I have tried Purina One weight management and also Iams weight loss. I have 2 cats - one is 8 yrs. old & 17 lbs., the other is 4 years old & 9 lbs.

Those foods are very high in carbohydrates, and in spite of their claims on the bag, will not help your cats to lose weight. Nature intended for cats to eat meat, not grain, and that's what is in both of those foods. They need to eat way too much of it to satisfy their body's needs for protein. Grain-based diets are the reason cats are obese, and develop diabetes. Put them on a better quality diet, and their weight will drop. You'll also need to limit their food as well. Look at the ingredients in what you're feeding them - the first ingredient is corn, and then there are the "by-products" which is the waste of the slaughterhouse industry. It's beaks, tendons, spinal chords, offal, diseased organs - anything that can't be marketed as meat. There isn't really any nutrition in there for them so they overeat to compensate.
Go to the pet store and get them a higher quality food free of corn and by products. The best thing you can do is find Innova's EVO for them - it's grain free, all meat (think Atkins diet for cats). By feeding them a better quality diet, their health will improve and their weight as well.

Some cats are just big genetically,.. no amount of diet will alter that.
You can try to give more exercise,..play with string, rub catnip on scratch towers/poles, etc.
gd.luck.

I think you should go to http://www.littlebigcat.com and read Dr. Jean Hovfe's articles, "Feline Obesity" and "The Right Weight Loss Program for Cats".
There is also an excellent article on feline obestity and the diet needed to correct it at: http://www.thepetcenter.com
When you use the "weight management" foods from Purina or Iams you are simply depriving your cat of meat protein and loading them up on carbohydrates which will not satisfy them or give them the proper nutrition for optimum health.

Tell them to read the diet more carefully and promise to stick to it! LOL!!! (okay, joke over).
Make sure you control the amount of food they are given. 2 servings of Lean Cuisine is not going to help a human, neither is 2 servings of cat food going to help.
And as always, make sure exercise is involved. If necessary, dedicate extra time to playtime with them.

