Ketosis is the metabolic state when blood ketone levels reach a certain level (around 0.5 mmol/L). People will typically enter ketosis when they restrict carbohydrates (e.q. by following the Ketogenic diet) or eat little to no calories (e.g. fasting for multiple days).
In general, the body will not enter ketosis as long as there are enough carbs available from the diet or stored glycogen (the storage form of sugar) to provide the cells with energy. As long as sugar is available ( and you don’t consume exogenous ketones or medium chain triglycerides), your body will do just fine using glucose as its primary fuel source. In fact, many people will go throughout life without ever entering ketosis while maintaining optimal health.
If it is true that ketosis isn’t necessary for optimal health, then this raises a couple of questions. What’s the purpose of ketosis? and wouldn’t we do just fine by burning fat and sugar for fuel?
To get a better idea of why we have the ability to burn ketones for fuel, let’s approach these questions.
From a health perspective, ketones have been found to have many unique properties that sugar can not emulate. For starters, ketones burn much more efficiently than sugar, providing us with a more efficient source of energy while forming less reactive oxygen species. Ketones also increase mitochondrial efficiency and production, which improves the ability of ketones burning cells to produce energy and resist aging.
Studies have also found ketones to be neuroprotective antioxidant that can help reverse and prevent brain damage while triggering the proliferation of new brain cells and new connections between existing brain cells. As a result of burning ketones, the brain also experiences a shift in the balance between two neurotransmitters called GABA and Glutamate. In others words, ketones help prevent excessive neuronal activity that can cause uncontrollable behaviours that are common in neurological disorders like epilepsy, autism, and parkinson’s disease.
When we consider the evidence altogether, it is obvious as to why the body prefer to burn ketones for fuel. However, this is not the legitimate reason why we evolved the ability to get into ketosis.