title: High-glycemic-index carbohydrate meals shorten sleep onset.
abstract: BACKGROUND
  Dietary carbohydrate intake has been shown to increase the plasma concentration of tryptophan, a precursor of serotonin and sleep-inducing agent.
  
  
  OBJECTIVE
  To investigate the role of carbohydrate in sleep induction, we explored the effect of glycemic index (GI) and meal time on sleep in healthy volunteers.
  
  
  METHODS
  We compared the effect of high- and low-GI carbohydrate-based meals ingested 4 h before bedtime on sleep quality. We also evaluated the effect of the timing of high-GI meals (4 h compared with 1 h) on sleep quality. Twelve healthy men (aged 18-35 y) were administered standard, isocaloric (3212 kJ; 8% of energy as protein, 1.6% of energy as fat, and 90.4% of energy as carbohydrate) meals of either Mahatma (low GI = 50) or Jasmine (high GI = 109) rice 4 h before their usual bedtime. On another occasion, the high-GI meal was given 1 h before bedtime. The participants underwent a familiarization night followed by 3 test nights in random order 1 wk apart.
  
  
  RESULTS
  A significant (P = 0.009) reduction in the mean (+/-SD) sleep onset latency (SOL) was observed with a high-GI (9.0 +/- 6.2 min) compared with a low-GI (17.5 +/- 6.2 min) meal consumed 4 h before bedtime. The high-GI meal given 4 h before bedtime showed a significantly shortened SOL compared with the same meal given 1 h before bedtime (9.0 +/- 6.2 min compared with 14.6 +/- 9.9 min; P = 0.01). No effects on other sleep variables were observed.
  
  
  CONCLUSIONS
  We showed that a carbohydrate-based high-GI meal resulted in a significant shortening of SOL in healthy sleepers compared with a low-GI meal and was most effective when consumed 4 h before bedtime. The relevance of these findings to persons with sleep disturbance should be determined in future trials.
authors.affiliation: School of Exercise and Sport Science, Faculty of Health Sciences, The University of Sydney, Sydney, Australia.
authors.forename: Ahmad
authors.initials: A
authors.lastname: Afaghi
authors.forename: Helen
authors.initials: H
authors.lastname: O'Connor
authors.forename: Chin Moi
authors.initials: CM
authors.lastname: Chow
mesh_terms: D000293:Adolescent; D000328:Adult; D001786:Blood Glucose / Q000032:analysis; D004040:Dietary Carbohydrates / Q000008:administration & dosage / Q000494:pharmacology*; D005260:Female; D038321:Glycemic Index / Q000502:physiology*; D006801:Humans; D006815:Hunger / Q000502:physiology; D008297:Male; D012527:Satiation / Q000502:physiology; D012894:Sleep Stages / Q000187:drug effects* / Q000502:physiology
chemical_list: D001786:Blood Glucose; D004040:Dietary Carbohydrates