I have the most experience with time restricted feeding which is a daily extension of the overnight fast until midday. Sixteen hours of fasting and a window of 8 hours for eating or 16:8. I do this nearly every day. Sometimes I will extend the fasting to as much as 22 or 23 hours and essentially eat one large meal that day (OMAD).
That practice initially helped me lose weight. It works by making it easier to eat less. I combine that practice with weightlifting 5 days a week.
I have been deliberately eating more the last year or so while lifting heavy in order to build more muscle and try to hit a certain goal. So the practice isn't exclusively for losing weight.
But doing this practice for years means that I feel much more in control of eating and my weight. When I decide to cut again it seems pretty straightforward. Extend my normal fast from 16 to 22 hours a day and eat one large healthy meal a day (OMAD) and the weight will fall back off fairly quickly.
I have, much more rarely, extended a fast to about 40 to 46 hours.
Having done a pretty fair amount of reading of scientific literature and other people's experiences along with observing my own body I am convinced that it is contributing in a very positive way to my overall health.
My approach:
- Follow a cyclical pattern. Your body/metabolism evolved to endure periods of hunger as well as taking advantage of relative plenty. Try to flex your metabolism each week by eating little or no food for 24+ hours, then eating one meal per day (nutrient dense, see below), then eating two per day, increasing until you eat to satiety (just before going back into the extended fast).
- This is a bit like treating each week as an annual seasonal cycle. For my schedule, Sun night through Wed morning is Winter (mostly fasting), Wed/Thu is Spring (one meal per day), Fri/Sat is Summer (two meals), Sunday is Autumn and feasting before Winter comes.
- You'll be eating much less in total volume, so focus on maximum nutrition density when (re)feeding. This means eating things like (grass-fed) liver and heart, wild-caught fish and bivalves, vegetables and leafy greens to replenish nutrients and minerals. From a nutritional standpoint, this is not so much a keto/hflc/carnivore/paleo approach, it's really just: Eat meat and vegetables. During the Summer/Fall cycle of my week I'll deviate a little and add berries or low glycemic veggies.
- I exercise with high intensity twice per week. Once on Wed morning (ideally fasted), and once on Sunday morning. The rest of the week I just do a bit of stretching/mobility. This isn't critical to the fasting program, but I find that the metabolism flexing through fasting is a positive stress that complements the physical activity (also a positive stress).
So, that's it. The cyclical nature of it feels good to me, it feels a bit more natural, the nutritional part feels really good, and I've had really good results from an energy level and body composition standpoint.