"What’s the Ideal BMI and Waist Size?"
We seem to have become inured to the mortal threat of obesity.
If you go back in the medical literature a half century or so
when obesity wasn’t just run-of-the-mill,
the descriptions are much more grim:
“Obesity is always tragic, and its hazards are terrifying.”
But it’s not just obesity. Of the 4 million deaths every year
attributed to excess body fat, nearly 40% of the victims
are just overweight, not obese.
According to two famous Harvard studies, weight gain
of as little as 11 pounds from early adulthood through middle age
increases the risk of major chronic diseases,
such as diabetes, cardiovascular disease, and cancer.
The flipside, though, is that even modest weight loss
can have major health benefits.
What’s the optimal BMI?
The largest studies in the United States and around the world
found that having a normal body mass index, a BMI from 20 to 25,
is associated with the longest lifespan.
Put all the best available studies with the longest
follow-up together and that can be narrowed down even further
to a BMI of 20 to 22. That would be about
between 124 to 136 pounds for someone who stands five-foot-six.
You can pause the video here to use this unisex chart
to see what your optimal weight might be based on your height.
But, even within a normal BMI, the risk of developing
chronic diseases, such as type 2 diabetes, heart disease,
and several types of cancer starts to rise towards the upper end,
even starting as low as a BMI of 21.
A BMI of 18.5 and 24.5 are both considered within the normal range,
but a BMI of 24.5 may be associated with twice
the heart disease risk compared 18.5.
Look at this diabetes graph among women, a five-fold difference
in diabetes rates all within the so-called ideal range under 25.
Just as there are gradations of risk within a normal BMI range,
there is a spectrum within obesity.
Class III obesity, a BMI over 40, can be associated
with the loss of a decade of life or more.
At a BMI greater than 45, such as a five-foot-six person
at 280 pounds, life expectancy may shrink
to that of a cigarette smoker.
There are, however, so-called “obesity skeptics”
that argue that the health consequences of obesity are unclear
or even greatly exaggerated. They are a motley bunch,
ranging from feminists, queer theorists, and new ageists
to “far right wing, pro-gun, pro-America websites
where the idea [is] that obesity alarmists are nanny-state
communists who simply want to stop us from having fun….”
Unlike activists who, for example, organized to raise
consciousness and stamp out the AIDS epidemic,
the size acceptance movement appears to have the opposite goal,
rallying for less public awareness and treatment of the problem.
(They do have good slogans though:
“We’re here, we’re spheres, get used to it!”)
I’m all for fighting size stigma and discrimination—
I have a whole section on weight stigma in my new book—
but the adverse health consequences of obesity
are an established scientific fact.
Can’t you be fat but fit?
In a study of more than 600 centenarians
(those living over 100) only about 1% of the women
and not a single one of the men were obese.
But there does appear to be a rare subgroup of obese individuals
who don’t suffer the typical metabolic costs
such as high blood pressure and cholesterol.
This raises the possibility that there may be such thing as
“benign obesity” or “healthy obesity.”
It may just be a matter of time, though,
before the risk factors develop.
And even if they don’t, followed long enough,
even quote-unquote “metabolically healthy” obese individuals
are at increased risk of diabetes, and fatty liver disease
and cardiovascular events such as heart attacks,
and/or premature death.
Bottom line: there is strong evidence
that so-called “healthy obesity” is a myth.
Many “fat-activists” try to downplay the risks of obesity,
even as they may be among the epidemic’s greatest victims.
Lynn McAfee is the director of medical advocacy
for the Council on Size and Weight Discrimination
and routinely takes part in obesity conferences
and government panels on obesity.
“I’m not actually particularly that interested in [health],”
she is quoted as saying, “and God I hate science.”
There was a book originally published in the '80s, and then repeatedly republished,
entitled "DIETING MAKES YOU FAT".
Since most people who lose weight go on to regain it,
the concern is that there may be adverse health consequences
of so-called yo-yo dieting.
This idea emerged from animal studies that showed,
for example, detrimental effects of starving and refeeding obese rats.
This captured the media's attention, leading to a pervasive common belief
about the dangers of weight cycling, discouraging people from even trying.
