"Is the Obesity Paradox Real or a Myth?"
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 1800's, 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 decades some predict we may lose 2 to 5 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 that 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' 6" )
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.
And just being overweight,155-185 pounds, appeared to be protective
compared to those who were normal weight,115 to 155 pounds.
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, the study ignited a firestorm of controversy
in the public health community. The study was called ludicrous, flawed, misleading.
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
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 to show
an 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,
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,
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.
So people who are abnormally thin--- in other words, ideal weight---
could actually be taking care of themselves, but may be 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
from more than 10 million people from hundreds of studies
in dozens of countries,
the largest evaluation of BMI and 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 randomizing 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, exercise alone may extend lifespan even without weight loss,
but there also appears to be a similar longevity benefit
of weight loss through dietary means alone.