Some would say keto is a way of eating as opposed to a diet that can been seen as a temporary change of eating habits.
I've never heard anybody say that keto causes brain fog. In fact a lot of people describes the opposite result which I would think most search results are about. There's also something called "keto flu" which some people experience for some time when they switch to a keto diet.
These terms are pretty vague and the best way to get a better understanding is too try keto yourself. It's just a different way if eating. You don't have to cook fancy meals and you can stop at any time.
I did keto for 5 months or so back in 2014. I found the brain fog description very apt. I couldn't think beyond a couple of moves ahead, which began affecting my work. Going back to a normal diet I was fine again.
Because saying "it depends on the person" is akin to saying "there are too many (possibly unknown) variables at play to actually figure out what causes what".
Nutritional sciences have it hard. it's basically impossible to really isolate cause and effect while staying moral with complex organisms like humans
Especially because it might not be up to the human, since our digestion relies on symbiotic gut bacteria, which we don’t have good ways to test what they even are.
If you're having trouble concentrating on a ketogenic diet it's likely that you're not eating enough vegetables, and might be eating too much protein.
Too much protein can take you out of ketosis, but people think they can just eat lean hamburger three times a day.
If the fat/protein ratio is right, the inability to focus can be a symptom of electrolyte deficiency, particularly sodium, potassium, and magnesium. You should be getting potassium and magnesium from vegetables, but supplements can be a useful diagnostic tool: If you take 400 mg of potassium and find, an hour later, that you're thinking more clearly, that's data.
Don't overdo it with electrolyte supplements, though; too much sodium can increase the calcium in your blood enough to give you kidney stones, if you're lucky, and worse effects if you're unlucky. Too much potassium can mess with your heart.
Eating more protein doesn't take you out of ketosis, that's just a myth; it will just lower the amount of keytones that are being produced. If only are protein or nothing at all and you would still be in ketosis.
I’m 4 years into carbohydrate recovery and strict keto. I expect to live the rest of my life this way. I have not experienced brain fog after my first few weeks of withdrawal.
Keto diets are usually (not always!) used to lose weight.
Calorie restriction is a sure way to get brain fogs, and it's easy to inadvertently be in caloric deficit when on keto, because you have to give up many foods, and there are no sudden cravings for sugary/starchy food.
The problem with keto is, just like with "normal" diets is the wildly different formulations.
You can do keto with trash food or simply bad ingredients (e.g. vegetable oils for fat, various processed "keto snacks") and aside from maybe some weight loss you won't experience any of the real and sustainable benefits.
This is why you can't go with people's testimonials, I can guarantee you that people who say keto didn't work for them simply didn't know how to formulate the diet properly.
Is keto intended to be a long term diet?