Well just cut down a bit on any and all carbs regardless of colour - cos they are the main thing that human bodies use to obtain their glucose - even though it's entirely possible to make glucose out of protein and fat, it's a bit harder work for the body, hence as long as it gets enough from carb, it doesn't bother converting anything else to glucose.
Of course the body needs some of the other stuff in the food anyway, but any excess of any food doesn't just magically evaporate - the body automatically stores it 'in case of a period of starvation' - which of course never happens in this day and age - so we're just lumbered with the body fat that's the body's 'starvation larder'.
Diabetes is a term for the inability of a body to efficiently (if at all as in Type 1) deal with carbohydrate for whatever out of shedloads of reasons, it can't.
High, or long term, steroid treatment can cause it. But there again, so can statins if you happen to be one of the people that they have that effect on. If it is only the drug(s) then if you're only on them temporarily then it may be possible to reverse that effect but not if there's no alternative treatment for whatever it is.
So as I said - just try and help yourself in the easiest way possible, by cutting down on carbs (and sugar is simply just another carb as far as I'm concerned) Even lettuce has some carbs if you eat half a ton of it so nobody's expecting anyone to eliminate them ALL - but everyone's tolerance for them is finite, and totally different same as the colour of your hair (30+ different shades in any head of natural hair, unless you had it dyed this morning) or eyes.
Testing different foods with a BG monitor is the only way to do a spot check.