I'm a big fan. I just completed by 9th round of the Prolon 5-day "fast mimicking" diet. It's the best cleanse I've ever tried. It's not easy, but each round gets easier. If you aren't familiar, it's a meal kit where each day you only eat what's in the box for that day. This puts your body into what it thinks is a water only fast, but you are consuming food and nutrients, just enough to go undetected. So you go through the phases of kestosis and autophagy for benefits like a clear mind, "cellular rejuvenation", energy, and other benefits.
The food itself is plant-based and based on Dr. Longo's longevity diet. I HIGHLY recommend the newest version called "Next Gen" because the original flavors are powdered soups while the new ones are pre-made and much better tasting. No weird ingredients, very clean. You also get an "l-drink" to retain muscle mass which you loose in traditional fasting. There are italian olives, kale crackers, and bars as well. I love them all, but some people are olive averse.
Be careful with this if you have a history of disordered eating, and I did let my doctor know about it when I started. I did loose weight and belly fat, but the focus is on repairing damaged cells with weight loss as a nice side affect. I also use the 1-day reset kits to do intermittent fasting, where I "fast" for one day a week using the kit and that works great for me. Take advantage of the support systems like daily Zoom calls with a nutritionist, it's included in the cost of the kit and very helpful!