HEALTH PSYCHOLOGY, 1991, 70(2), 133-142 Copyright © 1991, Lawrence Erlbaum Associates, Inc.

Gender Differences in Eating Behavior and Body Weight Regulation Barbara J. Rolls, Ingrid C. Fedoroff, and Joanne F. Guthrie

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Department of Psychiatry and Behavioral Sciences Johns Hopkins University School of Medicine Gender differences in food intake and selection first appear in adolescence. Men consume more calories than women, and the sexes have different eating styles, which indicate that women have been socialized to eat in a more feminine manner. Women experience more food-related conflict than men do, in that they like fattening foods but perceive that they should not eat them. Pressures to be thin are present in early adolescence, as noted by dieting behavior starting in very young girls. Women experience more dissatisfaction with their body weight and shape than men do. Sociocultural and psychological factors may be important in the etiology of eating disorders, which are much more prevalent in females than in males. Thus, further studies of gender differences in eating behavior will be important for understanding the etiology of eating and body-weight disorders and for designing gender-appropriate treatments. Key words: anorexia nervosa, body weight, bulimia nervosa, eating, gender, obesity

In infancy and childhood, boys and girls show similar eating behavior (L. L. Birch, personal communication, August 1989). Gender differences in eating behavior surface in adolescence, which is a time when both physiological changes and social pressures begin to exert their influence. Prepubertal boys and girls are similar in lean body mass, skeletal mass, and body fat (Johnston, 1985). However, just before puberty, there are extraordinary physical changes such as the "fat spurt." By maturity, women have 2 times as much body fat as men, whereas men have 1.5 times the lean body mass and the skeletal mass as women (Warren, 1983). After puberty, females experience large monthly hormonal changes. Several studies (e.g., Blaustein & Wade, 1976; Wade, 1975) have indicated that these hormonal changes may influence food intake and selection. Food intake of several mammalian species shows systematic variation across the ovarian cycle. This is well documented in the rat, in which food intake is low around the time of ovulation. It is thought that estrogen inhibits food intake and that progesterone may counteract this inhibitory effect or actually increase food intake. The same pattern is seen in humans. Gong, Garrel, and Calloway (1989) studied food intake across the menstrual cycle in normally cycling women. Intake tends to be lowest around ovulation when estrogen is highest, and intake is highest at the luteal phase when estrogen is lowest. Appetite ratings also show this pattern in women with premenstrual syndrome (Both-Orthman, Rubinow, Hoban, Malley, & Grover, 1988). Bowen and Grunberg (1990) also found that sweet-food intake and preference were significantly higher for women just before menstruation, during the luteal phase of their cycle. Less is known about how sex hormones affect food selection and intake in men. There is an indication that the gonadal hormones may affect taste preferences (Doty, 1978). Several studies indicate that males prefer sweeter foods than females Requests for reprints should be sent to Barbara J. Rolls, Department of Psychiatry and Behavioral Sciences, Meyer 1-108, Johns Hopkins University School of Medicine, 600 North Wolfe Street, Baltimore, MD 21205.

do (Enns, Van Itallie, & Grinker, 1979; Green, Desor, & Mailer, 1975). The food choices of men reflect this preference for sweet (see next section).

GENDER DIFFERENCES IN FOOD SELECTION AND INTAKE Adolescents Gender differences in food selection and intake appear in adolescence. Boys, with their greater average body weight and higher resting metabolic rate, generally require a higher energy intake than do girls. The disparity is the highest during the adolescent years. The Food and Nutrition Board of the National Academy of Sciences has established a recommended energy intake of 3,000 kcal/day for 15- to 18-year-old males engaged in light-to-moderate activity, whereas the recommendation for females of the same age range and activity level is 2,200 kcal/day (Food and Nutrition Board, 1989). The second National Health and Nutrition Examination Survey, 1976 to 1980 (NHANES II; Life Sciences Research Office, 1989), conducted by the U.S. Department of Health and Human Services, reported the mean energy intake of American 16- to 19-year-old males to be 3,048 kcal/day, whereas that of females of similar age was reported to be 1,687 kcal/day. Thus it appears that males are consuming recommended amounts of calories, on the average, whereas females are consuming lower-than-recommended amounts. Females' lower caloric intake may result from eating smaller amounts of the same variety of foods as males and/or by altering their selection to emphasize foods lower in caloric density (Axelson, 1986). In terms of the percentage of total calories consumed, macronutrient intake does not differ between adolescent boys and girls. However, because adolescent boys consume considerably more food than do girls, they are less at risk from nutritional inadequacies (George & Krondl, 1983; Truswell & Darnton-Hill, 1982). Despite reported similarities in macronutrient intakes, boys and girls have been found in some

