Grok sez that’s FMD.
It gives you the specific items you can have during the five days, and you can't carry anything over to the next day.
It stops all sorts of inflammatory pathways, allows your body to identify defective cells and proteins and digest them, then readies a bunch of stem cells to go out and repair or grow tissue, once you restart eating.
It is very hard to do on your own. The best is to buy it, on sale, or just do a true water-only fast for five days. The added benefit of the Prolon kit is that it saves your muscles from being eaten for calories, during the diet.
You can get it as cheap as $120 on special sales like Black Friday. Just do it three times in a row (three months) and see what changes for you.