5
Nutritional Concerns of Military Women

The Military Recommended Dietary Allowances (MRDAs) (AR 40-25, 1985), based on the 1980 edition of the Recommended Dietary Allowances (RDAs) (NRC, 1980), dictate the nutrient content and density of operational (field) rations and military dining hall menus. Recent attempts to revise the MRDAs were considered in a 1995 letter report by the Committee on Military Nutrition Research (CMNR) (IOM, 1995a). The MRDAs, like the RDAs, feature nutrition allowances designated specifically for women, but unlike the RDAs, these allowances are not age specific. Because the RDAs themselves also are currently under revision, the Committee on Body Composition, Nutrition, and Health (BCNH committee) believed that it was beyond the scope of this report and its collective expertise to evaluate the adequacy of the MRDAs for active-duty women at this time. Instead, this chapter focuses on several nutritional issues deemed by the committee to be of particular concern for active-duty women.

Consequences Of Chronic Dieting

In the previous chapter, evidence was presented that suggests a high percentage of active-duty military women chronically or repeatedly engage in dieting practices that may put their health at risk. The long-term health consequences of one aspect of this chronic food restriction,



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--> 5 Nutritional Concerns of Military Women The Military Recommended Dietary Allowances (MRDAs) (AR 40-25, 1985), based on the 1980 edition of the Recommended Dietary Allowances (RDAs) (NRC, 1980), dictate the nutrient content and density of operational (field) rations and military dining hall menus. Recent attempts to revise the MRDAs were considered in a 1995 letter report by the Committee on Military Nutrition Research (CMNR) (IOM, 1995a). The MRDAs, like the RDAs, feature nutrition allowances designated specifically for women, but unlike the RDAs, these allowances are not age specific. Because the RDAs themselves also are currently under revision, the Committee on Body Composition, Nutrition, and Health (BCNH committee) believed that it was beyond the scope of this report and its collective expertise to evaluate the adequacy of the MRDAs for active-duty women at this time. Instead, this chapter focuses on several nutritional issues deemed by the committee to be of particular concern for active-duty women. Consequences Of Chronic Dieting In the previous chapter, evidence was presented that suggests a high percentage of active-duty military women chronically or repeatedly engage in dieting practices that may put their health at risk. The long-term health consequences of one aspect of this chronic food restriction,

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--> weight cycling, were discussed and appear to be insignificant. In this section, several major health implications of chronic restrictive dieting are described. Energy Deficit and Cognitive Function Military readiness may be affected by chronic energy deficit. The original studies of semi-starvation by Keys et al. (1950) demonstrated that long-term food restriction is associated with reduced heart rate, lethargy, depression, and irritability. While the subjects in these studies complained of changes in intellectual functions such as concentration, judgment, and memory, the testing protocol used in these studies did not demonstrate a serious impairment. More recent research has focused on the impact of chronic dieting on cognitive functions. Chronic dieting may have a negative impact on cognitive functions, such as attention, vigilance, and reaction time, that may be important in a military setting. For example, evidence suggests that restrained eating (that is, conscious control of eating in relation to concerns about weight) may result in preoccupation with food and eating, binge eating once food is available, and increased emotional responsiveness (Polivy, 1996). Chronic dieters may be more distractible than nondieters and are less able to concentrate on rote tasks in the face of noise or other environmental distractions (Polivy, 1996); they may also display poorer vigilance, poorer immediate memory, and have slower reaction times (Green and Rogers, 1995; Green et al., 1994; Kretsch et al., 1997). Short-term dieting has been reported to decrease plasma tryptophan and brain serotonin function (as indicated by an increase in tryptophan-stimulated prolactin secretion) and to increase irritability and sleep disturbance in women (Anderson et al., 1990; Goodwin et al., 1987a, b). Studies on the psychological effects of chronic dieting have produced mixed results. For example, some studies have reported depression, anxiety, decreased self-esteem, and other negative psychological outcomes among dieters (Brownell and Rodin, 1994; French and Jeffery, 1994; Polivy, 1996). However, other studies have reported positive psychological findings, such as improved mood and decreased depression (French and Jeffery, 1994). The positive findings may be associated with use of behavior therapy when dieting, which may counteract some of the negative psychological impacts of chronic dieting (French and Jeffery, 1994). As mentioned previously, dieting behavior may also be a risk factor for the development of eating disorders, but its causal strength is unclear (French and Jeffery, 1994). Female Athlete Triad Chronic restrictive dieting and high levels of exercise have been associated with amenorrhea and a related increase in the risk of osteoporosis and stress fracture of the lower extremities and pelvis in a syndrome known as the female athlete triad (ACSM, 1997; Bennell et al., 1995). A considerable amount of research has been devoted to pinpointing the nutritional factor(s) responsible for, as well as the mechanisms involved in, female athlete triad. In a review that focused on women who participate in competitive athletics, the frequency of stress fractures was reported to be four times higher in women who report irregular menses than in eumenorrheic