From my blog:
WEIGHT LOSS FOR CATS
Why do cats get fat? It can be a combination of issues, or just one. First the obvious - overfeeding. This may happen either because you're giving in to the begging or because you're free-feeding (keeping food available all day) and your cat is not self-regulated. The second reason is feeding inappropriate, low-quality food (most dry foods). The third would be medical reasons I'm not qualified to discuss, but they're rare. Most cats are fat simply because they're fed the wrong food and are fed too much.
Is it bad for cats to be overweight? Of course! It's very bad. It often leads to diabetes, not to mention that fat cats probably don't feel very cat-like. Who would when dragging around extra pounds?
Why is dry food bad? With very few exceptions, dry food is not appropriate food for cats. It's chock full of carbs/sugar, doesn't provide enough meat-based protein, and is often loaded with grains such as wheat or corn (which provide those carbs/sugars). Wheat, corn and soy are known allergens and in many cats will cause digestive upsets. Not to mention most also contain "meal" and "byproducts." Cats are obligate carnivores who need to eat a diet high in protein (from meat) and fat and very low in carbs. The mouse is the perfect cat food - meat, organs and bones, with perhaps a tiny bit of grains that may exist in the mouse's stomach. In addition, dry food leaves cats dehydrated. They do not instinctively drink enough water because they're designed to get it IN their food. This results in concentrated urine which can lead to all sorts of problems. And it DOES NOT CLEAN THE TEETH! Really - think about - does dry food clean OUR teeth? If it did wouldn't dentists prescribe cookies instead of brushing?
What should cats eat? Cats should eat a species appropriate diet which very much resembles Atkins (Catkins). A raw diet is the very best, so long as it's properly supplemented to meet a cat's nutritional needs. There are many raw feeding forums available through Yahoo Groups that one can join to learn more. The next best choice is a good quality canned food (or even a commercially prepared raw diet such as Nature's Variety). These foods will have meat listed as the first ingredient, will not contain corn, wheat or soy, may include organ meats, and will not list "meal" or "byproducts." See the What to feed link for suggestions. Additionally, the brand By Nature Organics is a very good food, and at 150 calories per 6oz can, is a very good choice for weight loss.
What about supplements for weight loss? The addition of L-Carnitine to a cat's diet may assist with weight loss. 250-500 mg per day can be added to assist with weight loss. It is probably best to start with a lower dosage until you see how your cat reacts.
How soon will I see results? Cats need to lose weight slowly, at the rate of no more than 1 pound per month, and often less. This is because rapid weight loss may cause hepatic lipidosis (fatty liver) which can be fatal.
In a nutshell, most cats are fat because they've been fed too much (free-feeding or indulging them) and because they're fed dry food which is NOT appropriate food for them due to the grain/carb/sugar content. Cats are obligate carnivores who need to eat a high meat-based protein diet, which is also high in fats and low in carbs.
Many vets, who are sadly ignorant on the topic of proper cat nutrition, will recommend prescription diet foods (usually dry). Cats are expected to lose weight on a starvation diet of 1/4 or 1/3 cup of food per day. Everyone is miserable in these situations.
The solution is to switch the fat cat (and any others in the household as well) to a good quality canned food. Because these foods are species appropriate, the cat will lose weight at a safe, slow pace (no more than 1 pound per month). Switching foods needs to occur slowly, and if you're trying to get a kibble junkie to eat canned food, that will happen naturally.
How much should cats eat?
This varies. Average cats may eat between 20-30 calories per pound per day. But note that that is IDEAL pounds. Using 25 calories per day for example, an 8 pound cat could eat 200 calories per day. By the same token, a cat who weighs 20 pounds but should weigh 10 could eat 250 calories per day. You multiply the ideal weight by the calories to arrive at that figure. When working toward weight loss, it's perhaps best to start at the lower end of the scale (20).
How do I find out how many calories are in cat food? See the link "Values in canned food." If it's not listed there, you'd need to contact the manufacturer.....I believe that link provides some help there as well.
That's it. Easy as pie. Not only will fat cats lose weight, but it and any others in the home will reap many benefits of eating a speciies appropriate diet.
See the links below for detailed information on this topic.
UPDATE: Poppy lost 5 pounds and Sophie lost 2 following this plan (from October to October). Each cat gets one can (5.5oz) of Nature's Variety Instincts per day. No one is starving or miserable. My vet is happy with her progress and so am I. Only 4 pounds to go!

definitely play with your kitties as much as you can. just like with humans, in order to lose weight they need to be active. Pull out that string and run around the house with it trailing behind you. I would try that twice a day, morning and night for about 10 minutes a few times a week. good luck!

Unfortunately, the same management techniques used for humans work very poorly for cats. Cats are carnivores, humans are not. Lowering the amount of fat in dry food, like the weight loss diets, doesn't help a cat lose weight, as it increases the amount of carbohydrates. Feeding your cats a species appropriate diet will enable them to lose weight. Switch your cats completely off dry food, the cause of obesity, to a quality meat canned food (or raw) with no gravy, grains, fruits or vegetables as fillers. They will naturally lose weight and stay at an appropriate weight on an appropriate diet.

Dont feed them human food. Also you could try to get them to go on a walk with you. I know that it isnt typical to take a cat on a walk... but would it really hurt to try. I mean I am sure that it couldnt hurt. Hope that this helps!!!!

well, it depends on what breed of cat you have if you have a british shorthair then don't bother putting them on a diet I have one and we got her 3 years ago she was twelve pounds when we got her and weve tried every cat diet and none of them work shes actualy gaining weight now she's thirteen puonds any other breed then I can't help you.

Just try not to feed them junk food and human food.

Play with them more. Try to get them running around more. Like my cats love chasing after those little stuff mice and the jingly balls.

Feeding your cats dry food is like going on a diet and eating Twinkies at every meal.
There are some excellent answers, the one gal that wrote the really long answer is right on. Sorry can't remember her name.
www.catinfo.org
read this article for all the healthy choices
in food for your cat.
www.geocities.com/jmpeerson/canfood.ht...
Janet and Binky's Cat food chart
This will not only help your cats weight problems but keep them from UTI's and Diabetes, Kidney Failure and a dozen other problems.

