Anecdatally - I've been on omad (one meal a day, just dinner) for coming up on a year. I only weighed myself once every couple of months at a friends house as I don't own a scale. Over the last year, I dropped 28lbs without much effort beyond adapting to the routine over the first month or so, and then gained 8 lbs. back over the winter due to being relatively sedantary, and adding alcohol back to my life. (red wine, whiskey, and worst vice of of all, cider)
This may seem like a small amount to lose over a year for such an extreme diet (~12% of body weight at lowest), but the number overlooks how much I really enjoy eating when I do eat. No snacks, no hidden sugar crap, but bulking size portions without desserts. An example would be if I had to eat fast food because I was out, it would be some gourmet organic hipster double fancy burger where all the animals involved were probably raised with music lessons or something, with another normal single burger instead of fries, and the idea of sugar water is absurd. Only eating at dinner, at least 75% of my meals include salad or large vegetable servings as well, so even if it's small, most eating habits don't include that, so there's a net trade off. So still a somewhat perverse meal size that would qualify as gluttony to an observer, but limited by OMAD availability. I can't say it's virtuous and healthy at all (a lot of chicken burritos), and it's less a diet or scheduling as managing ones tendency of abusing food, but since I'm not wired for moderation, this has been something that works.
I have a few black espressos every morning, and go until about 5pm or later before having a normal (if extra enjoyable) dinner.
First few weeks are hard, and I got through them with mint tea and chai tea (no milk or sugar) during the day when I was really struggling. I started in April, so the snow was gone and I could get out for walks at lunch, and I found exercise was the absolute best hunger killer. I avoid dieting in principle because I think it becomes a weird and pious substitute activity that appeals to a sense of purity I don't have. Starting in April felt right because every animal is basically starving by April anyway.
In terms of nutrition, it has been red meat once or twice a week, salad at most meals, high fat. Gyms were closed last year, so I walked an hour a day 4-5 days a week and threw in some occasaional dumbell sets on boring conference calls. I got about 90mins of extra productivity/HN from the time I would have spent prepping and eating meals, and coupled with work from home and no-commute, I added 3h a day to take on addtional consulting clients for short periods.
I'm still overweight (6'2/220), but it's controlled, my YoY billings are up 20% and I have a more appreciative relationship to food.