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--> women (Lloyd, 1993). Several questions must be answered with regard to the female athlete triad. These include how diet and or exercise contribute to menstrual status, and whether it is menstrual status alone or in combination with nutritional status that increases the risk for osteoporosis and stress fracture. In the review by Lloyd, menstrual history is shown to be an independent risk factor for musculoskeletal injury. Considerable research has sought to elucidate the factors that contribute to amenorrhea in the athlete. Energy Intake The question of whether reduced energy intake or negative energy balance is responsible for the hormonal imbalance associated with the female athlete triad has been investigated using models of self-imposed energy restriction (dieting), eating restraint, and controlled studies of energy intake and expenditure. The effect of a brief period of imposed energy restriction on sex hormone and menstrual status was examined by Kurzer and Calloway (1986). Following 1 month on a diet containing recommended levels of all nutrients and providing 40 kcal/kg body weight (during which time weight remained constant), the energy intake of six normal weight women was decreased by 59 percent (with intake of all other nutrients remaining adequate) for 1 month. During the latter period, weight loss ranged from 7 to 15 lb (3.2 to 6.7 kg), and the two leanest women (who also lost the most weight) became anovulatory and amenorrheic. Rock and coworkers studied 76 college women (BMI 19–25), none of whom had ever been diagnosed with an eating disorder. In addition to performing clinical assessments of hormonal status, the researchers administered a survey intended to assess dieting behavior. (This survey had been developed by the investigators and was based on the Diagnostic and Statistical Manual of Mental Disorders, 4th edition [DSM-IV] criteria for eating disorders.) Based on the results of the survey, women were divided into three groups: nondieters, intense dieters, and at-risk (pathological) dieters; intense and pathological dieting were not defined in the report, but pathological dieting was associated with significantly lower fat intake and a somewhat lower total energy intake as indicated by the food diaries the women were instructed to keep for two 3-d periods. During the 1-mo study, women who ovulated reported significantly higher intakes of energy, carbohydrate, and fat, and higher percentages of fat in their diets than women who did not ovulate or appeared to be at increased risk for amenorrhea (as determined by serum concentrations of estradiol and progesterone, and by menstrual history). The authors concluded that dieting practices that would not be considered diagnostic of a true eating disorder could increase the risk for amenorrhea. However, the validity of these findings is difficult to assess because the dieters and nondieters did not differ at the beginning of the study with respect to body mass index (MBI) or percent body fat. The authors did not indicate whether the women who were identified as dieters lost weight, and the survey of dieting practices had not been validated against other instruments. In a study comparing young women (average age 26.2 ± 0.8 years) with irregular menses (oligomenorrhea) whose scores on the Eating Attitudes Test (Garner et al., 1982) indicated the presence of an eating disorder (n = 13) with those whose test scores indicated no eating disorder (n = 61), Dumoulin and coworkers (1996) found no difference between groups with respect to BMI, estradiol, dehydroepiandrosterone (DHEA), and several measures of luteinizing hormone

