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2019-02-05 chinawungbo2 1819 0 0  

Until last year, Borris would never turndown a pork chop. He was partial to ice cream during the summer and loved aSunday roast in the winter – including beef with Yorkshire pudding, pigs inblankets, mashed potatoes, and a selection of vegetables.

直到去年,博里斯(Borris)才开始拒吃牛排。在过去,他夏天偏爱冰激凌,冬天喜欢周日烤肉,包括烤牛肉配约克郡布丁、猪肉饼、土豆泥及各种蔬菜。博里斯是一只5岁的骑士查理王猎犬(Cavalier King Charles Spaniel)。

Borris is a five-year-old Cavalier KingCharles Spaniel. By the time his owner, Annemarie Formoy, entered him into thePDSA Pet Fit Club competition, which helps obese cats and dogs slim down, hewas 28kg – almost double his recommended weight. It took two people to lift himinto the car, he had arthritis in one leg and his breathing was laboured.Thanks to a tailored six-month diet and exercise regime he is now 7kg lighterand has just been crowned joint competition winner with Sadie the Labrador.

他的主人福尔莫伊(Annemarie Formoy)把他送到动物之家宠物减肥健身俱乐部(PDSA Pet Fit Club)参赛时,他已经28公斤重了,是正常体重的两倍。他一条腿有关节炎,而且呼吸困难,要两个人一起才能把他抬上车。经过6个月的节食治疗及锻炼,他轻了7公斤,和名为萨迪(Sadie)的拉布拉多犬获得了减肥赛的并列第一名。

Borris, at his heaviest, was not alone. Theworldwide prence of pet obesity lies between 22% and 44%, and rates seem tobe rising. The reasons why are fairly predictable. Owners of overweight dogsfeed them more snacks and table scraps, are more likely to have their petspresent as they prepare their own meals and are less likely to walk them daily.Owners of obese cats tend to use food as a reward and play with them less. If adog owner is obese, the chances are their pet will be too (this doesn’t applyto cats).


But obesity also seems to be occurring evenin some domestic and wild animals who aren’t being overfed or under-exercised.If these findings are true, something else must be driving obesity anduncovering those could help tackle our own epidemic with the condition.


More than 1.9 billion human adults areoverweight. Of these, more than 650 million are obese – that’s about 13% of theworld’s adult human population. The worldwide prence of obesity has nearlytripled since 1975. And childhood obesity has risen alarmingly too – anestimated 41 million children under the age of five are overweight or obese.


The first animal clue lies at the paw ofthe obesity-prone Labrador retriever. “Labradors are consistently the headlineact when it comes to overweight dogs,” says Eleanor Raffan, a veterinarian andgeneticist at the University of Cambridge. She and fellow researchersdiscovered that a genetic mutation present in around a quarter of Labradors,was associated with obesity. For each copy of the mutation – which occurred ina gene called POMC – a dog was about 2kg heavier. Most of the animals theresearchers studied had one copy of the mutation, but fewer had two.

从动物身上找到的第一条线索是,肥胖的拉布拉多寻回犬的爪子。剑桥大学兽医及遗传学家拉芬(Eleanor Raffan)说:“对于肥胖的狗来说,拉布拉多一直排名首位。”她和其他研究人员发现,约有四分之一的拉布拉多狗带有与肥胖相关的基因变异。这种变异发生在名为POMC的基因中,一条狗每发生一次变异,就会增重约2公斤。大多数动物带有一个基因突变,但有少数动物带有两个突变。

“These are dogs always in the kitchen when owners are preparing food,sticking around looking for a tidbit even if there’s not much chance of gettingone, or scavenging yucky stuff on walks,” Raffan says. “But they’re not doingthat because it’s fun. They’re doing it because they’re hungry.”


That’s because POMC mutations disrupt thebrain’s leptin-melanocortin pathway, which regulates food intake and energyexpenditure, ultimately influencing body weight. As a result, the behaviour ofthese Labradors becomes very food-motivated. There’s a lesson here for humans,Raffan says. “The drive to eat is as every much of a physiological drive anddominating thought as the feeling of being thirsty.”

