cat vomitting

Question
my elderly cat vomits after eating.  she is hungry, and wants to eat.  She goes to the vet and she does get a shot to help settle her stomach once a month.  it is not so effective as she still vomits sometimes.  it's becoming a real problem.  i have tried all the 'recommended' diets by the vet.  then to make matters worse she has tooth problems so she cannot eat anything hard, and i cannot give her the tartar control food.  her teeth cannot be taken care of because of her age and a heart problem.
i have been giving her canned food only, but sometimes she still throws that up.  i tried to put some bulk in by putting oatmeal, it worked for 2 feedings, then she throwed up.  i am worried that she is being undernourished.
what can i do?  thank you.

Answer
First off, I apologize for the delay in my response.  I have been quite

busy and unable to access the internet for several days.  I'm very sorry to hear about your cat's problem.  However, I'm all too familiar with it.  I would HIGHLY recommend changing to an food that does not contain grains, by-products, etc.  Please see my main allexperts page for general info regarding commercial pet food.  Also, I have a lot of information regarding feeding schedules, diet, sensitive stomachs, etc. in my past answers if you have the time to browse them.

I have had a lot of success using the Nature's Variety and Wellness brands of food.  The large commercial brands contain irritating dyes, potentially toxic (not to mention very cheap and terrible quality by-products, grains (which cats DO NOT need), among other fillers...even paper mill by-products in the dry varieties!  MANY cats cannot tolerate these fillers and ingredients...and it's no wonder!  Even brands such as Science Diet, Iams, and Eukanuba which are marketed as the 'best' and healthies are no such thing...there is a huge markup on them and the profit margin is huge...and vets make a fortune selling them.  They contain the cheapest quality products...thus greatly increasing company profits.  

Your cat my have an underlying stomach or intestinal problem due to her age and years of feeding regular commercial food.  I would really suggest switching to any of the Wellness or Nature's Variety brand of foods.  Foods containing rabbit are among the very best for animals with sensitive stomachs and/or allergies...as the proteins in rabbit meat are different from other meat proteins and much easier to digest.  Nature's Variety makes a wonderful rabbit based canned food and also a frozen food that comes in little round patties that are easily thawed prior to feeding.  You should only be feeding twice per day...no more than that.  Leaving food out for cats to graze on all day is the worst thing that can be done...carnivores were meant to eat larger portions less frequently and grazing can lead to obesity, pickiness, and even vomiting and diarrhea...as frequent small meals can irritate a carnivores digestive tract...because it's structurally made to eat larger portioned meals and not constantly be digesting small quantities throughout the day and night.

Since you are facing a problem with tarter buildup also, I would recommend feeding canned am and pm...IMMEDIATELY after she eats the canned put down dry (Wellness or Nature's Variety which are grain-free and contain less sugar than other commercial dry foods).  After she walks away from the bowl immediately pick the food up and keep all food up until the next feeding.  You can also feed the raw food and offer dry immediately afterwards which will help remove debris from her teeth.  In addition, it is perfectly okay to offer raw meats...I routinely feed raw chicken (on the bones), beef, pork, etc. to all of my cats and dogs...cooked bones, in particular cooked chicken bones are what can cause problems because they become brittle and easily splinter when cooked.  However, raw meat on the bone is THE BEST thing for removing tarter and preventing plaque buildup on the teeth.  I have been feeding cats and dogs raw meat with bones for years...and even my oldest animals have no signs of plaque on their teeth.  The tough part is getting an older cat, who is already addicted to the sugars in a high-grain food to start eating a raw...which isn't sweet by comparison.  However, if you can get her to eat some raw chicken on the bone, it should greatly help.
Hopefully this info will help.  If you have any further questsions at all, please just reply to this message.  ...oh, and as for her being undernourished...as long as you leave ample water out at all times she can easily go a day or two without eating.  If she is overweight (you can't see ribs) then it shouldn't be an issue.  If she is very skinny and sickly, search the web for Platinum Performance Feline...as it's among the best feline supplement that I have found and can safely be added to an entirely raw diet.  If she starts eating a high quality canned or dry, as I've mentioned, they are excellent and will not need further supplementation.
Best of luck with your cat.