Never have business meetings right after lunch; or, why carbohydrates make you sleepy

Your mother probably told you that eating a big meal right before bedtime would give you nightmares. Maybe not nightmares, but research has shown that avoiding meals close to bedtime can help reduce sleep disturbances like insomnia or waking up too early. Are there foods that will help improve sleep?

Researchers in Australia noted that high-Glycemic-Index carbohydrates can increase the blood's level of a macronutrient known as tryptophan, which is a precursor for brain serotonin, a sleep-inducing hormone. They theorized that carbohydrates might then help people go to sleep more quickly and perhaps even improve their sleep quality (Am J Clin Nutr 2007;85(2):426-30).

To test their hypothesis, they recruited twelve healthy men between the ages of 18 and 35 who had normal sleep patterns. One night per week for four weeks they spent in the sleep laboratory, where their sleep quality and the time between going to bed and sleeping was recorded. The first night was a control night: no meal was given. The second through fourth nights, once per week thereafter, each subject was given one of the following types of meals: a high-GI meal given about four hours before bedtime, a high-GI meal given one hour before bedtime, and a low-GI meal given four hours before bedtime. During each visit, the subjects were asked to rate how sleepy they felt on a four-point scale every thirty minutes after their meal.

The scientists found that the high-GI meal given four hours before bedtime reduced a subject's time to sleep by almost 50% when compared to the low-GI meal also eaten four hours before bed. Similarly, the high-GI meal eaten one hour before bedtime shortened the time to sleep by just over 38% compared to the low-GI meal. The subjects also reported feeling sleepier after the high-GI meals, regardless of when they ate. Their sleep quality remained about the same.

What this means for you

The meal in this study was limited to all carbohydrates: in this case, two different types of rice. Large amounts of protein with your meal can reduce the Glycemic Index of the meal as a whole, so if you're having trouble getting to sleep, make sure you eat early enough and that your evening meal is well balanced between carbohydrates, fat, and protein. On the other hand, lunchtime is probably not the best time to be eating a big pasta dish if you have business meetings in the afternoon.

First posted: February 23, 2007