Is a 40-day water fast healthy?

As long as you have enough fat in your body to do it. And that you're also taking nutrition along the way. B vitamins, electrolytes, the vitamin D, omega-3 fatty acids and the trace minerals. And then make sure that you know how to come off that diet because it's one of the best things to do if you have cancer, but a 40 day fast is pretty intense. And of course you're going to lose some serious weight. It's therapeutic in some cases and definitely cancer is one of them.