Hockenbury Discovering Psychology 5th txtbk

328 CHAPTER 8 Motivation and EmotionExcess Weight and ObesityKey Theme• Many different factors contribute to the high rates of overweight andobesity in the United States and other countries.Key Questions• What is BMI?• What factors contribute to excess weight and obesity?From buses to billboards, movies and magazines to MTV, images of beautiful peopleare everywhere. They come in a vast variety of ethnicities, wardrobes, and poses, butthe beautiful people have one thing in common: They are thin. Without question, the“thin ideal” is pervasive in American culture. In fact, over the past decades, actresses,models, Miss America Pageant winners, Playboy centerfolds, and even cartoon charactershave become progressively thinner (Grabe & others, 2008).But there is an enormous gap between the cultural ideal of a slender body andthe cultural reality of the expanding American waistline. Far from conforming to the“thin ideal,” more than two-thirds of American adults are above their healthyweight (Ogden & others, 2007).CRITICAL THINKINGHas Evolution Programmed Us to Overeat?Could eating less help you live longer? Numerous correlationalstudies of humans and experiments with rodents and Rhesusmonkeys have consistently come to the same conclusion: Eatinga restricted but balanced diet produces a variety of health benefitsand promotes longevity (e.g., Barzilai & Gupta, 1999; Cefalu& others, 1997; Weindruch, 1996). So if eating a calorically restrictedbut balanced diet confers numerous health benefits andpromotes longevity, why do so many people overeat?University of British Columbia psychologists John P. J. Pinel,Sunaina Assanand, and Darrin R. Lehman (2000) believe that theevolutionary perspective provides several insights. For animals inthe wild, food sources are often sporadic and unpredictable.When animals do find food, competition for it can be fierce,even deadly. If an animal waited to eat until it was hungry andits energy reserves were significantly diminished, it would runthe risk of starving or falling prey to another animal.Thus, the eating patterns of many animals have evolved sothat they readily eat even if not hungry (Berthoud, 2007).Overeating when food is available ensures ample energy reservesto survive times when food is not available.For most people living in food-abundant Western societies,foraging for your next meal is usually about as life-threateningas waiting your turn in the Taco Bell drive-through lane. Accordingto Pinel and his colleagues, people in food-rich societies donot eat because they are hungry or because their bodies are sufferingfrom depleted energy resources. Rather, we are enticed bythe anticipated pleasure of devouring that supersize burrito orcalzone. In other words, we are motivated to eat by the positiveincentive value of highly palatable foods.When a food with a high positive incentive value is readilyavailable, we eat, and often overeat, until we are satiated by thatspecific taste, which is termed sensory-specific satiety. Shouldanother food with high positive incentive value become available,we continue eating and overconsume (Raynor & Epstein,2001). As noted in the text, this is referred to as the cafeteriadiet effect. From the evolutionary perspective, there is adaptivepressure to consume a variety of foods. Why? Because consuminga varied diet helps promote survival by ensuring that essentialnutrients, vitamins, and minerals are obtained.But unlike our ancient ancestors scrounging through thewoods for seeds, fruits, and vegetables to survive, today’shumans are confronted with foraging for burgers, cheese fries,and Oreo McFlurries. Therein lies the crux of the problem. AsPinel and his colleagues (2000) explain, “The increases in theavailability of high positive-incentive value foods that haveoccurred over the past few decades in industrialized nations—increases that have been much too rapid to produce adaptiveevolutionary change—have promoted levels of ad libitum consumptionthat are far higher than those that are compatible withoptimal health and long life.”CRITICAL THINKING QUESTIONS Look back at the section on motivation theories. How mighteach theory (instinct, drive, incentive, arousal, and humanistic)explain the behavior of overeating? How might the insights provided by the evolutionaryexplanation be used to resist the temptation to overeat?