A vivid demonstration of the supremacy of physiological needs came when Ancel Keys and his research team (1950) studied semistarvation among wartime conscientious objectors. After three months of normal eating, they cut in half the food intake of 36 men selected from 200 volunteers. The semistarved men became listless and apathetic as their bodies conserved energy. Eventually, their body weights stabilized at about 25 percent below their starting weights.

More dramatic were the psychological effects. Consistent with Maslow’s idea of a needs hierarchy, the men became food obsessed. They talked food. They daydreamed food. They collected recipes, read cookbooks, and feasted their eyes on delectable forbidden foods. Preoccupied with their unfulfilled basic need, they lost interest in sex and social activities. As one participant reported, “If we see a show, the most interesting part of it is contained in scenes where people are eating. I couldn’t laugh at the funniest picture in the world, and love scenes are completely dull.”

The semistarved men’s preoccupations illustrate how powerful motives can hijack our consciousness. When you are hungry, thirsty, fatigued, or sexually aroused, little else may seem to matter. When you’re not, food, water, sleep, or sex just don’t seem like such big things in your life, now or ever.

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In University of Amsterdam studies, Loran Nordgren and his colleagues (2006, 2007) found that people in a motivational “hot” state (from fatigue, hunger, or sexual arousal) easily recalled such feelings in their own past and perceived them as driving forces in others’ behavior. (You may recall from Chapter 8 a parallel effect of our current good or bad mood on our memories.) In another experiment, people were given $4 cash they could keep or draw from to bid for foods. Hungry people overbid for a snack they would eat later when sated, and sated people underbid for a snack they would eat later when hungry (Fisher & Rangel, 2014). Likewise, when sexually motivated, men more often perceive a smile as flirtation rather than simple friendliness (Howell et al., 2012). Grocery shop with an empty stomach and you are more likely to see those jelly-filled doughnuts as just what you’ve always loved and will be wanting tomorrow. Motives matter mightily.

11-2 What physiological factors produce hunger?

Keys’ semistarved volunteers felt their hunger because of a homeostatic system designed to maintain normal body weight and an adequate nutrient supply. But what precisely triggers hunger? Is it the pangs of an empty stomach? So it seemed to A. L. Washburn. Working with Walter Cannon (Cannon & Washburn, 1912), Washburn agreed to swallow a balloon attached to a recording device (FIGURE 11.4). When inflated to fill his stomach, the balloon transmitted his stomach contractions. Washburn supplied information about his feelings of hunger by pressing a key each time he felt a hunger pang. The discovery: Washburn was indeed having stomach contractions whenever he felt hungry.

Can hunger exist without stomach pangs? To answer that question, researchers removed some rats’ stomachs, creating a direct path to their small intestines (Tsang, 1938). Did the rats continue to eat? Indeed they did. Some hunger similarly persists in humans whose ulcerated or cancerous stomachs have been removed.

If the pangs of an empty stomach are not the only source of hunger, what else matters?

People and other animals automatically regulate their caloric intake to prevent energy deficits and maintain a stable body weight. This suggests that somehow, somewhere, the body is keeping tabs on its available resources. One such resource is the blood sugar glucose. Increases in the hormone insulin (secreted by the pancreas) diminish blood glucose, partly by converting it to stored fat. If your blood glucose level drops, you won’t consciously feel the lower blood sugar. But your brain, which is automatically monitoring your blood chemistry and your body’s internal state, will trigger hunger. Signals from your stomach, intestines, and liver (indicating whether glucose is being deposited or withdrawn) all signal your brain to motivate eating or not.

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How does the brain integrate these messages and sound the alarm? The work is done by several neural areas, some housed deep in the brain within the hypothalamus, a neural traffic intersection (FIGURE 11.5). For example, one neural arc (called the arcuate nucleus) has a center that secretes appetite-stimulating hormones. When stimulated electrically, well-fed animals begin to eat. If the area is destroyed, even starving animals have no interest in food. Another neural center secretes appetite-suppressing hormones. When electrically stimulated, animals will stop eating. Destroy this area and animals will eat and eat, and become extremely fat (Duggan & Booth, 1986; Hoebel & Teitelbaum, 1966).

