Well if you don't eat you don't have what to shit, that's most probably the case. You can always use laxatives for heavy constipation, but in this case just eat more before the sessions
and in a case like this with constipation, predominantly vegetables and fruits, esp liquids like V8 and other forms of tomato juice -- they are easier to process than meat, and cheese and bread have constipating effects. In fact, giving bread and water to prisoners is not so much meant as a means up pumping up the privation, it is that after a few days of this, the digestive tract will set up like concrete and it hurts like all get out . . . I think a case can be made that it is contrary to the Geneva Convention for gaolers to do so . . .
Also there was a famous discussion of cheese and digestion in the 1989 film
Uncle Buck, which I think was the other film in the double feature when I saw
Drugstore Cowboy in the theatre all those years ago. The latter is an eloquent anti-drugs film which is liked by many people on both sides of the debate, and is especially cathartic to watch after dealing with an arsehole junior detective pharmacist, leech Communist politicians and misinformed doctors and terrorist nurses . . .
A month later, I read in
Le Devoir and the
Montréal Gazette that there was a rash of people breaking into pharmacies by sawing holes in walls and roofs and hiding in bathrooms in the US Middle West, meaning that the people who did it read the book too, which I strongly recommend, because like
Fear & Loathing In Las Vegas, they left out things so as not to come out with a seven-hour film, including at least two more heists and a discussion of blues (oxymorphone tablets, Numorphan) which a lot of people thought were 10 mg diazepam tablets, called Blue Bombers. There are also some tips in there like how to get atropine out of tablets to which it was added and so on.