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surveys to differ in their food beliefs and food choices. In a Canadian survey, boys indicated more frequent selection of foods higher in fat, salt, and sugar, whereas the girls chose more vegetables. These differences in selection were related to perception of health beliefs and palatability (George & Krondl, 1983).

foods stereotypically associated with caloric restriction, such as low-calorie soft drinks.

Adults

Given these gender-related differences in food selection, it is not unreasonable to hypothesize that the sexes might differ in other aspects of their eating behavior. Nevertheless, most studies of eating behavior do not attempt to distinguish between the sexes. There are, however, several investigations indicating that this should be a part of future work.

In adulthood, energy needs of men continue to exceed those of women, although the difference in recommended intakes is slightly decreased from adolescence. Among 19- to 50-yearold adults, recommended intakes are set at 2,900 kcal/day for men and 2,220 kcal/day for women (Food and Nutrition Board, 1989). NHANES II data show that, although caloric intakes of men continue to be higher than those of women, the disparity in caloric intakes is not as great in adults as in adolescents. For instance, caloric intakes of 30- to 39-year-old men average 2,554 kcal/day, and intakes of women in the same age range average 1,596 kcal/day. Basiotis, Thomas, Kelsay, and Mertz (1989) analyzed the results of a 1-year dietary intake study conducted with normal, healthy, 20- to 5 3-year-old men and women and found that the estimated average daily energy intake of the men was 901 kcal greater than that of the women when all other variables (age, height, weight, etc.) were held constant. They also found that, with increasing age, caloric intakes declined more in men than in women —for women, an increase in age by 1 year resulted in a decrease in caloric intake of 2.2 kcal/day, on the average; among men, each additional year was associated with a decreased intake of 29.7 kcal/day. In adulthood, as in adolescence, there seems to be little difference in the nutritional quality of the diets of men and women after adjustments are made for differences in total energy consumed (Windham, Wyse, Hurst, & Gaurth Hansen, 1981). Differences in food usage, however, have been noted. Cronin, Krebs-Smith, Wyse, and Light (1982) used 3-day dietary data of participants in the 1977-1978 Nationwide Food Consumption Survey conducted by the U.S. Department of Agriculture (USDA) to examine the relationship of food usage patterns to sex, race, and other sociodemographic variables. Men reported significantly more frequent consumption of meats, dairy products and several carbohydrate-rich foods such as breads, cereals, desserts, and sweets than did women. On the other hand, women were more likely to consume fruit, yogurt, coffee, tea, and low-calorie carbonated beverages. Comparison of this 1977-1978 data with data collected by the USD A in 1985 indicates that women and men continued to differ in their use of some food items (Life Sciences Research Office, 1989). Both men and women reported decreased consumption of beef and pork, but the decrease in mean intake of these foods was greater for women than for men. Reported consumption of low-calorie carbonated beverages by both male and female respondents increased dramatically in 1985. However, women still consumed more of these beverages than men. These changes in reported food consumption since 1977 indicate that both men and women are becoming more concerned with avoidance of excess fat and calories; yet, women continue to exceed men in their usage of

