I imagine Fluffies to be close to human infants. They need to eat little but often, a trait put in by Hasbio so the Fluffy would be less likely to starve due to a forgetful owner.
It’s also why Ferals manage to cling on by chewing on the little food they’re able to find
They need to eat all the time because their digestive system is shit at absorbing nutrients, so they turn food into shit extrememly fast and can shit mere minutes after eating.
Id bet they can eat a fuckton, and they just shit it out faster the more you feed them. Maybe a Fluffy can handle like, 8 kg of food before it dies from overfeeding?
Suppose we base ourselves on the diet of a medium-sized dog and double it due to its defective digestive system, we could deduce that it would be 600 kcal per meal and this if you do not over-pamper or over-feed this shitrat and this would be food, the amount would double if they are liquid foods or skettis, in conclusion it is cheaper for you to have a pet pig than one of these shitrats xD
Given how fat bestest and sensitive foals get, the limit may be more related to leptin and ghrelin (appetite hormones) than to stomach capacity. We know fluffies can stretch to abnormal limits, as seen in pregnancy, so there may not be a set limit.
My guess is the limit is related to the quickness of the eating, give 1kg of food to a healthy store bought fluffy and it will explode, but repeat with a really overweight one and can chug the kilo easily