The first thing to mention is that oversupply is a far far more common problem than food allergies/ reactions. And it's often mistaken for food allergies/ intolerance.
Your comment about overproduction problems got me thinking. Oversupply basically means that as your breast is producing so much milk a baby will fill up on a greater proportion of foremilk than his friend with the mother who doesn't have oversupply. So because foremilk has the vast majority of the lactose this causes increased wind/ digestive discomfort/ green poos (because the foremilk moves more quickly through the body). This symptoms can look like food intolerance issues.
But the main differences:
Oversupply is very likely to be accompanied by an overactive letdown so baby will often splutter at the breast/ bob off/ choke. They will also be more prone to spitting-up, hiccuping, gassiness.This wouldn't necessarily happen with food intolerance issues.
Weight gain can be very good (despite the foremilk imbalance they are still getting a lot of milk overall) or relatively poor (really only filling up on foremilk). But with food intolerance/allergy issues - weight gain is usually not great (rather than have the high weight gain option).
Mothers with oversupply pump extremely large amounts in comparison to their peers.
Mothers with oversupply have a slightly higher chance of blocked ducts/ mastitis.
But to be honest the similiarities are so great - there aren't a lot of differences!
If you have a known oversupply issue then it's more likely to be a foremilk imbalance rather than a food intolerance problem as food intolerance/ allergy is so rare in comparison. And the symptoms are very similiar (poos are mucousy and green, gas, digestive discomfort, fussiness).
On the breastfeeding helpline one of the first things we are taught to ask the mother of a colicky baby are a series of questions to rule out a foremilk imbalance e.g. do you do double-sided feeding and how do you make the decision to change sides? and various questions to rule out oversupply.
This article is quite useful:
http://www.lalecheleague.org/FAQ/oversupply.html