GENDER DIFFERENCES IN EATING BEHAVIOR

Responses to Variety in the Diet We have conducted a series of experiments that show clearly that variety in the diet acts as a stimulant of food intake. Our early experiments on variety suggested that females might be more responsive to the stimulatory effect of variety than males. Thus, male subjects ate only slightly more when offered three flavors of yogurt than when offered one flavor, whereas the females showed a significant difference between conditions (Rolls et al., 1981). Shortly after the publication of this study, Beatty (1982) found that a variety of flavors of ice cream stimulated additional intake only in females and not in males. The subjects were eating in a group, which appears to be the explanation for the sex difference. Berry, Beatty, and Klesges (1985) found that a variety of flavors of ice cream enhanced intake in both males and females when they were eating alone, but in the males, there was such a large social facilitation of eating that this could have masked the effect of variety (see Figure 1). Thus, there is no clear evidence that the sexes differ in their responsiveness to the stimulatory effect of variety on food intake. The studies do suggest, however, that there should be further studies on gender differences in the social facilitation of eating. Masculine or Feminine Eating Style Several types of studies suggest that sex differences in eating behavior may result from learning a masculine or feminine eating style. This style may involve the amount of food eaten in a meal or snack, the types of foods selected, as well as actual eating behaviors such as bit size and eating rate. When Green (1987) observed ad libitum food consumption by 19 men and 23 women in a laboratory setting over a 6- to 7-hr time period, she found that men consumed significantly more calories than women, partly because they consumed significantly larger (more caloric) bites and sips than women did. When Hill and McCutcheon (1984) asked male and female subjects to eat two doughnuts, women took more bites and longer to eat than men. The slower eating rate was accomplished by taking smaller bites. These gender differences are partially, but not entirely dependent on body size. Socialization differences between men and women regarding mealtime etiquette may account for these effects. Women may have been taught to take small bites, which would decrease the

GENDER DIFFERENCES IN EATING BEHAVIOR

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Females

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portrayed as eating a small breakfast and lunch or a large breakfast and lunch. Ratings of the male target were not affected by differences in meal size, but the female target who ate the smaller meals was considered to be more feminine, less masculine, more concerned about her appearance, better looking, and more likely to possess stereotypically feminine personality traits (see Figure 2). In another study, Mori and Pliner (1987) found that female subjects ate significantly less when with a desirable male partner than with other females or a less desirable male. In contrast, male subjects did not eat more or less with a desirable woman, although they did show an overall tendency to eat less with female than with male partners. Klesges, Bartsch, Norwood, Kautzman, and Haugrud (1984) unobtrusively observed 294 males and 245 females eating at both formal and fast-food restaurants and found that females, but not males, ate significantly less when eating in large groups. These results suggest that self-presentation of femininity is an important determinant of eating behavior.

3 flavors

PRESSURES TO BE THIN Satisfaction With Body Weight and Shape Females

Males

FIGURE 1 Mean ice cream intake (g) of males and females as a function of social setting and number of flavors available (1 or 3). Modified from "Sensory and Social Influences on Ice Cream Consumption by Males and Females in a Laboratory Setting" by S. L. Berry, W. W. Beatty, and R. C. Klesges, 1985, Appetite, 6, p. 43. Copyright 1985 by Academic Press Inc. (London) Limited. Adapted by permission.

intervals between bites, decrease eating rate, and increase the number of bites. Because eating style differs between the sexes, we (B. Rolls, P. Pirraglia, S. Stoner, & L. Laster, 1990) tested the hypothesis that the way food is presented will have different effects on intake in men and women. We compared intake of sandwiches presented either as substantial whole units or as more dainty cocktail pieces, the idea being that men would prefer the whole units and women would prefer the smaller units. We found that men ate significantly more of the whole sandwiches than of the sandwiches cut into parts, but women showed no difference between conditions. Additionally, in comparing sexes, we confirmed that men ate significantly more than women in both conditions. We also discovered that men's rate of eating (grams per minute) was significantly higher for both conditions. This finding indicates that a feminine eating style involves consuming less than men at a slower rate than men, regardless of the mode of presentation. Another study (Chaiken & Pliner, 1987) has tested the hypothesis that "eating lightly" is a sex-role-appropriate behavior for women and consequently that women who eat smaller amounts of food will be perceived as more feminine than those who eat large meals. Male and female subjects read a food diary attributed to a male or female target who was

