Hockenbury Discovering Psychology 5th txtbk

Biological Motivation329How is healthy weight determined? For statistical purposes, the most widely usedmeasure of weight status is body mass index, abbreviated BMI. For adults, thebody mass index provides a single numerical value that reflects your weight in relationto your height (see Figure 8.5). A healthy BMI falls between 18 and 25. Generally,people with a BMI between 25 and 29.9 are considered overweight, unlesstheir high BMI is due to muscle or bone rather than fat. Thus, it is possible to havea high BMI and still be very healthy, as are many athletes or bodybuilders. In contrast,people who are obese have a BMI of 30 or greater and an abnormally highproportion of body fat.Let’s break down the statistics on obesity and overweight. More than one-third ofthe adult U.S. population are considered to be overweight. But another third ofadults—over 72 million people—are considered medically obese, weighing in with aBMI of 30 or above (Ogden & others, 2006, 2007). Beyond the United States, rapidlyincreasing rates of obesity have become a global health problem. More than onebillion adults are overweight, and at least 300 million of these are clinically obese(World Health Organization, 2009).As people age, they tend to gain excess weight. The percentage of overweightpeople increases throughout adulthood, peaking in the fifth and sixth decades oflife. However, excess weight is also a problem in early life. Over 17 percent of U.S.children and adolescents are overweight. Even more unsettling, almost 14 percentof 2- to 5-year-olds—that’s one out of every eight preschoolers—is overweight(Ogden & others, 2006).The body mass index, or BMI, is onemeasure of weight status. The BMI providesa single numerical value that representsyour height in relation to your weight. Todetermine your BMI, grab a calculator andfollow these steps:Step 1. Multiply your weight in poundsby 703 __________Step 2. Square your height in inches__________Step 3. Divide step 1 by step 2__________ This is your BMI.If your BMI is: You are:18.4 or below Underweight18.5 to 24.9 Healthy weight25.0 to 29.9 Overweight30.0 and above ObeseSource: Centers for Disease Control and Prevention (2009).Figure 8.5 Calculating Your BMI:Where Do You Weigh In?Factors Involved in Becoming OverweightAt the simplest level, the only way you can become overweight is if your caloricintake consistently exceeds your energy expenditure—the essence of positive energybalance. So the critical question is this: What kinds of factors are creating positiveenergy balance for so many people?Too Little Sleep: Disrupting Hunger Hormones Multiple studies have shownthat going without adequate sleep disrupts the hunger-related hormones leptinand ghrelin (Taheri & others, 2004). In one study, the sleep of healthy youngmen was restricted to just four hours a night for two nights. In response, bloodlevels of the appetite-suppressing hormone leptin fell by 18 percent and theappetite-increasing hormone ghrelin soared by 24 percent. This significantlyincreased feelings of hunger, especially for foods with high carbohydrate content(Spiegel & others, 2004). Other research has shown that adults who sleep onlyabout five hours a night are 50 percent more likely to be obese (Gangwisch,2004).Positive Incentive Value: Highly Palatable Foods Rather than being motivatedby hunger, we are often enticed to eat by the positive incentive value of the availablefoods and the anticipated pleasures of consuming those highly palatable foods(Epstein & others, 2007). Did someone say Ben and Jerry’s ice cream?GEECH, reprinted by permissionof United Feature Syndicate, Inc.body mass index (BMI)A numerical scale indicating adult height inrelation to weight; calculated as (703 weight in pounds)/(height in inches) 2 .obeseCondition characterized by excessive bodyfat and a body mass index equal to orgreater than 30.0.