A 30 day water fast while also working out would be very risky, unless you had daily medical supervision to monitor electrolytes and blood sugar levels.

My H and I have experimented with fasting for a maximum of 72 hours in order to reset our immune systems. This is with the permission of our doctors. Research shows that a fast of up to three days several times a year can restart healthy stem cell production, especially for people with cancer and immune problems. That's why we're doing it.

Sorry to say, but fasting to lose weight is a very bad idea. Most research shows that people who go on very low calorie diets tend to become obsessed with food, depressed, self-injuring, isolated, disinterested in sex and generally miserable. Those symptoms can last quite a while.

Starvation -- fasting is a form of starvation -- for extended periods can slow the metabolism down. When eating recommences, the body tends to store calories as fat because it is preparing for the next food shortage. This is something that is well documented in parts of the world that have suffered famine. It's probably hardwired into our genetic make-up because our long-ago ancestors lived in a world where food shortages and famine were common. Starvation cues the body to fatten up again quickly as soon as food becomes available.

Fasting for 30 days in order to lose weight could very well trigger an eating disorder and future weight gain.

At the end of WWII, the military sponsored the Minnesota Starvation Experiment to determine the effects of semi-starvation on the human body and psyche. The volunteers did not fast. They ate the food that was available in war-torn Europe where people were subsisting on much less food than they were used to eating. Below is a summary of the results of the starvation study. Please research this subject carefully before you subject your body and your mind to this kind of extreme stress.

Minnesota Starvation Study Summary

Among the conclusions from the study was the confirmation that prolonged semi-starvation produces significant increases in depression, hysteria and hypochondriasis as measured using the Minnesota Multiphasic Personality Inventory.

Indeed, most of the subjects experienced periods of severe emotional distress and depression.[1]:161 There were extreme reactions to the psychological effects during the experiment including self-mutilation (one subject amputated three fingers of his hand with an axe, though the subject was unsure if he had done so intentionally or accidentally).[5]

Participants exhibited a preoccupation with food, both during the starvation period and the rehabilitation phase. Sexual interest was drastically reduced, and the volunteers showed signs of social withdrawal and isolation.[1]:123–124

The participants reported a decline in concentration, comprehension and judgment capabilities, although the standardized tests administered showed no actual signs of diminished capacity.

There were marked declines in physiological processes indicative of decreases in each subject’s basal metabolic rate (the energy required by the body in a state of rest), reflected in reduced body temperature, respiration and heart rate.

Some of the subjects exhibited edema in their extremities, presumably due to decreased levels of plasma proteins given that the body's ability to construct key proteins like albumin is based on available energy sources.