x
Glucose plays an important role…even in ketosis!
In a 1967 study by Owen et al., it was demonstrated that during prolonged starvation ketones could provide up to 70% of the brain’s energy requirement. But have you ever wondered why ketones can’t entirely replace glucose and why the brain still requires glucose even in a state of extreme ketosis?
When our cells make energy in the form of ATP via the krebs cycle, important molecules for proper brain function (e.g. neurotransmitters) are also made by “stealing” intermediates from the cycle and using them as building blocks - something called cataplerosis. This depletion of intermediates is countered by cataplerosis’ opposition, anaplerosis, and it is very important that these two processes are maintained in balance.
Glucose supplies the carbons that contribute to anaplerosis and replace these intermediates, whereas ketones do not! Ketones only contribute to cataplerosis, throwing this system out of balance.
If ketones were to provide 100% of the brain’s energy requirements we would have no way to replenish the kreb cycle intermediates. And while it’s not been confirmed, it is very likely that the brain’s requirement for glucose even in extreme ketosis is at least in part to sustain anaplerosis to avoid burning out the krebs cycle.
So next time you hear someone disparaging glucose, remind them that we need it to live! Your brain will thank you for it
