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