Fast track to health

It gen­er­ates ma­jor buzz. But does the re­search on in­ter­mit­tent fast­ing stack up, or is it sim­ply star­va­tion re­branded? Read on...

Women's Health Australia - - CONTENTS - By Caro­line Wil­liams

Are fast­ing di­ets like the 5:2 all they’re cracked up to be? We get the low­down

WWe sus­pect you first heard about fast­ing from that one friend who never fails to jump on the lat­est health trend just be­fore it hits peak take-up, no doubt over a late Jape­nese fu­sion din­ner where she es­chewed food in favour of re­gal­ing you with the sci­ence be­hind eat­ing in­ter­mit­tently. She’s done the 5:2, tried the 16:8 (“it’s the same sci­ence, just eas­ier to fol­low!”) and is cur­rently evan­ge­lis­ing about the five-days-ev­ery-three-months fast­ing mim­ick­ing diet. Yep, we’ve been there!

Since 5:2 came into our lives in 2012, in­ter­mit­tent fast­ing – the con­cept of shun­ning kilo­joules for hours or days at a time – has been touted as a mag­i­cal way to re­duce the risk of heart dis­ease, di­a­betes and can­cer, while melt­ing belly fat and of­fer­ing your di­ges­tive sys­tem a re­boot. The premises of the 5:2 (cut­ting back to 2100kj two days a week) and the 16:8 (eat­ing all your day’s food within an eight-hour win­dow) are ba­si­cally the same. When you give your body a break from eat­ing, it be­gins feed­ing off your fat re­serves.

An­other it­er­a­tion, the fast­ing mim­ick­ing diet (FMD) – which first hit head­lines in 2015 but is now gar­ner­ing main­stream in­ter­est as fast­ing rises in pop­u­lar­ity – is a five­day pro­gram based on the re­search of Dr Val­ter Longo, a bi­ol­o­gist at the Uni­ver­sity of South­ern Cal­i­for­nia.

It’s de­signed to make your body think all it’s be­ing fed is wa­ter, while keep­ing ac­tual star­va­tion at bay via a kilo­joule-con­trolled, sci­en­tif­i­cally de­vel­oped diet. But it doesn’t come cheap: it costs $400 to buy the five-day kit de­vised by Dr Longo and sold as Prolon in the US.

Hang on a minute. De­priv­ing your­self of food goes against all your in­stincts, not to men­tion the di­etary ad­vice we’re al­ways hear­ing. So, is this lat­est nu­tri­tion trend re­ally the prod­uct of sci­en­tific de­vel­op­ments – or is the diet in­dus­try hav­ing the last laugh?

Run­ning on empty

The sci­ence is fairly sim­ple. When you put your­self on the 5:2 or the 16:8, you starve your body of the en­ergy it usu­ally gets from food, which forces it to seek its fuel in­ter­nally. First, you’ll utilise the sugar in your blood­stream. When that’s gone, it’s time to tap into the liver’s glyco­gen stores. Af­ter a day or so of eat­ing fewer kilo­joules than your body needs, these too will run out, so your body has no op­tion but to start burn­ing fat.

But pro­po­nents of the FMD in­sist that when you fast for longer than a day or two, the ben­e­fits go be­yond weight loss. Yes, the five-day plan pushes your body into ke­to­sis – the meta­bolic state in which the body burns fat for en­ergy, made fa­mous by the Atkins diet (and keto breath) – but some­thing else is go­ing on.

A short pe­riod of se­vere kilo­joule de­pri­va­tion forces the body to save as much en­ergy as pos­si­ble by be­gin­ning to break down and di­gest its own cells, a process called au­tophagy. Sounds scary, but Longo in­sists you bear with it. The body is in­tel­li­gent enough to start with dead or dam­aged cells that aren’t worth the en­ergy to sus­tain – the ones that con­trib­ute to age­ing and are more likely to turn can­cer­ous. In other words, the body be­comes health­ier, seem­ingly younger and at less risk of dis­ease. Un­til the FMD came along, the only way to trig­ger au­tophagy was to go on a wa­teronly diet – some­thing no di­eti­tian would rec­om­mend without close mon­i­tor­ing. In this way, Longo’s fast of­fers a sys­tem clean-up that prom­ises to torch fat while also boost­ing gen­eral cel­lu­lar health and de­liv­er­ing nu­tri­ents via the food.

Hu­man na­ture

One im­por­tant thing to know? Most of the stud­ies that sell fast­ing as a nu­tri­tional win point to re­sults found in mice. Pe­ri­odic fast­ing of ro­dents in a lab set­ting re­duced fat, in­creased life­span and cut in­ci­dences of can­cer and in­flam­ma­tion – linked to every­thing from heart dis­ease to de­pres­sion. And where some of the mice’s cells were lost to au­tophagy in the or­gans, mus­cles and bones, they were re­placed with new ones.

