I don't think so, although personally not an ideal way of losing weight.
However, the obese tend to lose weight much more rapidly at the beginning than the non-obese, and especially so when the fat deposits are "soft" as opposed to "hard".
The added benefits are much more cleansing, healing and more heightened senses which can discourage the faster into going back to old and unhealthy eating habits.
A short-term fast will definitely kick-start your weightloss and a plant-based diet thereafter will continue the process, but the downside is a lowered state of metabolism caused by water-only which can last for several weeks post fast.
Post-fast include some mild exercise graduating to more intense forms (over several weeks) and avoid mixing a protein food with a starch food at the same meal: a known and major culprit as a cause of weight-gain.