My hubby has been on Keto for 8 months now, we started last year with my diabetes out of control and had to make some drastic eating changes, we count March as when we started. He has lost 130 pounds (not all but most from the Keto), has achieved his first weight loss goal, now is only about 20-30 pounds from what he weighed in High School. Keto is high fat, moderate protein, and extremely low carb, he's typically under 30 for the day. He is doing well on it, loves the food and all that, and has had labs done every 3 months or so and is doing well for the most part in that. He has gone from pre-diabetic/insulin resistant to normal. In terms of "non-scale victories" his weight was giving him back and knee issues and he had given up bowling which was one of his primary hobbies, thinking he'd never be able to do it again. We go almost every Sunday morning now, the lanes are cheap and he typically doesn't have to work OT unfortunately with our Seattle snow storm and a broken machine, they will be working tomorrow so no bowling. It's a change for us, going bowling or for walks instead of going to a buffet...
A couple of months ago he added intermittent fasting which is also working well for him and goes well with Keto but you don't have to do both. He has an "eating window" of 4 hours, between 2:00 PM (when work is over) to 6:00 PM. Me, I do feel better with the small protein based snacks every two hours (like a hard boiled egg, piece of cheese, 2 tbl peanut butter) which is the complete opposite of keto.
I'm somewhat skeptical about the long-term viability of this diet. I understand he is in a weight loss phase, but human breath is not supposed to smell like that.
I have also lost about 100 pounds, but I started 7 years ago. I'm not willing to give up salads and the occasional fruit so I take in about 60 carbs a day, dietician says I'm good up to around 100. I really believe in not dieting, the changes I've been making I have to do the rest of my life. Hate the term "lifestyle changes" but they work. Sure the "do this and lose 5 pounds a year" doesn't sound like much help when you are 280, but do enough of them and keep them up and in a couple of years it becomes noticeable.
The big news for me though is my diabetes is under control. Last February my glucose level was 350 and I was put on insulin for the first time, had been on metformin for 7 or so years, that's when I started making my lifestyle changes. Around Thanksgiving my doctor took me off insulin and reduced my other medications. Today the glucose was a little higher than my usual 105, 116, but as long as I'm under 130 my doctor is happy with me.