Probably not ice cream, but pudding. In Tristan Taormino’s “Ultimate Guide to Anal Sex for Women”, Chloe Nichole demonstrated how she prepares for a scene with multiple enemas, with the goal of cleaning out her colon very thoroughly. It’s the only way these actresses can survive the seemingly mandatory “ATM” (if you don’t know, you don’t want to know, and I wish I didn’t) without suffering dire medical consequences. Judging by how through a job Chole did, she could easily loaded her colon with pudding and consumed it with no harmful effects.
As Ron Jeremy said in Porn Star: The Legend of Ron Jeremy:
Viagra and the like have made it easier for more guys to get into the field. Back in the day there were few who could do the job. Which was why you kept seeing the same guys over and over again. They were reliable “woodsmen”, able to get “wood” when needed. Jeremy was famous for being able to supply an orgasm on cue, even to a countdown.
By the way, most of the 70s, New York era male porn stars, and many of the female ones, were real actors. They took a porn or two to make money and star in a film, hoping to move into mainstream films. With very few exceptions, they didn’t manage to do so. But it wasn’t for lack of trying. As Judith Crist said about the opening scene of The Devil in Miss Jones: “Oscars have been won for worse work.”
According to the Smoking Gun, they used a chocolate soy paste.