The lowdown on in­ter­mit­tent fast­ing

THEY’RE A HOT TREND RIGHT NOW – BUT DO FAST­ING DI­ETS RE­ALLY WORK? LINDA MU­SIC IN­VES­TI­GATES

Good Health (Australia) - - Content -

Eat very lit­tle today, eat as much as you want to­mor­row. Stop eat­ing af­ter tonight’s din­ner and eat noth­ing un­til lunchtime to­mor­row. Skip break­fast and lunch al­to­gether, mak­ing sure to leave 24 hours be­tween meals… Hmm. With so many in­ter­mit­tent fast­ing pro­grammes out there, it’s no won­der we’re feel­ing be­wil­dered. To add to the con­fu­sion, ad­vo­cates are promoting it not only as a way to lose weight, but as the an­swer to all our health prob­lems, yet oth­ers only high­light the dangers. De­pend­ing on what you read, in­ter­mit­tent fast­ing can in­crease longevity, re­duce choles­terol lev­els, de­crease in­flam­ma­tion, re­lieve asthma, de­crease your chances of can­cer and even re­verse di­a­betes. But what ex­actly is it, how do you ac­tu­ally do it and are the health ben­e­fits re­ally worth it?

In­ter­mit­tent fast­ing in­volves cy­cling be­tween pe­ri­ods of eat­ing and pe­ri­ods of not eat­ing. This can mean reg­u­larly ab­stain­ing from food dur­ing cer­tain time pe­ri­ods, re­duc­ing your calo­rie in­take for a cou­ple of days each week or, for the stronger-willed, not eat­ing for 24 hours once or twice a week.

1 Calo­rie-con­trolled in­ter­mit­tent fast­ing

Made pop­u­lar by Dr Michael Mosley’s 5:2 Diet and Krista Varady’s Ev­ery Other Day Diet, this form of fast­ing does not re­quire that you go with­out food. Rather, it al­lows you to eat ev­ery day, re­strict­ing your calo­rie in­take on fast­ing days and eat­ing nor­mally on the oth­ers. The 5:2 Diet rec­om­mends that you re­strict your­self to 500-600 calo­ries for at least two days per week. The Ev­ery Other Day Diet rec­om­mends lim­it­ing calo­ries to 500 calo­ries on al­ter­nate days. Ac­cred­ited di­eti­tian Gabrielle Maston ex­plains that this type of fast­ing helps us to lose weight in two ways. “Firstly, by tak­ing in less en­ergy from food, the

If you’re hav­ing a fast­ing day, don’t waste most of your al­lowance on items like white bread and pasta that are full of empty calo­ries. In­stead go for whole foods and lots of veges to keep your­self feel­ing full and get­ting all the nu­tri­ents you need.

body needs to ex­pend its fat stores, which leads to weight loss.”

The sec­ond and un­ex­pected way that in­ter­mit­tent fast­ing helps lead to weight loss is by chang­ing peo­ple’s psy­chol­ogy.

“When caloric in­take is re­duced,” says Maston, “you get used to eat­ing less and your per­cep­tion about how much you need to eat on the non-fast­ing days changes. What tends to hap­pen is that peo­ple start to eat less on these days be­cause they feel they don’t need to eat as much.”

She be­lieves that in­ter­mit­tent fast­ing is eas­ier to main­tain than tra­di­tional di­ets.

“It’s more sus­tain­able than a diet in which you forgo the things you en­joy eat­ing on a daily ba­sis. Peo­ple can gen­er­ally stick to this type of in­ter­mit­tent fast­ing for about three months – com­pared to one or two months for a typ­i­cal daily calo­rie-re­stricted diet.”

The pros

In her stud­ies on al­ter­nate-day fast­ing, Krista Varady, as­so­ciate pro­fes­sor of nu­tri­tion at the Univer­sity of Illi­nois in Chicago, found that peo­ple not only lost weight and de­creased their body fat per­cent­age, but also re­duced their to­tal choles­terol lev­els and im­proved their blood pres­sure.

