I will make a couple of generalizations
Lets see,
if you were eating 6 meals, with 50g of carbs each, thats 300g total, spread out nicely each day.
If you go during SD to 400g and split that into three meals, its a total of 133g/meal. (even if you dont change total intake, thats 100g/meal)
It takes a small while for the body to uprate enzymes for digestion of carbohydrates, and extra fat per meal will be slowing transit time slightly. So it maybe causing the bloating that way. If any of the carb is managing to get past the upper intestine to the lowr intestine before digestion, this may be the probelm (have gas?
)
Short term changes lead to problems, especially if you have been low carbing for awhile, then dump in a bolus of carbs. Make sure you drink HEAPS of water as well. (about 1litre for every 60-100g carbs). I know it seems a lot, but it dilutes the entire meal so you dont draw fluid from the body into the bowel (more bloating and GI distress.