 You may have heard the expression knowledge is power. Well, today we're going to give you more power to control your diet and lifestyle by giving you the facts. Welcome to the Nutrition Facts Podcast, I'm your host, Dr. Michael Greger. Today, we look at a condition that comes with a multitude of serious health issues—obesity. And we start with the best ways to figure out our optimal weight based on our height. We seem to become inert to the mortal threat of obesity. If you go back in the medical literature a half century or so, when obesity wasn't just run-of-the-mill, the descriptions are much more grim. Obesity is always tragic, and its hazards are terrifying. But it's not just obesity. Of the 4 million deaths every year attributed to excess body fat, nearly 40% of the victim are just overweight, not obese. According to two famous Harvard studies, weight gain of as little as 11 pounds from early adulthood through middle age increases the risk of major chronic diseases, such as diabetes, cardiovascular disease, and cancer. The flip side, though, is that even modest weight loss can have major health benefits. What's the optimal BMI? The largest studies in the United States and around the world found that having a normal body mass index, a BMI from 20 to 25, is associated with the longest lifespan. Put all the best available studies with the longest follow-up together, and that can be narrowed down even further to a BMI of 20 to 22. That would be about between 124 to 136 pounds for someone who stands 5 foot 6. But even with a normal BMI, the risk of developing chronic diseases, such as type 2 diabetes, heart disease, and several types of cancer, starts to rise towards the upper end, even starting as low as a BMI of 21. A BMI of 18.5 and 24.5 are both considered within the normal range, but a BMI of 24.5 may be associated with twice the heart disease risk compared to 18.5. Just as there are gradations of risk within a normal BMI range, there is a spectrum within obesity. Class III obesity, a BMI over 40, can be associated with a loss of a decade of life for more. At a BMI greater than 45, such as a 5 foot 6 person at 280 pounds, life expectancy may shrink to that of a cigarette smoker. There are, however, so-called obesity skeptics that argue that the health consequences of obesity are unclear or even greatly exaggerated. They are a motley bunch, ranging from feminists, queer theorists, and new-ages to far-right-wing pro-gun pro-America websites, where the idea is that obesity alarmists are nanny-state communists who simply want to stop us from having fun. Unlike activists who, for example, organize to raise consciousness and stamp out the AIDS epidemic, the size acceptance movement appears to have the opposite goal, rallying for less public awareness and treatment of the problem. They do have good slogans, though. We're here. We're spheres. Get used to it. I'm all for fighting size, stigma, and discrimination, but the adverse health consequences of obesity are an established scientific fact. Can't you be fat but fit? In a study of more than 600 centenarians, those living over 100, only about 1% of the women and not a single one of the men were obese. But there does appear to be a rare subgroup of obese individuals who don't suffer the typical metabolic costs, such as high blood pressure and cholesterol. This raises the possibility that there may be such a thing as benign obesity or healthy obesity. It may just be a matter of time, though, before the risk factor is developed. And even if they don't follow long enough, even quote-unquote metabolically healthy obese individuals are at increased risk of diabetes and fatty liver disease, and cardiovascular events such as heart attacks, indoor premature death. Bottom line, there is strong evidence that so-called healthy obesity is a myth. Many fat activists try to downplay the risk of obesity, even as they may be among the epidemic's greatest victims. Lynn McCaffey is the director of medical advocacy for the Council on Size and Weight Discrimination, and routinely takes part in obesity conferences and government panels on obesity. I'm not actually particularly that interested in health, she's quoted as saying, and God, I hate science. In our next story, we look at the obesity paradox with some studies that suggest that some overweight individuals live longer. Martin Luther King Jr. warned that human progress is neither automatic nor inevitable, and the same may be true of the human lifespan. In the 1800s, life expectancy was less than 40, but has been steadily increasing over the last two centuries, gaining about two years per decade. That is until recently. Longevity gains have faltered or even reversed. Thanks to the obesity epidemic, we may now be raising the first American generation to live shorter lives than their parents. The downward trend in longevity is expected to accelerate as the current younger generation, who started out heavier and earlier than ever before, ages into adulthood. If the obesity epidemic continues, unchecked current trends signal a potential looming social and economic catastrophe. In the coming decade, some particularly may lose two to five or more years of life expectancy in the United States. I mean, to put that into perspective, a miracle cure for all forms of cancer would only add 3.5 years to the average American lifespan. In other words, reversing the obesity epidemic might save more lives than curing cancer. The evidence being overweight increases your risk for debilitating diseases like diabetes is considered indisputable. But surprisingly, there's controversy surrounding body weight and overall mortality. In 2013, CDC scientists published a meta-analysis in the Journal of the American Medical Association suggesting being overweight was actually advantageous. Yes, grade 2 or 3 obesity, like being average height, 5 foot 6, and weighing about 215 plus pounds, was associated with living a shorter life. But grade 1 obesity between about 185 to 215 pounds at that height was not. And just being overweight, 155 to 185 pounds, appeared to be protective compared to those who were normal weight, 115 to 155. The overweight individuals, BMI 25 to 30, appeared to live the longest. Headline writers were giddy. Being overweight can extend your life. Dreading your diet? Don't worry, plump people live longer. Extra pounds might mean lower chance of death. Not surprisingly, this study ignited a firestorm of controversy in the public health community. The study was called ludicrous, flawed, misleading. The chair of nutrition and Harvard lost his cool calling the study really a pile of rubbish. Fearing the food industry might exploit this study in the same way the petroleum industry misuses controversy over climate change. Public health advocates can't just dismiss data they find inconvenient, though. I mean, science is science. But how could being overweight increase the risk of life-threatening diseases, yet at the same time make you live longer? This became known as the obesity paradox. The solution to the puzzle appears to lie with two major sources of bias. The first being, confounding by smoking. The nicotine in tobacco can lead to weight loss. So