Understanding Psychology (10th Ed)

FIGURE 1
Use this procedure to fi nd 
your body mass index.
To calculate your body mass index, follow these steps:
1. Indicate your weight in pounds: 
pounds
2. Indicate your height in inches: 
inches
3. Divide your weight (item 1) by your height (item 2), and write the outcome here: 
4. Divide the result above (item 3) by your height (item 2), and write the outcome here: 
5. Multiply the number above by 703, and write the product here: 
. This 
is your body mass index.
Example:
For a person who weights 210 pounds and who is 6 feet tall, divide 210 pounds by 72 
inches, which equals 2.917. Then divide 2.917 by 72 inches (item 3), which yields .041. 
Multiplying .041 (from item 4) by 703 yields a BMI of 28.5.
Interpretation:
• Underweight = less than 18.5
• Normal weight = 18.5–24.9
• Overweight = 25–29.9
• Obesity = BMI of 30 or greater
Keep in mind that a BMI greater than 25 may or may not be due to excess body fat. For 
example, professional athletes may have little fat but weigh more than the average 
person because they have greater muscle mass.
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 Module 
30 
Human Needs and Motivation: Eat, Drink, and Be Daring 
319
factor is changes in the chemical composition of the blood. For instance, changes in 
levels of glucose, a kind of sugar, regulate feelings of hunger. In addition, the hormone 
insulin leads the body to store excess sugar in the blood as fats and carbohydrates. 
Finally, the hormone ghrelin communicates to the brain feelings of hunger. The produc-
tion of ghrelin increases according to meal schedules as well as the sight or smell of 
food, producing the feeling that tells us we’re hungry and should eat (Teff, 2007; Wren 
& Bloom, 2007; Kojima & Kangawa, 2008). 
The brain’s hypothalamus monitors glucose levels (see Figure 2). Increasing evi-
dence suggests that the hypothalamus carries the primary responsibility for monitor-
ing food intake. Injury to the hypothalamus has radical consequences for eating 
behavior, depending on the site of the injury. For example, rats whose lateral hypo-
thalamus is damaged may literally starve to death. They refuse food when it is offered; 
unless they are force-fed, they eventually die. Rats with an injury to the ventromedial 
hypothalamus display the opposite problem: extreme overeating. Rats with this injury 
can increase in weight by as much as 400%. Similar phenomena occur in humans 
who have tumors of the hypothalamus (Woods & Seeley, 2002; Seymour, 2006; Fedeli 
et al., 2009). 
Although the important role the hypothalamus plays in regulating food intake 
is clear, the exact way this organ operates is still unclear. One hypothesis suggests 
that injury to the hypothalamus affects the  weight set point,  or the particular level 
of weight that the body strives to maintain, which in turn regulates food intake. 
Acting as a kind of internal weight thermostat, the hypothalamus calls for either 
greater or less food intake (Capaldi, 1996; Woods et al., 2000; Berthoud, 2002).
In most cases, the hypothalamus does a good job. Even people who are not 
deliberately monitoring their weight show only minor weight fl uctuations in spite of 
substantial day-to-day variations in how much they eat and exercise. However, injury 
to the hypothalamus can alter the weight set point, and a person then struggles to 
meet the internal goal by increasing or decreasing food consumption. Even tempo-
rary exposure to certain drugs can alter the weight set point (Cabanac & Frankham, 
2002; Hallschmid et al., 2004; Khazaal et al., 2008). 
Genetic factors determine the weight set point, at least in part. People seem 
destined, through heredity, to have a particular  metabolism,  the rate at which food 
is converted to energy and expended by the body. People with a high metabolic rate 
can eat virtually as much as they want without gaining weight, whereas others with 
low metabolism may eat literally half as much yet gain weight readily (Jequier, 2002; 
Westerterp, 2006).