Blood vessels connect the hypothalamus to the rest of the body, so it can respond to our current blood chemistry and other incoming information. One of its tasks is monitoring levels of appetite hormones, such as ghrelin, a hunger-arousing hormone secreted by an empty stomach. During bypass surgery for severe obesity, surgeons seal off or remove part of the stomach. The remaining stomach then produces much less ghrelin, and the person’s appetite lessens (Ammori, 2013; Lemonick, 2002). Besides insulin and ghrelin, other appetite hormones include leptin, orexin, and PYY; FIGURE 11.6 describes how they influence our feelings of hunger.

Experimental manipulation of appetite hormones has raised hopes for an appetite-reducing medication. Such a nose spray or skin patch might counteract the body’s hunger-producing chemicals or mimic (or even increase) the levels of hunger-dampening chemicals.

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The complex interaction of appetite hormones and brain activity may help explain the body’s apparent predisposition to maintain itself at a particular weight. When semistarved rats fall below their normal weight, their “weight thermostat” signals the body to restore the lost weight. Fat cells cry out (so to speak) “Feed me!” and grab glucose from the bloodstream (Ludwig & Friedman, 2014). Thus, hunger increases and energy expenditure decreases. This stable weight toward which semistarved rats return is their set point (Keesey & Corbett, 1983). In rats and humans, heredity influences body type and approximate set point.

Our bodies regulate weight through the control of food intake, energy output, and basal metabolic rate—the rate of energy expenditure for maintaining basic body functions when at rest. By the end of their 6 months of semistarvation, the men who participated in Keys’ experiment had stabilized at three-quarters of their normal weight, while taking in half of their previous calories. How did their bodies achieve this dieter’s nightmare? They reduced their energy expenditure, partly through inactivity but partly because of a 29 percent drop in their basal metabolic rate.

Some researchers, however, doubt that our bodies have a preset tendency to maintain optimum weight (Assanand et al., 1998). They point out that slow, sustained changes in body weight can alter one’s set point, and that psychological factors also sometimes drive our feelings of hunger. Given unlimited access to a wide variety of tasty foods, people and other animals tend to overeat and gain weight (Raynor & Epstein, 2001). For these reasons, some researchers have abandoned the idea of a biologically fixed set point. They prefer the term settling point to indicate the level at which a person’s weight settles in response to caloric intake and expenditure (which are influenced by environment as well as biology).

11-3 What cultural and situational factors influence hunger?

Our internal hunger games are indeed pushed by our physiological state—our body chemistry and hypothalamic activity. Yet there is more to hunger than meets the stomach. This was strikingly apparent when Paul Rozin and his trickster colleagues (1998) tested two patients with amnesia who had no memory for events occurring more than a minute ago. If, 20 minutes after eating a normal lunch, the patients were offered another, both readily consumed it … and usually a third meal offered 20 minutes after the second was finished. This suggests that part of knowing when to eat is our memory of our last meal. As time passes since we last ate, we anticipate eating again and start feeling hungry.

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Body chemistry and environmental factors together influence not only the when of hunger, but also the what—our taste preferences. When feeling tense or depressed, do you crave starchy, carbohydrate-laden foods? Are you like ardent football fans who, after a big loss, tend to take solace in high-calorie foods (Cornil & Chandon, 2013)? Carbohydrates boost the neurotransmitter serotonin, which has calming effects. When stressed, both rats and many humans find it extra rewarding to scarf Oreos (Artiga et al., 2007; Sproesser et al., 2014).