Even the animal data is inconclusive though.
For example, weight cycling mice makes them live longer.
Most importantly though, a review of the human data concluded
that evidence for an adverse effect of weight cycling appears sparse,
if it exists at all.
Bottom line: Yo-Yo Dieting is Better Than None.
Ideally, we'd get down to a BMI of 20 to 22, but body mass index doesn't
take the composition of the weight into account. For example,
bodybuilders are heavy for their height, but can be extremely lean.
The gold standard measure of obesity is percentage body fat,
but an accurate calculation can be complicated and expensive.
All you need to measure BMI is height and weight,
but it may underestimate the true prevalence of obesity.
The World Health Organization defines obesity
as a body fat percentage over 25% in men or 35% in women.
At a BMI of 25, which is considered just barely overweight,
body fat percentages in a representative US sample of adults varied between
14% and 35% in men, and 26% and 43% in women.
So you could be normal weight but actually obese.
Using the BMI cutoff for obesity only about 1 in 5 Americans were obese
back in the 90's, but based on their body fat, the true proportion
even back then was closer to 50%.
Half of America is not just overweight, but obese.
So just using BMI, doctors may misclassify more than half
of obese individuals as being just overweight or even normal weight
and miss an opportunity to intervene.
The important thing is not the label, though, but the health consequences.
Ironically, BMI appears to be an even better predictor
of cardiovascular disease death than percentage body fat.
I mean, that suggests that excess weight from any source, fat or lean,
may not be healthy in the long run.
The lifespan of bodybuilders does seem to be cut short.
They have about a third higher mortality rate than the general population.
The average age of death was around 48 years old, but this may well be due
in part to the toxic effects of anabolic steroids on the heart.
Pre-eminent nutritional physiologist Ancel Keys (after which K-rations were named)
suggested the mirror method.
If you really want to know whether you are obese,
just undress and look at yourself in the mirror.
Don't worry about our fancy laboratory measurements; you'll know!
All fat is not the same, though.
There is the pinchable superficial flab
that you may see jiggling about your body,
but then there's the riskier, deeper visceral fat which coils around
and infiltrates your internal organs.
Measuring BMI is simple, cheap, and effective, but does not take into account
the distribution of fat on the body,
whereas waist circumference can provide a measure
of the deep underlying belly fat.
Both BMI and waist circumference can be used to predict the risk of death
due to excess body fat, but even at the same BMI there appears to
be nearly a straight-line increase in mortality risk with widening waistline.
Someone with normal-weight central obesity, meaning someone
not even overweight according to BMI,
but fat around the middle may have up to twice the risk of dying
compared to even someone who's obese according to their height and weight.
This is why the current recommendations recommend
measuring both: BMI and waist circumference.
This may be especially important for older women who lose approximately
13 pounds of bone and muscle as they age from 25 to 65,
while quadrupling their visceral fat stores (men tend to only double).
So even if a woman doesn't gain any weight based on the bathroom scale,
she may be gaining fat.
What's the waistline cut-off?
Increased risk of metabolic complications
start at an abdominal circumference of 31.5" in women, and 37" in most men,
though closer to 35.5" for South Asian, Chinese, and Japanese men.
The benchmark for substantially increased risk starts
at about 34.5" for women, and 40" for men.
Once you get over an abdominal circumference of about 43" in men,
mortality rates shoot up about 50%, compared to men
with 8-inch-smaller stomachs.
And women suffer 80% greater mortality risk at 37.5" compared to 27.5".
The reading of a measuring tape may translate into years off one's lifespan.
The good news is the riskiest fat is the easiest to lose.
Your body appears smart enough to preferentially shed
the villainous visceral fat first.
Although it may take losing
as much as 20% of your weight to realize significant
improvements in quality of life for most individuals
with severe obesity, your disease risk drops almost immediately.
At 3% weight loss (just like 6 pounds for someone weighing 200 pounds)
your blood sugar control and triglycerides start to get better.
At 5%, your blood pressure and cholesterol improve.
Just a 5% weight loss (about 10 pounds for someone starting at 200)
may cut your risk of developing diabetes in half.