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--> (LH) and follicle-stimulating hormone (FSH); however, those diagnosed with eating disorders had increased variability in their LH values and elevated testosterone levels. Among women with no evidence of eating disorders, LH variability was negatively associated with energy and carbohydrate intake (as measured using food diaries and interviews). Eating restraint, defined as the conscious limitation of food intake to prevent weight gain, and assessed using a diagnostic instrument such as the 3-Factor Eating Questionnaire (Stunkard and Messick, 1985), has been associated with alterations in the menstrual cycle such as shortened luteal phase, decreased progesterone surge, and failure to ovulate (Barr et al., 1994a; Schweiger et al., 1992). In the study by Schweiger and coworkers (1992), restrained eaters (n = 9) reported a 23 percent lower energy intake than unrestrained eaters (n = 13); however, in the study by Barr and coworkers (1994a), no significant difference was observed between high- (n = 9) and low- (n = 9) restraint eaters with respect to self-reported intake of carbohydrate, fat, or total energy; physical activity levels; BMI; or body fat. These authors theorize that self-reported food intake may be inaccurate, and that restrained eating behavior may influence menstrual status by acting as a stressor rather than by inducing negative energy balance. Loucks and coworkers (Loucks, 1996) have shown that the decreased bone density in amenorrheic athletes is associated with decreased production of estrogen and suppression of pulsatile secretion of LH. Studies examining the effect of exercise and energy intake on athletic amenorrhea by Loucks and coworkers have shown that self-reported energy intake in both amenorrheic and eumenorrheic female athletes was lower than would be predicted by their physical activity level (as measured by activity monitors) and maintenance of body weight. Subsequent research by this group has shown that the decrease in LH pulsatility observed in amenorrheic athletes is due not to exercise per se but to the balance between energy intake and expenditure. A role for carbohydrate availability has also been hypothesized by this group (Loucks et al., 1996). Dietary Fiber Research performed and reviewed by Lloyd (1993) at a 1991 conference compared the diets of oligomenorrheic and eumenorrheic athletes and sedentary women (28 subjects in total). This study found that the athletes consumed significantly more energy, carbohydrates, calcium and phosphorous than nonathletes, while the only difference in dietary patterns between the oligomenorrheic and eumenorrheic athletes was that the oligomenorrheic athletes consumed approximately twice as much dietary fiber as their eumenorrheic counterparts. Lloyd proposed that the increase in dietary fiber was responsible for the hypoestrogenism and bone loss in this group. Decreased bone density was observed in both mildly and severely oligomenorrheic women. Interpretation of the results is confounded by small sample size as well as greater intake of calcium and phosphorous and lower body fat in the athletes compared with the sedentary women (see below). A similar pattern of decreased bone density and increased dietary fiber has been observed in vegetarian women. These associations suggest but do not prove that a relationship among energy balance, fiber intake, and body composition may influence menstrual status, bone density, and risk for musculoskeletal injuries. Lloyd has proposed two possible mechanisms to explain the bone loss. One possibility is that calcium bioavailability is significantly reduced in a

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--> high-fiber diet. The other possibility is that dietary fiber may have an effect on estrogen metabolism and subsequent excretion, which would indirectly influence bone loss. A number of studies have shown an inverse correlation between dietary fiber intake and plasma estradiol and/or estrone (Bagga et al., 1995; Boyd et al., 1997; Goldin et al., 1994; Kaneda et al., 1997; Rose et al., 1991, 1997), while others have observed no effect of dietary fiber by itself (Dorgan et al., 1996). Other reported effects of dietary fiber include decreases in estrone sulfate, testosterone, androstenedione, and sex hormone binding globulin (Goldin et al., 1994). Unfortunately, most studies that have shown a relationship between fiber and gonadal steroids have not ruled out the possibility that the observed effect is due to a decrease in fat or total energy intake. Two studies were conducted in such a way that the results may be interpreted to suggest that dietary fiber may exert an effect on gonadal steroids independent of the effects of other dietary factors. Goldin and coworkers (1994) placed 48 premenopausal women (27.1 ± 4.3 years) on a controlled 40 percent fat/12 g fiber/d diet for 4 weeks; subsequently, the subjects were placed on one of seven isocaloric experimental diets (20, 25, or 40% fat; 12 or 40 g fiber/d) for 8 weeks. The decreases in serum total estradiol and sex hormone binding globulin were primarily attributable to increased fiber. Rose and coworkers (1991) divided premenopausal women into three groups, each of which was asked to consume daily supplements of wheat, corn, or oat bran (15 g/d) for 2 months. An association was observed between supplemental wheat bran and decreases in estradiol and estrone with no decrease in dietary fat or energy from the previous diet. Dietary Fat Significant reductions in dietary fat have been associated with increases in the length of the follicular phase of the menstrual cycle (Reichman et al., 1992) and serum FSH levels; and decreases in serum estrone, estradiol (Bagga et al., 1995; Boyd et al., 1997; Goldin et al., 1994), estrone sulfate, testosterone, androstenedione, DHEA, sex hormone binding globulin (Goldin et al., 1994), and progesterone (Boyd et al., 1997). The real effects of very low fat diets are difficult to determine because, as described earlier, these diets tend to be high in fiber and may be low in total energy; in addition, compliance with very low fat diets is difficult to determine and may be poor. The 2-mo feeding study by Goldin and coworkers (1994) described above, in which the effects of dietary fat could be separated from those of fiber, showed that fat intake was the primary contributor to the decrease in free estradiol, androstenedione, and testosterone. A long-term randomized control trial to examine the effects of a low fat, high carbohydrate diet on breast cancer risk among premenopausal women has shown that after 2 years, intervention subjects, whose food records show that they are consuming an average of 20 percent fat and 60 percent carbohydrate, have significantly decreased estradiol and progesterone and increased FSH compared to controls (Boyd et al., 1997). In a study of 90 premenopausal women by Dorgan and coworkers (1996), when the researchers examined 7-d food records and controlled for energy intake, the ratio of polyunsaturated to saturated fat in the diet appeared to be inversely related to serum estradiol and estrone levels during the luteal phase of the menstrual cycle, while total fat in the diet appeared unrelated to hormone levels.