The CSIRO re­ports sim­i­lar find­ings. In their 16-week study, peo­ple took part in in­ter­mit­tent fast­ing that in­cluded three low-calo­rie fast­ing days per week, three calo­rie-con­trolled days and one day when they could eat what­ever they wanted. On av­er­age, par­tic­i­pants lost 11kg and saw im­prove­ments in choles­terol, in­sulin, blood pres­sure and blood glu­cose lev­els.

The ben­e­fits of in­ter­mit­tent fast­ing ap­pear to ex­tend be­yond weight loss and im­proved biomark­ers. In an eight-week study con­ducted by the US Na­tional In­sti­tute on Ag­ing, over­weight adults with mod­er­ate asthma re­duced their diet to 20 per cent of their nor­mal daily in­take. Par­tic­i­pants lost weight and saw a de­crease in in­flam­ma­tion mark­ers and a sig­nif­i­cant im­prove­ment in their asthma symp­toms.

the cons

De­spite these ben­e­fits, Maston warns that this form of fast­ing isn’t for every­one. “For some peo­ple, it en­cour­ages binge­ing on the non-fast­ing days, which of­ten takes the form of eat­ing foods with lit­tle nu­tri­tional value. It’s one thing to re­duce calo­ries, but peo­ple need to look at a com­bi­na­tion of re­duc­ing calo­ries and eat­ing whole, nu­tri­ent-dense foods.”

If you plan to work out on fast­ing days, it’s im­por­tant to lis­ten to your body and stop if you feel faint or light­headed. Try to eat a carb-rich snack af­ter high-in­ten­sity work­outs, to help your glyco­gen-de­pleted mus­cles re­cover.

2 24-hour fast­ing

Prob­a­bly the most chal­leng­ing form of in­ter­mit­tent fast­ing is the 24-hour fast. As the name sug­gests, it in­volves not con­sum­ing any­thing ex­cept wa­ter for 24 hours. The fast typ­i­cally be­gins af­ter you eat a meal such as din­ner – you then ditch food un­til the same time the next day.

The pros

An­i­mal stud­ies con­ducted by the US Na­tional In­sti­tute on Ag­ing have shown an in­crease in longevity and im­proved cog­ni­tive func­tion with this type of in­ter­mit­tent fast­ing. In one study, rats who were starved ev­ery sec­ond day lived 83 per cent longer on av­er­age than rats who weren’t fasted. In a sim­i­lar study, it was con­cluded that in­ter­mit­tent fast­ing can im­prove age-re­lated de­cline in brain func­tion in rats. How­ever, the re­searchers stress that hu­man stud­ies are re­quired be­fore claims about longevity and cog­ni­tive func­tion can be made. Per­min­der Sachdev – sci­en­tia pro­fes­sor of neu­ropsy­chi­a­try at the Cen­tre for Healthy Brain Age­ing at the Univer­sity of NSW – agrees but points out that many stud­ies of cen­te­nar­i­ans show that re­strict­ing calo­ries

The the­ory is it takes about six hours be­fore the body en­ters a fasted state

As well as those with type 2 di­a­betes, in­ter­mit­tent fast­ing is not ad­vised for those with a his­tory of eat­ing dis­or­ders, or in the case of preg­nancy. To be on the safe side, if you’re con­sid­er­ing fast­ing, talk first to a health prac­ti­tioner.

leads to an ex­tended and health­ier life­span. the cons Maston ar­gues that this form of fast­ing is dan­ger­ous as it car­ries a risk of de­hy­dra­tion and elec­trolyte im­bal­ances, among other things. “Fast­ing for 24 hours stops peo­ple lis­ten­ing to what their bod­ies are telling them. Our bod­ies are very good at send­ing us hunger cues. Twenty-fourhour fasts over­ride these cues and are the op­po­site of in­tu­itive eat­ing, which is how we should be eat­ing,” she says. 3 Time-re­stricted eat­ing

An­other pop­u­lar vari­a­tion of in­ter­mit­tent fast­ing is time-re­stricted eat­ing. For most peo­ple, this means eat­ing their last meal at night and not eat­ing again un­til lunchtime the fol­low­ing day.

