How to put on some weight on my cat

I have two cats, one, Izzy, is nice and well filled out but not too plump; the other, Pinky, is, I think, too thin. They eat the same food but I would like to put just a few pounds on Pinky. I can feel his ribs and I don't think that's right. But, I don't know what I can feed him to "fatten" him up a bit. I don't want to give him cream or anything like that. Does anyone know if there is some kind of supplement that I could give him. He has a very good appetite, that's not a problem, but just can't seem to put on any weight. Vet says there is nothing physically wrong with him and he is totally healthy.
Thanks everyone and anyone for your help.

Well you should be able to easily feel his ribs and he should have a waist, can you easily see or feel his spine or tail bones? Can you post a picture, from the top and from the side straight on? Or search for a weight chart for cats and compare. Make sure he's actually underweight before you start feeding more? A few pounds is a lot on a cat. Do you free fed the cats?

You should be able to feel ribs, theyre too fat if you cant. Chances are izzy could lose a few pounds and pinky is how a cat should be. Most people think the ideal weight on cats and dogs are "too skinny". Post a picture though

Unless you can see(on short haired cats) or feel his spine vertebrae(which go the length of the tail as well) on both the back and tail(Sirius happens to have a very skinny tail so I think I'll always be able to feel his tail bones) the cat is at it's ideal weight. Sirius is filling out, he really was too thin when I got him from the rescue but now he's at a good weight. If your vet says he's fine and doesn't need to gain weight then he really is and I wouldn't worry about it. You should be able to feel their ribs.

It is a lot easier to keep them at an ideal weight than to try and make them lose weight since the loss has to be done very slowly. Trust me I have been there and it's a PITA to do. I forgot to reduce the amount I was feeding Attitude after she was spayed and she only had 0.5- 1 lb to lose and it took over 6 months to get her there(that includes the time it took to find the correct amount to feed her and Nuts so she lost weight but wasn't dropping it too quickly.)

Taryn

I have one cat that I have to consistently watch to ensure she doesn't drop below 11 pounds, and that's the lowest the vet is comfortable with her carrying. As a kitten into young adulthood, I had a really hard time keeping weight on her and the only thing that finally worked (and continues to work) is a raw-fed diet.

I assume you're feeding kibble; can you either start feeding canned foods (which are generally higher in protein, with more of that protein actually coming from meats the cat can digest) and/or can you start giving Pinky an extra meal a day of about an ounce of plain, raw meats like chicken, turkey, beef, etc. (not deli meats or anything that's been marinated)? Either of these could work, but especially the one raw meal, as you would be giving Pinky exactly what his body is both craving and is built to process in a most incredibly efficient manner.

Good luck! I know what it's like to worry about a cat becoming or staying too thin.

AC