title: Diurnal variation of human sweet taste recognition thresholds is correlated with plasma leptin levels.
abstract: OBJECTIVE
  It has recently been proposed that the peripheral taste organ is one of the targets for leptin. In lean mice, leptin selectively suppresses gustatory neural and behavioral responses to sweet compounds without affecting responses to other taste stimuli, whereas obese diabetic db/db mice with defects in leptin receptor lack this leptin suppression on sweet taste. Here, we further examined potential links between leptin and sweet taste in humans.
  
  
  METHODS
  A total of 91 nonobese subjects were used to determine recognition thresholds using a standard stair-case methodology for various taste stimuli. Plasma leptin levels were determined by an enzyme-linked immunosorbent assay at several timepoints during the day under normal and restricted-meal conditions.
  
  
  RESULTS
  The recognition thresholds for sweet compounds exhibited a diurnal variation from 0800 to 2200 h that parallels variation for leptin levels, with the lowest thresholds in the morning and the highest thresholds at night. This diurnal variation is sweet-taste selective-it was not observed in thresholds for other taste stimuli (NaCl, citric acid, quinine, and mono-sodium glutamate). The diurnal variation for sweet thresholds in the normal feeding condition (three meals) was independent of meal timing and thereby blood glucose levels. Furthermore, when leptin levels were phase-shifted following imposition of one or two meals per day, the diurnal variation of thresholds for sweet taste shifted in parallel.
  
  
  CONCLUSIONS
  This synchronization of diurnal variation in leptin levels and sweet taste recognition thresholds suggests a mechanistic connection between these two variables in humans.
authors.affiliation: Section of Oral Neuroscience, Graduate School of Dental Sciences, Kyushu University, Fukuoka, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Nakamura
authors.forename: Keisuke
authors.initials: K
authors.lastname: Sanematsu
authors.forename: Rie
authors.initials: R
authors.lastname: Ohta
authors.forename: Shinya
authors.initials: S
authors.lastname: Shirosaki
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Koyano
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Nonaka
authors.forename: Noriatsu
authors.initials: N
authors.lastname: Shigemura
authors.forename: Yuzo
authors.initials: Y
authors.lastname: Ninomiya
mesh_terms: D000328:Adult; D002940:Circadian Rhythm / Q000502:physiology*; D019343:Citric Acid / Q000494:pharmacology; D005260:Female; D006801:Humans; D007328:Insulin / Q000097:blood; D020738:Leptin / Q000097:blood*; D008297:Male; D011803:Quinine / Q000494:pharmacology; D012965:Sodium Chloride / Q000494:pharmacology; D012970:Sodium Glutamate / Q000494:pharmacology; D013650:Taste Buds / Q000187:drug effects / Q000502:physiology; D013652:Taste Threshold / Q000502:physiology*; D055815:Young Adult
chemical_list: D007328:Insulin; D020738:Leptin; D019343:Citric Acid; D012965:Sodium Chloride; D011803:Quinine; D012970:Sodium Glutamate