Martin Luther King Jr. warned that human progress
Martin Luther King Jr. warned that human progress

is neither automatic nor inevitable,
is neither automatic nor inevitable,

and the same may be true of the human lifespan.
and the same may be true of the human lifespan.

In the 1800's, life expectancy was less than 40, but has been steadily increasing
In the 1800's, life expectancy was less than 40, but has been steadily increasing

over the last two centuries, gaining about two years per decade.
over the last two centuries, gaining about two years per decade.

That is until recently. Longevity gains have faltered or even reversed.
That is until recently. Longevity gains have faltered or even reversed.

Thanks to the obesity epidemic, we may now be raising
Thanks to the obesity epidemic, we may now be raising

the first American generation to live shorter lives than their parents.
the first American generation to live shorter lives than their parents.

The downward trend in longevity is expected to accelerate
The downward trend in longevity is expected to accelerate

as the current younger generation (who started out heavier and earlier
as the current younger generation (who started out heavier and earlier

than ever before) ages into adulthood.
than ever before) ages into adulthood.

If the obesity epidemic continues unchecked, current trends
If the obesity epidemic continues unchecked, current trends

signal a potential "looming social and economic catastrophe."
signal a potential "looming social and economic catastrophe."

In the coming decades some predict we may lose 2 to 5 or more years
In the coming decades some predict we may lose 2 to 5 or more years

of life expectancy in the United States.
of life expectancy in the United States.

I mean, to put that into perspective, a miracle cure for all forms
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.
of cancer would only add 3.5 years to the average American lifespan.

In other words, reversing the obesity epidemic
In other words, reversing the obesity epidemic

might save more lives than curing cancer.
might save more lives than curing cancer.

The evidence that being overweight increases your risk
The evidence that being overweight increases your risk

for debilitating diseases like diabetes is considered indisputable,
for debilitating diseases like diabetes is considered indisputable,

but surprisingly there's controversy surrounding body weight
but surprisingly there's controversy surrounding body weight

and overall mortality. In 2013, CDC scientists published
and overall mortality. In 2013, CDC scientists published

a meta-analysis in the Journal of the American Medical Association
a meta-analysis in the Journal of the American Medical Association

suggesting being overweight was actually advantageous.
suggesting being overweight was actually advantageous.

Yes, grade 2 or 3 obesity, like being average height (5' 6" )
Yes, grade 2 or 3 obesity, like being average height (5' 6" )

and weighing about 215+ pounds, was associated with living a shorter life.
and weighing about 215+ pounds, was associated with living a shorter life.

But grade 1 obesity, between about 185-215 pounds at that height, was not.
But grade 1 obesity, between about 185-215 pounds at that height, was not.

And just being overweight,155-185 pounds, appeared to be protective
And just being overweight,155-185 pounds, appeared to be protective

compared to those who were normal weight,115 to 155 pounds.
compared to those who were normal weight,115 to 155 pounds.

The overweight individuals, BMI 25 to 30, appeared to live the longest.
The overweight individuals, BMI 25 to 30, appeared to live the longest.

Headline writers were giddy: Being overweight can extend your life..."
Headline writers were giddy: Being overweight can extend your life..."

"Dreading your diet? Don't worry... plump people live LONGER"
"Dreading your diet? Don't worry... plump people live LONGER"

"Extra pounds might mean lower chance of death"
"Extra pounds might mean lower chance of death"

Not surprisingly, the study ignited a firestorm of controversy
Not surprisingly, the study ignited a firestorm of controversy

in the public health community. The study was called ludicrous, flawed, misleading.
in the public health community. The study was called ludicrous, flawed, misleading.

The chair of nutrition at Harvard lost his cool, calling the study
The chair of nutrition at Harvard lost his cool, calling the study

"really a pile of rubbish," fearing the food industry might exploit this 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.
in the same way the petroleum industry misuses controversy over climate change.

Public health advocates can't just dismiss data
Public health advocates can't just dismiss data

they find inconvenient though. I mean, science is science.
they find inconvenient though. I mean, science is science.