But you’re not a mouse. In hu­mans, stud­ies com­par­ing short-term fasts – such as 5:2 and 16:8 – with kilo­joule-con­trolled di­ets con­sis­tently sug­gest they’re no more ef­fec­tive at shift­ing weight and im­prov­ing meta­bolic mark­ers than any other kind of diet. And when it comes to the pro­tec­tive im­pact of pe­ri­ods of pro­longed fast­ing, the ev­i­dence is lim­ited. A re­cent pi­lot trial of the FMD on hu­mans in Longo’s lab showed find­ings of a 3 per cent av­er­age body fat re­duc­tion, low­ered blood glu­cose and lower lev­els of in­flam­ma­tory mark­ers.

But the ev­i­dence for au­tophagy was cir­cum­stan­tial at best.

Longo in­sists that even healthy peo­ple could ben­e­fit from a pe­ri­odic fast. The sci­en­tist whose re­search led to the de­vel­op­ment of the 5:2 diet is un­con­vinced. “We have no ev­i­dence of ben­e­fits for peo­ple who are a healthy weight,” says Dr Michelle Harvie, a re­searcher at the Uni­ver­sity of Manch­ester, who first looked into fast­ing as a way to help women at risk of breast can­cer to lose weight. “All the ev­i­dence is for weight loss among the over­weight.” As for the prom­ise of longevity, we’ll just have to wait and see.

Oth­ers point out that fast­ing isn’t the only way to lure your body into a re­plen­ish­ing state. The al­ter­na­tive

is called ex­er­cise, and the the­ory goes that, just like fast­ing, get­ting your sweat on puts the body into a state of mild stress, stim­u­lat­ing it to re­pair it­self. It also gives the brain a boost by trig­ger­ing the re­lease of a chem­i­cal called brain-de­rived neu­rotrophic fac­tor (BDNF), which in­creases the brain’s ten­dency to make new neu­rons and cre­ate and main­tain con­nec­tions. This might ac­count for the clear head many peo­ple boast of dur­ing a fast and af­ter a good old sweat ses­sion.

Nil by mouth?

If you’d con­fessed to starv­ing your­self a few years ago, you’d have been met with con­cern. To­day, re­place the word ‘starve’ with ‘fast’ and you’re more likely to be met with a know­ing smile. But do the two mean the same thing? Yes, ac­cord­ing to Longo – and that’s the point. In or­der for fast­ing to trig­ger a sys­tem re­boot, the body needs to think that it’s starv­ing. “Your body tips over into star­va­tion quite quickly – but that’s a good thing,” he ex­plains. “Af­ter a cou­ple of days, it starts killing off cells.” All very well if you’re do­ing it in a con­trolled way, like the FMD, but take it too far and it can prove fa­tal – peo­ple have died from do­ing wa­ter-only fasts.

Fast­ing can also in­duce an emo­tional fall­out, lead­ing to an un­healthy re­la­tion­ship with food. “This can hap­pen to peo­ple who al­ready have a pat­tern of dis­or­dered eat­ing,” says Dr He­lena Popovic, an MD spe­cial­is­ing in the ap­pli­ca­tion of neu­ro­science to weight man­age­ment. “If you’ve been a binge eater or chronic di­eter, you’re go­ing back to the ‘I just have to hold out’ [men­tal­ity] then, when you’re al­lowed to eat, you overdo it. These peo­ple may find that in­ter­mit­tent fast­ing trig­gers binge-eat­ing cir­cuits in their brain that might have been dor­mant for a while.

“I def­i­nitely sup­port fast­ing in what­ever way a per­son wants, as long as they’re the right per­son for it,” Popovic adds. “We’re all in­di­vid­u­als. Fast­ing works re­ally well for some, and not so well for oth­ers in terms of their psy­cho­log­i­cal ap­proach to it.”

Fact ver­sus fic­tion

The fi­nal word? Epi­demi­ol­o­gist Dr Ben­jamin Horne, who re­cently re­viewed the ev­i­dence, found that fast­ing is gen­er­ally safe when done ev­ery other day for a year, or five days in suc­ces­sion once a month. But it’s im­por­tant to be across the risks: faint­ing, de­hy­dra­tion and mal­nu­tri­tion. “No study I know of has given us in­for­ma­tion re­gard­ing the thresh­old for mal­nu­tri­tion, which likely de­pends on the in­di­vid­ual,” he says. And with no re­search com­par­ing dif­fer­ent fast­ing meth­ods in hu­mans, it’s hard to know which works best. While it’s ac­cepted that there are peo­ple who shouldn’t fast – chil­dren, preg­nant and breast­feed­ing women and any­one with a BMI un­der 18.5 – if your goal is to burn fat, then stud­ies sug­gest a short-term fast can work.

Speak­ing of short term, Popovic says an overnight fast is re­ally all you need. “If ev­ery per­son on the planet left at least 12 hours be­tween din­ner and break­fast, that would lead to huge im­prove­ments in health and longevity, gut health, and would lower the risk of obe­sity,” she says.

As for longevity-boost­ing, more re­search is needed. Clearly, fast­ing’s ben­e­fits are sub­jec­tive. It can be safe, but it may not be the health­i­est op­tion. Per­haps ask if your ef­forts would be bet­ter spent on an­other Bdnf-booster: a gym pass.

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