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--> The question must be asked whether the hormonal changes brought about by low fat or high fiber diets can be responsible for changes in menstrual status or ovulatory function. While a number of studies on the impact of low fat or high fiber diets on endocrine function have observed changes in the length of the luteal or follicular phase of the cycle, most have not addressed the question of whether ovulatory function changes. However, the study by Bagga and coworkers (1995), in which 12 healthy eumenorrheic women adhered to a 10 percent fat diet (containing 25–35 g/d fiber and approximately 1,500 kcal/d energy) for 2 months, observed no change in ovulatory function despite significant decreases in serum estrone and estradiol and a significant decrease in body weight and body fat. Other Nutrients Several groups of investigators have attempted to examine the influence of vegetarian diets on menstrual status, on the assumption that a vegetarian diet may be lower in saturated fat and/or higher in fiber than an omnivorous diet. A 6-mo study of 23 vegetarian and 22 nonvegetarian eumenorrheic women (20–40 years of age) assessed eating behavior by the 3-Factor Eating Questionnaire and dietary intake by 3-d food records (Barr et al., 1994b). This study found that although vegetarian women tended to have lower BMI and body fat, and their menstrual cycles had longer luteal phases, these women actually showed less dietary restraint than the nonvegetarian women and had fewer anovulatory cycles. Although there were no differences between restrained and nonrestrained eaters with respect to energy, macronutrient, or fiber intake, eating restraint tendencies (as assessed by the survey) were associated with ovulatory dysfunction. No significant differences were observed between lacto-ovo-vegetarians (who consumed dairy products and eggs) and vegans (who consumed no animal products). The potential association of a vegetarian diet with amenorrhea is further complicated by the results of a recent population-based study comparing vegetarian adolescents (12–20 years of age) with a comparison group of nonvegetarians; this study found that vegetarian adolescents (81% of whom were female) were almost twice as likely to report frequent dieting, four times as likely to report intentional vomiting, and eight times as likely to report laxative abuse as nonvegetarians would (Neumark-Sztainer et al., 1997). Thus, at least among adolescents, vegetarianism may be a risk factor for disordered eating. Inge and coworkers (1993) performed dietary assessments of a group of female ballet dancers and found that the calcium intake of amenorrheic dancers was significantly less than the RDA, while intakes of iron and zinc were adequate and significantly greater than the intake of these nutrients by enmenorrheic athletes. Role of Body Fat The possibility that menstrual status is influenced by percent body fat or fat distribution has been of considerable interest. While several investigators have found significant associations between percent body fat and amenorrhea among athletes or dancers (Crist and Hill, 1990; Frisch et al., 1992, 1993; To et al., 1997), others have found only weak or no associations (Estok et al., 1991; Hetland et al., 1995). A 1991 review of the studies to date concluded that while body fat

