Obesity

• 1. Introduction

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  Obesity carries a number that has come to define it: a body mass index over 30, calculated by dividing a person's weight by the square of their height. In 2022, more than 1 billion people worldwide lived with this medical condition, made up of 879 million adults and 159 million children. That figure was more than double the adult cases registered in 1990, and four times the number of affected children. Multiple organizations classify it as a disease, including the World Health Organization, the United States, Canada, Japan, Germany, and the European Parliament. Others, such as the United Kingdom, do not. The condition is a leading preventable cause of death across the globe. Yet a Latin root, an ancient surgeon, a single gene, and a network of neurons in the brain all hide inside this story. So does a paradox where extra weight sometimes helps people survive. The questions ahead are simple to ask and hard to answer. Why has the world grown heavier so fast? Who decides what counts as too much? And why is the weight, once lost, so rarely kept off?

• 2. Measuring The Body

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  Body mass index sorts people into bands: underweight below 18.5, ideal weight from 18.5 to 24.9, overweight from 25 to 29.9, and obese at 30 and above. The U.S. Centers for Disease Control and Prevention splits obesity further into class 1, class 2, and class 3 across the ranges of 30, 35, and 40-plus. Surgical literature adds harsher labels still, naming severe, morbid, and super obesity at thresholds that remain disputed. Asian populations face negative health consequences at a lower BMI than Caucasians, so some nations redrew the lines. Japan defines obesity as any BMI greater than 25, while China uses a figure above 28. Among scholars, the preferred measure is not BMI at all but body fat percentage, the ratio of fat weight to total body weight. The American Society of Bariatric Physicians treats levels above 32 percent for women and 25 percent for men as obese. BMI's blind spot is muscle. It cannot tell lean mass from fat. More than half of all NFL players register as obese by BMI, and one in four as extremely obese, yet their mean body fat percentage of 14 percent sits in a healthy range. Sumo wrestlers show the same gap. One study of college-aged wrestlers found that 40 percent were no longer obese when judged by body fat with a cutoff below 25 percent. Canada uses BMI sparingly, leaning instead on the Edmonton Scale, which weighs quality of life, mental health, and mobility. In Ireland, the condition now carries a longer name: a complex, chronic and relapsing disease.

• 3. The Weight On Health

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  Excess body fat underlies 64 percent of diabetes cases in men and 77 percent in women, one of the strongest links the condition holds. Beyond type 2 diabetes, the list runs long: coronary heart disease, congestive heart failure, stroke, fatty liver disease, gallstones, gout, osteoarthritis, sleep apnea, and cancers of the esophagus, colon, pancreas, kidney, and more. Health consequences split into two camps. Some come from sheer fat mass, like joint wear and sleep apnea. Others come from the rising number of fat cells, which alter the body's response to insulin and push it toward a proinflammatory, prothrombotic state. The CDC has found obesity to be the single strongest risk factor for severe COVID-19 illness, and a study from the RAK Hospital tied it to greater risk of long COVID. In 2021, the World Health Organization estimated the condition caused at least 2.8 million deaths each year. On average it shortens life by six to seven years. A BMI of 30 to 35 costs two to four years, while severe obesity at 40 or above takes ten. The lowest mortality risk sits at a BMI of 20 to 25 in non-smokers, with danger climbing in either direction. In Asians, the risk begins to rise between 22 and 25. High BMI marks risk but does not directly cause these diseases. The deeper drivers are diet and physical activity, the same forces that built the problem in the first place.

• 4. The Survival Paradox

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  First described in 1999, the obesity survival paradox emerged among people undergoing hemodialysis, where extra weight seemed to improve outcomes. It surfaced again in those with heart failure and peripheral artery disease. People with heart failure and a BMI between 30 and 34.9 showed lower mortality than those of normal weight. One explanation is plain: people often lose weight as they grow sicker, so thinness can mark illness rather than health. Patients with class 1 obesity and heart disease face no greater rate of further heart problems than normal-weight patients with the same condition. Even after cardiac bypass surgery, no rise in mortality appears among the overweight and obese. The benefit has limits and rivals. One study credited the more aggressive treatment obese people receive after a cardiac event. Another found that once chronic obstructive pulmonary disease is taken into account in peripheral artery disease, the advantage disappears. At greater degrees of obesity, the risk of further cardiovascular events climbs again.

• 5. Why The World Grew Heavier

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  The United States had the highest dietary energy availability in 1996 at 3654 calories per person per day, climbing to 3754 by 2003. Late in the 1990s, Europeans had 3394 calories, developing parts of Asia 2648, and sub-Saharan Africa 2176. From 1971 to 2000, U.S. obesity rates rose from 14.5 percent to 30.9 percent as people simply ate more. Women's average intake grew by 335 calories a day and men's by 168, most of it from carbohydrates rather than fat. Sweetened beverages now supply almost 25 percent of daily food energy in young American adults, alongside potato chips. Fast food tells a parallel story. Between 1977 and 1995, U.S. consumption of fast-food meals tripled and the energy from them quadrupled. Cheap calories trace back to policy. The U.S. farm bill subsidizes corn, soy, wheat, and rice, making processed food inexpensive next to fruits and vegetables. The body's other half of the equation is movement. At least 30 percent of the world's population gets insufficient exercise, much of it from mechanized transport and labor-saving machines at home. Lawrence D. Frank's 2004 study on community design and time spent in cars drew more than 2,600 citations. His 2005 work built a walkability index for Atlanta, finding that people in the most walkable areas were 2.4 times more likely to meet activity recommendations. A 2006 study of his linked a 5 percent rise in walkability to a 32.1 percent jump in time spent walking or biking. Television viewing tracks with obesity in both children and adults, rising in proportion to hours watched. Notably, obese people consistently under-report what they eat, a gap confirmed in calorimeter rooms and by direct observation.

