"What's the Ideal Waist Size?"
There was a book originally published in the 80's, 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.