Ivy is too skinny :(

[Sterluv]

She used to be at a good weight but she's lost a lot of it and I'm afraid she's too thin When she rolls up into ball I can see her backbone a lot. Luna is slightly chubby and they eat the same things. Why is she getting so thin, and is there anything I can do to help her gain some more weight? Thank you

[souffle]

Weight loss is quite common as hamsters get older. They are less able to process food and also tend to be less active so the muscles are not so toned.
You should check her teeth to ensure she is able to eat well and also give her a good health check looking for anything that might indicate an illness.
Older hamsters should not be given lots of protein as it can strain the kidneys but some extras more frequently like porridge and babyfood can help them keep weight on especially as the weather gets colder and they need more food to keep themselves warm.

[Sterluv]

Thank you

[ercvt]

Luna and Ivy are together in the same cage, right? If so, I would make sure that Luna is letting Ivy eat as well.
I totally agree with checking her teeth and also making sure that she is able to get to her bowl easily. If there are a lot of levels, make sure it is on the one she is normally on or on the bottom. Or put multiple bowls, or low lids for her to eat from.