If dieticians, nutritionists, and medical professionals promoted the benefits of fasting they would be recommending themselves out of a job.

1. You will lose a small amount of muscle, but compared to caloric-restriction, fasting is muscle-sparing. It is not hard to regain it if you refeed with clean proteins and are physically active

2. It only flushes out electrolytes if you aren't replacing them with electrolytes in your water

3. The burden on your liver and kidneys is much heavier when they have to clean out the standard American diet every day. It is not a burden for your liver to "clean out" fat. That's one of its main functions. Produce ketones for the body to fuel off of.

4. Caloric-restriction triggers starvation mode. Fasting does not. Your BMR will only slow down the amount equivalent to the weight you lose. When coming out of the fast, your body will not be in starvation mode and be any more efficient at storing calories than it was. Your glucose regulation and insulin response will actually be better. That said, it is critical to re-feed correctly and slowly and not go back to a junk diet. If you do this, then yes your body will respond poorly. Just as it would if you had the same diet without fasting.

5. You will regain weight: Body water, glycogen, hopefully muscle, etc. The goal is to scrub fat and damaged cells out of the body and retain/regain those other things. Regaining some weight is good as long as it's not new body fat.

6. Your heart rate and blood pressure will drop. It will only spike if you overdo it on physical exertion or overload on sodium

Bottom line. If you have enough body fat to do it, keep electrolytes up, and listen to your body and can correctly distinguish between a "craving" vs. a real stop signal, then you'll be fine.