They’re not the only cul­prits when it comes to gain­ing weight – habit and the en­vi­ron­ment also play a part

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Ear­lier this year, a gov­ern­ment re­port re­vealed that we are con­sum­ing an av­er­age of 14 per cent fewer calo­ries than we did in the 1970s. Surely a cause for cel­e­bra­tion? Not so fast. While we are eat­ing less, we are also get­ting fat­ter. The lat­est re­search re­veals how our habits and en­vi­ron­ment are mak­ing us big­ger, with­out us even re­al­is­ing it…


In Fe­bru­ary re­searchers at Uni­ver­sity College Lon­don (UCL) re­ported that the more stressed peo­ple are, the heav­ier they are likely to be. In stress­ful sit­u­a­tions, cor­ti­sol floods the body with glu­cose, giv­ing mus­cles the en­ergy to run or fight. Cor­ti­sol also in­hibits the pro­duc­tion of in­sulin, leav­ing blood­sugar lev­els high. With chronic stress, this cir­cu­lat­ing and un­used glu­cose is stored as body fat or as vis­ceral fat around or­gans. Thus it’s no sur­prise that the UCL trial showed that peo­ple with higher lev­els of cor­ti­sol were heav­ier, had a higher body mass in­dex and larger waists, which, ac­cord­ing to Dr Sarah Jack­son who led the study, is ‘a risk fac­tor for heart dis­ease, di­a­betes and pre­ma­ture death’.


Theresa May has said that toxic air is the fourth largest health risk in the UK be­hind can­cer, obe­sity and heart dis­ease. Stud­ies also sug­gest that smog-filled air might af­fect metabolism. Last year US sci­en­tists showed that preg­nant rats breath­ing Bei­jing’s pol­luted air for three weeks gained sig­nif­i­cantly more weight than those given clean air to breathe, de­spite the an­i­mals eat­ing the same diet.


Ac­cord­ing to re­cent sur­veys, most Bri­tons sit or lie down for more than 20 hours a day. ‘Only ly­ing down burns fewer calo­ries per hour than sit­ting, which uses up less than 70,’ says John Brewer, a pro­fes­sor of ap­plied sport science at St Mary’s Uni­ver­sity, Twick­en­ham. How­ever, it’s not just the re­duced daily calo­ries burnt through a lack of move­ment that can pile on the pounds. Stud­ies have linked pro­longed sit­ting to a re­duc­tion in the en­zymes that help to metabolise fat and su­gar in the body, exacerbating weight gain.


Last year sci­en­tists at King’s College Lon­don pub­lished two pa­pers in the jour­nal Pro­ceed­ings of the Nu­tri­tion So­ci­ety show­ing how the tim­ing of meals in­flu­ences weight gain. One of the pa­pers found that peo­ple who ate their meals with vary­ing fre­quency – con­sum­ing any­thing from three to nine snacks or meals a day – had less healthy in­sulin and choles­terol lev­els and weighed more than those who stuck to a con­sis­tent six small meals a day. ‘We found that adults con­sum­ing calo­ries dur­ing reg­u­lar meals – at sim­i­lar times from one day to [the] next – were less obese than peo­ple who have ir­reg­u­lar meals, de­spite con­sum­ing more calo­ries over­all,’ said Dr Gerda Pot, one of the re­searchers. The other pa­per in­cluded ev­i­dence that peo­ple who eat more calo­ries later at night are more likely to be obese. At night the body is more likely to store calo­ries con­sumed as fat than burn them as en­ergy. Stud­ies have also shown that late-night snack­ing (when your body thinks you should be sleep­ing) also causes your cells to be­come more re­sis­tant to in­sulin, caus­ing raised blood-su­gar lev­els and, in time, fat ac­cu­mu­la­tion.


Too much or too lit­tle sleep can dis­rupt your cir­ca­dian rhythms, caus­ing blood-su­gar and meta­bolic fluc­tu­a­tions, and make ex­tra pounds more likely. Sleep­ing for fewer than five hours a night is thought to af­fect the ‘hunger’ hor­mones – lep­tin and ghre­lin – stim­u­lat­ing appetite so that more high-calo­rie foods are con­sumed when you are tired. Too much sleep has been linked to the im­paired abil­ity of fat cells to re­spond to in­sulin, a fat-stor­age hor­mone. Ac­cord­ing to the Uni­ver­sity of Glas­gow, short sleep du­ra­tion (less than seven hours) and long sleep du­ra­tion (more than nine hours) in­crease the risk of obe­sity for some peo­ple. Dr Ja­son Gill and his team at the In­sti­tute of Car­dio­vas­cu­lar and Med­i­cal Sci­ences found that long sleep­ers with a high ge­netic risk of obe­sity were about 4kg heav­ier, and short sleep­ers were about 2kg heav­ier, than those with a sim­i­larly high ge­netic obe­sity risk who slept reg­u­lar hours.


It’s not just the calo­ries in al­co­holic drinks that con­trib­ute to weight gain. Ac­cord­ing to the char­ity Drinkaware, re­search shows that al­co­hol re­duces the amount of fat your body burns for en­ergy. Our bod­ies are able to store pro­tein, car­bo­hy­drates and fat, but not al­co­hol. When our sys­tems need to get rid of al­co­hol, do­ing so takes pri­or­ity and other pro­cesses – such as burn­ing fat – are slowed down. The Bri­tish Di­etetic As­so­ci­a­tion’s Ais­ling Pig­ott says: ‘When you drink, the liver stops re­leas­ing glyco­gen. That means your blood-su­gar lev­els are low­ered and you feel hun­grier, lead­ing you to eat more as a re­sult.’


Re­cent an­i­mal tri­als have sug­gested a high-salt diet may af­fect fat cells, mak­ing them larger and caus­ing weight gain if you also con­sume too many calo­ries. In April re­searchers from the Ger­man Aero­space Cen­ter, Ber­lin’s Max Del­brück Cen­ter for Molec­u­lar Medicine and Ten­nessee’s Van­der­bilt Uni­ver­sity re­ported that salty food ac­tu­ally di­min­ishes thirst while in­creas­ing hunger. In their trial on ten vol­un­teers, who were put on two sim­u­lated flights to Mars, they showed that a high-salt diet caused the kid­neys to con­serve wa­ter so the sub­jects drank less. The vol­un­teers also com­plained about be­ing hun­gry and, in real-life cir­cum­stances, that could cause overeat­ing, they said. Re­searchers ob­serv­ing mice on a high-salt diet found that con­serv­ing wa­ter in the kid­neys re­quired a lot of en­ergy, which could ex­plain why they ate more.


Sci­en­tists at UCL were among the first to pro­pose that ris­ing cen­tral heat­ing use might be linked to obe­sity. Even turn­ing down the ther­mo­stat a cou­ple of notches can make a dif­fer­ence. Cooler tem­per­a­tures trig­ger what sci­en­tists call a pre-shiver re­ac­tion that prompts the body’s stores of good ‘brown’ fat to act. Un­like the white fat that set­tles on our hips and thighs, brown fat burns calo­ries and pre­vents weight from pil­ing on by gen­er­at­ing about 300 times more heat than any other or­gan in the body. Three years ago sci­en­tists at the Maas­tricht Uni­ver­sity Med­i­cal Cen­tre re­ported that set­ting the ther­mo­stat at 19C is suf­fi­cient to burn calo­ries – any warmer than that and you could find the pounds creep­ing on.

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