I have an indirect experience with it, if it'd be of any help. My husband is on keto for the last 2 years and he isn't doing it because he thinks it’s fashionable. He is pre-diabetic, and he's only 34. For a long time, nearly for 5 years before he started the diet, he felt “miserable”. He'd always be fatigued. He'd come home from work and pass out on the couch, then wake up in the middle of the night and stay awake for the rest of the night. He told me he had concentration issues, had an erratic routine, or no routine. I'm not kidding, it was driving me crazy. And not to forget his night sweats! He'd soak up the pillow cover in perspiration. He then heard of the diet through a friend who had been following it for about a while. He did a lot of research on the diet. It seemed to make a lot of sense to him. He'd talk about it non-stop for about a month before he even began the diet. Back then, I thought it'd really pass and that it was one of those crazy fad diets. Now 2 years later, he amazes me. I have never seen someone stick to a diet so staunchly. Like he admits, he has a very strong motive to do it. What drives him is the way he feels about himself. He's not fatigued anymore and feels like a “normal person” in his words. Losing 20 lbs was just a small perk! He did not do it to lose weight. He did it to control his diabetes and cholestrol. I wish you could hear it from the horse’s mouth on the scientific backing of this diet. Unfortunately he's not a Quora addict like I am. So, I'm only addressing your direct questions. If you did some research, I'm sure you'd find out more about how carbs get broken down as sugar and so insulin is produced in the body, and how it's different with keto, etc etc.
On the other hand, I was trying to lose baby weight and since my husband lost a lot of weight, I decided to try it as well. I lasted just a month. I did not feel any drastic difference in how I felt, but honestly I did have a few episodes where I felt very very sleepy at work - probably because I cheated on the diet with a bit of carbs. I did lose about 7–8 lbs that month. But may be I was losing weight anyways. I'm not sure. But we did test my keto levels using keto strips and I was in very good keto inspite of the teensy cheats every now and then.
This diet is a piece of (keto)cake for my husband because he detests sugar, sweet and can totally do without carbs. He does have a few favorites that he has foregone. In his words, it's a very small compromise compared to how his life has changed. Once in a blue moon, I do dig up new keto recipes and try to cook something nice for him(though he insists it is absolutely unnecessary).
Also, I’m not saying that everybody will have the same effect. But from the many keto groups that I follow, I do see people commenting on how awesome they feel.
What he eats:
Breakfast: Eggs with Brocolli and avocado oil - that's everyday!
Lunch: Varies between chicken, pork, bacon with a side of salad with lots of cheese and oil - I try different recipes of chicken with minimal or no carbs. When we eat out, he binges on steak and ribs, which I don't make at home.
Dinner: a variation of the same he's had for lunch.
Diet coke: At least 3 to 5 cans of 300ml everyday (much to everybody's horror)
He drinks once in a while. It’s not advisable to drink while on keto. He has one pint of very low carb and keto-friendly beer like miller light, michelob ultra, etc. If he goes overboard, he falls out of keto.
There’s no limit as to how much he can eat. He generally loads up on fat. Like I understand, your diet should comprise of 70% fat, 25% protein and 30 gm of carbs - this may vary.
My husband is an absolutely non-fussy eater and generally can eat the same meal the whole week. Sometimes I do surprise him with Keto chocolate mousse and other similar treats. But he's no sucker for those and can live without it.
As a snack, he eats of lot of nuts - pecan, walnut, almonds, cashew and when he wants to penny-pinch, peanuts. He never gets any hunger pangs. The oil abstains you from feeling hungry.
There are numerous websites that provide the yummiest of keto recipes. My husband’s mantra is to keep it simple. That sustains you in the diet for long. I generally look for Indian keto recipes, but eventually figured that anything you cook is fine as long as you maintain the keto ratio for fat, protein and almost-no-carb. Should also add that the spice level my husband could eat has gone down drastically.
I’d be happy to help if you need more info.
Update: 3 years later, hubby is still going strong on keto. And another baby later, I’ve taken another plunge into keto - started out with simple goals. It’s been roughly a month and I definitely feel lighter.