Earlier quoted context omitted.
It was eating wheat for me as well. Once I started eating according to the ketogenic diet, I no longer needed naps during the day.
I'm another one of these: stopped eating wheat, immediately needed less sleep. Does anyone know of any research on this phenomenon? There are obviously lots of anecdotes, but I can't find any studies.
tl;dr: the insulin spike from high glycemic index foods causes sleepiness, and low insulin sensitivity which can be caused by sleep debt and lack of exercise exacerbates it.
https://en.wikipedia.org/wiki/Postprandial_somnolence
> When foods with a high glycemic index are consumed, glucose is absorbed rapidly from the gastrointestinal tract into the bloodstream, and in individuals with normal carbohydrate metabolism, insulin levels rise concordantly to drive glucose into the body's tissues and maintain blood glucose levels in the normal range. Insulin stimulates the uptake of valine, leucine, and isoleucine into skeletal muscle, but not uptake of tryptophan. ... Uptake of tryptophan by the brain thus increases. In the brain, tryptophan is converted to serotonin, which is then converted to melatonin. Increased brain serotonin and melatonin levels result in sleepiness.