• 6. Genes And The Brain

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  People carrying two copies of the FTO gene weigh on average 3 to 4 kilograms more and face a 1.67-fold greater risk of obesity than those without the risk allele. As of 2006, more than 41 sites on the human genome had been linked to the condition when the environment allows. Inheritance runs strong. Eighty percent of the children of two obese parents become obese, against less than 10 percent for children of two normal-weight parents. The thrifty gene hypothesis offers an evolutionary reason. During ancient food scarcity, those who stored energy as fat survived famine, a trait that turns harmful where food is steady. Critics have pushed back, spawning the drifty gene and thrifty phenotype hypotheses. Obesity also anchors rare syndromes like Prader-Willi, Bardet-Biedl, Cohen, and MOMO. In children with severe obesity before age 10 and a BMI more than three standard deviations above normal, 7 percent carry a single point mutation. The biology stayed nearly unexplored until 1994, when J. M. Friedman's laboratory discovered the leptin gene. Leptin and ghrelin, made in the body's periphery, govern appetite by acting on the hypothalamus. Within it, the melanocortin pathway is the best understood circuit. The arcuate nucleus holds two neuron groups in opposition. NPY and AgRP neurons stimulate feeding and block satiety. POMC and CART neurons do the reverse. Leptin tips the balance, inhibiting the first group and stimulating the second. A failure in leptin signaling, through deficiency or resistance, leads to overfeeding and may explain certain forms of obesity.

• 7. Treating And Spending

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  Bariatric surgery is the most effective treatment, spanning gastric banding, Roux-en-Y bypass, vertical-sleeve gastrectomy, and biliopancreatic diversion. One study found weight loss between 14 and 25 percent at 10 years and a 29 percent drop in all-cause mortality compared with standard measures, though complications strike about 17 percent of cases and 7 percent need reoperation. Medication has a thornier past. Of 25 anti-obesity drugs withdrawn between 1964 and 2009-23 worked by altering brain neurotransmitters, and deaths were linked to seven products. Six are now approved for long-term use: liraglutide, naltrexone/bupropion, orlistat, semaglutide, tirzepatide, and phentermine/topiramate. After stopping GLP-1 agonists like semaglutide, people regain on average more than half, 50 to 70 percent, of the lost weight within a year. Keeping weight off is the harder fight. Long-term maintenance through lifestyle change succeeds in only 2 to 20 percent of cases. Even so, 87 percent of National Weight Control Registry participants held a 10 percent loss for a decade. Adherence matters more than the specific diet chosen. The bill is staggering. U.S. medical costs attributable to obesity reached $190.2 billion in 2005, more than a fifth of all medical spending. The Lancet Commission on Obesity in 2019 put the global cost at $2 trillion a year, near 2.8 percent of world GDP, and called for a treaty modeled on tobacco control. Workers feel it directly. Duke University employees with a BMI over 40 filed twice as many workers' compensation claims and lost more than 12 times as many work-days as lean colleagues. Women with obesity earn 6 percent less and men 3 percent less for equivalent jobs.

• 8. A Symbol Through Time

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  The word comes from the Latin obesitas, meaning stout, fat, or plump, first recorded in English in 1611 by Randle Cotgrave. Long before that, Hippocrates warned that corpulence is not only a disease itself but the harbinger of others. The Indian surgeon Sushruta, in the 6th century BCE, tied obesity to diabetes and heart disorders and prescribed physical work as a cure. For most of human history, scarcity made fat a sign of wealth and prosperity, common among high officials in ancient East Asian civilizations. The first sculptures of the human body, carved 20,000 to 35,000 years ago, depict obese females, the Venus figurines read by some as emblems of fertility. Greek and Roman art turned away from corpulence in keeping with ideals of moderation. The Renaissance brought it back into view, flaunted in portraits of Henry VIII and Alessandro dal Borro, and in the heavyset women of Rubens, whose name gave us Rubenesque. Then taste reversed. Across the 19th century, slimness became the desirable standard in the Western world. The shift shows in the numbers: from 1922 to 1999, the average height of Miss America winners rose by 2 percent while their average weight fell by 12 percent. Attitudes still split by place and era. The obesus of Ancient Greek comedy was a glutton and a figure of mockery. In much of Africa, obesity remains a sign of wealth and well-being, more so since the HIV epidemic began. In 2014, the European Court of Justice ruled that morbid obesity can count as a disability when it blocks full participation in working life, so that firing someone on those grounds is discriminatory.