if you're skinnier because you smoke, well then no wonder you'd live a shorter life with a slimmer waist. The failure to control for the effect of smoking in studies purporting the show in obesity paradox leads to the dangers of obesity being grossly underestimated. The second major source of bias is reverse causality. Instead of lower weight leading to life-threatening diseases, is it more likely that life-threatening diseases are leading to lower weight? I mean, conditions such as hidden tumors, chronic heart and lung disease, alcoholism, and depression can all cause unintentional weight loss months or even years before they're even diagnosed. It's normal to be overweight in this country, right? So people who are abnormally thin, in other words, ideal weight, I mean, could actually be taking care of themselves, right? But maybe heavy smokers, elderly and frail, or seriously ill with weight loss from their disease. To put the obesity paradox issue to the test once and for all, the global BMI mortality collaboration was formed, reviewing data for more than 10 million people from hundreds of studies in dozens of countries, the largest evaluation of BMI mortality in history. To help eliminate bias, they omitted smokers and those with known chronic disease, and then excluded the first five years of follow-up to try to remove from the analysis those with undiagnosed conditions who lost weight due to an impending death. And the results were clear, being overweight, and all grades of obesity were associated with a significantly greater risk of dying prematurely. So adjusting for these biases leads to eliminating the obesity paradox altogether. In other words, the so-called obesity paradox appears to be just a myth. Indeed, when intentional weight loss is actually put to the test, people live longer. There are bariatric surgery studies like the SOS trial that show weight loss reduces long-term mortality and randomizes people to weight loss through lifestyle changes shows the same thing. Losing a dozen pounds through diet and exercise was found to be associated with a 15% drop in overall mortality. Now, I mean, exercise alone may extend the lifespan even without weight loss, but there also appears to be a similar longevity benefit of weight loss through dietary means alone. Finally today, what are the effects of weight loss on kidney function, fatty liver disease, and natural killer cell activity, our first line of immune defense against cancer? In the ABCs of Health Consequences of Obesity, I is for immunity. The SOS trial, which followed the fates of thousands of bariatric surgery patients for a decade or two, compared to a control group that maintained their weight, and those who surgically lost about 20% of their body weight not only lived longer, thanks in part to less diabetes and less cardiovascular disease, but they also got less cancer. This may be because anti-tumor immunity appears to be affected by weight. Natural killer cells are your immune system's first line of defense against cancer cells, well as many viral infections, and their function is severely impaired in obesity. Randomized obese individuals to a weight loss program, though, and there was a significant reactivation of their natural killer cell function within just three months. The program involved an exercise component, though, and so it's hard to tease out the impact of the weight loss itself, since physical activity alone can boost natural killer cell activity. On the other end of the immune spectrum, obesity is suspected to be a causal risk factor for the development of the autoimmune disease multiple sclerosis. This suggests obesity is associated with the worst of both worlds when it comes to immune function, under activity when it comes to protecting against cancer, and infection, but over activity when it comes to certain inflammatory autoimmune conditions. J is for jaundice. Thanks to the obesity epidemic, non-alcoholic fatty liver disease is now the most common liver disorder in the industrialized world. Fat doesn't just end up in our belly and thighs, but inside some of our internal organs. More than 80% of individuals with abdominal obesity may have fatty infiltration into their liver, and those with severe obesity, the prevalence can exceed 90%. This can lead to inflammation, scarring, and ultimately, cirrhosis and liver cancer. Currently, this non-alcoholic fatty hepatitis is the leading cause of liver transplants in American women and men are expected to catch up in 2020. K is for kidneys. Obesity is one of the strongest risk factors for chronic kidney disease as well. Your kidneys compensate for the metabolic demands of the excess weight by redlining to what's called hyperfiltration to deal with the extra workload. This resulting increased pressure within the kidneys can damage the sensitive structures and increase the risk of kidney failure over the long term. What about LMNOP through Z? If you want to continue through the alphabet, well, L could be diminished lung function, M for metabolic syndrome, and so on. There's even an X for xyphodenia, a pain at the tip of the bottom of the breastbone from being bent forward by an expanding abdomen. Given the myriad health conditions associated with excess weight, annual medical spending attributable to obesity is nearly $2,000 per year, with obese workers with multiple conditions costing companies up to $10,000 more in health care coverage compared to lean counterparts. This may actually account for some of the wage gap that obese employees experience as companies try to pass along these costs beyond just brazen discrimination. Between health care costs and diminished productivity in terms of lost workdays, the total lifetime cost of obesity for children and teens has been estimated to exceed $150,000. Some estimates beg the national cost of obesity, about $150 billion, with another $50 billion per year added by 2030 as our increasingly heavy baby boomers continue to age. Others diametrically disagree, based on the morbid fact that obese individuals may not live as long. Just as the medical costs of tobacco-related diseases may be more than offset by the shortened survival of smokers, the lifetime health care costs of obese individuals may turn out to be lower because they're expected to die so much sooner. So the true cost may be more in lives, rather than dollars. To see any graphs, charts, graphics, images, or studies mentioned here, please go to the Nutrition Facts podcast landing page. There you'll find all the detailed information you need, plus links to all the sources we cite for each of these topics. For a vital timely text on the pathogens that cause pandemics, you can order the e-book, audiobook, or hard copy of my book, How to Survive a Pandemic. For recipes, check out my new How Not to Diet cookbook. It's beautifully designed with more than 100 recipes for delicious and nutritious meals. And all proceeds I receive from all my books go to charity. There's no ads, no corporate sponsorships, strictly non-commercial, not selling anything. Just put it up as a public service as a labor of love as a tribute to my grandmother, whose own life was saved with evidence-based nutrition.