About two weeks ago NPR program Fresh Air, Terry Gross interviewed neuroscientist Penelope Lewis about work at the Sleep and Memory Lab at the University of Manchester in England. You can both listen to and read the transcript here. Naturally, my ears perked up when this part of the conversation took place:
GROSS: Now you advise eating your last meal of the day in four to five hours before you go to bed, but then having a light snack - how long before you go to bed?
LEWIS: About an hour before you go to bed.
GROSS: And why is that helpful to have a snack?
LEWIS: Well, it could be helpful for two reasons. Firstly, we all know how hard it is to fall asleep if you're hungry, so you want to avoid that. But secondly, there are certain foods which contain proteins which actually promote sleep. And so and what they are is proteins that get broken down and processed to form neurotransmitters that promote sleep. And so if you have a snack that contains those, it can actually help you to sleep.
GROSS: And what foods have that function?
LEWIS: Well, there are lots of different foods, but things like bananas, turkey. I think tuna fish was one. There are a whole range of very common foods that contain these proteins.
And with that rather vague answer (I think I could actually hear the "Dammit Terry, I'm a neuroscientist, not a dietitian" in her voice), and my guess is that there were many people that hit the Internet to search for "these foods that contain proteins that actually promote sleep." And these people probably also got a wealth of conflicting information about when to snack before bed, what to snack on before bed, etc. So what exactly are "these proteins that contain sleep?"
First of all, I do have to disclose that I haven't read her book yet as I have only made it to the "put it on my Amazon.com wish list" stage so far. If she does wind up saying something different in the book than what I inferred from the interview, I will definitely do a post about "SkepticRD eats crow" or something like that. Anyway, I have a feeling that she was talking about eating foods that contains an essential amino acid (a.k.a. a protein building block that we must get from our diet) called L-tryptophan. In short, tryptophan helps us produce a neurotransmitter called serotonin, which puts us in a better mood and helps us relax, and then the serotonin in turn helps us make melatonin, a hormone that helps us control our sleeping and waking cycles. So, it sounds like we should eat something like tuna (which does contain tryptophan) before bed and then have plenty of blissful sleep, right? (Of course in my house, the sleep would be interrupted by the cat trying to sit on my head, but that's another story).
Unfortunately for those of you who were hoping to find a miracle, as Dr. Ben Goldacre of "Bad Science" fame is fond of saying, "I think you'll find it's a bit more complicated than that." When we eat foods that contain tryptophan, which includes pretty much all animal protein (including dairy), nuts/seed, and legumes/soy, we wind up storing that in the body so that it can hang out waiting to be made into niacin or serotonin. For the "serotonin boost" however, you will need the help of carbohydrate containing food to take that stored tryptophan to convert it to serotonin.
Before you eat that entire bag of tortilla chips for bed however (and you know who you are), keep in mind that you maybe only need about 15 grams of carbohydrate to put this into effect (that is maybe about 10 tortilla chips). Naturally, you probably shouldn't have something that is empty of nutrition either, and I know I can't stop at 10 tortilla chips, so I don't even start (I just commandeer the bowl at restaurants). A cup of berries, a small apple, a handful of sweet potato fries or chips (preferably homemade), 15 baby carrots, or even some home-popped popcorn would suffice.
Now, I can see a whole bunch of people with wide eyes thinking, "Oh, that's why I had trouble sleeping when I was doing a very low carbohydrate diet" and then another group of people furrowing their brows thinking "wait a minute, I started sleeping better when I reduced my carbohydrate intake." In the first group, you probably had the same rough adjustment that many people have when switching from primarily glucose to ketones for fuel, so you probably sleep a little better once your body adjusted and/or you were able to increase your carb intake after the first phase. The second group might have started eating more protein when they reduced their carbs, or if they were diabetic/pre-diabetic the lack of blood sugar swings probably contributed to better sleep. Keep in mind too that your quality of sleep, as mentioned by Dr. Lewis in the interview, is impacted by more than just your diet. If you have improved your diet, but you don't have a regular schedule, or your room isn't dark enough, or you're drinking too much caffeine close to bed time, or you drink too much alcohol close to bedtime, or you're taking a medication that impacts sleep, you still have some other problems to work out for you to get the rest you need.
Take home message--eat an adequate amount of protein during the day, and having a small amount of nutrient rich carbohydrate foods might help you sleep better, but think about other parts of your lifestyle that might be interfering with sleep as well.