"Is not the object of every Revelation to effect a transformation in the whole character of mankind, a transformation that shall manifest itself, both outwardly and inwardly, that shall affect both its inner life and external conditions?"
A Spiritual Fast
Baha'is practice fasting as a discipline for the soul; they see abstaining from food as an outer symbol of a spiritual fast.
By this they mean the practice of self-restraint in order to distance oneself from all the appetites of the body and so concentrate on oneself as a spiritual being and get closer to God.
Abstaining from food is not an end in itself but a symbol, and if it doesn't result in improvements in character and concern for others then it has not been undertaken in the right spirit.