Water-only-fasting according to thirst would be remedial in adrenal fatigue, as this allows the body to self-heal by rest. By rest I mean physiological/physical/mental and emotional rest.
More importantly would be the lifestyle habits post fast in terms of diet/rest/fresh air/judicious sunbathing/exercise and an abundance of sleep, making use of each of these by knowing their bodily demand for each.
Enemas exacerbate the problem of constipation making things ultimately worse and have been found to be enervating by the most experienced fasting supervisors.
Constipation has two main causes: inadequate dietary fiber and a lack of exercise, the latter of which makes the bowels lazy, just as muscles will waste through lack of use.

Whether glands function (endocrine system including the adrenals) efficiently or not, depends on their nerve and food supply. If the blood is normal, their supply of food is normal; if the nervous system is normal, they are properly energized. With pure blood and normal nerve force, gland function will be normal. These depend upon our conduct: our mode/style of living.
What causes a gland to function? Nerve energy. No doubt inter-glandular uniformity exists, but over all is a nervous system that furnishes energy for the work. Full nerve energy spells good function. When nerve energy is lowered, functions lag. Glandular function cannot be normal in an enervated body. Glandular malfunctioning is an effect, not a cause.
The body works in unison, (holistically) or tries to achieve a state of equilibrium known as Homeostasis, so if our lifestyle/dietary habits lead to an overworked system, then we suffer the consequences: the body then decides which part or organ is susceptible to disease or malfunction, and in this case your adrenals and bowels.

A fast will go a long long way in correcting your health-issues by diverting digestive energy (the most demanding of bodily energies) into cleansing and self-healing, but ultimately it will be your lifestyle choices post-fast that will maintain and improve your overall state of good health.

Chrisb1.