Intermittent Fasting: What is it, and how does it work?

With intermittent fasting, you only eat during a specific time. Fasting for a certain number of hours each day or eating just one meal a couple days a week, can ... SkipNavigation COVID-19Updates Masksarerequiredinsideallofourcarefacilities.Wearevaccinatingalleligiblepatients.Learnmore: Vaccines,Boosters&AdditionalDoses|Testing|PatientCare|VisitorGuidelines|Coronavirus|EmailAlerts FindmoreCOVID-19testinglocationsonMaryland.gov. HealthHome WellnessandPrevention IntermittentFasting:Whatisit,andhowdoesitwork? ShareonFacebook ShareonTwitter ShareonLinkedin ShareonPinterest ShareviaEmail PrintthisPage FoodandNutrition Intermittentfastingisaneatingplanthatswitchesbetweenfastingandeatingonaregularschedule.Researchshowsthatintermittentfastingisawaytomanageyourweightandprevent—orevenreverse—someformsofdisease.Buthowdoyoudoit?Andisitsafe? Whatisintermittentfasting? Manydietsfocusonwhattoeat,butintermittentfastingisallaboutwhenyoueat. Withintermittentfasting,youonlyeatduringaspecifictime.Fastingforacertainnumberofhourseachdayoreatingjustonemealacoupledaysaweek,canhelpyourbodyburnfat.Andscientificevidencepointstosomehealthbenefits,aswell. JohnsHopkinsneuroscientistMarkMattson,hasstudiedintermittentfastingfor25years.Hesaysthatourbodieshaveevolvedtobeabletogowithoutfoodformanyhours,orevenseveraldaysorlonger.Inprehistorictimes,beforehumanslearnedtofarm,theywerehuntersandgathererswhoevolvedtosurvive—andthrive—forlongperiodswithouteating.Theyhadto:Ittookalotoftimeandenergytohuntgameandgathernutsandberries. Even50yearsago,itwaseasiertomaintainahealthyweight.JohnsHopkinsdietitianChristieWilliams,M.S.,R.D.N.,explains:“Therewerenocomputers,andTVshowsturnedoffat11p.m.;peoplestoppedeatingbecausetheywenttobed.Portionsweremuchsmaller.Morepeopleworkedandplayedoutsideand,ingeneral,gotmoreexercise.” Nowadays,TV,theinternetandotherentertainmentareavailable24/7.Westayawakeforlongerhourstocatchourfavoriteshows,playgamesandchatonline.We’resittingandsnackingallday—andmostofthenight.” Extracaloriesandlessactivitycanmeanahigherriskofobesity,type2diabetes,heartdiseaseandotherillnesses.Scientificstudiesareshowingthatintermittentfastingmayhelpreversethesetrends. Howdoesintermittentfastingwork? Thereareseveraldifferentwaystodointermittentfasting,buttheyareallbasedonchoosingregulartimeperiodstoeatandfast.Forinstance,youmighttryeatingonlyduringaneight-hourperiodeachdayandfastfortheremainder.Oryoumightchoosetoeatonlyonemealadaytwodaysaweek.Therearemanydifferentintermittentfastingschedules. Mattsonsaysthatafterhourswithoutfood,thebodyexhaustsitssugarstoresandstartsburningfat.Hereferstothisasmetabolicswitching. “IntermittentfastingcontrastswiththenormaleatingpatternformostAmericans,whoeatthroughouttheirwakinghours,”Mattsonsays.“Ifsomeoneiseatingthreemealsaday,plussnacks,andthey’renotexercising,theneverytimetheyeat,they’rerunningonthosecaloriesandnotburningtheirfatstores.” Intermittentfastingworksbyprolongingtheperiodwhenyourbodyhasburnedthroughthecaloriesconsumedduringyourlastmealandbeginsburningfat. IntermittentFastingPlans It’simportanttocheckwithyourdoctorbeforestartingintermittentfasting.Onceyougethisorhergo-ahead,theactualpracticeissimple.Youcanpickadailyapproach,whichrestrictsdailyeatingtoonesix-toeight-hourperiodeachday.Forinstance,youmaychoosetotry16/8fasting:eatingforeighthoursandfastingfor16.Williamsisafanofthedailyregimen:Shesaysmostpeoplefinditeasytostickwiththispatternoverthelongterm. Another,knownasthe5:2approach,involveseatingregularlyfivedaysaweek.Fortheothertwodays,youlimityourselftoone500–600caloriemeal.AnexamplewouldbeifyouchosetoeatnormallyoneverydayoftheweekexceptMondaysandThursdays,whichwouldbeyourone-mealdays. Longerperiodswithoutfood,suchas24,36,48and72-hourfastingperiods,arenotnecessarilybetterforyouandmaybedangerous.Goingtoolongwithouteatingmightactuallyencourageyourbodytostartstoringmorefatinresponsetostarvation. Mattson’sresearchshowsthatitcantaketwotofourweeksbeforethebodybecomesaccustomedtointermittentfasting.Youmightfeelhungryorcrankywhileyou’regettingusedtothenewroutine.But,heobserves,researchsubjectswhomakeitthroughtheadjustmentperiodtendtostickwiththeplan,becausetheynoticetheyfeelbetter. WhatcanIeatwhileintermittentfasting? Duringthetimeswhenyou’renoteating,waterandzero-caloriebeveragessuchasblackcoffeeandteaarepermitted. Andduringyoureatingperiods,“eatingnormally”doesnotmeangoingcrazy.You’renotlikelytoloseweightorgethealthierifyoupackyourfeedingtimeswithhigh-caloriejunkfood,super-sizedfrieditemsandtreats. ButwhatWilliamslikesaboutintermittentfastingisthatitallowsforarangeofdifferentfoodstobeeaten—andenjoyed.“Wewantpeopletobemindfulandtakepleasureineatinggood,nutritiousfood,”shesays.Sheaddsthateatingwithothersandsharingthemealtimeexperienceaddssatisfactionandsupportsgoodhealth. Williams,likemostnutritionexperts,regardstheMediterraneandietasagoodblueprintofwhattoeat,whetheryou’retryingintermittentfastingornot.Youcanhardlygowrongwhenyoupickcomplex,unrefinedcarbohydratessuchaswholegrains,leafygreens,healthyfatsandleanprotein. IntermittentFastingBenefits Researchshowsthattheintermittentfastingperiodsdomorethanburnfat.Mattsonexplains,“Whenchangesoccurwiththismetabolicswitch,itaffectsthebodyandbrain.” OneofMattson’sstudiespublishedintheNewEnglandJournalofMedicinerevealeddataaboutarangeofhealthbenefitsassociatedwiththepractice.Theseincludealongerlife,aleanerbodyandasharpermind. “Manythingshappenduringintermittentfastingthatcanprotectorgansagainstchronicdiseasesliketype2diabetes,heartdisease,age-relatedneurodegenerativedisorders,eveninflammatoryboweldiseaseandmanycancers,”hesays. Herearesomeintermittentfastingbenefitsresearchhasrevealedsofar: Thinkingandmemory.Studiesdiscoveredthatintermittentfastingboostsworkingmemoryinanimalsandverbalmemoryinadulthumans. Hearthealth.Intermittentfastingimprovedbloodpressureandrestingheartratesaswellasotherheart-relatedmeasurements. Physicalperformance.Youngmenwhofastedfor16hoursshowedfatlosswhilemaintainingmusclemass.Micewhowerefedonalternatedaysshowedbetterenduranceinrunning. Diabetesandobesity.Inanimalstudies,intermittentfastingpreventedobesity.Andinsixbriefstudies,obeseadulthumanslostweightthroughintermittentfasting. Tissuehealth.Inanimals,intermittentfastingreducedtissuedamageinsurgeryandimprovedresults. Isintermittentfastingsafe? Somepeopletryintermittingfastingforweightmanagement,andothersusethemethodtoaddresschronicconditionssuchasirritablebowelsyndrome,highcholesterolorarthritis.Butintermittentfastingisn’tforeveryone. Williamsstressesthatbeforeyoutryintermittentfasting(oranydiet),youshouldcheckinwithyourprimarycarepractitionerfirst.Somepeopleshouldsteerclearoftryingintermittentfasting: Childrenandteensunderage18. Womenwhoarepregnantorbreastfeeding. Peoplewithdiabetesorbloodsugarproblems. Thosewithahistoryofeatingdisorders. But,Williamssays,peoplenotinthesecategorieswhocandointermittentfastingsafelycancontinuetheregimenindefinitely.“Itcanbealifestylechange,”shesays,“andonewithbenefits.” Keepinmindthatintermittentfastingmayhavedifferenteffectsondifferentpeople.Talktoyourdoctorifyoustartexperiencingunusualanxiety,headaches,nauseaorothersymptomsafteryoustartintermittentfasting. FindaDoctor SpecializingIn: Nutrition WeightLoss AtAnotherJohnsHopkinsMemberHospital: HowardCountyGeneralHospital SibleyMemorialHospital SuburbanHospital FindaTreatmentCenter FindAdditionalTreatmentCentersat: HowardCountyGeneralHospital SibleyMemorialHospital SuburbanHospital Related FamilyMeals:CanTheyMakeYouHealthier? Barley,Farro,SorghumandMore:9WholeGrainstoTry BroccoliCheeseEggScramble AvocadoBlueberryMuffins RequestanAppointment FindaDoctor 410-955-5000 Maryland 855-695-4872 OutsideofMaryland +1-410-502-7683 International FindaDoctor SeeMore Related FoodandNutrition FamilyMeals:CanTheyMakeYouHealthier? FoodandNutrition Barley,Farro,SorghumandMore:9WholeGrainstoTry HeartHealthyRecipes BroccoliCheeseEggScramble RelatedTopics FoodandNutrition