Ketones, the body's energy alternative to glucose, are produced by the liver in response to a scarcity of carbohydrates. As you already know, they're the special molecules that give ketosis its name. They're measurable in larger quantities in the bloodstream when fasting, going many hours without food during sleep, and, of course, when going low carb.
But they don't just serve as a replacement for glucose when powering muscles and doing physical work. Ketones play a huge role in fueling the low-carb body's most important organ and control center -- the brain.
Does the brain need carbohydrates?
The brain is the body's most energy-consuming organ. Despite comprising only, on average, about 2% of body weight, the brain needs to use up to a quarter of the energy the body consumes on a daily basis.
When living the sugar and carb heavy lifestyle lived by most inhabitants of the developed world, our brains rely on a near-constant supply of glucose from carbs to perform their all-important functions. But just because we're used to burning carbs doesn't mean we have to.
It may come as a surprise that the majority of the human brain (up to 75%) is able to use ketones for energy. Despite popular belief, this means that when we stop chowing down on carbs, our brains will continue to function, perhaps even better than before.
So does the brain need carbs? No. The brain does need glucose, but keto has you covered.
What happens to the brain in ketosis?
When starting keto, the normal amount of glucose coming in to power the brain gets abruptly and drastically reduced. This sudden change can be an uncomfortable one. Eventually, as the body gets more into ketosis, glucose will be replaced by ketones, on which the brain can run efficiently.
During the initial transition/adjustment period, however, the liver can't produce ketones fast enough to keep up with the brain's energy needs. The body hasn't "learned" yet how to effectively run on its own fat stores or create fuel from non-carbohydrate sources.
The sudden deficit of carbs can result in dizziness, difficulty sleeping, headache, or brain fog. Your brain misses carbs when they go away, and it'll let you know.
But, like the other keto flu side effects, it doesn't last long. Staying hydrated, getting more electrolytes, and getting plenty of calories from health fats during the transition period can make all the difference.
After ketosis is achieved, ketones provide most of the brain's energetic needs. There still remains roughly 20 - 25% of the brain that does indeed require glucose and can accept no alternatives. That necessary glucose can be provided in part by the very small allotment of daily carbs allowed on keto, or it can come from gluconeogenesis, the process by which the liver makes glucose from the body's stored fat. Even though parts of the brain need glucose, it doesn't have to come from carbs at all.
In short, the transition from glucose to ketones can feel rough, but it's worth sticking with keto for the end result: a brain and body that will not need to be fed continuous carbs. A ketone-fueled brain has its advantages.
Ketones > Glucose
To start, ketones are a more efficient fuel than glucose when it comes to brain energy. Along with making you "feel smart," this molecule has a lot more going for it.
As more research on keto gets done, the benefits of the ketogenic brain come further to light. The oldest proof of keto's neurological benefits comes from Ancient Greece, where early physicians linked fasting to fewer seizures in people who suffered from them.
Later, after the advancement of science and discovery of ketones, we now know that causing the brain to run on ketones, whether through fasting or the keto diet, can be a lifesaving treatment for even persistent and drug-resistant epilepsy.
Another interesting study deals with Alzheimer's Disease. Scientists have discovered that the degenerative diseasde happens when the brain loses its ability to metabolize glucose properly, due to insulin resistance. (According to some, Alzheimer's should be called "Type 3 Diabetes" because of this.) According to the study, Alzheimer's patients with elevated levels of ketones in their blood (from supplements) saw improvements in cognition significantly better than those in the control group.
It's theorized that ketones are a neuroprotective antioxidant. Do they make you stay forever young? In a sense: They prevent degeneration and damage by free radicals, and that can slow down the brain's aging process! It also looks like they're linked to greater overall neural stability.
A lot of keto practitioners report feeling levels of mental sharpness and elevated mood that they never thought possible. Compared to the sluggish, tired, and grumpy carb-powered brain, it's almost like we were designed to run on ketones all along. Some scientists think the brain actually does, in fact, prefer them!