There is a gender distinction in the way men and women feel about their body shape and their weight. Women are less satisfied with their body shape than men (Connor-Greene, 1988; Drewnowski & Yee, 1987) and perceive themselves as being overweight, whereas many men are more likely to see themselves as underweight and want to be heavier. These sex differences are also seen in perceived satisfaction with body weight. Men are satisfied with what they perceive their body weight to be more often than are women. Women desire to be thinner than they perceive themselves to be and thinner than men actually like them to be (Fallon & Rozin, 1985). In addition to a sex difference in the desire to be thin, there is a strong correlation with social class. Gender and family income were the strongest predictors of adolescents expressing a desire to be thin (Dornbusch et al., 1984). Girls from a higher income family were more likely to express a desire to be thin than girls from a lower income family. Almost half the adolescent girls in this study wanted to lose weight and this number increased as the family income increased whereas very few boys indicated a desire to be thinner regardless of income (see Figure 3). The Ideal Female Shape Throughout history, certain ideals of body weight and shape have influenced the way women have viewed and treated their bodies. Women's status has been more dependent on physical attributes than that of men, and therefore they are under more pressure to conform to the current physical ideal (Mazur, 1986; Seid, 1989). For example, from the 16th to the 19th century, the lush fleshy nudes painted by Titian, Rubens, and Renoir represented the accepted view of attractive womanhood of that period. This preferred female body type re-

ROLLS, FEDOROFF, GUTHRIE

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Female Target Large meal

Small meal

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0

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FIGURE 2 Perceptions of target as a function of the sex of the target and meal size. Ratings of a female target on the four listed variables were affected by whether she was reported to have eaten a large or a small meal. There was no difference in ratings for the male target regardless of meal size. Possible scores ranged from 1 to 5. Modified from "Women but Not Men, Are What They Eat: The Effect of Meal Size and Gender on Perceived Femininity and Masculinity" by S. Chaiken and P. Pliner, 1987, Personality and Social Psychology Bulletin, 13(2), p. 171. Copyright 1987 by the Society for Personality and Social Psychology, Inc. Adapted by permission of Sage Publications, Inc.

Male Female

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FIGURE 3 Percentages of adolescents wanting to be thinner by level of family income. Modified from "Sexual Maturation, Social Class, and the Desire to Be Thin Among Adolescent Females" by S. M. Dornbusch, J. M. Carlsmuth, P. D. Duncan, R. T. Gross, J. A. Martin, P. L. Ritter, and B. Siegel-Gorelick, 1984, Developmental and Behavioral Pediatrics, 5(6), p. 310. Copyright 1984 by Williams & Wilkins. Adapted by permission.

mained generally the standard until the 1920s. During this decade, there was a radical change in the perceived feminine ideal body shape; the new shape was thin, less curvaceous, almost boylike and nearly devoid of female secondary sexual

characteristics. To acquire this body shape, women increasingly turned to dieting. At this time, many doctors and the popular press documented and commented on the increased prevalence of eating disorders and girls starving themselves to attain that fashionable boyish figure (Silverstein, Perdue, Peterson, Vogel, & Fantini, 1986; Silverstein, Peterson, & Perdue, 1986). This flapper style went out of fashion in the 1930s, women adjusted accordingly, and the incidence of dieting decreased (Mazur, 1986). Since the 1960s, however, slenderness has been judged by women to be one of the most important determinants of physical attractiveness (Horvath, 1981). A study by Garner, Garfinkel, Schwartz, and Thompson (1980) plotted changes in the weight of centerfold models in Playboy magazine. This and data from the Miss America Pageant and women's magazines indicate a shift toward a thinner standard for body weight in recent years. However, it was also found that population weights for women over this period were increasing. Concordantly, there was an increase in the number of diet articles in women's magazines. A recent survey of figure measurements of fashion models (Morris, Cooper, & Cooper, 1989) has found an indication of a change in body proportions. Over a period of 20 years, height, waist, and, to a slight degree, bust measurements increased, whereas

GENDER DIFFERENCES IN EATING BEHAVIOR

hip size remained the same. This shift to a larger waist measurement in comparison to a small bust increase and no change in hip size results in a less curvaceous figure, reflecting the current trend toward a leaner look for women. Today, the present cultural ideal of the feminine figure has led women to resort to dieting to attain this goal. More than 75% of women in a study (Schwartz, Thompson, & Johnson, 1981) cited appearance, rather than health, as the reason for desiring to lose weight.

