10% Human: How Your Body’s Microbes Hold the Key to Health and Happiness. Alanna Collen

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СКАЧАТЬ Animals dying of a viral infection would normally be skinny, not fat. Was it possible that a virus could induce weight gain in chickens? Could this be the explanation behind his patients’ difficulties in losing weight? Dhurandhar, excited to know more, set up an experiment. He injected one group of chickens with the virus, and left another group alone. Sure enough, three weeks later, he found that the infected birds were far fatter than the healthy ones. It seemed as if the virus had made them gain weight as they fell ill. Could it be that Dhurandhar’s patients, and countless other humans around the world, were also infected with the virus?

      What is happening to our species is on such an enormous and unprecedented scale, that in the distant future, when humanity looks back on the twentieth century, they’ll remember it not just for two world wars, nor solely for the invention of the internet, but as the age of obesity. Take a human body from 50,000 years ago and one from the 1950s, and they will look more similar to one another than either does to the average human body today. In just sixty years or so, our lean, muscular, hunter-gatherer-like physiques have been encased inside a layer of excess fat. It’s something that has never happened to humans on this scale before, and no other animal species – apart from the pets and livestock we care for – has succumbed to this anatomy-changing disease.

      One in every three adults on Earth is overweight. One in nine is obese. That’s the average across all countries, including those where under-nutrition is more common than being overweight. Looking just at the figures for the fattest of countries is even harder to believe. On the South Pacific island of Nauru, for example, around 70 per cent of adults are obese, and a further 23 per cent are overweight. Just 10,000 people live in this tiny country, and only about 700 of them are a healthy weight. Nauru is officially the fattest nation on Earth, but it is closely followed by most of the other South Pacific islands and several Middle Eastern states.

      In the West, we have gone from being skinny enough that no one thought to comment on, worry about, or count the number of overweight people, to being fat enough that it would be quicker to count those that remain skinny. Roughly two in three adults are overweight, and half of those are not just overweight, but obese. The United States, despite its reputation, is seventeenth in the world rankings, with a mere 71 per cent of the population overweight or obese. As for the UK, it ranks thirty-ninth, with 62 per cent of adults overweight (including 25 per cent obese): the highest figures in Western Europe. Even among children in the Western world, being too fat is shockingly common, with up to one-third of under-twenty-year-olds overweight – half of them obese.

      Obesity has crept upon us in a way that makes it seem almost normal. Yes, there is a steady stream of articles and news pieces about the obesity ‘epidemic’ to remind us that it is actually a problem, but we have very quickly adapted to living in a society where most people are overweight. We are quick to assume that fatness is the next step along from greediness and laziness, but if that’s the case, it’s quite an indictment of human nature. Looking at our other achievements as a species over the past century or so – the inventions of mobile phones, the internet, aeroplanes, life-saving medicines and so on – suggests we are not all just lying around, stuffing ourselves with cake. The fact that lean people are now in the minority in the developed world, and that this change has happened in just fifty or sixty years, after thousands upon thousands of years of human leanness, is shocking – just what are we doing to ourselves?

      On average, people in the Western world have gained roughly a fifth of their own body weight in the last fifty years alone. If your allotted time on Earth had fallen so that your ‘today’ fell in the 1960s, not the 2010s, you would, in all likelihood, be considerably lighter. People who are 11 stone in 2015 might well have been just over 9 stone in 1965, no special efforts required. Today, to regain a pre-1960s weight, tens of millions of people are perpetually on a diet, attempting to deprive themselves of foods for which their brains have a deep-rooted desire. But despite the billions of dollars spent on fad-dieting, gym-going and pill-taking, obesity levels rise inexorably.

      This rise has taken place in the face of sixty years of scientific research into effective weight-maintenance and weight-loss strategies. In 1958, back when being overweight was still relatively rare, one of the pioneers of obesity research, Dr Albert Stunkard, said: ‘Most obese persons will not stay in treatment for obesity. Of those who stay in treatment, most will not lose weight. And of those who do lose weight, most will regain it.’ He was broadly right. Even half a century later, success rates in trials of weight-loss intervention strategies are extremely low. Often, less than half of participants achieve weight loss, and for most it’s just a few kilos over a year or more. Why is it so very hard?

      Up to now, among those looking for explanations – and perhaps excuses – for their weight, genetics has been the fashionable place to lay the blame. Differences in human DNA, though, have not proved to be particularly illuminating when it comes to weight gain, with only a tiny proportion of our susceptibility to obesity explained by genes. In 2010, a huge study was conducted by a team of hundreds of scientists who hunted through the genes of a quarter of a million people in the hope of finding some that were associated with weight. Astonishingly, they discovered just 32 genes in our 21,000-strong genome that seemed to play a role in weight gain. The average difference in weight between people with the very lowest genetic likelihood of obesity and the very highest was just 8 kg (17 lb). For those who would like to blame their parents, that equates to between 1 per cent and 10 per cent extra risk of becoming overweight, and that’s for those people who are in possession of the worst combination of those gene variants.

      Regardless of the genes involved, genetics could never be the full explanation for the obesity epidemic, because sixty years ago almost everyone was slim, despite having broadly the same gene variants as the human population today. What probably matters far more is the impact that a changing environment – our diets and lifestyles, for example – has on the workings of our genes.

      Our other favourite explanation is that of a ‘slow metabolism’. ‘I don’t have to watch what I eat, I’ve got a quick metabolism,’ must be one of the most irritating comments a lean person can make, but it has no basis in science. A slow metabolism – or more correctly, a low basal metabolic rate – means that a person burns relatively little energy whilst doing absolutely nothing at all – no moving, no watching TV, no doing mental arithmetic. Metabolic rates do vary from person to person, but it is actually overweight people who have the faster metabolisms, not lean people. It simply takes more energy to run a big body than a small one.

      So if genetics and low basal metabolic rates aren’t behind the obesity epidemic, and the amount we eat and move doesn’t fully explain our collective weight gain, what is the explanation? Like many people, Nikhil Dhurandhar wondered if there’s more to it than we assume. The possibility that a virus could be causing or exacerbating obesity in some people played on his mind. He tested fifty-two of his human patients in Mumbai for antibodies to the chicken virus – evidence that they had been infected by it at some stage. To his surprise, the ten most obese of these patients had had the virus at some point. Dhurandhar made up his mind; he would stop trying to treat obesity and start researching its causes instead.

      We have reached the point in human history where we are considering, in the United Kingdom at least, that redesigning and re-routing the digestive system that evolution has given us is the best way to prevent us from eating ourselves to death. It seems that gastric bands and bypasses, which reduce the size of the stomach and prevent people from consuming everything that their brains and bodies tell them to, are the most effective and the cheapest way to get a grip on the obesity epidemic and its consequences for our collective health.

      If diets and exercise are so futile that gastric bypasses are our only hope for significant weight loss, what does that say for the straightforward application of the laws of physics – energy intake minus energy burned equals energy stored – to us as animals governed by the laws of biochemistry?

      As we are just beginning to learn, it’s not that simple. As the warblers and many hibernating mammals СКАЧАТЬ