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[narrator] Everybody wants to look good,
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and in many places in the world,
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that means thin, but there's a problem.
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We're eating more calories.
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Obesity rates worldwide have soared.
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And this has fueled what is now
a $66 billion dieting industry in the US,
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of bestselling books, frozen meals,
membership programs,
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powders and pills,
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all claiming to hold the secret
to weight loss.
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-[man] Results guaranteed!
-But we haven't found the secret yet.
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Dozens of studies have found that most
people only lose a little bit of weight
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and often gain it right back.
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So why do so many of us keep dieting?
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And why do diets fail?
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[man] Everything you need
for a beautiful change is in this can.
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[man 2] We have been given a lot
of misinformation,
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usually by those looking to make a profit.
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[woman] When it comes to weight loss,
you got to be realistic.
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There really is no need
for all of this confusion.
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[man] It's a great day when the scales
at last seem to shout "success!"
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[narrator] Americans said they averaged
five diets
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over the course of their lifetimes.
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For women, it was seven.
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And there are plenty of diets
to choose from.
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New ones are coming out all the time,
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claiming to be on the cutting edge
of scientific research.
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But for the most part,
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it's just the same diets coming back
again and again,
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and often their claims aren't supported
by science.
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For instance, the ketogenic diet
and the original Atkins diet claimed
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that by cutting carbs, dieters could eat
even more calories and still lose weight.
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Studies have found that not
to be the case.
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And the Paleo diet? Our Paleolithic
ancestors didn't actually eat that way.
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There's lots of evidence they ate grains.
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There are diets based on your body,
like eating according to your blood type.
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Only there's no rigorous scientific
evidence to support that one, either.
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Science has long rejected the concept
of a detox
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because our bodies have evolved
to do a great job
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ridding us of harmful stuff all
on its own.
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Diet supplements, particularly in the form
of pills, are barely regulated,
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so manufacturers don't even need to prove
that they're effective.
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And then there are low-fat diets,
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but just because you see "low-fat"
on a label doesn't mean it's healthy.
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It could be packed full
of sugar and calories.
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But when it comes to low-fat
and low-carb diets,
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there's no shortage of conflict.
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[woman]
New recruits, new rules and a new enemy.
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Fat.
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Fat is the enemy of our health, right?
Apparently not.
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[man] Carbs are your friend.
They are not your enemy.
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-Sugar is public enemy number one.
-[man] Right.
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And carbs are bad hombres.
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[narrator]
In 2018, Dr. Christopher Gardner
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and his team at Stanford University
created a study.
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We were trying
to look at two really popular diets,
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low-fat versus low-carb.
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We didn't ask anybody to figure out
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how many calories they needed
to restrict to lose weight.
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We actually focused just
on avoiding high-fat
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or high-carbohydrate foods in each group,
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but really also focusing on
not being hungry.
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[narrator] They recruited 609 volunteers
with 15 to 100 pounds of weight to lose
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and randomly assigned them
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to either a low-fat or a low-carb diet
for one year.
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Diets that I did beforehand
were minimal at best.
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This was a totally new experience for me.
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I attended the dinner
for the result reveal
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and all the data was laid out.
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It was a surprise that it didn't matter.
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[narrator] The results?
They were virtually identical.
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Some people did lose a lot of weight,
but most did not.
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Jeanne lost six pounds,
and Yvette gained four.
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So why do diets work for some people
and not others?
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There's one simple answer.
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Diets don't work for most people
because most people can't stick to them.
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Yet, many of us still see that
as a personal failure.
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And that's partly because of how diets
are marketed...
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I lost 39 pounds...
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[narrator] ...as drastic weight loss
that's easy and achievable.
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[narrator]
An approach that dates back to 1863,
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when a British mortician
named William Banting
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published the first blockbuster diet book.
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Banting's Letter on Corpulence,
Addressed to the Public,
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was a 16-page,
effectively low-carbohydrate plan.
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[woman] It's a very sympathetic
and autobiographical account
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that was distinct from early,
authoritative medical accounts,
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and he does it with sort of compassion,
a little bit of humor.
