The doctors kept assuming I had sleep apnea... To be fair all the symptoms did fit with sleep apnea, my weight, my need for long periods of sleep, brain fog, all of it. Despite that they sent me to sleep studies over and over again and the sleep studies never came back with anything indicating apnea. As far as they could tell I just had a lot of trouble falling asleep. So I got a diagnosis of delayed sleep phase disorder.
But no matter how many times they rules out sleep apnea every new doctor insisted that must be it and refused to seriously consider anything else.
As for food groups, not really. I do have a celiacs test pending for shits and giggles but im not expecting anything from that. I have been using a continuous glucose monitor (im not diabetic though) and the blood respond to various foods has been very revealing.
Have you tried a CGM for non-diabetics?