CHAPTER 5

What Causes Obesity?

PART 1 A Question of Balance

In the last three decades, obesity has doubled in children aged 2-5 and 12-19 and tripled in children aged 6-11. While genetics may well play a part in 25-85% of cases, heredity alone can’t account for this sudden epidemic of obesity. The more likely scenario is that, over time, most humans evolved genes that helped us cope with times when food was scarce. But these genes are unsuited to the world we now live in, where high-calorie food is quickly and cheaply available. READ MORE

And this glut of calories is not being balanced by more physical activity to help burn them off. On the contrary, children have become less active as television, computers, and video games consume more and more of their leisure time. The balance between calories consumed and calories burned off has been upset. This is why so many of our children are overweight or obese.

A number of factors contribute to the problem. Consumption of fiber-rich food, like fruits, vegetables, and whole grains, has decreased. Portion sizes have increased greatly in the last 20 years. Advertising aimed at children promotes candy, sugary cereals, sodas, and fast food. And kids spend many hours of the day engaged in sedentary activities, like watching TV and playing video games. LESS

PART 2 The Bottomless Soup Bowl Experiment

Kids, and people in general, can’t necessarily tell what an appropriate serving size is. In one well-known experiment, volunteer study subjects were asked to eat a bowl of soup. Some were given a normal bowl, but others ate from an ordinary-looking soup bowl that actually had a hidden tube, connected to a vat of soup, at the bottom. The researchers found that the volunteers who ate from “the bottomless soup bowl” ate 73% more soup than the volunteers who ate from the normal bowl. But the people who ate from the bottomless bowl didn’t report that they felt any more full than those who ate from the normal bowl! READ MORE

The experiment reveals that we tend to ignore the signals of fullness our body sends us. Instead, we rely on visual cues to tell us what makes up a single serving. So if kids are given, say, a 20-oz bottle of soda, or a supersized order of fries, they’re likely to eat the whole thing, regardless of how full they feel.

Studies have shown that although obese children don’t eat a great deal more than nonoverweight kids, they do tend to eat larger portions and higher calorie foods. Over time, the differences can add up. LESS

PART 3 Dwindling Activity

Young children tend to be physically active, but activity level drops off during adolescence. Girls in particular may experience peer pressure not to participate in sports. Some scientists think that not being physically active enough is at least as important, and maybe more important, than diet in contributing to adolescent overweight. READ MORE

There are a number of reasons for this increasing inactivity. Many schools have reduced the amount of time kids spend in physical education classes. In fact, less than 30% of high school students are enrolled in PE classes, and about one half of public elementary schools have PE only 1-2 days per week. The built environment can hinder physical activity, too. Housing developments may not have suitable areas for play and may also lack sidewalks, making walking or riding bikes difficult or even dangerous. LESS

PART 4 Screen Time

No parent will be surprised to learn that one huge factor in childhood obesity is the increased amount of time kids spend in front of a screen. In the US, kids spend almost 8 hours a day using electronic devices like computers, smart phones, and TVs—and that doesn’t even count the time they spend talking and texting on their cell phones. Using electronic devices takes up time they’d probably otherwise spend outside, playing sports, or being physically active in other ways. READ MORE

To make matters worse, during their viewing time kids are exposed to ads in just about every type of media—on TV, on the Internet, in text messages, in podcasts, and in online video episodes. The average child sees more than 40,000 commercials a year. The majority of those ads are for high-fat, high-sugar foods. Studies show that kids consume 167 extra calories per hour when watching TV, and most of those calories come from the same unhealthy foods they’ve seen advertised.

However, researchers have also found that the type of television kids watch is an important factor in childhood overweight. Noncommercial viewing (like watching DVDs and public television) is not associated with obesity in children. LESS

PART 5 Sleep, Family, and Environmental Chemicals

A Good Night’s Sleep
One surprising factor that may influence children’s weight is how much sleep they get. Researchers found that not getting enough sleep at night increases the risk that a child will become overweight or obese—and this held true even for infants and toddlers. Sleeping during the day didn’t have much effect on this risk. It’s not clear why amount of sleep would affect weight, but the researchers theorized that lack of nighttime sleep affects the regions of the brain that regulate tiredness and metabolism. READ MORE

All in the Family
If the parents in a family are obese, the kids are likely to be obese as well. If one parent is overweight or obese, a teenager has an 80% chance of being overweight. This is probably due to a combination of a genetic tendency to overweight along with family behavior and habits.

Medical Conditions and Environmental Causes
Sometimes an underlying medical condition, such as an endocrine disorder or certain genetic syndromes, can cause obesity. However, this happens only very rarely. If an underlying medical cause is suspected, a doctor can take the child’s medical history and perform a physical exam. Lab tests may be needed as well.

Environmental chemicals, particularly endocrine disruptors, may be implicated in childhood obesity. One such chemical is bisphenol A (BPA). BPA, which is used in making food and drink containers, mimics the effects of estrogen. When babies are exposed to it, either in utero or as newborns, their weight-control mechanisms may be disrupted. This can lead to obesity. LESS

Photo credit:

Two adults with two children
Copyright 2006 malias

Boys watching television
Copyright 2008 Chip Griffin