The most basic function of bodily fat is self-storage of food reserves.
In prehistoric times, natural selection favored genotypes that could endure harsh conditions by stocking the most fat.
With chronic malnutrition being the norm for most of human history, genetics evolved to favor fat storage.
So when did body fat become problematic?
The negative impacts of being overweight were not even noted in medical literature until as late as the 18th century.
Then, technological advances coupled with public health measures resulted in the betterment of the quantity, quality, and variety of food.
Sustained abundance of good food enabled a healthier population to boom economically.
Output increased, and with it, leisure time and waistlines.
By the mid 19th century, being excessively overweight, or obese, was recognized as a cause of ill health, and another century later, declared deadly.
What is the distinction between being overweight and being obese?
A calculation called the BMI breaks it down for us.
For example, if someone weighs 65 kilgorams and is 1.5 meters tall, they have a BMI of about 29.
Obesity is a condition of excess body fat that occurs when a person's BMI is above 30, just over the overweight range of 25 to 29.9.
While BMI can be a helpful estimate of healthy weight, actual body fat percentage can only really be determined by also considering information like waist circumference and muscle mass.
Athletes, for instance, have a naturally higher BMI.
So how does a person become obese?
At its most basic, obesity is caused by energy imbalance.
If the energy input from calories is greater than the energy output from physical activity, the body stores the extra calories as fat.
In most cases, this imbalance comes from a combination of circumstances and choices.
Adults should be getting at least 2.5 hours of exercise each week, and children a whole hour per day.
But globally, one in four adults and eight out of ten adolescents aren't active enough.
Calorie-dense processed foods and growing portion sizes coupled with pervasive marketing lead to passive overeating.
And scarce resources, and a lack of access to healthy, affordable foods creates an even greater risk in disadvantaged communities.
Yet, our genetic makeup also plays a part.
Studies on families and on separated twins have shown a clear causal hereditary relationship to weight gain.
Recent studies have also found a link between obesity and variations in the bacteria species that live in our digestive systems.
No matter the cause, obesity is an escalating global epidemic.
It substantially raises the probability of diseases, like diabetes, heart disease, stroke, high blood pressure, and cancer.
It affects virtually all ages, genders, and socioeconomic groups in both developed and developing countries.
With a 60% rise in child obesity globally over just two decades, the problem is too significant to ignore.
Once a person is obese, the climb to recovery becomes progressively steeper.
Hormonal and metabolic changes reduce the body's response to overeating.
After losing weight, a formerly overweight person burns less calories doing the same exercises as a person who is naturally the same weight, making it much more difficult to shed the excess fat.
And as people gain weight, damage to signaling pathways makes it increasingly difficult for the brain to measure food intake and fat storage.
There is, however, some evidence that well-monitored, long-term changes in behavior can lead to improvements in obesity-related health issues.
And weight loss from sustained lifestyle changes, or invasive treatments like bariatric surgery, can improve insulin resistance and decrease inflammation.
What was once an advantage for survival is now working against us.
As the world's population continues to slow down and get bigger, moving and consciously eating our way towards a healthier weight is essential to our overall well-being.
And with the epidemic affecting every country in the world for different socioeconomic reasons, obesity cannot be seen as an isolated issue.
More global measures for prevention are essential to manage the weight of the world.
So I know TED is about a lot of things that are big, but I want to talk to you about something very small.
So small, it's a single word.
The word is "misfit."
It's one of my favorite words, because it's so literal.
I mean, it's a person who sort of missed fitting in.
Or a person who fits in badly.
Or this: "a person who is poorly adapted to new situations and environments."
I'm a card-carrying misfit.
And I'm here for the other misfits in the room, because I'm never the only one.
I'm going to tell you a misfit story.
Somewhere in my early 30s, the dream of becoming a writer came right to my doorstep.
Actually, it came to my mailbox in the form of a letter that said I'd won a giant literary prize for a short story I had written.
The short story was about my life as a competitive swimmer and about my crappy home life, and a little bit about how grief and loss can make you insane.
The prize was a trip to New York City to meet big-time editors and agents and other authors.
So kind of it was the wannabe writer's dream, right?
You know what I did the day the letter came to my house?
Because I'm me, I put the letter on my kitchen table, I poured myself a giant glass of vodka with ice and lime, and I sat there in my underwear for an entire day, just staring at the letter.
I was thinking about all the ways I'd already screwed my life up.
Who the hell was I to go to New York City and pretend to be a writer?
Who was I?
I'll tell you.
I was a misfit.
Like legions of other children, I came from an abusive household that I narrowly escaped with my life.
I already had two epically failed marriages underneath my belt.
I'd flunked out of college not once but twice and maybe even a third time that I'm not going to tell you about.
(Laughter) And I'd done an episode of rehab for drug use.
And I'd had two lovely staycations in jail.
So I'm on the right stage.
(Laughter) But the real reason, I think, I was a misfit, is that my daughter died the day she was born, and I hadn't figured out how to live with that story yet.
After my daughter died I also spent a long time homeless, living under an overpass in a kind of profound state of zombie grief and loss that some of us encounter along the way.
Maybe all of us, if you live long enough.
You know, homeless people are some of our most heroic misfits, because they start out as us.
So you see, I'd missed fitting in to just about every category out there: daughter, wife, mother, scholar.
And the dream of being a writer was really kind of like a small, sad stone in my throat.
It was pretty much in spite of myself that I got on that plane and flew to New York City, where the writers are.
Fellow misfits, I can almost see your heads glowing.
I can pick you out of a room.
At first, you would've loved it.
You got to choose the three famous writers you wanted to meet, and these guys went and found them for you.