这是因为POMC突变,扰乱了大脑内管理食物摄入和能量消耗的瘦素——黑皮质素通道(leptin-melanocortin pathway),改变了食物摄入和能量消耗,最终影响体重。因此,拉布拉多犬变得一切行动受食物驱动。拉芬说,人类也是相同的道理。“想吃东西的欲望和口渴的感觉一样,生理需求主导我们的想法。”

Genes play a role in human obesity (theaverage heritability lies between 40% and 75%), but obesity caused by a singlegene is rare. POMC deficiency, associated with severe obesity in infancy, hasbeen reported in fewer than 50 people worldwide, although there are likelythousands of undiagnosed cases. But mostly, human obesity reflects multiplegenetic risk variants (each with small effects) interacting in a complex waywith environmental factors.


The good news is that animals could help usdisentangle those environmental factors, too. Factory farm animals aretraditionally fattened with antibiotics that transform their gut so they needless food to gain weight. New regulations have pushed antibiotic use in UKfood-producing animals to their lowest level since data were first publishedand the EU has banned antibiotics as growth promoters in feed.


If antibiotics fatten animals, could theybe doing the same to humans?


The answer to that question lies in yourgut. The microbiome describes the genomes of the vast colonies ofmicro-organisms – bacteria, fungi, protozoa, viruses, all 100 trillion of them– living in your digestive system. This community influences your weight:germ-free mice that receive gut microbes from an obese (human) twin gain moreweight and body fat than mice that receive microbes from the lean twin. Animbalance in the microbiome possibly leads to not only obesity, but irritablebowel syndrome, coeliac disease, and type 2 diabetes.


So what causes this sort of imbalance?There is a genetic element. But in studies of animals, high-intensitysweeteners and food additives like the emulsifiers used in many processed foodshave been linked to lower gut bacterial diversity. In humans, babies givenantibiotics in the first six months of life led to an increased risk of beingoverweight in later childhood, according to one study. Six weeks of antibioticsfor a heart infection was also linked to significant weight gain.


But before you throw away your life-savingantibiotics, remember these studies only show an association rather than clearcause and consequence. Certain antibiotics might even shift the balance of gutmicrobiota away from patterns associated with obesity. Knowing this, could wesomehow modify our microbiome to tackle obesity? Work is underway to do justthat, with probiotics and faecal transplantation under investigation.


Obesity isn’t just something that affectsdomestic animals, though. Wild animals fatten up, too, but it’s usually inrelation to seasonal cycles and food availability: they’ve learned to eat whenfood is plentiful. But researchers have seen unexpected weight gain inyellow-bellied marmots (large grass squirrels) in Colorado’s Rocky Mountainsbetween 1976 and 2008. Marmots are now waking up around a month earlier fromtheir eight-month hibernation, likely because climate change has altered thetime between first snow melt and first frost. These extra days mean morefeeding and fattening time. In the short-term, an extra 0.3kg could improvesurvival chances during hibernation and reproductive success afterwards.(Sadly, marmots will ultimately pay a high price as climate change increasesthe frequency of summer droughts.)

肥胖不仅只有家畜,野生动物也会发胖。野生动物会在食物充足时多进食,所以肥胖与季节变化和食物充足有关。研究人员还意外地发现,1976年至2008年间,科罗拉多州落基山脉(Rocky Mountains)黄腹土拨鼠(大型草原松鼠)的体重增加了。因气候变化改变了第一次结霜和融雪的时间,以往冬眠8个月,现在土拨鼠会提前一个月左右醒来,这些额外的日子,土拨鼠需要吃更多食物、增肥时间更长。短期而言,增重0.3公斤可以提高冬眠期的存活机会,提升繁殖成功率。让人难过的是,因气候变化会使夏天干旱多发,土拨鼠最终将付出高昂的代价。

Other environmental factors that affectobesity in animals – and perhaps humans – include sleep debt and lightpollution. Mice exposed to constant light have higher body mass indices (BMIs)and glucose levels than those exposed to normal light/dark cycles.


Oestrogen-disrupting chemicals likebisphenol-A (BPA) – found in food cans, some hard plastics, and certain typesof thermal paper used for receipts and tickets – are another potential culprit.Chemical manufacturers have challenged these links and the US Food and DrugAdministration currently supports its safety, but the European Food SafetyAuthority is currently re-uating the toxicity of BPA and, in January 2011,the European Commission prohibited BPA for the manufacture of polycarbonateinfant feeding bottles.


