Fat cells are not the only place though within the body where toxins are stored, and where although some or most are metabolized during a fast (depending on its length), it is known that when the body has completed its work of elimination by unmistakable signs such as clear urine, which was formerly dark; bright eyes; a pink tongue that was formerly coated; the breath becomes sweet and so on, this can occur with plenty of fat stores left in reserve.
The body discriminates between the food stores needed for sustenance and the effluent & toxic materials that are also stored in the body which are targeted first & foremost in elimination or as fuel.
This is why you are now experiencing far less if any detox symptoms on your second extended fast, with plenty of fat reserves still available (even extremely thin people with a low BMI have some stored fat reserves to hand) as the work of elimination was mostly accomplished first time around, and even continued post-fast. The body is always trying to expel toxins within the body even while eating: I can do no better here than quote Shelton.......
"Life is a master drama of nutrition and drainage under the control of the nervous system. If nerve or life-energy is abundant, the various organs of the body are well supplied and they function with due efficiency; digestion is good, respiration is normal, circulation is maintained at a high level, secretion and excretion are adequate. As a result, the cells are nourished, the fluids are kept sweet and clean and we have health in superabundance. However, if our nervous batteries have been permitted to run down, if our nerve or life-energy is low, ALL the functions of the body are correspondingly lowered. Digestion is then poor, secretion and excretion lag, circulation is below par, respiration is not efficient. The fluids and tissues of the body become sour and we have impaired health”
""Diseased" tissues are broken down, exudates, effusions and deposits are absorbed and either used or eliminated. The body utilizes everything it can dispense with during a fast in order to preserve the integrity of the essential tissues. The useless and least essential things are sacrificed first".