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Following the very modern format,
he's saying, "I sympathize with you.
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I was once in your shape.
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If you follow my plan,
I promise you you'll be saved."
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And the book became an instant bestseller.
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[narrator] Across much of Europe,
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people started using the word "Banting"
to mean dieting.
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In Sweden, they still do.
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They say, "Jag banting. I'm on a diet."
There's no word for "diet" in Swedish.
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[narrator] But for most of our history,
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being overweight was the exception,
not the norm.
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Meals had to be farmed and prepared.
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Just eating enough food took
a lot of effort.
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But in the West,
that all changed after World War II.
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[woman] Transportation systems
got better. Production systems got better.
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And companies were able
to start making foods
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that were in boxes
and that had a long shelf life.
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And people loved them
because they were so convenient.
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The classic processed food is what happens
to whole grains
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when you turn whole grains
into white flour.
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You remove the outer layer of bran
and you remove the wheat germ,
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and that's where all the vitamins,
minerals, and fiber are.
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[narrator] The solution? Put those
vitamins and minerals right back in.
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And many consumers who had never heard
of these nutrients before
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now connected their presence
in these new foods with health.
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And so the modern dieting industry
was born.
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[man] At lunch time,
instead of fattening food,
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they have delicious
Metrecal milkshake flavors
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to help stay slim and trim.
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[narrator] Metrecal was a canned
protein shake containing 225 calories
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in 14 different flavors,
fortified with vitamins and minerals.
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It was a sensation.
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The famed tiki bar Trader Vic's began
offering a 325-calorie liquid lunch.
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The upscale department store
Bergdorf Goodman released a purse flask
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for every secret Metrecal drinker.
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The Senate Restaurant offered it
on its menu.
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And even JFK was known to be a fan.
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But the Metrecal shake craze came
to an end.
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By the early 1980s,
the company stopped making them,
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partly because drinking
a chalky-tasting shake instead of meals
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is hard for most people to sustain
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and partly because it was overtaken
by the rise of other diet fads.
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And this is the bind we're in.
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The dieting industry pushes us
to cut calories,
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while the food industry primes us
to eat more of them.
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Everything changed with the increase
in body weight that occurred,
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starting in the 1980s.
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The United States government changed
its policy for subsidizing agriculture
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and gave farmers incentives to grow
as much food as they possibly could.
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[narrator] Food got cheaper,
and we ate a lot more of it,
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particularly between meals.
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In the late '70s, 28% of people ate
two or more snacks a day.
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By the mid '90s,
that number had climbed to 45%.
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In order to account for the weight gain
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that occurred among Americans
between 1980 and 2000,
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people had
to increase their caloric intake
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by about 500 calories a day.
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[narrator] Now that weight loss was
an urgent public health issue,
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government started pouring money
into research,
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which led to
a new scientific understanding
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as to why dieting is so hard.
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For seven seasons, Biggest Loser
has been bringing you new heroes.
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These people are not like you.
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They are you.
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[man] The Biggest Loser was
a unique research experience
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because for the first time
we could study people who were losing enormous amounts
of weight,
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more than 130 pounds on average
over seven months.
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And these people started off
with the most severe form of obesity.
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[narrator] Obesity is defined
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as a body mass index, or BMI, of over 30.
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This is the class the Biggest Loser
contestants belong to.
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And so we studied those folks six years
after the competition. They had regained about two-thirds
of the weight that they'd lost on average.
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One of the surprises was
that their metabolisms slowed down
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much more than you would expect.
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[narrator] The metabolism, what is it?
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Well, metabolism is basically
the energy required
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to keep your cells and tissues alive.
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[narrator] The food we eat is the source
of our energy.
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The majority of that energy,
that is 70 to 90%,
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is used exclusively
for bodily processes like digestion,
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keeping our heart beating,
our hair growing and so on.
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Not for walking, not for biking,
not for jogging.
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Physical activity is great
for muscle tone and our overall health,
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but it just doesn't burn
that many calories
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and after working out, people tend to eat
more calories, which also doesn't help.
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Losing weight isn't just a question
of willpower.
