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http://www.slate.com/id/2145689/nav/tap1/

Why We're Fatter

Five reasons you haven't thought of.

By Sydney Spiesel

Posted Thursday, July 13, 2006, at 12:46 PM ET

We

all agree—and despair—that obesity is on the rise. America has been

getting fatter for the past century, and the problem has worsened over

the past 35 years. We also all know the obvious

explanations.

Who would discount the role of new food-marketing practices, like

super-sizing or pushing soda sweetened with corn syrup? Or the

decrease—even elimination—of physical activity in school and in adult

life?

An important new paper,

though, cautions us to be skeptical that corn syrup and sitting around

are the only factors that matter for understanding the obesity

epidemic. The study's lead authors, and

of the University of Alabama at Birmingham,*

don't reject these explanations. But they suggest that the obvious

reasons for obesity are so popular and widely cited that they have

pushed out other equally plausible and well-supported contributing

factors. And if we ignore these factors, our proposals for addressing

obesity may well fail.

With the help of 20 contributors,

and put together a list of 10 alternate explanations for obesity,

each of them backed up by good research. In all likelihood, the rise in

obesity results from a combination of several of these factors, each

making its own contribution and perhaps interacting with other causes

in some yet-more-complicated way. Here are five of them:

Inadequate sleep:

Average sleep duration has been dropping for children and for adults—80

years ago adults slept an average of 8.77 hours nightly; now the

average is 6.85 hours. Sleep-deprived animals eat excessively, and

humans subject to sleep deprivation show increased appetite and an

increased Body Mass Index, the standard measure of excessive weight.

The apparent mechanism for this phenomenon is the effect that sleep deprivation has on at least two

hormones that influence appetite: leptin and ghrelin.

Sleep deprivation causes a decrease in leptin, which boosts appetite

and produces obesity, and increases ghrelin, a potent stimulator of

hunger and appetite. A study led by J.P. Chaput

and published in the International Journal of Obesity this spring found

that children who slept an average of 10.5 to 11.5 hours a night were

more at risk for obesity than children who slept between 12 and 13

hours a night. Kids who slept only eight to 10 hours a night were at

still greater risk. The study had methodological weaknesses (small

sample size, data mostly by parental report, absence of correction for

age). Still, the trend is striking and suggests that sleep deprivation

is associated with obesity in children as well as adults.

Chemical contamination:

The water, soil, and food to which we are exposed increasingly are

contaminated with chemicals—used in plastics, power transmission, and

even aircraft de-icing—that accumulate in the body and mimic or

interfere with hormones that regulate body functions. Some mimic female

hormones. Others block male hormone activity. Both properties lead to

increased fat accumulation.

Heating and air-conditioning:

Living in an environment that is excessively cold or warm forces the

body to expend calories to maintain a normal body temperature and thus

may keep weight down. In addition, high ambient temperatures seem to

kill appetite. So, turning up the air conditioning in the summer may

pad on extra pounds.

Smoking cessation:

Smoking also kills appetite, and it may be that the (otherwise

fortunate) decline in tobacco use has been contributing to population

weight gain. (Read a Slate

piece about this.)

Medications:

Most of the medications frequently prescribed to moderate moods and

depression or treat other mental illness, like Prozac (33 million doses

in the United States in 2002), Seroquel, or Risperdal, promote weight

gain. So do hormone medications, like birth-control pills,

anti-diabetic drugs, and blood-pressure medications. The total number

of patients taking such medications is unknown but clearly huge.

The

lesson of and 's study is clear: Until we have better

research that demonstrates which factors relating to the obesity rise

are the significant ones, we shouldn't put all our money into

interventions that target only food marketing and sedentary lifestyle.

That conclusion is further warranted by surprising additional recent

research. In one large study of more than 1,500 children,

attempts to increase physical activity and healthy eating had

absolutely no effect on obesity. Another study

of 7,000 children found that how close a child lives to the nearest

fast-food restaurant has no effect on obesity. Proximity to a

playground also doesn't matter.

Despite these findings, almost all doctors believe in our hearts

that eating and physical activity do

affect obesity rates. But sometimes you can know a cause, go after it,

and make no difference at all. For instance, it seems obvious that

increasing energy output—by walking to school, for instance, or

starting an intense gym program—will help decrease obesity.

Unfortunately, another study points out that what's obvious isn't

necessarily true.

T.J.

Wilkin and his colleagues at the Peninsula Medical School in Devon,

England, looked at three groups of English and ish children. They

measured physical activity using accelerometers, devices that record

duration and intensity of movement 600 times a minute. The idea was to

determine whether total daily activity level is essentially invariant

for any one child—"in her nature," as my mother would have said—or

whether it can be increased if a child goes to gym, walks to school, or

doesn't watch television. Wilkin and his team also tracked whether

children's daily activity level varied between weekdays, presumably

spent sedately in school, and weekends, presumably spent going wild. If

the total amount of expended energy remained constant despite the

typically different structure of a weekday vs. a weekend, then it would

suggest that daily total activity level is determined by something

internal and specific to each child. (Do adults have an internally

regulated daily activity level, too? I wish I could tell you, but we

have no idea of the answer yet.)

The results of Wilkin's study

would have brought despair to the many gym teachers who made my

childhood miserable. Their efforts, it turns out, were for naught:

Sluggard I was, and sluggard I was doomed to be. Wilkins and his team

found that every child has his or her own very consistent daily level

of activity. It remains the same on weekends and weekdays; it's not

affected by school physical education, or by whether the child walks or

drives to school, or how much time he spends awake or in front of a

television. We don't know what determines this intrinsic level of

activity. But engineering the environment to make available or even to

require more activity will apparently have little impact on children

whose nature is to be inactive.

All this makes me feel a bit

vindicated. The medical students and residents I teach are chronically

frustrated (and not a little angry) that my contribution to their

education about managing obesity is often unhelpful and discouraging.

Having read these new studies, I'm more depressed than ever.

Before

we write off obesity as a hopeless problem, though, one more thought:

As worried as I am about many of my heavy patients, I often do see

heartening improvement, especially in later adolescence (even if I am

skeptical that I played a role). The critical question is why some

young people thin down while others do not.

I don't have an

answer, but I do have an impression. It's that adolescents who lose

weight are more likely to have acquired a positive sense of themselves,

because they've had some academic or athletic success, or some other

notable accomplishment. Sometimes they have embarked on a successful

romantic relationship. And often parents and other adults in their life

focus on their strengths rather than harping on weight and appearance.

I

feel particularly moved to say this now because of a troublesome

development on the horizon. The Centers for Disease Control and

Prevention, the American Academy of Pediatrics, and the American

Medical Association are talking about renaming degrees of fatness in

children. Up to now, the heaviest children have been called

"overweight," and the next heaviest group classified as "at risk of

overweight." The tough-love talk being bandied about is that we should

tell it like it is, and call obese obese. I don't think so. The impulse

to rename reflects doctors' frustration at their inability to help

heavy children: If we can't help them, then it's time to blame them. If

I'm right, however, calling heavy children "obese" is likely to do the

opposite of what we want, by making them feel worse about themselves.