Energy for Your Life - Sources

Carbohydrates are NOT Essential

Fats are essential for energy and good health. Most of your organs prefer fatty-acids or ketones rather than glucose.

Carbohydrates are essential for energy and your brain is glucose dependent.

The human body is so adaptable that both those ideas are valid in different circumstances.

The human body has a HYBRID Metabolism, but there is a switch between the two metabolic systems.
Your body can't both run at once. The level of insulin in the blood is the switch.