Our preferences for sweet and salty tastes are genetic and universal. Other taste preferences are conditioned, as when people given highly salted foods develop a liking for excess salt (Beauchamp, 1987), or when people who have been sickened by a food develop an aversion to it. (The frequency of children’s illnesses provides many chances for them to learn food aversions.)

Culture affects taste, too. Bedouins enjoy eating the eye of a camel, which most North Americans would find repulsive. Many Japanese people enjoy nattó, a fermented soybean dish that “smells like the marriage of ammonia and a tire fire,” reports smell expert Rachel Herz (2012). Although many Westerners find this disgusting, Asians, she adds, are often repulsed by what Westerners love—“the rotted bodily fluid of an ungulate” (a.k.a. cheese, some varieties of which have the same bacteria and odor as stinky feet). Most North Americans and Europeans shun horse, dog, and rat meat, all of which are prized elsewhere.

Rats tend to avoid unfamiliar foods (Sclafani, 1995). So do we, especially animal-based foods. Such neophobia (dislike of things unfamiliar) surely was adaptive for our ancestors, protecting them from potentially toxic substances. Disgust works. Nevertheless, in experiments, people who repeatedly sample an initially novel fruit drink or unfamiliar food typically experience increasing appreciation for the new taste. Moreover, exposure to one set of novel foods increases our willingness to try another (Pliner, 1982, Pliner et al., 1993).

Other taste preferences also are adaptive. For example, the spices most commonly used in hot-climate recipes—where food, especially meat, is at risk of spoiling more quickly—inhibit bacteria growth (FIGURE 11.7). Pregnancy-related nausea and food aversions peak about the tenth week, when the developing embryo is most vulnerable to toxins. So there is biological wisdom to our taste preferences.

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To a surprising extent, situations also control our eating—a phenomenon psychologists have called the ecology of eating. Here are three situations you may have noticed but underestimated:

11-4 What factors predispose some people to become and remain obese?

Obesity can be socially toxic, by affecting both how you are treated and how you feel about yourself. Obesity has been associated with lower psychological well-being, especially among women, and increased depression (de Wit et al., 2010; Luppino et al., 2010; Riffkin, 2014). Obese 6- to 9-year-olds are 60 percent more likely to suffer bullying (Lumeng et al., 2010). And obesity has physical health risks. Yet few overweight people win the battle of the bulge. Why? And why do some people gain weight while others eat the same amount and seldom add a pound?

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Our bodies store fat for good reason. Fat is an ideal form of stored energy—a high-calorie fuel reserve to carry the body through periods when food is scarce—a common occurrence in our prehistoric ancestors’ world. No wonder people in developing societies have often found heavier bodies attractive: Obesity signals affluence and social status (Furnham & Baguma, 1994; Swami et al., 2011).

In parts of the world where food and sweets are now abundantly available, the rule that once served our hungry distant ancestors—When you find energy-rich fat or sugar, eat it!—has become dysfunctional. Pretty much everywhere this book is being read, people have a growing problem. A worldwide study of 188 countries (Ng et al., 2014) revealed that

According to the World Health Organization (WHO), an overweight person has a body mass index (BMI) of 25 or more; someone obese has a BMI of 30 or more. (See www.tinyurl.com/GiveMyBMI to calculate your BMI and to see where you are in relation to others in your country and in the world.) In the United States, the adult obesity rate has more than doubled in the last 40 years, reaching 36 percent, and child-teen obesity has quadrupled (Flegal et al., 2010, 2012). In 1990, no U.S. state had an obesity rate greater than 15 percent. By 2010, no state had an obesity rate of less than 20 percent (CDC, 2012).

