Written by Chrystal Moulton, Staff Writer. In a small human study, researchers found that sleep time is reduced by 38.3% if a high glycemic meal (sugar and substances that convert to sugar) is consumed 4 hours before bedtime.
Onset of sleep is determined by the availability of tryptophan to the brain. Generally, the ratio of tryptophan to other large neutral amino acids (such as L-tyrosine and L-leucine) allows us to determine the availability of tryptophan and the likely onset of sleep. In other words, a high ratio of tryptophan to large neutral amino acids (LNAA) would effectively increase the onset of sleep in individuals. Previous research has shown that insulin triggers uptake of large neutral amino acids (LNAA) into the muscles.(1) This would, in turn, naturally reduce LNAA levels in plasma and increase the ratio of tryptophan to LNAA. Glucose, the simplest form of sugar, triggers release of insulin into the bloodstream. Therefore, consuming foods that are high in glucose and other carbohydrates could help to reduce LNAA and increase tryptophan availability to the brain. In the present study (2), researchers wanted to test the effect of high glycemic index food on sleep onset.
Twelve healthy young men aged 18-35years old with normal body weight (body mass index (BMI): 18.5-25 kg/m2) were recruited for this study. Participants were given one of three standardized meals on 3 test days one week apart. They were given:
- A high glycemic index meal 4 hours before bedtime
- A high glycemic index meal 1 hour before bedtime
- A low glycemic index meal 4 hours before bedtime
Participants were screened for presence of any sleep disorders, mental disorders, chronic conditions, and drug abuse. Subjects also completed a two-week sleep diary before the full sleep study.
Researchers collected blood each day for glucose analysis before the meal and 15, 30, 45, 60, 90, and 120min after the meal for the “4 hours before bedtime” protocol and 15, 30, and 45min after the meal for the “1 hour before bedtime” protocol. Participants were surveyed on their level of sleepiness at 30min and 1h, 2h, 3h, and 4 hours after each meal. Urine samples were also taken before bedtime to the next morning to measure a stable metabolite of melatonin to determine the level of melatonin in the body during the testing period.
As expected, there was a significant spike in blood glucose 30-45mins after consumption of the high glycemic index meal versus the low glycemic index meal (336.2 ± 61.9 mmol/L vs. 237.1 ± 69.3 mmol/L, p=0.009). Urine tests for the melatonin metabolite showed no significant differences between the groups either before bedtime or throughout the night. Average sleep onset was significantly reduced by 8.5 ± 9.3min after consumption of the high glycemic index meal 4 hours before bedtime compared to the low glycemic index meal consumed 4 hours before bedtime (p=0.009). When comparing both high glycemic index meals, sleep onset was significantly reduced by 5.6 ± 6.3min (p=0.01).
Overall researchers were able to show that a high glycemic meal 4 hours before bedtime compared to a low glycemic meal shortened sleep onset by 48.6% in healthy sleepers. And when comparing both high glycemic meal groups, consumption 4 hours before bedtime significantly shortened sleep by 38.3%.
Source: Afaghi, Ahmad, Helen O’connor, and Chin Moi Chow. “High-glycemic-index carbohydrate meals shorten sleep onset.” The American journal of clinical nutrition 85.2 (2007): 426-430.
© 2007 American Society for Nutrition
Posted March 20, 2014.
Chrystal Moulton BA, PMP, is a 2008 graduate of the University of Illinois at Chicago. She graduated with a bachelor’s in psychology with a focus on premedical studies and is a licensed project manager. She currently resides in Indianapolis, IN.
References:
- Berry EM, Growdon JH, Wurtman JJ, Caballero B, Wurtman RJ. A balanced carbohydrate: protein diet in the management of Parkinson’s disease. Neurology 1991;41:1295–7
- Afaghi A, O’Connor H, Chow CM. High-glycemic-index carbohydrate meals shorten sleep onset. Am J Clin Nutr. 2007 Feb;85(2):426-30.
