Dog losing weight

Question
We have a dog that we got from a rescue league about 3 years ago.  We think she is a terrior mix.  She has been the sweetest dog (when she got to know us that is!) She was a badly abused dog before we got her.  Now she is simply SPOILED ROTTEN!!!! :) We love her to death!

Our problem is that she has started loosing weight over the last month or so.  She is normally a little piglet! She is the type to eat any & everything that you give her.  Even though she was losing weight, she still was eating just fine. Over the past 3 days she has started to cut back on her eating and now she has starting to vomit over the past 24 hours.  She also had some loose stool in my son's room...she has been house trained for 3 years & NEVER done that.  When she started vomiting, she will not touch her dog food, but will eat table scraps if you give them to her.  We don't normally give either of the dogs ANY table food.

We did change dog food about 6 weeks or so ago.  We used to buy Science Diet for sensitive skin.  We started buying Purina. We used to buy the sensitive skin food because my other dog had problems & it was just easier to buy the same for both dogs.  She no longer has a skin issue & so we changed back. The other dog hasn't seemed to have a problem with the food change.

Answer
I'm not going to comment on the Purina, or the Science Diet.,
However I will tell you this if your dog has lost a significant amount of weight,. as you have described and is developing other issues, such as the vomiting, you should have her vetted immediately. Just the unexplained weight loss alone could be a signal of cancer, or a blockage, or many other serious problems. Yes it could be nothing, but why risk the health and possibly life, of your dog. Take her to the vet immediately
best of luck
Cindi