In one digest of 97 studies of 2.9 million people, being simply overweight was not a health risk, while being obese was (Flegal et al., 2013). Fitness matters more than being a little overweight. But significant obesity increases the risk of diabetes, high blood pressure, heart disease, gallstones, arthritis, and certain types of cancer, thus increasing health care costs and shortening life expectancy (de Gonzales et al., 2010; Jarrett et al., 2010; Sun et al., 2009). Extreme obesity increases risk of suicidal behaviors (Wagner et al., 2013). Research also has linked women’s obesity to their risk of late-life cognitive decline, including Alzheimer’s disease and brain tissue loss (Bruce-Keller et al., 2009; Whitmer et al., 2008). One experiment found improved memory performance 12 weeks after severely obese people had weight-loss surgery and lost significant weight. Those not having the surgery showed some further cognitive decline (Gunstad et al., 2011).

Set Point and Metabolism Research on the physiology of obesity challenges the stereotype of severely overweight people being weak-willed gluttons. Once we become fat, we require less food to maintain our weight than we did to attain it. Fat has a lower metabolic rate than does muscle—it takes less food energy to maintain. When an overweight person’s body drops below its previous set (or settling) point, the brain triggers increased hunger and decreased metabolism. The body adapts to starvation by burning off fewer calories and seeking to restore lost weight. Blame your brain for weight regain (Cornier, 2011).

Lean people also seem naturally disposed to move about. They burn more calories than do energy-conserving overweight people, who tend to sit still longer (Levine et al., 2005). These individual differences in resting metabolism help explain why two people of the same height, age, and activity level can maintain the same weight, even if one of them eats much less than does the other.

The Genetic Factor Do our genes predispose us to eat more or less? To burn more calories by fidgeting or fewer by sitting still? Studies confirm a genetic influence on body weight. Consider two examples:

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The Food and Activity Factors Genes tell an important part of the obesity story. But environmental factors are mighty important, too.

Studies in Europe, Japan, and the United States show that children and adults who suffer from sleep loss are more vulnerable to obesity (Keith et al., 2006; Nedeltcheva et al., 2010; Taheri, 2004a,b). With sleep deprivation, the levels of leptin (which reports body fat to the brain) fall, and ghrelin (the appetite-stimulating stomach hormone) rise.

Social influence is another factor. One 32-year study of 12,067 people found them most likely to become obese when a friend became obese (Christakis & Fowler, 2007). If the obese friend was a close one, the odds of likewise becoming obese almost tripled. Moreover, the correlation among friends’ weights was not simply a matter of seeking out similar people as friends. Friends matter.

The strongest evidence that environment influences weight comes from our fattening world (FIGURE 11.8). What explains this growing problem? Changing food consumption and activity levels are at work. We are eating more and moving less, with lifestyles sometimes approaching those of animal feedlots (where farmers fatten inactive animals). In the United States, jobs requiring moderate physical activity declined from about 50 percent in 1960 to 20 percent in 2011 (Church et al., 2011). Worldwide, 31 percent of adults (including 43 percent of Americans and 25 percent of Europeans) are now sedentary, which means they average less than 20 minutes per day of moderate activity such as walking (Hallal et al., 2012). Sedentary occupations increase the chance of being overweight, as 86 percent of U.S. truck drivers reportedly are (Jacobson et al., 2007).

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The “bottom” line: New stadiums, theaters, and subway cars—but not airplanes—are widening seats to accommodate the girth growth (Hampson, 2000; Kim & Tong, 2010). Washington State Ferries abandoned a 50-year-old standard: “Eighteen-inch butts are a thing of the past” (Shepherd, 1999). New York City, facing a large problem with Big Apple bottoms, has mostly replaced 17.5-inch bucket-style subway seats with bucketless seats (Hampson, 2000). In the end, today’s people need more room.

Note how these findings reinforce a familiar lesson from Chapter 10’s study of intelligence: There can be high levels of heritability (genetic influence on individual differences) without heredity explaining group differences. Genes mostly determine why one person today is heavier than another. Environment mostly determines why people today are heavier than their counterparts 50 years ago. Our eating behavior also demonstrates the now-familiar interaction among biological, psychological, and social-cultural factors. For tips on shedding unwanted pounds, see TABLE 11.1.

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