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Dieting in Children and Adolescents A recent British study has shown that the food choices of many adolescents, particularly girls, will be influenced by their preoccupation with dieting and body weight (Wardie & Beales, 1986). Girls were more likely than boys to believe that foods could affect health, and they were more likely to attribute obesity to eating the wrong kinds of foods. Typically, however, the girls liked these foods as much as the boys. In some cases, the girls and boys were found to eat similar amounts of sweets and snacks. The failure to match disapproval of such foods with reduced preference suggests a greater conflict about fattening foods in adolescent girls than boys. Several studies show a high incidence of dieting and weight preoccupation at an early age. In a study of 7- to 13-year-olds, 45% wanted to be thinner and 37% had already tried dieting. After Grade 4 (around 8 years old), more girls than boys had tried to lose weight (Maloney, McGuire, Daniels, & Specker, 1989). Another study (Abraham, Mira, & Beaumont, 1983) found that 86% of the 106 female students studied had dieted successfully at some time. This suggests that most young women may pass through a phase of restricted eating and that this is part of typical development in Western culture and may not necessarily require treatment. On the other hand, many researchers have hypothesized that the increased pressure on women to achieve and maintain a low body weight may in fact contribute to the steady increase in prevalence of eating disorders (Bruch, 1978; Garner et al., 1980; Silverstein, Petersen, & Perdue, 1986). Dieting itself has been named as a factor in increasing an individual's vulnerability to overeating (or binging) after extended periods of "restrained eating" (Herman & Polivy, 1975). Of the female students surveyed by Abraham et al. (1983), 63% reported episodes of binge eating which they felt were outside of their control. This suggests some disordered eating patterns occurring in this dieting population.

ANOREXIA NERVOSA AND BULIMIA NERVOSA Incidence of Eating Disorders Approximately 90% of eating-disorder patients are female and consequently most of the information on anorexia nervosa and bulimia nervosa relates to females rather than males. Thus, this discussion on eating disorders deals mostly with material gathered on female patients. However, there is

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some research pertaining to the male patient population, and these findings are discussed later in this section. It is estimated that 1 of every 100 adolescent girls has anorexia nervosa (Lucas, Beard, O'Fallon, & Kurland, 1988; Yates, 1989), which is characterized by low body weight, amenorrhea, fear of fatness, and perception of distortion of body shape. Bulimia is characterized by binge eating following by fasting, purging, or vomiting and a fear of fatness. The incidence of bulimia nervosa has been estimated through surveys in the community and on college campuses. A community-based sample found an incidence rate of 1.9% (Cooper & Fairburn, 1983), whereas studies of college campuses have reported a range of 1.3% to 4% incidence (Drewnowski, Yee, & Krahn, 1988; Pyle et al., 1983; Schotte & Stunkard, 1987). Hart and Ollendick (1985) found five times the frequency of bulimia in women enrolled in universities compared to working women. Female medical students are also at high lifetime risk for bulimia, with an incidence rate of 15% (Herzog, Pepose, Norman, & Rigotti, 1985). There has been a dramatic increase in bulimia nervosa in the past 20 years, but the occurrence of anorexia has remained stable. Eating disorders do affect a relatively large percentage of the population in industrialized nations and have serious and sometimes life-threatening consequences. The mortality rate of anorexia and bulimia has been reported to range between 5% and 20%, and another 25% continue to have a chronic illness for the rest of their lives (Andersen, 1986; Theander, 1985). Etiology There are many factors involved in the etiology of both of these disorders and a multidisciplinary approach is best in attempting to understand this complex illness. Sociocultural, psychological, familial, developmental, and biological theories all offer valuable contributions to the understanding of the etiology of eating disorders and give some insight as to why these disorders occur primarily in females. Sociocultural. Anorexia and bulimia are most common in upper-class and middle-class 12- to 25-year-old females in developed countries (Szmukler, 1985), although Garfinkel and Garner (1982) noted that eating disorders are seen in wider age ranges and social classes. In the present day, weight dissatisfaction and dieting are considered normal for females (Rodin, Silberstein, & Striegel-Moore, 1985). Those individuals who internalize these values and beliefs, equating thinness with attractiveness and success, exhibit greater preoccupation with weight and dieting and may be more likely to develop an eating disorder (Striegel-Moore, Silberstein, & Rodin, 1986; Williamson, Kelley, Davis, Ruggiero, & Blouin, 1985). The environment is also a risk factor in developing an eating disorder. It has been suggested that the incidence of bulimia is greater in boarding schools and college dorms (Squire, 1983), especially in competitive stressful schools as well as on campuses where dating is emphasized (StriegelMoore et al., 1986). Certain professions that dictate a particular weight, such as dancing, acting, modeling, and athletics, put individuals at risk (Crago, Yates, Beutler, & Arizmendi,

