uttam tap can also be referred as : repentance
this does not only mean fasting but also includes a reduced diet, restriction of certain types of foods, avoiding tasty foods, etc. the purpose of repentance is to keep desires and passions in control. over-indulgence inevitably leads to misery. repentance leads to an influx of punya karmas.
meditation prevents the rise of desires and passions in the soul. in a deep state of meditation the desire to intake food does not arise. our first tirthankara, adinath bhagwan was in such a meditative state for six months, during which he observed nischay uttam tap. the only food he consumed during these six months was the happiness from within.