There is no "UT diet". Some say, avoid meat and bad food so that your urine tastes good enough to drink.
I eat meat and drink coffee and my urine is fine.
Just avoid everything you would avoid anyway to stay healthy: processed foods, foods containing Sugar especially, and gluten as that is doubtless an issue for you.
YES -- going straight to such a long fast is difficult. Most here start with shorter fasts, say, once a week, or, if you are very ill, simply having a small meal for dinner is ok. Others can tell you more about this.