I don't know what else I can do
I would have a go at radically changing which food types you are getting the calories from. Personally I find carbs are the devil, and I need to limit them to as few simple ones as possible (and eat only small quantities of whole grains).
I might not be a very good example to follow though because Simon (who can smell ketones, only a few people can) has noticed I go ketotic after long rides (or even medium ones sometimes). I must be breaking down a lot of fat and protein to supply myself with energy during the rides for this to happen.
If you actually want to try this on purpose then eat a diet of veggies, seeds, nuts, eggs and chicken breasts and nothing much else for a while. Avoid sugars, cereals, bread, potatoes, pasta and rice. I find this pretty easy to do by removing anything else from the house, but the hard bit is still to exercise while you are doing it. Robert Millar did rather well using that technique (although he didn't do the chicken breast or egg bit and was mostly vegan).