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Our bodies are actually pretty resistant
to weight change,
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especially when it's dropping.
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And then there's leptin,
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a hormone that signals to the brain
how hungry you are.
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A number of studies have found
that leptin levels are lower in people
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who've just lost weight.
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At the end
of the Biggest Loser competition,
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we could barely measure the levels
of leptin in their blood.
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So there is a sort of double whammy.
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You're burning fewer calories
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and you want to eat even more calories
than you did before you lost the weight.
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Most people are not gonna engage in
such extreme measures to lose weight
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or try to keep it off,
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but they still experience some
of the same metabolic changes
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and some of the same changes in leptin.
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[narrator] On top of all of that,
there's an aspect to our bodies
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and to dieting
that we really can't control.
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Our genes.
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More than 50% of the variation
between people and how heavy they are
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is due to their genetics.
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[narrator] That doesn't mean
your weight is determined by your genes,
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but certain genes make it much more likely
that you'll be overweight
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within a given environment.
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But one of the things that we also know is
that genetics haven't changed appreciably
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over the last 30 years
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that have corresponded with the rise
of the obesity epidemic.
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[narrator] Our genes may not have changed
much, but our food environment has.
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In the US, high-calorie processed food
is now often cheaper and easier to get
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than healthy food,
especially in low-income areas.
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That's partly why obesity rates
in the US can vary so widely
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across different ethnic groups.
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Millions of Americans also don't live
near a supermarket
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and can't easily get fresh food.
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The food environment
that was available to me
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and my community growing up,
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it was very restricted.
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The typical McDonald's, Popeyes,
you know, White Castle,
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a lot of fast food restaurants.
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[narrator] For centuries,
we had to grow and cook our meals
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and that knowledge was passed down
from parent to child.
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Urban farms like this one are trying
to bring that knowledge back
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for a new generation.
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Just being able to learn so much
about nutrition
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and implement that into my own life,
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it has really changed my life
for the better.
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[narrator]
With so many forces outside our control,
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our environments, our genes,
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dieting can feel hopeless.
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But it's not.
Remember that Stanford study?
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The emphasis it placed on eating
whole foods did lead to weight loss.
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And while some whole foods can be
pretty high in calories,
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they're typically more nutritious
and more filling,
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so you're less likely to lapse.
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By not focusing on counting calories,
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by focusing on lowering carbs
or lowering fats,
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they actually reported,
when we asked them what they were eating,
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achieving or realizing
a 500-calorie deficit per day.
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Our impression was that they weren't
feeling as hungry as they would have
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if we had said, "Okay,
take everything you're eating and cut back
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by a quarter or a third."
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[narrator]
And that is the key to successful dieting.
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Find the diet you can stick to,
so it's no longer a diet.
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It's just how you eat.
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A common comment we got from many of them
who are the most successful
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was that we had helped them change
their relationship to food.
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[narrator] And even if they didn't reach
their goal weights,
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that new relationship to food made a lot
of them healthier.
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I was able to step away
from that pre-diabetic range.
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I don't want to go out and eat lasagna
with pizza on the side.
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I want to go out
and eat maybe nice green salads
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and maybe I'll have that piece of pizza,
but I'll make it vegetarian or something.
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[laughs]
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[narrator] For much of human history,
we have lived in communities
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on the razor's edge
of food scarcity and famine,
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dreaming up magical lands
full of easy, delicious eating.
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The irony today is that many of us
the world over inhabit that magical land
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where we can eat as much as we want
whenever we want.
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Only in this version,
we're still struggling.
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I think the biggest reason
that diets fail people
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is because they focus solely
on the weight loss component.
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Human physiology is set up to make sure
that we maintain our weight,
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and physiology doesn't like being fought.
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[narrator] But diets can work.
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You just have to eat fewer calories
and sustain it.
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There's no one magic diet
that helps everybody do that.
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It really comes down to this.
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Dietary advice is really simple.
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You eat fruits and vegetables.
You don't eat too much junk food
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and you balance caloric intake
with the kind of activity level you have.
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You try to eat unprocessed foods
to the extent that you can.