Puberty entails transformation of every part of the body, each change affecting the others. Here we discuss biological growth, the nutrition that fuels that growth, and the eating disorders that disrupt it. Next we will focus on the two other aspects of pubertal transformation, brain reorganization and sexual maturation.

The first set of changes is called the growth spurt—a sudden, uneven jump in the size of almost every body part, turning children into adults. Growth proceeds from the extremities to the core (the opposite of the earlier proximodistal growth). Thus, fingers and toes lengthen before hands and feet, hands and feet before arms and legs, arms and legs before the torso. This growth is not always symmetrical: One foot, one breast, or even one ear may grow later than the other.

Because the torso is the last body part to grow, many pubescent children are temporarily big-footed, long-legged, and short-wasted. If young teenagers complain that their jeans don’t fit, they are probably correct—even if those same jeans fit when their parents bought them a month earlier. (Advance warning about rapid body growth occurs when parents buy their children’s shoes in the adult section).

As the growth spurt begins, children eat more and gain weight. Exactly when, where, and how much weight they gain depends on heredity, hormones, diet, exercise, and gender. By age 17, the average girl has twice the percentage of body fat as her male classmate, whose increased weight is mostly muscle.

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A height spurt follows the weight spurt; then a year or two later a muscle spurt occurs. Thus, the pudginess and clumsiness of early puberty are usually gone by late adolescence. Keep in mind, however, that puberty may dislodge the usual relationship between height and overweight or underweight. A child may be eating too much or too little for their height, but that may not be apparent in conventional measures of BMI (Golden et al., 2012).

At puberty, all the muscles increase in power. Arm muscles develop particularly in boys, doubling in strength from age 8 to 18. Other muscles are gender neutral. Both sexes run faster with each year of adolescence, with boys not much faster than girls (unless the girls choose to slow down) until the end of high school (see Figure 14.4).

In both sexes, organs mature in much the same way. Lungs triple in weight; consequently, adolescents breathe more deeply and slowly. The heart (another muscle) doubles in size as the heartbeat slows, decreasing the pulse rate while increasing blood pressure (Malina et al., 2004). Consequently, endurance improves: Some teenagers can run for miles or dance for hours. Red blood cells increase in both sexes, but dramatically more so in boys, which aids oxygen transport during intense exercise.

Both weight and height increase before muscles and internal organs: To protect immature muscles and organs, athletic training and weight lifting should be tailored to an adolescent’s size the previous year. Sports injuries are the most common school accidents, and they increase at puberty. One reason is that the height spurt precedes increases in bone mass, making young adolescents particularly vulnerable to fractures (Mathison & Agrawal, 2010).

One organ system, the lymphoid system (which includes the tonsils and adenoids), decreases in size, so teenagers are less susceptible to respiratory ailments. Mild asthma, for example, often switches off at puberty—half as many teenagers as children are asthmatic (MMWR, June 8, 2012). In addition, teenagers have fewer colds and allergies than younger children. This reduction in susceptibility is aided by growth of the larynx, which also deepens the voice, dramatically noticeable in boys but also evident in girls.

Another organ system, the skin, becomes oilier, sweatier, and more prone to acne. Hair also changes, becoming coarser and darker. New hair grows under arms, on faces, and over sex organs (pubic hair, from the same Latin root as puberty). Visible facial and chest hair is sometimes considered a sign of manliness, although hairiness in either sex depends on genes as well as on hormones.

Girls pluck or wax any facial hair they see and shave their legs, while boys proudly grow sideburns, soul patches, chinstraps, moustaches, and so on—with specifics dependent on culture and cohort. Sexual attraction is the goal.

Often teenagers cut, style, or grow their hair in ways their parents do not like, as a sign of independence. To become more attractive, many adolescents spend considerable time, money, and thought on their visible hair—growing, gelling, shaving, curling, straightening, highlighting, brushing, combing, styling, dyeing, wetting, and/or drying…. In many ways, hair is far more than a growth characteristic; it is a display of sexuality.

All the changes of puberty depend on adequate nourishment, yet many adolescents do not eat well. Teenagers often skip breakfast, binge at midnight, guzzle down unhealthy energy drinks, and munch on salty, processed snacks. One reason for their eating patterns is that their hormones affect the circadian rhythm of their appetites; another reason is that their drive for independence makes them avoid family dinners, refusing to eat what their mothers say they should. Family dinners in supportive families correlate with healthy adolescent eating and well-being, but that is less true when family relationships are poor (Meier & Musick, 2014).

