whether eating or fasting, exercise should be introduced on a gradual basis, building up slowly with mild exercise and progressing into more intense exercise as time goes by.
There are risk-factors to health in over-exercising too early when your body is not accustomed to it.
After saying that it really depends on your reasons for fasting: in a state of ill-health or disease then exercise is not advisable as the body needs all of its available energies for cleansing and healing, rather than wasted on expending it during exercise. All of the fasting supervisors from the past were in agreement on this, and which is my own view also.
However, if you are in relatively good health, with no specific ailments, fasting for weight-loss is recommended as a way of accelerating the loss of excess pounds, but again needs to be built-up slowly as previously mentioned.
The benefits of exercise while fasting?..............
Improved circulation and elimination of some bodily toxins via the skin thru perspiration.
Ketosis can also be brought on a little more quickly via anaerobic and intense exercise of short duration with periods of rest in-between, as illustrated by Dr Al Sears in his PACE programme, but I would definitely not advise any intense exercise, even of a short duration while fasting, as this will supply extra stress to various organs (especially the heart) and have inherently potential dangers.
However, your food reserves will become depleted much more rapidly and the fast would then have to be terminated sooner rather than later, which would be unfortunate if fasting for health and the recovery from disease.