A note of caution is needed, though.Focusing on these non-food related factors can distract from the undeniableimpact of supersized processed meals. The truth is we’re up against externalinfluences that are hard to resist: ingredients designed to tap into our rewardpathways, large portion sizes, and the commercial normalisation of routinesugar consumption, high fat snacks and sweetened drinks.


All this is coated by manipulativemarketing and conflicted interests. Studies from obesity researchers with foodindustry ties were five times more likely to find no association betweensugar-sweetened drinks and weight gain than studies whose authors reported nofinancial conflict of interest. One high profile researcher who argued againstcalorie listings by New York City restaurants had financial ties to Coca-Cola,PepsiCo, McDonald's, and Mars.


Animals are equally susceptible to theirresistible draw of processed food – city-dwelling tamarins in Medellín,Colombia, are fatter than their rural counterparts. Although more sedentarywith easier access to fruiting trees, they also gorge on biscuits and marshmallowsprovided by locals. One Thailand macaque made international headlines recentlywhen he became critically unwell through overfeeding by tourists.


If animals can teach us about the causes ofobesity, they might also help us understand its treatment and prevention. Andresearch in companion animals could hold greater relevance for humans since labrats often do not share our genetic diversity, psychosocial stressors orenvironment. Raffan’s Labrador study highlighted the greater similaritiesbetween canine and human POMC, compared to the rat model we traditionallystudy. Crucially, though, animals deserve to be helped and healed in their ownright – obese pets face osteoarthritis, cancer, cardiac and respiratoryproblems, reproductive disorders, urinary diseases, diabetes, and pancreatitis.


Overweight dogs also face reduced lifeexpectancy – their lifespan is up to two and a half years shorter compared todogs with a healthy body weight. For animals, the solutions sound familiar:regular exercise and a balanced food regimen. Specialist diets improve satietyso that dogs feel fuller for longer. Raffan suggests that highly food-motivateddogs can benefit from less in the bowl and more (or all) from puzzle feedersthat allow them to indulge their food obsession in a non-fattening way whilekeeping them mentally and physically active. But her key message is that weshouldn’t view obesity as some sort of moral failing in either owners or theirpets. “We’re so used to condemning humans who are overweight as being justgreedy and weak-willed,” she says. But, she points out, this is inaccurate:eating behaviour is susceptible to genetic drives – and dogs are an example ofthis. “Dogs don’t make value judgments. They eat because they’re hungry andthis variability in dogs is hardwired.”


Experts writing in the journal VeterinaryRecord also caution against condemning owners without helping them oraddressing underlying social problems. Although a pet’s forcible removal mightbe necessary if they are severely threatened, they acknowledge, “it cannot be ageneral solution to the widespread problem of canine and feline obesity”. Theybelieve that many owners don’t intentionally overfeed their pets, as reflectedby their tendency to underestimate their pets’ weight (it was a vet who toldFormoy that her dog was in trouble. “Borris looked a bit big but you just trymake excuses in your head,” Formoy says.) Similarly, few parents of overweightchildren recognise their child as overweight.

在《兽医记录》(Veterinary Record)期刊中发表评论的专家指出,只谴责宠物主人,不去帮助他们、不去解决潜在的社会问题是不对的。他们认为,如果宠物身体受到了严重的威胁,采取强制措施是必要的,但“对于猫狗过度肥胖这种普遍性问题而言,这不是好的解决方案”。许多宠物的主人并不是故意过度喂食,只是低估了自己宠物的体重。(一名兽医告诉福尔莫伊她的狗生病了。)福尔莫伊回答说:“博里斯看起来有点壮”,这只是感觉上的错误,就好比超重儿童的家长不会意识到自己小孩超重一样。

Socioeconomic status also influencesobesity in both humans and animals, partly linked to neighbourhoods with lessopen green spaces and fewer fitness resources. Regardless of whether you’retalking about a pet or a person, obesity is a societal health issue, not amoral one – and needs wider policy changes to be addressed.


As for Borris, Formoy says that hiscompetition win was bittersweet. Her father had been unwell when she signedBorris up. “He was my dad’s best mate and the competition encouraged my dad togo out on his mobility scooter with Borris by his side,” she says. Her fatherpassed away in July. “I thought in my head, ‘Dad, me and Borris are still goingto win this for you.’”


She and Borris have kept that promise.Today, Borris is busy chasing Charlie Cat around the house, his own arthritisand breathing difficulties relegated to the past. In his story of obesityconquered, Borris has a few lessons for us all.