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--> may show some correlation with menstrual status, there is no indication that body fat, per se, plays a role in regulating ovulatory function. Instead, the authors concluded, body fat appears to be an index of overall nutritional status and energy balance (Bronson and Manning, 1991). Finally, a recent study of 100 young women suffering from anorexia nervosa concluded that resumption of menses following commencement of treatment was associated with achievement of a critical weight but not with body fat (Golden et al., 1997). Risk For Musculoskeletal Injury And Female Athlete Triad in Active-Duty Military Women As reviewed earlier, numerous studies have shown that women in basic combat training (BCT) are at a greater risk for musculoskeletal injuries, including stress fracture, than are men in BCT. Risk factors identified by Jones and coworkers (1993) include aerobic fitness and higher and lower than average BMI, but not gender. Friedl (1996) reported that women with amenorrhea were at increased risk for stress fracture. The prevalence of female athlete triad among active-duty military women has not been well studied. Dietary restriction of the severity associated with anorexia would be expected to be underreported by military women. However, research showing that brief periods of energy imbalance may increase the risk for amenorrhea suggests that active-duty military women may be at increased risk for amenorrhea simply as a result of chronic dieting and exercise. The role of nutrition as a risk factor in the stress fractures reported in women in BCT has not been examined. Nutrient Adequacy of Weight Loss Diets Dieters who participate in organized weight loss programs typically select foods that provide a nutritionally balanced diet but that are restricted in energy content (French and Jeffery, 1994; Neumark-Sztainer et al., 1996). There are few data on the adequacy of nutrient intake of dieters who diet on their own (French and Jeffery, 1994). In the development of the Food Guide Pyramid (USDA, 1992; Welsh et al., 1992) nutritionally adequate diets for gender/age groups over the age of 2 years were designed for energy intakes that ranged from 1,300 to 3,000 kcal. If a person selects foods in their lowest-fat form, with no added sugars, from the nutrient-bearing food groups and does not select from the fats, oils, and sweets group, the range in the number of servings from the Food Guide Pyramid would provide 1,220 to 1,990 kcal (Welsh et al., 1992). Thus, it is possible to have a nutritionally adequate diet that is relatively restricted in energy content. The role of such diets in promoting weight loss will depend on the balance of energy intake with expenditure. While the report by Welsh and coworkers describes the feasibility of designing nutritionally adequate, low-calorie diets, Nicholas and Dwyer (1986) analyzed the nutritional profile of 15 popular, weight-reducing diets and found that none of the diets, including those that recommended supplements, met the RDA for all vitamins and minerals. The nutrients that were most often inadequate were zinc, iron, folate, and B6. However, as long as dieters focus on reducing high-fat (calorically dense) foods, it is possible to meet nutrient requirements.

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--> Summary Chronic dieting is associated with a number of health and behavioral consequences; these include a negative impact on cognitive function as determined by assessment of reaction time, vigilance, and short-term memory. Common dieting practices that would not be considered severe enough to constitute an eating disorder and may not result in significant changes in body weight or composition appear to increase the risk for amenorrhea and stress fracture, health problems previously believed to be associated only with more extreme energy depletion in the syndrome known as female athlete triad. Research has sought to elucidate the factors that contribute to the syndrome of female athlete triad, the result of a suppression of pulsatile pituitary secretion of LH, but its etiology remains unclear. Several possible dietary variables have been investigated including energy intake, the balance between energy intake and utilization, carbohydrate availability, dietary fiber, dietary fat, the ratio of fiber to fat, protein, and cholesterol intake. To date, it is not clear which of these factors or combination of factors are the most important. Evidence in support of a role for total body fat or body fat distribution in controlling menstrual function is contradictory and suggests that other factors, such as energy balance, may play a greater role. It is not possible at present to assess the impact of dieting practices among active-duty military women on their nutritional status. The prevalence of female athlete triad among these women and its possible contribution to the high level of stress fracture observed among women in BCT is also unknown. Influence Of Military Operational Rations And Dining Hall Meals On The Nutritional Status Of Active-Duty Military Women Results Of Military Nutrition Studies Studies of selected groups of military women have found intakes of several nutrients to be below the MRDA for those nutrients. King (1996) and King et al. (1993) reported the results of several studies showing that women in the field consuming operational rations had intakes of energy and several nutrients (iron, calcium, and folate) that were less than in garrison and below the MRDAs. The nutrient density of military rations may contribute to inadequate intakes if active-duty women are not able to consume the entire ration without feeling full or gaining weight, which is often the case since the nutrient density is based on intake of a level of energy that is considered adequate for the average male soldier (approximately 3,600 kcal/d). A study of U.S. Military Academy, West Point, cadets in 1990 showed that a significant percentage of female cadets were at increased risk for iron deficiency anemia, although the number of women taking supplemental iron as well as the occurrence of a recent blood drive confounded interpretation of the results (Friedl et al., 1990). Analysis of food intake for 1 week revealed that female cadets were at risk for consuming low levels of folate (Klicka et al., 1993), although folate status was not analyzed in the 1991 study reported earlier. A 1993 study of food consumed in garrison by 49 women in BCT at Fort Jackson, South Carolina (King et al., 1994) found that, contrary to previous expectations, the nutrient intake of women in garrison was not substantially greater than that in the field. Again, because the menu

