Hockenbury Discovering Psychology 5th txtbk

330 CHAPTER 8 Motivation and Emotioncafeteria diet effectThe tendency to eat more when a widevariety of palatable foods is available.leptin resistanceA condition in which higher-than-normalblood levels of the hormone leptin do notproduce the expected physiological response.weight cyclingRepeated cycles of dieting, weight loss, andweight regain; also called yo-yo dieting.The “Supersize It” Syndrome: Overeating In the past two decades, average dailycaloric intake has increased nearly 10 percent for men and 7 percent for women(Koplan & Dietz, 1999). Every day, we are faced with the opportunity to overeatat all-you-can-eat buffets and fast-food restaurants that offer to supersize your portionsfor only a few cents more.The Cafeteria Diet Effect: Variety More Consumed If variety is the spice oflife, it’s also a surefire formula to pack on the pounds. Offered just one choice or thesame old choice for a meal, we consume less. But when offered a variety of highlypalatable foods, such as at a cafeteria or an all-you-can-eat buffet, we consume more(Zandstra & others, 2000). This is sometimes called the cafeteria diet effect(Raynor & Epstein, 2001).Sedentary Lifestyles Four out of 10 American adults report that they neverexercise, play sports, or engage in physically active hobbies like gardening orwalking the dog. Both men and women tend to become more sedentary withage. When the averages are broken down by gender, more women (43 percent)than men (37 percent) lead sedentary lifestyles (National Center for HealthStatistics, 2000b).Average basal metabolic rates(calories burned per hour)504030Age (years)Figure 8.6 Age and Gender Differencesin Metabolism From infancy through adolescence,there is a steep decline in the rateat which your body uses energy for vitalfunctions, such as heartbeat, breathing,and body heat. Your BMR continues todecrease by about 2 to 3 percent duringeach decade of adulthood. At all points inthe lifespan, women’s metabolic rate is 3to 5 percent lower than men’s.Source: Stuart & Davis (1972).20MalesFemales406080BMR: Individual Differences and Lifespan Changes Noteveryone who overeats gains excess weight. One reason is thatpeople vary greatly in their basal metabolic rate, which accountsfor about two-thirds of your energy expenditure. On average,women have a metabolic rate that is 3 to 5 percent lower thanmen’s. Metabolism also decreases with age. Body metabolism ishighest during growth periods early in the lifespan (see Figure8.6). After declining sharply between infancy and early adulthood,BMR decreases more slowly, by about 2 to 3 percent perdecade of life. As your BMR decreases with age, less food is requiredto meet your basic energy needs. Consequently, it’s notsurprising that many people, upon reaching early adulthood,must begin to watch how much they eat.Of the six factors we’ve covered here, you can exert controlover five of them—all except BMR—to counteract becomingor remaining overweight. The bad news is that if people don’t exercisecontrol, all six factors can contribute to becoming obese.Factors Involved in ObesityEspecially in the past decade, there has been intensive research investigating thecauses of obesity—and for good reason. Health care costs directly attributable toobesity exceed $60 billion a year (Friedman, 2009). Regardless of how it develops,a BMI of 30 or above has life-threatening consequences (Kopelman, 2000).Annually, about 300,000 adult deaths in the United States are directly attributableto obesity. Several variables derail the normal mechanisms of energy homeostasisin obesity (see Friedman, 2000). In this section, we’ll summarize some ofthose factors.The Interaction of Genetics and Environment Current research suggests thatmultiple genes on multiple chromosomes are involved in creating susceptibility toobesity (Barsh & others, 2000; Friedman, 2009). People with a family history ofobesity are two to three times more likely than people with no such family historyto become obese. And, the more closely related two people are genetically, the morelikely they are to have similar body mass indexes.But genetics is not necessarily destiny. About 30 percent of the time, obese childrenhave obese parents. However, obesity also occurs about 30 percent of the timeamong children with parents who are of normal weight (Bouchard, 1997).