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Cohort and age are crucial. In the United States, each new generation eats less well than the previous one, and each 18-year-old tends to eat a less balanced diet than he or she did at age 10 (Larson et al., 2007). Most adolescents consume enough calories, but in 2013 only 16 percent of high school seniors ate the recommended three or more servings of vegetables a day (MMWR, June 13, 2014).

Deficiencies of iron, calcium, zinc, and other minerals are especially common during adolescence. Because menstruation depletes iron, anemia is more likely among adolescent girls than among any other age group. This is true everywhere, especially in South Asia and sub-Saharan Africa, where teenage girls rarely eat iron-rich meat and green vegetables.

Reliable laboratory analysis of blood iron on a large sample of young girls in developing nations is not available, but all indications suggest that many are anemic. Data is available for 18- to 23-year-old college women in Saudi Arabia (not among the poorest nations). About a fourth (24 percent) were clinically anemic and another fourth (28 percent) were iron-deficient (Al-Sayes et al., 2011). These numbers are especially troubling since almost all college women in Saudi Arabia are in good health, from wealthy families, and have never been pregnant. Those factors put them among the better-nourished young women in that nation.

Boys everywhere may also be iron-deficient if they engage in physical labor or intensive sports: Muscles need iron for growth and strength. The cutoff for iron-deficiency anemia is higher for boys than girls because boys require more iron to be healthy (Morón & Viteri, 2009). Yet in developed as well as developing nations, many adolescents of both sexes spurn iron-rich foods (green vegetables, eggs, and meat) in favor of iron-poor chips, sweets, and fries.

Similarly, although the daily recommended intake of calcium for teenagers is 1,300 milligrams, the average U.S. teen consumes less than 500 milligrams a day. About half of adult bone mass is acquired from ages 10 to 20, which means many contemporary teenagers will develop osteoporosis (fragile bones), a major cause of disability, injury, and death in late adulthood, especially for women.

One reason for calcium deficiency is that milk drinking has declined. In 1961, most North American children drank at least 24 ounces (about three-fourths of a liter) of milk each day, providing almost all (about 900 milligrams) of their daily calcium requirement. Fifty years later, only 12.5 percent of high school students drank that much milk and 19 percent (more girls than boys) drank no milk at all (MMWR, June 13, 2014).

Many economists advocate a “nudge” to encourage people to make better choices, not only in nutrition but also in all other aspects of their lives (Thaler & Sunstein, 2008). Teenagers are often nudged in the wrong direction. Nutritional deficiencies result from the food choices that young adolescents are enticed to make.

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Fast-food establishments cluster around high schools, often with extra seating that encourages teenagers to eat and socialize. This is especially true for high schools with large Hispanic populations, who are most at risk for obesity (Taber et al., 2011). Forty percent of Hispanic girls in U.S. high schools describe themselves as overweight, as do 27 percent of Hispanic boys (MMWR, June 13, 2014).

Price influences food choices, especially for adolescents, and healthy fast foods cost more than unhealthy ones. For example, compare the prices of a McDonald’s salad and a hamburger.

Nutritional deficiencies increase when schools have vending machines that offer soda and snacks, especially for middle school students (Rovner et al., 2011). An increasing number of laws require schools to encourage healthy eating, but effects are more apparent in elementary schools than high schools (Mâsse et al., 2013; Terry-McElrath et al., 2014).

Many adolescents spurn school lunches in favor of unhealthy snacks sold by in-school vending machines (who pay the school for prime placement) and nearby businesses. No wonder rates of obesity increase at about age 12.

Rates of obesity are falling in childhood but not in adolescence. Only three U.S. states (Kentucky, Mississippi, Tennessee) had high-school obesity rates at 15 percent or more in 2003; 22 states were that high in 2013 (MMWR, June 13, 2014). In Latin America, the nutritional focus is still on preventing underweight not preventing overweight, yet overall, about 1 teenager in 4 is overweight or obese (Rivera et al., 2014).