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1985; Garfinkel, Garner, & Goldbloom, 1987; Garner & Garfinkel, 1978; Yates, Leehey, & Shisslak, 1983). This is particularly evident when the emphasis is on appearance and weight rather than performance. The idealization of the thin female form and pressures on women to compete, and perform well, yet be attractive and feminine all contribute to the social pressures on women that could put them at risk for an eating disorder. Wrestlers, runners, and jockeys are some male groups that have been identified as being at a high risk for developing an eating disorder as a result of their chosen activity (King & Mezey, 1987; Yates, 1987). Psychological. There are several different traits associated with each disorder. Anorexics tend to display compliancy, limited spontaneity, perfectionism, and impaired autonomy. Both anorexics and bulimics have obsessive personality traits, such as being preoccupied with calorie counting and mental imaging of food (Rothenberg, 1986). Other characteristics they share include low self-esteem, a sense of ineffectiveness, and conflicts of identity and autonomy (Garfinkel et al., 1987; Katz, 1985). Bulimics tend to have a history of childhood maladjustment and are more likely to have been obese or to have had an obese mother. They are often extroverted and sexually active and typically have problems with alcohol abuse and have been in trouble with the law (i.e., for theft). There is often a history of unstable mood and attempted suicide. Garfinkel et al. (1987) proposed that this behavior implies a deficit in the regulation of affect and control. The appearance of these personality clusters in a developing girl may indicate the possibility of a burgeoning eating disorder. Male eating-disorder patients share some of these psychological characteristics with females who become ill. They have a self-critical perfectionistic personality and also suffer from low self-esteem and face conflict concerning issues of identity and autonomy from parents (Andersen, 1988). Familial. There are several pathological features in families that have been linked to the presence of an eating disorder. Although there is little evidence of causality, there seems to be certain dynamics in the families of individuals with eating disorders that serve to maintain or prolong the illness. The family of an anorexic tends to be enmeshing, overprotective, rigid, and achievement oriented (Yates, 1989). The family relationship deters autonomy and establishes dependency in the ill member. Whereas the family of the bulimic is less structured than that of the anorexic, there is increased overt conflict, emotional distance, rejection, and neglect (Humphrey, 1988). Mothers of bulimics are more emotionally distant rather than enmeshed with their daughters (Yates, 1989). Studies (Garfinkel et al., 1987; Katz, 1985; Piran, Kennedy, & Garfinkel, 1985) show that families of both bulimics and anorexics have a greater likelihood of a family history of an eating disorder and of an affective disorder and alcoholism in first-degree relatives. Additionally, these families are inclined to be overly focused on food, diet, weight, appearance, and physical fitness (Katz, 1985). Development. Girls are more concerned than boys in looking attractive during childhood. Children as young as 6

