Nu­tri­tion

At­tempts to lose weight by pe­ri­od­i­cally go­ing hun­gry can of­ten have the op­po­site ef­fect.

New Zealand Listener - - CONTENTS - by Jennifer Bow­den

At­tempts to lose weight by pe­ri­od­i­cally go­ing hun­gry can of­ten have the op­po­site ef­fect.

Ques­tion:

Michael Mosley’s 5:2 in­ter­mit­tent-fast­ing eat­ing plan is some­times called a diet. It seems to have some med­i­cal sup­port, but I can’t find any se­ri­ous re­search on it. Is in­ter­mit­tent fast­ing likely to fol­low the same pat­tern as other en­ergy-re­stricted di­ets, as you out­lined in the June 16 is­sue?

An­swer:

Whether you try to re­duce your body size through in­ter­mit­tent fast­ing or a stan­dard en­er­gyre­stricted diet, the same is­sue re­mains – are hu­mans ac­tu­ally able to con­sciously con­trol their body weight? Weight set­point the­ory would say no. Decades of re­search sug­gests that although we can lose weight in the short term, it is in­vari­ably re­gained within two to five years, and for as many as half of di­eters, more weight is re­gained than was orig­i­nally lost.

US obe­sity and neu­ro­science re­searcher Stephan Guyenet says there is no ev­i­dence to sug­gest in­ter­mit­tent fast­ing – cut­ting nor­mal calo­rie in­take by about three-quar­ters for two days in seven, say – is more ef­fec­tive for weight loss than daily por­tion con­trol for the av­er­age per­son. “An­other way of putting it is that nei­ther strat­egy is very ef­fec­tive for weight loss,” says Guyenet. He points to a 2016 study pub­lished in the jour­nal Nu­tri­ents that com­pared in­ter­mit­tent fast­ing with stan­dard en­er­gyre­stricted di­ets and found they were as good as each other at pro­duc­ing weight loss.

The dif­fi­culty we have trick­ing our body into down­siz­ing it­self comes down to neu­ro­science, he writes in his book The Hun­gry Brain. Weight set-point the­ory, which ex­plains why re­peated di­et­ing is un­suc­cess­ful at pro­duc­ing long-term change in body weight or shape, was de­vel­oped in the 1980s.

The the­ory sup­poses that we have an in­built con­trol sys­tem that dic­tates how much fat we carry and we can’t con­sciously or per­ma­nently change our weight be­cause our sub­con­scious will drive us to re­gain it.

It’s a bit like some­one else hav­ing the re­mote con­trol for your tele­vi­sion. You can try to man­u­ally change chan­nels, but the re­mote’s invisible force keeps switch­ing it back.

The cen­tral con­troller of our weight is thought to be lo­cated in the hy­potha­la­mus, which re­ceives feed­back from around the body on fat and ac­tiv­ity lev­els. The hy­potha­la­mus then in­flu­ences our

eat­ing habits and en­ergy ex­pen­di­ture to main­tain our weight set-point.

The con­troller does this by in­creas­ing hunger (as ev­ery di­eter knows, the more weight they lose, the more per­sis­tent hunger be­comes), in­creas­ing food re­ward value (mak­ing high-en­ergy foods more ap­peal­ing) and by slow­ing our meta­bolic rate. Within days of start­ing a self-im­posed famine, the body adapts to con­serve en­ergy by slow­ing the me­tab­o­lism down, mak­ing weight loss in­creas­ingly dif­fi­cult.

Welling­ton broad­caster Si­mon Mor­ton had been on a lowg­ly­caemic diet for the sake of his health. Af­ter he did an in­ter­view with exercise- and diet-book author Michael Mosley, he de­cided to try in­ter­mit­tent fast­ing. “In­ter­mit­tent fast­ing was a way of get­ting the weight down even fur­ther.”

How­ever, Mor­ton gave it up within a year af­ter find­ing hunger was af­fect­ing his mood and there­fore his fam­ily. “It be­came hard on my fam­ily be­cause I would get a bit ‘han­gry’.

“It was sort of to­tal ir­ri­tabil­ity as­so­ci­ated with feel­ing hun­gry that would man­i­fest as grumpi­ness. This void in my stom­ach would cre­ate a void in my sense of hu­mour and my abil­ity to tol­er­ate things.”

“This void in my stom­ach would cre­ate a void in my sense of hu­mour.”

Along with the stom­ach and other grum­bles, hunger can cause loss of en­ergy, lethargy, sleepi­ness, headaches, light-head­ed­ness and dif­fi­culty fo­cus­ing and con­cen­trat­ing.

At a pop­u­la­tion-health level, the ef­fect of in­ter­mit­tent fast­ing isn’t known. Fast­ing pro­po­nents es­pouse its po­ten­tial for im­proved gly­caemic con­trol and longevity. But the jury is still out over whether it is in­creas­ing rates of eat­ing dis­or­ders, an un­for­tu­nate and not al­to­gether un­ex­pected out­come of many en­er­gyre­stricted di­ets.

In­ter­mit­tent­fast­ing ad­vo­cate Michael Mosley.

Re­searcher Stephan Guyenet.

by Jennifer Bow­den

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