Any dry food is ineffective as a Diet food because it's filled with useless carbohydrates that your cat can not utilize.
You need to put all your cats on a strict controlled diet of wet food. The amount to feed per cat/per day should be about 5.5 ounces of wet (high quality grain free canned or Raw Meat/Bones/Organ) food.
The calories in that amount of wet food are sufficient for most "normal" sized cats. Of course a highly energetic cat will need more food to keep it healthy, and a lazy cat will need less food to keep it from getting obese. But 5.5 ounces of wet food per day is a good place to start.
Here is a fantastic site that will help you help your cat lose weight!
http://www.catinfo.org/feline_obesity.ht...
Let me share with you what I have learned about feline nutrition to help you make an informed decision on what diet you should feed your cats.
Many brands of manufactured cat foods claiming to be "healthy" really are not. In fact they are made of the lowest ingredients possible. I'm not saying that a cat can't live off them... just the same as you could live off hot dogs and Mac and cheese forever, but better choices can and should be made for your feline friends. I would not venture to say that any manufactured food is "best" for a cat but a grain free organic wet food would be a good start. Feeding canned is certainly better than feeding dry in all cases.
Cats were never meant to eat dry food, also known as cereals or kibble. We, humans, make them eat it for convenience to us. It has nothing to do with them or their nutritional needs. It's completely species inappropriate.
In the wild, cats derive their entire liquid intake from their prey. They do not have a thirst mechanism because they don't need it when eating a species appropriate diet. They get all they need from what they eat. So they do not drink water. Regular ol' house cats have descended from those same wild cats.
So in a home environment, your kitty does not get the moisture it needs from dry food and it???s almost always in a constant state of dehydration. Water fountains are encouraged to TRY to get your cat to drink more and your kitty may even enjoy it, but it will never meet its water intake needs drinking from a bowl.
Deadly feline illnesses such as diabetes, kidney failure, obesity, stones, urinary tract blockages and Urinary Tract Infections (FLUTD), with and without deadly crystals run rampant these days. Cats are not taking in enough water to stave them off. Proper water intake through a species appropriate diet alone can prevent most of these conditions.
Overall, wet is a better all around better for any cats diet, be it canned or Raw and they should never be fed dry cereal kibble if we wish to most closely match their wild nutritional and dietary needs. Kibble meets our needs??? not our cats.
It is also bogus that kibble cleans teeth. DRY FOOD DOES NOT CLEAN TEETH. It's an old myth that has been scientifically disproved for years, but old-school vets drilled it into people's heads for so long (and sadly still do) that people still believe it. Cats can not ???chew???. They do not have chewing teeth. They have meat ripping pointy carnivorous teeth. They do not have molars. They may ???crunch??? a piece of food once to crack and break it??? but they are absolutely unable to chew a hard piece if food. Want your cat to have clean teeth? Give them an appropriately sized raw bone. :o)
I personally feed a Raw Meat and Bones based diet to my cats and they are very healthy on it. I HIGHLY recommend it. Once I got the hang of it and felt comfortable with it it's a snap to prepare. It's something you might want to consider someday. They are obligate carnivores after all and must derive ALL their nutrients from meat based sources. They are unable to absorb them from any other source. Despite thousands of years of domestication they remain strictly carnivorous. True and honest meat eaters and that is what they need most. Protein from meat!
If you are interested in feeding a raw diet some great places to start learning are http://www.catinfo.org/ , http://www.catnutrition.org/ , and http://www.felinefuture.com/nutrition/ .
If you would like to try raw with your cats and don???t want to get all technical about it but want to try a trusted, time tested and balanced raw diet you can order from http://www.felinespride.com/products/cat... . I purchased this myself when I first started and my cats loved it!
If raw is not an option for you please be aware that there are three Categories of Pet Foods:
-"Grocery store" foods ??“ (Generic Brands and cheap name brands) Those foods found in grocery stores and mass-market retailers are made with lower-quality, less-digestible, inexpensive ingredients and are therefore a cheaper alternative. While easy on the pocketbook, "grocery store" foods normally do not provide your cat with the healthiest, most nutrient-dense ingredients.
