In looking at the past 30 years, during which time obesity rates have soared, many authorities say we got lazier, when in fact we had an exercise and aerobics boom, says Taubes. "Americans have been working out more than ever."
Today's list looks at 10 American lifestyle changes that occurred in the past 30 years and contributed to a rate of 14 percent obesity in the 1970s climbing to 34 percent today. Coming up: the influence of environment.
Screen time: On average, U.S. adults spend more than eight hours a day in front of screens, whether sitting at a computer, watching television or playing a video game, according to a 2009 study by Ball State University's Center for Media Design. The average American spends more than five hours a day in front of the television. Such inactivity is particularly a problem in children. "We've taken activity — as a fun way of playing — out of the daily lives of our children, and turned them toward screens," says Dr. Jim Marks, a pediatrician and director of the Robert Wood Johnson Foundation, which helped compile the 2011 F as in Fat Report on the nation's obesity epidemic.
Lack of sleep: The obesity epidemic parallels the rise in sleep deprivation, and that's no coincidence, says Dev Sikder, researcher and assistant professor at Sanford-Burnham Research Institute, in Lake Nona. Many metabolic hormones, including insulin, which regulates fat storage, rise during the day and fall at night. This regulation is part of a normal, healthy circadian rhythm. Sleep deprivation, however, forces insulin to stay at high levels, which triggers the body to store fat. A review study out of Harvard, and published in Obesity in 2008, looked at 36 studies of the link between lack of sleep and weight gain. Authors concluded that sleep deprivation appeared to influence weight gain through effects on appetite, physical activity and body temperature. The link was stronger in children, but longitudinal studies in adults found a positive association as well.
Air conditioning: The addition of cooling systems into homes and workplaces, while comforting, encourages people who would otherwise spend time outdoors to stay inside, says Dr. Steve Smith, obesity expert and scientific director of Sanford-Burnham Translational Research Institute, in Orlando. A study from the University of Alabama at Birmingham, which appeared in the International Journal of Obesity, suggests that the rising use of air conditioning and central heating in homes and offices was associated with America's weight crisis because our bodies have to expend less energy warming up and cooling down.
Bigger plates: Since 1960 the surface area of the average dinner plate has increased 36 percent, according to Brian Wansink, a food psychologist at Cornell University, and author of "Mindless Eating." As a result, portions that used to look ample appear dwarfed. In repeated studies conducted at the Cornell Food and Brand Lab, Wansink found that subjects consistently served themselves larger portions, and ate more, if they had larger plates or bowls than if they had smaller ones. Study subjects also consistently estimated that the number of calories in a piece of cake served on a large plate was fewer than in the same size piece served on a smaller plate.
More medicine: A growing use of medications that cause weight gain have put pounds on Americans. Among the more common culprits are anti-depressants, epileptic medications, beta-blockers, steroids, insulin, antihistamines, oral and injectable contraceptives, and retrovirals (for treating HIV/AIDS), says Dr. Luis Aronne, an obesity expert from Weill Cornell University Medical Center. Many medications that treat hypertension, bipolar disorder and migraines also contribute, and the use of all have been on the rise over the past few decades.
Eating out: The more you eat out, the more likely you are to be fat, say obesity experts who have studied the link between eating at restaurants and obesity. A third of the calories Americans eat come from restaurants, including fast-food franchises, which is almost double what it was 30 years ago, according to the USDA. "Eating one meal away from home each week translates to roughly two extra pounds a year," says Lisa Mancino, a food economist for the USDA.
Food deserts: Many communities, especially in lower-income areas, don't have easy access to markets that sell fresh fruits and vegetables. About 23 million Americans live in food deserts, neighborhoods that do not have supermarkets and instead are inundated with fast-food restaurants and convenience stores. These provide residents with ample opportunities to buy calorie-dense, nutrient-poor foods, says 2011 F as in Fat Report, co-sponsored by Trust for America's Health.
Longer commutes: More employees are driving more hours to work, which cuts into time available for physical activity. An American worker now spends on average more than 100 hours a year commuting, according to the U.S. Census Bureau's American Community Survey. More than 3.2 million American workers (2.4 percent of the workforce) commute more than 90 minutes one way, according to the Bureau of Transportation Statistics.
Workplace: An increasing number of jobs require almost no physical activity, said the fat report, by Trust for America's Health. And many jobs offer no opportunity for physical activity during the workday. The deck is further stacked by cafeterias and lunch sites that offer unhealthy options, the report noted.
Labor-saving devices: Electric can openers, power lawn mowers, remote controls, clothes dryers and hundreds of other labor-saving devices have contributed to Americans expending less energy each day. "The very advances we celebrate for their labor-saving convenience undermine our health," says Smith.
What can we do about it? Small changes in behavior add up: Limiting the amount of television you watch, getting enough sleep, not looking for the closest parking space but rather choosing the farthest one. All these behavior shifts can contribute to attaining and maintaining a healthier weight, say experts. If you have a desk job, get up every hour and walk around the building. Take the stairs, not the elevator. Use a hand mower and an old-fashioned can opener once in awhile. Instead of looking for ways to save steps and energy, look for ways to increase both.
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Why we're fat: 40 reasons
Sunday: How diet contributes to obesity.
Monday: The role played by heredity.
Today: How lifestyle changes have affected our weight.
Wednesday: The influence of environment and government policies.