title: The internal circadian clock increases hunger and appetite in the evening independent of food intake and other behaviors.
abstract: OBJECTIVE
  Despite the extended overnight fast, paradoxically, people are typically not ravenous in the morning and breakfast is typically the smallest meal of the day. We assessed whether this paradox could be explained by an endogenous circadian influence on appetite with a morning trough, while controlling for sleep/wake and fasting/feeding effects.
  
  
  METHODS
  Twelve healthy non-obese adults (six males; age, 20-42 years) were studied throughout a 13-day laboratory protocol that balanced all behaviors, including eucaloric meals and sleep periods, evenly across the endogenous circadian cycle. Participants rated their appetite and food preferences by visual analog scales.
  
  
  RESULTS
  There was a large endogenous circadian rhythm in hunger, with the trough in the biological morning (8 AM) and peak in the biological evening (8 PM; peak-to-trough amplitude = 17%; P = 0.004). Similarly-phased significant endogenous circadian rhythms were present in appetites for sweet, salty and starchy foods, fruits, meats/poultry, food overall, and for estimates of how much food participants could eat (amplitudes 14-25%; all P < 0.05).
  
  
  CONCLUSIONS
  In people who sleep at night, the intrinsic circadian evening peak in appetite may promote larger meals before the fasting period necessitated by sleep, whereas the circadian morning trough would theoretically facilitate the extended overnight fast. Furthermore, the circadian decline in hunger across the night would theoretically counteract the fasting-induced hunger increase that could otherwise disrupt sleep.
authors: Medical Chronobiology Program, Division of Sleep Medicine, Department of Medicine, Brigham and Women's Hospital, Boston, MA, USA. fscheer@rics.bwh.harvard.edu
authors: Frank A J L
authors: FA
authors: Scheer
authors: Christopher J
authors: CJ
authors: Morris
authors: Steven A
authors: SA
authors: Shea
mesh_terms: D000328:Adult; D001066:Appetite / Q000502:physiology*; D001831:Body Temperature; D002755:Choice Behavior; D057906:Circadian Clocks / Q000502:physiology*; D004435:Eating / Q000502:physiology*; D002149:Energy Intake; D005215:Fasting; D005260:Female; D005518:Food Preferences; D006801:Humans; D006815:Hunger / Q000502:physiology*; D008297:Male; D012890:Sleep; D013997:Time Factors; D055815:Young Adult