What does it mean to ‘be in ketosis’? And when you are not in ketosis, what does your body do with dietary fat? Can fat only be burned for energy when in keto, or just more efficiently? Doesn’t our body go in and out of keto / fat burning naturally when food intake varies? Low carb vs keto?

Question

What does it mean to ‘be in ketosis’? And when you are not in ketosis, what does your body do with dietary fat? Can fat only be burned for energy when in keto, or just more efficiently? Doesn’t our body go in and out of keto / fat burning naturally when food intake varies? Low carb vs keto?

In: 17

Answer 1

Your body stores energy primarily in three forms: proteins, fats and glycogen (kind of like starch/carbs). Glycogen is preferentially utilised/used at higher rates and before fat which is preferentially utilised/used at higher rates than proteins. At any given moment, your body will break down some amount of all three and also produce some amount of all three. When we aren’t eating, this balance shifts towards breaking these down for energy than producing them.

Because we only store so much glycogen in our body, eventually that runs out. So the primary source of energy stores becomes fats. Fats can be broken down into free fatty acids or turned into ketones; when we have glycogen these ketones are low because our primary energy source is the glycogen or stuff that isn’t stored. Free fatty acids can’t enter the brain, but ketones can, and we want to keep some amount of glucose around because red blood cells can only use glucose. So to get around these limitations, our body goes into ketosis where fat is mobilised in the form of ketones to keep our brain alive. So ketosis is where ketone levels go up because we don’t have glycogen stores anymore.

When you’re not in ketosis, dietary fat is still being mobilised and used up, but mostly in the form of free fatty acids rather than ketones. Ketosis doesn’t burn fat more ‘efficiently’, rather its the primary source of energy that isn’t proteins. Our body will go in and out of ketosis but we generally have enough glycogen stores to last us longer than for ketosis to really happen, unless our carb intake becomes so low that we’re reliant on ketosis.

A keto diet is designed around achieving ketosis, whilst a low carb diet doesn’t necessarily meet ketosis. A keto diet is important in the control of some types of seizures. Low carb (and ‘keto’) diets kind of came into existence because of the supposed benefits of higher fat and lower carb diets.