-Premium foods ??“ (Iams/Eukanuba, Purina One, Hills Science Diet, Nutro and such) Foods often found in grocery stores, pet stores, and veterinarian offices that contain higher-grade ingredients, but still include many elements of "grocery store" food, such as artificial colors, artificial flavors, chemical preservatives, and "filler" ingredients such as corn and wheat products, by-products and even animal digest. Yuck! Premium foods are usually more expensive than "grocery store" foods because their ingredients are sometimes of a higher quality, and are therefore somewhat more beneficial and digestible. But don???t be fooled, some of those same so called Premium brands are sometimes worse than grocery store foods, but they charge prices like they are better. They aren???t!
-Healthy foods ??“ (Wellness, Merrick, Eagle Pack, Drs Foster & Smith) The newest addition to the pet food market - provide pets with the highest quality, healthiest, and most nutritious ingredients. They are typically available for purchase online or direct from the manufacturer. Some better retailers are starting to carry them now. Complete Petmart carries a few healthy brand foods. Foods in the Healthy class contain nutrient-rich ingredients. Formulated to provide optimum health benefits for pets, these foods often use real meat as the primary protein source, carbohydrate-rich whole grains like brown rice and barley and whole, fresh fruits and vegetables. They should not contain artificial preservatives, flavors, or colors. They will almost always be fortified with additional vitamins and minerals, and will use the best natural sources for fatty acids to help build healthy skin and a beautiful coat. Because healthy foods use high quality ingredients, you should expect to pay a little more than you would for other types of pet food. Remember, though, with healthy foods you can feed less since healthy foods are more nutrient-dense than other types of food so it often evens out or cost???s les than feeding foods filled with cheap non-nutritional by-products fillers.
With all that information in mind, when you are choosing a new cat food, study the ingredients. All ingredients on pet food labels are listed by weight. Meaning whatever ingredients are listed first on the list, there is more in there. The first ingredients listed should be whole meat ingredients, protein sources, such as Chicken or Turkey. NOT just the word ???meat???! Who the heck knows what that is? The word Chicken Meal is ok, but it should be a secondary ingredient, not first. Meal is the meat dehydrated and ground into a powder.
The ingredients also should NOT include any by-products or animal digest whatsoever. Those are disgusting left over animal parts that are scraped off the filthy floors of meat and poultry plants. They should just go into the trash but they put them into pet food instead. EW!!!! Also make sure there are no artificial colors or flavors. And make sure there is no BHA and BHT used preservatives. These preservatives have been shown to cause cancer in both cats and dogs. Bad Bad stuff and it???s in almost every cat treat on the market. :(
So, in summery of the ingredients??? if you see the words by-products, Animal Digest, the word ???meat??? alone, Corn, Corn Gluten, Wheat Gluten, or BHA or BHT??? stop reading, put down that product and move on to the next.
Be aware that when switching to a Healthy, Holistic or Organic food, you will pay for what you get. Good foods are not cheap. They are pricey and will cost you more than cheaper products, just like steak costs more than hotdogs. But again, you will be feeding a better food and improving the over all health of your pet. This in turn leads to less vet visits for illness now and more importantly later in life in their geriatric years. You will also feed less of this food on a per animal basis because a smaller amount of food contains what your cat needs. Overall healthy wet foods are well worth it, if only for the piece of mind that the ingredients are better for your cat than cheap crap.
You can start your research for a healthy cat food here if you are not ready to try feeding a Raw diet:
http://www.onlynaturalpet.com
If you want to buy in a store, Complete Petmart is a good store and carries quite a few natural, organic, and holistic blends. Also check with your local feed/grain stores.
I highly recommend you take the time to research for yourself, but the information I have given should get you off to a good start. Good luck choosing a new healthy food!

well there is a certain brand of food that is especially diet food. Try yuor local petstore. I suggest PetSmart or PETCO. It may be expensive but is worth it for your pet. :)

I really wouldn't worry about the cat that weights 9lbs. That is pretty normal. As for the 17lb cat, if the food is not working, talk to your vet, they may have special weight loss food that actually works. It can be pretty expensive though.

you could go to your local vet and get cat science diet my dog is on it and only weighs 10 pounds. she is a shiz-tzu