What buddhist is saying about ketones is correct. I've personally experienced it and there's a ton of science on it.
For the vast majority of people, their brain runs on glucose, because they eat a lot of carbs/sugar every day. So yeah, most doctors would say the brain runs on glucose as its primary fuel. But we can only store about 100g of glucose (as glycogen) in the liver, so after about 24 hours, the brain would run out of glucose and die if another fuel were not available. Humans would be incapable of going more than a day without food.
If you fast for several days, or eat <30g carbs or so for several days, the brain switches to running on ketones instead of glucose, derived from body fat, and it results for most people in enhanced mental clarity, reduced appetite, and more energy. When people talk about feeling mildly euphoric from fasting, or having improved senses or focus, it's because their brain switched over to ketones. Ketones produce more energy per unit than glucose, and cause less oxidation/inflammation in the process. And interestingly, if the brain has access to both glucose and ketones at the same time, it uses the ketones preferably. So it's a more potent and more efficient brain fuel by every measure I've seen. Some animal studies show longevity increases on a ketogenic diet.
Ketogenic diets also outperform high-carb diets in terms of weight loss, improving cholesterol profile, reducing Alzheimer's risk, etc in humans in several peer-reviewed published studies. Cancer cells run on glucose even more than regular cells, so ketogenic diets can also potentially slow tumor growth, or even reverse it in some cases, especially when combined with conventional treatment. A ketogenic diet makes someone almost seizure-proof as well, so it's an option for people with frequent seizures if medicines don't work for them.
It's a big topic of research right now, since a lot of things are still unclear about it over longer periods of time, and the full benefits are still being explored. A person can remain in the state indefinitely if they eat enough calories but stay under 20-50g/day of carbs.
For the vast majority of people, their brain runs on glucose, because they eat a lot of carbs/sugar every day. So yeah, most doctors would say the brain runs on glucose as its primary fuel. But we can only store about 100g of glucose (as glycogen) in the liver, so after about 24 hours, the brain would run out of glucose and die if another fuel were not available. Humans would be incapable of going more than a day without food.
If you fast for several days, or eat <30g carbs or so for several days, the brain switches to running on ketones instead of glucose, derived from body fat, and it results for most people in enhanced mental clarity, reduced appetite, and more energy. When people talk about feeling mildly euphoric from fasting, or having improved senses or focus, it's because their brain switched over to ketones. Ketones produce more energy per unit than glucose, and cause less oxidation/inflammation in the process. And interestingly, if the brain has access to both glucose and ketones at the same time, it uses the ketones preferably. So it's a more potent and more efficient brain fuel by every measure I've seen. Some animal studies show longevity increases on a ketogenic diet.
Ketogenic diets also outperform high-carb diets in terms of weight loss, improving cholesterol profile, reducing Alzheimer's risk, etc in humans in several peer-reviewed published studies. Cancer cells run on glucose even more than regular cells, so ketogenic diets can also potentially slow tumor growth, or even reverse it in some cases, especially when combined with conventional treatment. A ketogenic diet makes someone almost seizure-proof as well, so it's an option for people with frequent seizures if medicines don't work for them.
It's a big topic of research right now, since a lot of things are still unclear about it over longer periods of time, and the full benefits are still being explored. A person can remain in the state indefinitely if they eat enough calories but stay under 20-50g/day of carbs.
