Sleep and food – what do we know?

We all know that the caffeine in coffee or tea can keep us awake.  What about foods that make us sleepy?  Thanksgiving dinner comes to mind, the supposed sleep-inducer being the turkey, although it’s more likely because it’s a big meal.  For people looking to combat insomnia or create better sleep quality, eating Thanksgiving dinner every night just isn’t practical.  There are a variety of studies investigating possible sleep-food effects, but so far there are two significant problems with many of these studies:

  1. Small sample sizes — some studies only had 6 people, many had around 12, which doesn’t make for convincing data.
  2. Short duration — many studies were only for one day.  Again, the effect could just be something random that day.

When you’re talking about something as complex as sleep, these limitations aren’t surprising.  Any such study needs to collect data on the phases of sleep: Rapid Eye Movement (REM — associated with dreams), Slow Wave Sleep (SWS — a deep restorative sleep), Sleep-Onset Latency (SOL — how long it takes to fall asleep), wake after sleep-onset (WASO — insomnia), sleep efficiency (SE – quality of the sleep experience) and possibly other metabolic variables.  Subjects are hooked up to all kinds of measuring equipment while sleeping.  Who is going to volunteer for that?  Most people are too busy, so no wonder many of the studies are done with “healthy young adults” (i.e. college students).  All of whom bring along with own personal variables, from caffeine consumption to exercise level, to weight to what kind of mattress or pillow they prefer.  Sleep is complicated, so measuring it accurately is also going to be complicated, and study results may not be very helpful.

Meal composition, intake of certain nutrients and unique effects of specific foods are all research targets for the sleep effects of food.  Take milk.  We’ve all heard the advice to drink a glass of milk — or better yet warm milk — before bedtime, because milk is supposed to enhance sleep.  True?  In fact, milk doesn’t have a consistent impact on sleep quality, but there’s a slight wrinkle to this.  So-called “nighttime milk” may have some beneficial impact on sleep quality.  When cows are milked in the evening, you get nighttime milk, which is higher in the sleep-inducing hormone melatonin than morning milk.  It stands to reason that milk with higher melatonin content might be helpful.  Research suggests the concentration needs to be about 10 times higher than daytime milk melatonin to have an effect.  How do you tell?  You don’t.  There is no labeling requirement or official measurement standards for melatonin in any foods, nor are there approved label claims for melatonin content.  There’s no labeling for “nighttime milk”.  You might have to buy your own cow and milk it at night.

There has been a lot of research on the impact of total diet on sleep.  High carb, low carb, high fat, high protein, low glycemic index and ketogenic diets have all been studied.  There are a few general conclusions.  High carb, particularly simple carbs and sugar, tend to increase REM sleep and reduce the restorative slow wave sleep.  High fat is associated with poor sleep efficiency and less REM.  A Mediterranean style diet was linked to better sleep efficiency.  There are a variety of theoretical metabolic explanations for all of these findings, such as the effects of higher insulin and energy availability from a high intake of simple carbs.  And of course, not everyone will react the same to the same types of diets or meals.

Melatonin is a hormone made by animals, including humans and cows, which regulates the sleep-wake cycle and other metabolic systems.  Plants don’t sleep, but some also make this chemical, which may have a protective role as an anti-oxidant. You can buy melatonin supplements, but you can also get melatonin from foods.  Two unique foods do stand out as potential sleep enhancers because of their unusual melatonin content:

  1. Kiwi
  2. Tart Cherries

While kiwis are a popular and widely available fresh fruit, tart cherries are another matter.  These are pie cherries, not the cherries you eat fresh.  They have a mouth-puckering tang, which makes them good for pie as long as you use enough sugar.  Who decided to investigate them for sleep enhancement?  I have no idea, although it’s not surprising that a lot of the research on tart cherries is funded by cherry producer organizations.  Adults with insomnia experienced improved sleep when drinking two 8-oz glasses of tart cherry juice/day.  Studies using kiwi found that eating 2 kiwi fruits an hour before bedtime reduced sleep disorders.

For the person with insomnia, this might sound really attractive: a simple solution using healthful foods.  The problem is you have to eat/drink those foods every day.  It’s not a quick fix cure.  Kiwis are juicy, high fiber, have significant vitamin C and are modest calorie (about 40-45 each, or not quite 100 for two), so not a bad choice.  Tart cherry juice is, well,… tart.  It’s not super-acidic like lemon juice, but it’s not sugary sweet.  It has a rich, deep fruity flavor.  Two glasses a day might get to be a bit much.  Also it will set you back $2-$3 per day, along with about 300 calories.  If you’re watching calories, you’d have to shave 300 calories off your diet somewhere else.   And be sure to buy pure tart cherry juice, not some sugar-sweetened cherry drink.

Other foods with above average melatonin content include bananas, plums, grapes, wine, pineapple and olive oil.  A sleep-enhancing dinner might include a salad with olive oil dressing, a glass of red wine or tart cherry juice, and a fruit salad with banana, pineapple and kiwi.

The impact of diet and food on sleep remains a mystery.  At best, we know the two are related.  But blaming your sleep disturbances on food or trying to cure yourself with food might not work.  Sleep is impacted by plenty of other factors, from stress and anxiety to breathing problems, medical problems, prescription drugs, alcohol use, caffeine intake, hydration and allergies.  Happily, the high melatonin foods are mostly healthy for other reasons, so adding them to your diet could be a win-win strategy.

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