The the­ory is it takes about six hours with­out food be­fore the body en­ters a fasted state, when it be­gins to break down fat for en­ergy. For most peo­ple, the only time their bod­ies reach a fasted state is when they’re asleep. Ad­vo­cates of timer­e­stricted eat­ing ar­gue that by skip­ping break­fast, you re­main in a fasted state for longer, which re­sults in in­creased fat loss.

Dr Nick Fuller, one of Aus­tralia’s lead­ing obe­sity re­searchers and au­thor of

In­ter­val Weight Loss, dis­agrees. “By skip­ping meals, you’re set­ting your­self up for fail­ure,” he says. “When­ever en­ergy in­take is re­duced, whether by in­ter­mit­tent fast­ing or other forms of di­et­ing, your body un­der­goes the same meta­bolic re­sponse. First, your me­tab­o­lism de­creases; sec­ond, it causes an in­crease in the ap­petite hor­mones that tell you to eat more. You will lose weight, but your body will do all it can to get back to its set point.” Fuller be­lieves our bod­ies are tuned to a set point – the nat­u­ral weight they will work to try to main­tain. “Once you stop fast­ing and start eat­ing nor­mally, your body will drive your weight back to where you started, or even higher.” The pros One ma­jor ben­e­fit of in­ter­mit­tent fast­ing, shown across mul­ti­ple stud­ies, is that it re­duces blood glu­cose lev­els. Given high blood glu­cose lev­els are a ma­jor risk fac­tor in de­vel­op­ing type 2 di­a­betes, this is good news.

Sachdev, of the Cen­tre for Healthy Brain Age­ing, ex­plains that re­duc­ing blood glu­cose lev­els leads to a cas­cade of health ben­e­fits, in­clud­ing a re­duced risk of ath­er­o­scle­ro­sis and stroke, re­duced cell dam­age and bet­ter im­mune func­tion.

“It there­fore slows the age-re­lated de­cline in brain func­tion and im­proves vas­cu­lar brain health, both of which are im­por­tant for cog­ni­tive dis­or­ders in later life, in­clud­ing de­men­tia,” he says.

Fuller’s not con­vinced. He says these re­sults are due to weight loss and not fast­ing. “Fast­ing causes short-term weight loss and, as a re­sult, you can see an im­prove­ment in blood glu­cose lev­els.” the cons In­deed fuller ar­gues that fast­ing isn’t sus­tain­able in the long term, so once you rein­tro­duce foods and re­gain the weight, you’ll be worse off than when you be­gan.

Skip­ping meals is par­tic­u­larly dan­ger­ous for peo­ple with type 2 di­a­betes, es­pe­cially those who are in­sulin de­pen­dent, he warns. “Skip­ping meals puts those who have di­a­betes and are tak­ing in­sulin at huge risk of harm, as they need small, reg­u­lar meals to reg­u­late their blood glu­cose lev­els.”

A less im­me­di­ate dan­ger, says Maston, is overeat­ing. “When peo­ple re­strict them­selves to eat­ing within a short time­frame, their pri­mal in­stinct kicks in. For many peo­ple, if they feel they’re go­ing to have to go with­out, they’ll try to get in as much food as they can dur­ing that pe­riod.”

This can cause prob­lems such as re­flux and feel­ings of nau­sea due to the in­creased vol­ume of food con­sumed in one sit­ting. 4 But wait, there’s more…

More ex­treme forms of fast­ing in­clude multi-day fasts of 10 days or more, dur­ing which noth­ing but wa­ter is con­sumed – although some full-on fasts even dis­cour­age drink­ing wa­ter.

Maston warns there are se­ri­ous med­i­cal dangers as­so­ci­ated with ex­tended fasts. “Not eat­ing for long pe­ri­ods re­sults in mal­nu­tri­tion and elec­trolyte im­bal­ances such as potas­sium de­fi­ciency, which can lead to heart at­tack and even death,” she says.

Muscle wast­ing is also com­mon as the body goes into star­va­tion mode and be­gins to break down muscle to pro­tect the vi­tal or­gans. In women, long-term fasts can re­sult in bone loss and the re­pro­duc­tive sys­tem shut­ting down.

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