Sleepiness after a meal or postprandial somnolence as its called, is interesting. I have always lamented at how if I could just get that deep sleepiness feeling right when im suppose to go to bed, things would be ssooooo fucking awesome!
Everyone knows that "carby" meals make you sleepy, but it doesnt work with 100% consistency. Sometimes carby meals dont have any affect on me at all. What I have noticed is that usually for a meal to make me sleepy, it needs to be 1) large & carby , and 2) the first meal of the day, breaking an extended fast.
Theres been a number of studies showing that exercise in the morning helps one sleep at night. And theres an interesting thing on that wikipedia article about the large neutral amino acid transporter. Wikipedia says that one of the possible explanations for postprandial somnolence is insulin stimulating BCAA uptake into skeletal muscle, but NOT tryptophan, thereby leaving tryptophan as the more abundant amino acid in the blood, giving it exclusive access to the transporter. ( apparently under basal conditions all the amino acids 'compete' for transport into the brain )
The result of more insulin is more tryptophan into the brain -> more seretonin -> more melatonin in the brain.
During my "socially defiant" days when im doing a more high-carb diet, I notice that I sleep much more deeper and longer than compared to when im on ketosis and lowcarbing. Also, now and then, I watch some of durianriders videos for a good laugh, and one thing he boasts often about is how he gets 12hrs of sleep at night followed by some gibberish mumble that "carbs = brain seretonin". Another thing that durianrider is fanatic about is dates. I couldnt help but notice wikipedia has this little gem on its tryptophan page "It is particularly plentiful in dried dates"
This could all be rubbish as im speculating here, but when lowcarbing, the only time you spike insulin is with protein heavy meals. But heres the crux, during such a meal, you also spike plasma amino acids. So when lowcarbing, you always spike insulin and plasma BCAA together, thereby never giving tryptophan a selective advantage at getting into the brain via the large neutral amino acid transporter.
Besides, how exactly does tryptophan get into the brain anyway?
What if the large neutral amino acid transporter is the only way it can get in?
Does that mean on a lowcarb diet, tryptophan is ALWAYS fighting with the other amino acids for entry, because your always spiking insulin and plasma amino acids simultaneously? Is it even worse if your never exercising and never making your muscles more insulin sensitive?
Here is exactly where the exercise anecdote comes in, exercise makes your muscle insulin sensitive, and insulin only drives tryptophan's competitors into muscle, not tryptophan itself! This explains why exercise in the morning is affective for sleep, because if you exercise in the morning, its generally before any food intake. So if you exercise in the morning, you get insulin sensitive muscles ready for the next meal to suck up all those serum BCAA, leaving tryptophan alone in the blood to enter the brain uninhibited.
Ofcourse, exercise need not be necessary, the other spin-off to this argument is that while lowcarbing, it might be good now and then to spike insulin without spiking plasma amino acids. And what better way to do this than a bag of dried dates? ( since dried dates are a good source of tryptophan ). Another good thing about dates is that they do not contain any starch, its mostly more complex carbs like sucrose/fructose, so the assault on your blood sugar will be more timid.
So heres my conclusion, if your lowcarbing and having difficulty sleeping, try having a bag of dried dates now and then, have them ON THIER OWN, not with any other food. Dried dates are not hyper-palatable, I can usually only get through about 130grams ( 88g carbs ) of them before my body tell me "hey fat dude, thats enough!" and I push the bag away. And im usually a big eater aswell.