Cells have the capacity to use two main types of energy. The reasons posture muscles are red is that they store oxygen. Posture muscles eat oxygen. They are not powerful, but they are capable of holding you up the entire day without getting tired. Practicing mellow trains your oxygen system. Part of the oxygen system can only be trained with mellow.
During mellow you are relaxed and awake. The heart rate does not increase, and might even decrease, yet your body is still eating oxygen. This means that the oxygen system is strained. When the oxygen system is strained, at reacts by strengthening the oxygen system, which might include making more red blood cells, increasing the capacity of the lungs (which is known to happen when living at higher altitudes), etc.
What makes things confusing is that the sugar system is intertwined with the oxygen system, and both sugar and oxygen are transported in the blood. As you move from mellow to tedious, the entire system morphs so as to deliver proportionally more sugar. As you move from low to high intensity exercise, the entire system also morphs to deliver proportionally more sugar. A marathon runner has a much different physiology than a weight-lifter. A person who is chronically tedious has a much different physiology than a person who is chronically mellow. Health is some combination of low and high intensity, as is success in actual life. The purpose of getting your schedule right is so you can be both successful and healthy.
Carbs and Mellow
This information is presented in a certain order so as to simplify the number of elements you have to play with. The sugar system proportionally feeds higher intensity, and the oxygen system feeds the lower intensity activities and states of mind. It is easy to imagine that if you were to play a very intense soccer or basketball game, your muscles would have had eaten lots of sugar, depleting your reserves, and would be hungry for carbs afterwards. It is also easy to imagine that if you did a long, slow bike ride, your muscles would have eaten lots of oxygen, much fewer carbs, and you might not even be that hungry. In both cases, the cells are eating certain fuel, and due to a deficit, suck that fuel in from the blood, which gets it from the air or liver or intestines. So if you imagine the tow truck again, it moves forward in a certain gear, and due to a gradient, brings the appropriate fuel forward which is represented by the car being towed. Even if you don’t fully understand this yet, it will gradually become clear.
But what happens if your activity stays the same and you don’t eat anything? Fasting is not some new technique someone invented. It happens every night already, or does it? It sort of depends on how fasting is defined.
But suppose you have an easy day and have a mellow personality and don’t eat anything. Your cells do not stop eating. At some point, however, some of the nutrition in the blood gets depleted, and digestion will actually be stimulated for good reason. The key concept has to do with the gradient. Because the cells continue to eat from the blood, the blood becomes depleted, and now the blood wants to suck nutrition in from the intestines or liver. In other words, the nutrition delivery system is stimulated by not eating assuming the cell activity stays the same. So both exercise and fasting stimulate the nutrition delivery system.