Why we're fatter.

Health and medicine explained.
July 13 2006 12:46 PM

Why We're Fatter

Five reasons you haven't thought of.

Illustration by Robert Neubecker. Click image to expand.

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, David Allison and Scott Keith 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.

Advertisement

With the help of 20 contributors, Allison and Keith 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 Allison and Keith'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.

TODAY IN SLATE

Politics

Blacks Don’t Have a Corporal Punishment Problem

Americans do. But when blacks exhibit the same behaviors as others, it becomes part of a greater black pathology. 

I Bought the Huge iPhone. I’m Already Thinking of Returning It.

Scotland Is Just the Beginning. Expect More Political Earthquakes in Europe.

Lifetime Didn’t Think the Steubenville Rape Case Was Dramatic Enough

So they added a little self-immolation.

Two Damn Good, Very Different Movies About Soldiers Returning From War

Medical Examiner

The Most Terrifying Thing About Ebola 

The disease threatens humanity by preying on humanity.

Students Aren’t Going to College Football Games as Much Anymore, and Schools Are Getting Worried

The Good Wife Is Cynical, Thrilling, and Grown-Up. It’s Also TV’s Best Drama.

  News & Politics
Weigel
Sept. 19 2014 9:15 PM Chris Christie, Better Than Ever
  Business
Moneybox
Sept. 19 2014 6:35 PM Pabst Blue Ribbon is Being Sold to the Russians, Was So Over Anyway
  Life
Inside Higher Ed
Sept. 19 2014 1:34 PM Empty Seats, Fewer Donors? College football isn’t attracting the audience it used to.
  Double X
The XX Factor
Sept. 19 2014 4:58 PM Steubenville Gets the Lifetime Treatment (And a Cheerleader Erupts Into Flames)
  Slate Plus
Slate Picks
Sept. 19 2014 12:00 PM What Happened at Slate This Week? The Slatest editor tells us to read well-informed skepticism, media criticism, and more.
  Arts
Brow Beat
Sept. 19 2014 4:48 PM You Should Be Listening to Sbtrkt
  Technology
Future Tense
Sept. 19 2014 6:31 PM The One Big Problem With the Enormous New iPhone
  Health & Science
Medical Examiner
Sept. 19 2014 5:09 PM Did America Get Fat by Drinking Diet Soda?   A high-profile study points the finger at artificial sweeteners.
  Sports
Sports Nut
Sept. 18 2014 11:42 AM Grandmaster Clash One of the most amazing feats in chess history just happened, and no one noticed.