Craig,
After a prolonged period of not eating carbs to any extent you will find that you don't have the intestinal flora (bacteria) to deal with the digestive remains of plant based foods.  This can cause bloating and much discomfort if you suddenly eat a high carb meal.  BG will spike dramatically also as your pancreas has shut down and can't supply large amounts of insulin anymore.  All of this is reversible of course, just start eating carbs again and soon the body will adapt to that environment.

What you see with the blueberries is that they have very low carb content and what carbs they do have are simple sugars.  These are easily absorbed and there is little left except the skins and their coloring agents which pass through unmolested since you don't have the bacteria necessary to break them down further.  If you were taking BG readings you should have seen these spike significantly and rather quickly (15 -30 min after eating) as your pancrease isn't prepared to quickly respond with insulin anymore.

When you eat fruits with significant indigestible bulk like apples, peaches, pears, etc., there is a large load of "fiber" and this ferments as is passes through and without the good bacteria to help break it down, it creates gas and a host of other issues that can make you very uncomfortable for a while.

Lex

Lex and Andrew,

I did suspect gut flora. As a raw vegan, I'd eat blueberry pudding and that never happened and those contained a LOT of blueberries! When I first went carnivorous, I had digestive problems so intestinal flora was probably a factor there as well.
Since blueberries aren't high in carbs and the carbs they do have are mostly fructose, which doesn't require insulin, I thought I'd push my limits. Eating raw cheese gave me more of a carb-sensitve type of reaction than the berries did. I woke very hungry the next morning (I'm never hungry in the morning let alone most of the day) as if I had produced too much insulin in response to the cheese, which is supposed to be mostly fat and very low carb. I've read that dairy can cause hyperinsulinemia.
I had been eating wild fruits, which must contain even less sugar judging by sweetness so I should have been used to some carb intake. They weren't as deeply colored so maybe I just didn't notice any remnants in my stool.

When I was eating a mixed SAD diet, I probably had the right ratio of gut flora. Even then, hardly anything would come out looking like it went in, except for corn. My digestive problems on SAD were mainly heartburn and acid reflux.   

I'm glad you're doing better re digestion Andrew. Batsey? I've been called "batty" before.

Craig