years devalue obesity, and for a young girl to be overweight often results in social isolation (Johnson & Connors, 1987). After puberty, girls have twice as much fat as boys (Warren, 1983). During adolescent maturation, boys acquire more lean muscle and develop toward what is the accepted male ideal. However, girls gain more fat and grow away from the lean female ideal and this leads to more dissatisfaction with their body as compared to boys (Striegel-Moore et al., 1986). Timing of development seems to be important particularly for girls. Girls who are early developers are heavier and unhappier with their weight (Simmons, Blyth, & McKinney, 1983). Women continue through adulthood being concerned and unhappy about their weight and shape, and even 62-year-old women listed a change in body weight as their second major concern after memory loss (Striegel-Moore et al., 1986). Concern with body weight and shape leads to dieting as a way to take control and gain independence. These concerns, coupled with other risk factors, can increase the possibility of developing an eating disorder. Biological. Although there is considerable evidence that the psychosocial pressures to diet mentioned so far are significant in the etiology of eating disorders, there may also be biological influences. Twin studies indicate a genetic predisposition for eating disorders. Researchers (Crisp, Hall, & Holland, 1985) have found a 55% concordance rate of monozygotic twins for an eating disorder with only a 7% concordance rate for dizygotic twins. Other studies have reported similar findings (Garfinkel & Garner, 1982; Nowlin, 1983; Vandereycken & Pierloot, 1981). A variety of endocrine changes are associated with eating disorders (Halmi, Ackerman, Gibbs, & Smith, 1987; Newman & Halmi, 1988), but it is not clear whether these are involved in the etiology of the disorders or are associated with the aberrant eating and starvation. One recent study is intriguing in that it suggests that the hypothalamic-pituitary-gonadal axis might be causally linked to the etiology of eating disorders. In this study (Kreipe, Strauss, Hodgman, & Ryan, 1989), women with subclinical eating pathology had considerably more menstrual abnormalities (greater than 90%) than control women with normal eating habits. It may be that a poorly regulated hypothalamic-pituitary-gonadal axis, reflected in the menstrual abnormality, provides the biological substrate leading to eating pathology. More longitudinal studies of women at risk for eating disorders are needed. Another study (Goodwin, Fairburn, & Cowen, 1987) indicates that dieting alters serotonin, a brain neurotransmitter, in women but not in men. Serotonin is known to be important in regulating appetite, mood, pain, and sleep. L-tryptophan was administered to normal-weight males and females to assess changes in brain serotonin function before and after 3 weeks of dieting. There was an increase in the prolactin response to L-tryptophan in females but not in males. The researchers suggested that dieting caused the alterations in brain serotonin-mediated response and concluded that dieting alters brain serotonin function in females but not males. This research indicates that this biological difference may be part of the explanation for why eating disorders are more prevalent in women than in men.

GENDER DIFFERENCES IN EATING BEHAVIOR

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Eating Disorders in Males A potential problem for such biological explanations is that about 10% of the eating-disordered population is male (Andersen, 1986). Some of these men, but not all, fall into high-risk groups such as wrestlers or jockeys, in which the pressure to be thin is great. Also, a recent study (Drewnowski & Yee, 1987) indicated that 40% of young male students want to lose weight. They suggest that previous studies indicating that men were content with body weight just looked at group means, which hid the fact that about half the males studied wanted to lose weight and about half wanted to gain weight. Although still controversial, there is some suggestion that males with eating disorders have problems with psychosexual development and gender identity and that perhaps a quarter are homosexual (Fichter & Daser, 1987). Other researchers (Herzog, Norman, Gordon, & Pepose, 1984; Robinson & Holden, 1986; Schneider & Agras, 1987) have also reported that anorexic and bulimic males may have increased homosexual or bisexual preferences. Significantly fewer bulimic men are married than bulimic women. This could indicate that men with this illness may have more difficulty forming intimate close heterosexual relationships or that they are not interested in them and prefer a homosexual alliance. There have been some differences between male and female eating disorders noted in the literature. Fichter, Daser, and Postpischil (1985) recounted that males have more preoccupation with food and weight, hyperactivity, greater sexual anxiety, and a premorbid involvement with athletics. Crisp, Burns, and Bhata (1986) also noted the over activity of male eating-disorder patients and reported that vomiting behavior indicates a good prognosis for males but a bad prognosis for females. Vomiting did not correlate with poor outcome for eating disorders in males; rather, there was a trend for bulimia and vomiting to be correlated with good outcome in this follow-up study. Males list the reasons for dieting as (a) to be more attractive to another male or female, (b) because of an actual history of obesity, and (c) for muscular definition. Females specify slimming and appearance as the major reasons (Andersen, 1988). There is also a sex difference in how the weight loss is achieved. Men tend to use exercise and women prefer to decrease food intake (Yates et al., 1983). It is hoped that understanding the risk factors for eating disorders in men and noting the differences between males and females will lead to a greater understanding of the etiology of the disorders in both sexes and will also help in designing gender-appropriate treatments.

OBESITY Sex Differences in Body Fat Women have a greater fat-to-lean tissue ratio than men, which leads to a lower basal metabolic rate because fat is less metabolically active than lean body tissue. This, plus the fact that they are often of smaller stature than men, means that their energy requirements will be lower than those of men.

