EndocrineCephalicPhaseResponsestoFoodCues: ASystematicReview

Abstract

Cephalicphaseresponses(CPRs)areconditionedanticipatoryphysiologicalresponsestofoodcues.Theyoccurbeforenutrientabsorptionandare hypothesizedtobeimportantforsatiationandglucosehomeostasis.Cephalicphaseinsulinresponses(CPIRs)andpancreaticpolypeptideresponses (CPPPRs)arefoundconsistentlyinanimals,buthumanliteratureisinconclusive.Weperformedasystematicreviewofhumanstudiestodetermine the magnitude and onset time of these CPRs. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were usedtodevelopasearchstrategy.Thetermsincludedinthesearchstrategywerecephalicorhormoneresponseorendocrineresponsecombined withinsulinandpancreaticpolypeptide(PP).Thefollowingdatabasesweresearched:Scopus(Elsevier),ScienceDirect,PubMed,GoogleScholar,and TheCochraneLibrary.Initially,582originalresearcharticleswerefound,50wereincludedforanalysis.Aninsulinincrease(≥1μIU/mL)wasobserved in41% ofthe treatments(totaln=119). In22% of all treatmentsthe increasewas significant frombaseline. The median(IQR) insulin increasewas 2.5(1.6–4.5)μIU/mL,30%abovebaselineat5±3min afterfoodcueonset(basedonstudytreatmentsthatinduced≥1μIU/mLinsulinincrease).A PPincrease(>10pg/mL)wasfoundin48%ofthetreatments(totaln=42).In21%ofthetreatments,theincreasewassignificantfrombaseline.The median(IQR)PPincreasewas99(26–156) pg/mL,68%above baselineat9±4min after foodcueonset(basedonstudytreatmentsthatinduced ≥1 μIU/mL insulin increase). In conclusion, CPIRs are small compared with spontaneous fluctuations. Although CPPPRs are of a larger magnitude, both show substantial variation in magnitude and onset time. We found little evidence for CPIR or CPPPR affecting functional outcomes, that is, satiationandglucosehomeostasis.Therefore,CPRsdonotseemtobebiologicallymeaningfulindailylife