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--> offered in the dining hall was the same for men and women, nutrient analysis revealed that levels of vitamin B6, folic acid, calcium, magnesium, iron, and zinc would be significantly below the MRDA for women who consumed the amount of energy required to maintain their weight. That is, the nutrient density of this menu did not provide the optimum amounts of these nutrients, according to the nutrient density standards of the MRDAs. Mean intakes as a percentage of the MRDA were: vitamin B6 (76%), folic acid (65%), calcium (73%), magnesium (89%), iron (90%), and zinc (73%). These intakes, if accurate, indicate that, on average, at least two-thirds of the MRDA was consumed. Evidence from this same study also revealed that recent efforts to lower the fat content of dining hall menus (Department of the Army Military Nutrition Initiatives) has resulted in a significant decrease, from 1988 to 1993, in the percentage of women deriving 35 percent or more of their calories from fat, although the average fat intake for all participants did not decrease and is still approximately 33 percent (Westphal et al., 1995), above the 30 percent level recommended by the Nutrition and Your Health: Dietary Guidelines for Americans (USDA/DHHS, 1995). Total energy intakes were approximately the same from the 1988 study to the 1993 study. The nutritional and health status of the same BCT class of women studied by King and coworkers (1994) was reported by Westphal and coworkers in 1995. Status of calcium, magnesium, the B vitamins, and vitamins C and A (as determined by standard clinical methods) improved or did not change during the course of BCT. The prevalence of iron deficiency (as defined by a serum ferritin level of less than 20 µg/liter) increased from 15 percent of the trainees at baseline to 19 percent at completion, which is significantly higher than in a comparable civilian population (Westphal et al., 1995). However, some questions were raised by the CMNR regarding the clinical parameters used to define iron status in the Westphal study (IOM, 1995b). Anemia (as defined by a hemoglobin of less than 12 g/dl) was associated with poorer performance on the physical fitness test, although there was improvement in endurance in all subjects over the course of BCT. Serum folate levels were in the low-normal range and declined throughout the course of BCT. Finally, although serum calcium status appeared to be normal, the incidence of stress fracture among these and other women in BCT and the low calcium intake provided by the dining hall menu suggested that calcium balance may be of concern, although it is unlikely that brief decreases in calcium balance are associated with stress fracture (Personal communication, B. Specker, South Dakota State University, Brookings, 1998). Finally, because national surveys have reported that many civilian women in the United States do not consume adequate amounts of some nutrients, such as iron and calcium (NHANES III, Third Report on Nutrition Monitoring in the U.S.), there is reason to believe that even active-duty women who consume the majority of their meals in nonmilitary locations are at risk for inadequate intakes of these nutrients. Friedl and coworkers (1990) found in their study of U.S. Military Academy cadets that nutritional status was positively associated with the percentage of meals consumed in the dining hall. The majority of active-duty military women reside in barracks (quarters) or in private homes and consume the majority of their meals, not in military dining halls or as operational rations, but in the same settings as civilian women. No studies could be identified that have evaluated the nutritional status of active-duty women in situations other than BCT and brief field-training exercises. Thus, it is impossible at this time to evaluate the nutritional status of most active-duty women.

