It is very important with any overweight animal (but especially ones with high metabolisms like rats) that you do not cut their amount of food too much too quickly. Feeding them too little all of a sudden when they are used to eating a lot can send their bodies into "starvation" mode, where they won't lose the weight but will start conserving every bit of energy, and it can even cause heart problems like a heart attack!
That is very true. When trying to loose weight, be it a person or an animal, you always want to do it very gradually. Rapid weight loss is not good.
