaten in the absence of carbohydrates. That is because excess carbohydrates turn to fat, which is stored, but excess fat is broken down and excreted.