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Females have three major milestones in their lives which are marked by an increase in body fat: adolescence, pregnancy, and menopause (Rodin et al., 1985). Male development is not characterized by similar fat-producing changes. As aging progresses, women are also more likely to gain more fat as their basal metabolic rate decreases. Men experience a similar metabolic slowing and some lean-tissue reduction, and there is a consequent increase in percentage of body fat, but they do not gain as much fat as females (Rodin et al., 1985). The usual distribution of body fat differs between the sexes so that men tend to have proportionately more abdominal fat than females and women have proportionately more lower body fat (Krotkiewski, Bjorntorp, Sjostrom, & Smith, 1983). Rebuffe-Scrive et al. (1985) showed that, in women, fat-cell metabolism in the hip or femoral region appears to be associated with changes in female sex-hormone levels associated with the menstrual cycle, pregnancy, and lactation. In menstruating women, lipoprotein lipase (LPL) activity is elevated in the femoral adipocytes, leading to accumulation of adipose tissue in this region. This pattern is accentuated during pregnancy, leading to increased fat storage in the hip region, but is reversed in lactation, when LPL activity is decreased and lipid mobilization is increased. These changes suggest that, in women, the accumulation of fat in the hip region serves the function of providing a stored energy supply that can be utilized during lactation. Higher levels of abdominal fat, indicated by an elevated waist-hip ratio are associated with a greater incidence of diabetes (Lundgren, Bengtsson, Blohme, Lapidus, & Sjostrom, 1989; Ohlsson, Larsson, & Svardsudd, 1985) as well as elevated serum lipids and cardiovascular problems (van Gaal, Vansant, van Campenhout, Lepoutre, & Leeuw, 1989). Higher levels of lower body fat seem to be somewhat more benign in their health effects; therefore, one might speculate that, although women are under more pressure than men to be thin, obese men are more likely to have an obesity-related health risk. However, recent evidence that obesity is a significant risk factor for coronary heart disease in middle-aged women (Manson et al., 1990) indicates that the health risks of obesity in women should not be underestimated. Gender and Weight Loss Men and women in the United States react to being overweight in different ways. Women are more likely to believe they are overweight, to experience more anxiety because of being overweight, and to make more attempts to lose weight. It has been believed that men are more successful in reducing weight, but several recent studies have contradicted this view (Forster & Jeffery, 1986; Jeffery, Snell, & Forster, 1985). Although comparisons of the prevalence of overweight in men and women are complicated by the absence of an objective standard of obesity that is independent of sex, most studies indicate a slightly higher prevalence of obesity in women than in men (Forster & Jeffery, 1986). Recent studies have found sex differences in weight loss and weight-loss maintenance over a period of time. A 4- or 5-year follow-up of outcomes for men and women following a

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15-week behavioral weight-loss program showed an overall trend for all groups to regain the weight lost. Only 3% maintained their weight loss. Consistent sex differences were found, with the women who had early-onset obesity maintaining loss the best (Kramer, Jeffery, Forster, & Snell, 1989). Another study found that women maintained weight loss better than men (Forster & Jeffery, 1986). This study also found sex differences in the number of weight-loss attempts (more for women); women reported feeling less confident in being able to control their eating, and they had lower selfesteem than men. Women reported they ate more in response to mood states and periods of low self-esteem, whereas men reported overeating in social situations. These findings suggest that sex-specific weight-loss programs should be employed. Women need more help with mood-related eating problems, whereas men need more help with eating in social situations.

CONCLUSIONS At present, we have little understanding of how different foods and different environmental situations affect normal eating behavior in males and females. Although males and females have different eating habits, with males eating more and females often eating smaller amounts at a slow rate to present a feminine image, such sex differences are often not examined in studies of eating behavior. There is a large body of evidence (see review by Striegel-Moore et al., 1986) that sociocultural, psychological, and biological factors can affect not only eating habits, but also body-image satisfaction and dieting behavior, and that these factors have different effects in males and females. Increased knowledge of normal behavior in males and females would lead to a better understanding of the antecedents of disordered eating behaviors — such as anorexia nervosa, bulimia nervosa, and obesity, which have different prevalence rates in the sexes —and would be extremely important in designing gender-appropriate treatments.

ACKNOWLEDGMENTS This work was supported by National Institute of Diabetes and Digestive and Kidney Diseases Grants DK40968 and DK39177 to Barbara J. Rolls.

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