You got set up at the Gramercy Park Hotel, where you got to drink Scotch late in the night with cool, smart, swank people.
And you got to pretend you were cool and smart and swank, too.
And you got to meet a bunch of editors and authors and agents at very, very fancy lunches and dinners.
Ask me how fancy.
Audience: How fancy?
Lidia Yuknavitch: I'm making a confession: I stole three linen napkins -- (Laughter) from three different restaurants.
And I shoved a menu down my pants.
(Laughter) I just wanted some keepsakes so that when I got home, I could believe it had really happened to me.
You know?
The three writers I wanted to meet were Carole Maso, Lynne Tillman and Peggy Phelan.
These were not famous, best-selling authors, but to me, they were women-writer titans.
Carole Maso wrote the book that later became my art bible.
Lynne Tillman gave me permission to believe that there was a chance my stories could be part of the world.
And Peggy Phelan reminded me that maybe my brains could be more important than my boobs.
They weren't mainstream women writers, but they were cutting a path through the mainstream with their body stories, I like to think, kind of the way water cut the Grand Canyon.
It nearly killed me with joy to hang out with these three over-50-year-old women writers.
And the reason it nearly killed me with joy is that I'd never known a joy like that.
I'd never been in a room like that.
My mother never went to college.
And my creative career to that point was a sort of small, sad, stillborn thing.
So kind of in those first nights in New York I wanted to die there.
I was just like, "Kill me now.
I'm good.
This is beautiful."
Some of you in the room will understand what happened next.
First, they took me to the offices of Farrar, Straus and Giroux.
Farrar, Straus and Giroux was like my mega-dream press.
I mean, T.S. Eliot and Flannery O'Connor were published there.
The main editor guy sat me down and talked to me for a long time, trying to convince me I had a book in me about my life as a swimmer.
You know, like a memoir.
The whole time he was talking to me, I sat there smiling and nodding like a numb idiot, with my arms crossed over my chest, while nothing, nothing, nothing came out of my throat.
So in the end, he patted me on the shoulder like a swim coach might.
And he wished me luck and he gave me some free books and he showed me out the door.
Next, they took me to the offices of W.W. Norton, where I was pretty sure I'd be escorted from the building just for wearing Doc Martens.
But that didn't happen.
Being at the Norton offices felt like reaching up into the night sky and touching the moon while the stars stitched your name across the cosmos.
I mean, that's how big a deal it was to me.
You get it?
Their lead editor, Carol Houck Smith, leaned over right in my face with these beady, bright, fierce eyes and said, "Well, send me something then, immediately!"
See, now most people, especially TED people, would have run to the mailbox, right?
It took me over a decade to even imagine putting something in an envelope and licking a stamp.
On the last night, I gave a big reading at the National Poetry Club.
And at the end of the reading, Katharine Kidde of Kidde, Hoyt &amp; Picard Literary Agency, walked straight up to me and shook my hand and offered me representation, like, on the spot.
I stood there and I kind of went deaf.
Has this ever happened to you?
And I almost started crying because all the people in the room were dressed so beautifully, and all that came out of my mouth was: "I don't know.
I have to think about it."
And she said, "OK, then," and walked away.
All those open hands out to me, that small, sad stone in my throat ...
You see, I'm trying to tell you something about people like me.
Misfit people -- we don't always know how to hope or say yes or choose the big thing, even when it's right in front of us.
It's a shame we carry.
It's the shame of wanting something good.
It's the shame of feeling something good.
It's the shame of not really believing we deserve to be in the room with the people we admire.
If I could, I'd go back and I'd coach myself.
I'd be exactly like those over-50-year-old women who helped me.
I'd teach myself how to want things, how to stand up, how to ask for them.
I'd say, "You!
Yeah, you!
You belong in the room, too."
The radiance falls on all of us, and we are nothing without each other.
Instead, I flew back to Oregon, and as I watched the evergreens and rain come back into view, I just drank many tiny bottles of airplane "feel sorry for yourself."
I thought about how, if I was a writer, I was some kind of misfit writer.
What I'm saying is, I flew back to Oregon without a book deal, without an agent, and with only a headful and heart-ful of memories of having sat so near the beautiful writers.
Memory was the only prize I allowed myself.
And yet, at home in the dark, back in my underwear, I could still hear their voices.
They said, "Don't listen to anyone who tries to get you to shut up or change your story."
They said, "Give voice to the story only you know how to tell."
They said, "Sometimes telling the story is the thing that saves your life."
Now I am, as you can see, the woman over 50.
And I'm a writer.
And I'm a mother.
And I became a teacher.
Guess who my favorite students are.
Although it didn't happen the day that dream letter came through my mailbox, I did write a memoir, called "The Chronology of Water."
In it are the stories of how many times I've had to reinvent a self from the ruins of my choices, the stories of how my seeming failures were really just weird-ass portals to something beautiful.
All I had to do was give voice to the story.
There's a myth in most cultures about following your dreams.
It's called the hero's journey.
But I prefer a different myth, that's slightly to the side of that or underneath it.
It's called the misfit's myth.
And it goes like this: even at the moment of your failure, right then, you are beautiful.
You don't know it yet, but you have the ability to reinvent yourself endlessly.
That's your beauty.
You can be a drunk, you can be a survivor of abuse, you can be an ex-con, you can be a homeless person, you can lose all your money or your job or your husband or your wife, or the worst thing of all, a child.
You can even lose your marbles.
You can be standing dead center in the middle of your failure and still, I'm only here to tell you, you are so beautiful.
Your story deserves to be heard, because you, you rare and phenomenal misfit, you new species, are the only one in the room who can tell the story the way only you would.
And I'd be listening.
Thank you.
(Applause)