One reason for poor nutrition among teenagers is anxiety about body image—that is, a person’s idea of how his or her body looks. Few teenagers welcome every change in their bodies. Instead, they tend to focus on and exaggerate imperfections (as did the three girls in the anecdote that opens this chapter). Two-thirds of U.S. high-school girls are trying to lose weight, even though only one-fourth are actually overweight or obese (MMWR, June 8, 2012).

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Few adolescents are happy with their bodies, partly because almost none look like the bodies portrayed online and in magazines, movies, and television programs that are marketed to teenagers (Bell & Dittmar, 2011). Unhappiness with appearance—especially with weight for girls—is documented worldwide: including in South Korea, China, and Greece (Kim & Kim, 2009; Chen & Jackson, 2009; Argyrides & Kkeli, 2014).

Dissatisfaction with body image can be dangerous, even deadly. Many teenagers, mostly girls, eat erratically or ingest drugs (especially diet pills) to lose weight; others, mostly boys, take steroids to increase muscle mass. (Developmental Link: Teenage drug abuse is discussed in Chapter 16.) Eating disorders are rare in childhood but increase dramatically at puberty, accompanied by distorted body image, food obsession, and depression (Le Grange & Lock, 2011). Such disorders are often unrecognized until they get worse in emerging adulthood.

Adolescents sometimes switch from obsessive dieting, to overeating, to overexercising, and back again. Obesity is an eating disorder at every age. (Developmental Link: Obesity is discussed in Chapter 8 and in the epilogue.) Here we describe three other eating disorders likely to begin in adolescence.

A body mass index (BMI) of 17 or lower, or loss of more than 10 percent of body weight within a month or two, indicates anorexia nervosa, a disorder characterized by voluntary starvation and a destructive and distorted attitude about one’s own body fat. The affected person becomes very thin, risking death by organ failure. Staying too thin becomes an obsession.

Although anorexia existed earlier, it was not identified until about 1950, when some high-achieving, upper-class young women became so emaciated that they died. Soon anorexia was evident among teenagers and young adults of every income, nation, and ethnicity; the rate spikes at puberty and again in emerging adulthood.

Certain alleles increase the risk of developing anorexia (Young, 2010), with higher risk among girls with close relatives who suffer from eating disorders or severe depression. Although far more common in girls, boys are also at risk.

About three times as common as anorexia is bulimia nervosa (also called binge–purge syndrome). This disorder is clinically present in 1 to 3 percent of female teenagers and young adults in the United States. They overeat compulsively, consuming thousands of calories within an hour or two, and then purge through vomiting or laxatives. Most are close to normal in weight and therefore unlikely to starve. However, they risk serious health problems, including damage to their gastrointestinal systems and cardiac arrest from electrolyte imbalance.

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Binging and purging are common among adolescents. For instance, a survey found that in the last 30 days of 2013, 6.6 percent of U.S. high-school girls and 2.2 percent of the boys vomited or took laxatives to lose weight, with marked variation by state—from 3.6 percent in Nebraska to 9 percent in Arizona (MMWR, June 13, 2014).

A disorder newly recognized in DSM-5 is binge eating disorder. Some adolescents periodically and compulsively overeat, quickly consuming large amounts of ice cream, cake, or any snack food until their stomachs hurt. When bingeing becomes a disorder, overeating is typically done in private, at least once weekly for three months. The sufferer does not purge (hence this is not bulimia) but feels out of control, distressed, and depressed.

All adolescents are vulnerable to unhealthy eating. Autonomy and body image can lead to disorders. Teenagers try new diets, go without food for 24 hours (as did 19 percent of U.S. high-school girls in one typical month), or take diet drugs (6.6 percent) (MMWR, June 13, 2014). Many eat oddly (e.g., only rice or only carrots), begin unusual diets, or exercise intensely.

Parents are slow to recognize eating disorders, and delay getting help that their children need (Thomson et al., 2014). Yet the research on all the eating disorders finds that family function (not structure) is crucial (Tetzlaff & Hilbert, 2014).

A combination of causes leads to obesity, anorexia, bulimia, or bingeing. At least five general elements—cultural images, stress, puberty, hormones, and childhood experiences—make disordered eating more likely.

A developmental perspective notes that healthy eating begins with childhood habits and family routines. Most overweight or underweight newborns never develop nutritional problems, but children who are overweight or underweight are at risk. Particularly in adolescence, family-based therapy for eating disorders is more successful than therapy that focuses only on the individual (Couturier et al., 2013; Murray et al., 2014).

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