The body always seeks out glucose (and its stored form, glycogen) for fuel. Limiting carbohydrates mean limiting the body’s favourite fuel and so it must adapt. The alternative solution is to burn stored fat instead. The metabolic shift from burning glucose to fat produces ketones. Ketones are important because while the body is burning fat for energy, the brain doesn’t have the ability to do this. Instead, the brain will fuel on ketones produced by the liver instead. Once the body fuels on fat and the brain fuels on ketones, you are in ketosis.