But how could being overweight
But how could being overweight

increase the risk of life-threatening diseases, yet at the same time
increase the risk of life-threatening diseases, yet at the same time

make you live longer? This became known as the obesity paradox.
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 solution to the puzzle appears to lie with two major sources of bias,

the first being confounding by smoking.
the first being confounding by smoking.

The nicotine in tobacco can lead to weight loss.
The nicotine in tobacco can lead to weight loss.

So if you're skinnier because you smoke, well, then
So if you're skinnier because you smoke, well, then

no wonder you'd live a shorter life with a slimmer waist.
no wonder you'd live a shorter life with a slimmer waist.

The failure to control for the effect of smoking in studies purporting to show
The failure to control for the effect of smoking in studies purporting to show

an obesity paradox leads to the dangers of obesity being grossly underestimated.
an obesity paradox leads to the dangers of obesity being grossly underestimated.

The second major source of bias is reverse causality.
The second major source of bias is reverse causality.

Instead of lower weight leading to life-threatening diseases,
Instead of lower weight leading to life-threatening diseases,

isn't it more likely that life-threatening diseases are leading to lower weight?
isn't it more likely that life-threatening diseases are leading to lower weight?

Conditions such as hidden tumors, chronic heart and lung disease, alcoholism,
Conditions such as hidden tumors, chronic heart and lung disease, alcoholism,

and depression can all cause unintentional weight loss
and depression can all cause unintentional weight loss

months or even years before they're even diagnosed.
months or even years before they're even diagnosed.

It's normal to be overweight in this country.
It's normal to be overweight in this country.

So people who are abnormally thin--- in other words, ideal weight---
So people who are abnormally thin--- in other words, ideal weight---

could actually be taking care of themselves, but may be heavy smokers,
could actually be taking care of themselves, but may be heavy smokers,

elderly and frail, or seriously ill with weight loss from their disease.
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,
To put the obesity paradox issue to the test once and for all,

the Global BMI Mortality Collaboration was formed, reviewing data
the Global BMI Mortality Collaboration was formed, reviewing data

from more than 10 million people from hundreds of studies
from more than 10 million people from hundreds of studies

in dozens of countries,
in dozens of countries,

the largest evaluation of BMI and mortality in history.
the largest evaluation of BMI and mortality in history.

To help eliminate bias, they omitted smokers and those
To help eliminate bias, they omitted smokers and those

with known chronic disease, and then excluded the first five years
with known chronic disease, and then excluded the first five years

of follow-up to try to remove from the analysis those
of follow-up to try to remove from the analysis those

with undiagnosed conditions who lost weight due to an impending death.
with undiagnosed conditions who lost weight due to an impending death.

And the results were clear: being overweight, and all grades of obesity,
And the results were clear: being overweight, and all grades of obesity,

were associated with a significantly greater risk of dying prematurely.
were associated with a significantly greater risk of dying prematurely.

So, adjusting for these biases leads to eliminating
So, adjusting for these biases leads to eliminating

the obesity paradox altogether.
the obesity paradox altogether.

In other words, the so-called obesity paradox appears to be just a myth.
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,
Indeed, when intentional weight loss is actually put to the test,

people live longer.
people live longer.

There are bariatric surgery studies like the SOS trial that show weight loss
There are bariatric surgery studies like the SOS trial that show weight loss

reduces long-term mortality, and  randomizing people to weight loss
reduces long-term mortality, and  randomizing people to weight loss

through lifestyle changes shows the same thing.
through lifestyle changes shows the same thing.

Losing a dozen pounds through diet and exercise was found to be associated
Losing a dozen pounds through diet and exercise was found to be associated

with a 15% drop in overall mortality.
with a 15% drop in overall mortality.

Now, exercise alone may extend lifespan even without weight loss,
Now, exercise alone may extend lifespan even without weight loss,

but there also appears to be a similar longevity benefit
but there also appears to be a similar longevity benefit

of weight loss through dietary means alone.
of weight loss through dietary means alone.