I didn't make up the hypothesis. It's a well known clichéd bit of advice.

I thought food only stays in the stomach for a certain amount of time, after that it goes into the intestines for the goodness to start being sucked out of it. If anything is left solid at that stage it's missing out on time to provide anything useful. If anything is still left solid at the end of that stage you've been eating sweetcorn you get nothing from it.

And something more like real juices might be nice. Thanks! I may get back to you.