An animal that is too skinny is not really healthy, as it does not have a lot of reserves to rely on when ill or when there is a little less food. In chameleons it is not easy to see if it is skinny or not. It is natural to see the ribs of a chameleon on its body. They also have a rather flat body shape that does not really show a fatty belly like we are used to with other pets like cats, dogs and horses. In short, it is hard to correctly asses if your chameleon looks normal for a chameleon or is a bit too skinny.
To asses the body fat of a chameleon you need to look at its back and the bone ridge on its back. Your chameleon is probably too skinny if you see a clear ridge on its back. Check its back when your chameleon is completely calm, as it could flatten its body when it feels threatened or is stressed. This will make a healthy chameleon also appear to be skinnier.
You can also check out the belly of your chameleon to see how much fat it has. The belly should be a bit rounded when the chameleon is relaxed and calm. It should not be a straight line from front legs to its back legs.
If you know more about chameleons you will quickly asses the condition of a chameleon. You will know what a healthy chameleon will look like, and what a skinny chameleon will look like. A skinny chameleon also has skinny legs, a skinny tail and a skinny head. Its just when you are inexperienced that you should asses the chameleons back and belly.