Hi Mighty,
Of course if someone decides to use the water-only-fast as a means of losing weight as their primary goal, that is a choice only they can make, and no one but no one is saying that this is either right or wrong or whatever.

However, we know that in the fasting-state, the metabolic-rate will slow down to conserve energy, and usually from the outset. According to the Mayo Clinic,(not my favorite people to quote from) "your body compensates by slowing down bodily processes and conserving calories for survival." So the lower the calorific intake, the more your body will hang on to its fat stores, and ultimately so with zero-calories as on a water-only-fast.

On this basis, the body will instinctively preserve its vital tissues and food reserves to the maximum on a water-only-fast, in an effort to prolong life and ultimately in the prevention of actual starvation. How often do we hear on the forum here how a fasters weight loss has stagnated, and sometimes for several days at a time for this very reason.

Shelton had this to say..............
"Metabolism is lowered from one-fourth to two-fifths during the fast. This falls quite rapidly during the first part of the fast until the true physiological minimum for metabolism is reached. From this point on, until the return of hunger, metabolism is maintained at a fairly uniform level. If food is not consumed when hunger returns there follows, soon, a rapid dropping of metabolism to new low, but pathological levels".

Dr Joel Fuhrman MD (a prodigy of Sheltons) fasting specifically for weight loss is not recommended from the outset for the majority of his patients as he prefers to limit food intake with a low-calorie but nutrient-dense diet in order to lose the bulk of this, and to maitain the metabolic rate which burns more calories, and then followed by a fast to rid the body of its toxemia and the disease his patients are suffering from; this is especially so for his heart-patients who have otherwise been recommended by Orthodoxy to have an angioplasty or a heart by-pass.

We also know that water-only-fasting-according to thirst was first known and spoken about as the "rest-cure", and where all the bodily processes will go into "hibernation-mode": some bodily processes such as bowel function/activity will for the most part shut down altogether/respiration will decrease, and the vital organs are afforded a well-earned break. So by exercising during a water-only-fast, we are literally going against the grain of what our bodies are needing and demanding physically as well as physiologically.

I think we could all learn a lesson from Nature here where animals either in the wild or domesticated will restrict their physical activity to the max' extent possible if they need to fast. They know better than you or I, and instinctively, that to engage in physical activity during a period of physiological rest is inadvisable.
I always say that each case of anyone desiring to lose weight via fasting should be judged on merit and the condition of the faster at the time, and where it is highly probable that there are those who may have an underlying, and as yet undiscovered health condition, where rest is paramount during a fast and where activity/exercise during it could serve to exacerbate the problem, even to the point of causing a fatality.

So in conclusion, if anyone wishes to lose weight as their primary goal by exercising during a fast, I would say that as long as they are aware of their present state of health, and there are no underlying health conditions which would require absolute rest, that is their own choice, but it would not be mine I'm afraid.

Take care.

Chrisb1.