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--> A large-scale survey of nutrition knowledge and attitudes and food intake practices among active-duty Army personnel worldwide, The Army Food and Nutrition Survey 1996, was recently completed. Of the approximately 3,000 respondents to this survey, nearly 500 were women. Data gathered in the survey show, for example, that women averaged approximately 2.9 servings per day of vegetables and 2.5 servings of fruit (in comparison, the 1991 Five a Day for Better Health Survey showed that 49% of women consumed 2.5 to < 5 servings of fruits and vegetables per day [DHHS, 1991]). Active-duty Army women also consumed an average of 1.8 servings of meat, 2.3 servings of dairy foods, 0.2 servings of grains, 0.6 servings of (breakfast) cereals, and 0.2 servings of legumes per day. The data appeared to suggest that women who held meal cards (ate the majority of their meals in the military dining facility) had a greater intake of fruits, vegetables, dairy products, grains, meat, and french fries per day than those who ate their meals off-post (Warber et al., in preparation). Data on the associations among individual dieting behavior, nutrition knowledge and attitudes, and food intake were not available as of yet from the survey. In addition, no information was available from the survey on the actual nutrient intakes of the respondents or on their nutrient status, and because the survey was anonymous, the results could not be linked to medical records. Under another Defense Women's Health Research Program grant, James P. DeLany and coworkers are in the process of evaluating energy utilization by female Army personnel in a variety of work situations (IOM, 1996a). Complete assessment of the energy requirements of the average woman soldier will have to await analysis of the results of this and other studies. Impact of Altered Nutrient Status The data on nutrient status of active-duty women suggest that in both field and garrison dining situations, women are at increased risk for inadequate iron, calcium, and folic acid intake. The potential consequences to performance and health of deficiencies in these nutrients as well as in protein will be reviewed briefly. Iron A prolonged inadequate dietary intake of iron can lead to iron deficiency, which may have adverse physical and cognitive effects independent of those associated with restricted energy intake. These effects include depressed immune function, impaired cognitive development, behavioral disturbances (pica), impaired body temperature regulation, and reduced exercise and work performance (Beard et al., 1996). The negative effects have been associated primarily with iron deficiency anemia; the impact of iron deficiency without anemia is more subtle and difficult to detect (Beard et al., 1996). Physical performance and iron. Iron deficiency anemia is responsible for a significant decrease in work capacity, particularly when hemoglobin concentrations fall to less than 10 g/dl. The decrease in maximum oxygen consumption (VO2max) is related to the decrease in the capacity of blood to transport oxygen. The effect of iron deficiency without anemia on work capacity

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--> was thought to be inconsequential; however, recent data (Zhu and Haas, 1997) show that VO2max and endurance in iron-depleted women without anemia are reduced and related to serum ferritin concentration (the index of iron storage) but not to hemoglobin. Cognitive function and iron. Most studies on iron status and cognition to date have focused on infants and schoolchildren and have reported a negative impact of iron deficiency on behavior and development. It is unclear whether these deficits are reversible with iron treatment (IOM, 1993). Only a few studies have examined the impact of iron deficiency on cognitive function in adolescents and adults. Iron-deficient adolescent and young adult women who received iron treatment had better cognitive function than controls in several studies (Ballin et al., 1992; Bruner et al., 1996; Groner et al., 1986; Webb and Oski, 1973). However, one cross-sectional study of iron status in young adults reported no relationship between low iron stores and cognitive function, (Fordy and Benton, 1994). A study is in progress by Sandstead (1996) and coworkers to examine the role of iron supplementation and iron deficiency in the cognitive function of active-duty military women. More data in this area are needed, but the potential negative cognitive effects of iron deficiency and anemia, coupled with its negative physical effects, underscore the need to ensure that military women consume adequate amounts of iron to ensure readiness. Impact of exercise on iron status. Most studies examining iron status and exercise have focused on highly trained athletes and have reported that iron losses are higher in endurance-trained athletes than in the reference groups (Weaver and Rajaram, 1992). A few studies report on the impact of exercise on the iron status of sedentary women as they first begin fitness exercise. Most of these studies found an initial decline in iron status (beyond that associated with hemodilution) among women at the start of the exercise program (Hegenauer et al., 1983; Kilbom, 1971; Lyle et al., 1992; Rajaram et al., 1995; Rowland et al., 1988). Data are conflicting on whether adaptation of iron status to fitness exercise occurs without increased iron intake via supplements or meat (Blum et al., 1986; Lyle et al., 1992; Rajaram et al., 1995). Athletes with iron deficiency severe enough to result in anemia improved their work performance with increased iron intake through food or supplements (Karamizrak et al., 1996), but the impact of increased iron intake on performance in nonanemic, iron-depleted athletes is less certain (Clarkson and Haymes, 1995; Karamizrak et al., 1996). Some preliminary evidence suggests that iron supplementation of nonanemic women can improve aerobic capacity (Personal communication, J. Haas, Cornell University, Ithaca, N.Y., 1997). Calcium A prolonged inadequate intake of calcium may have negative effects on skeletal health. An adequate calcium intake is important for attaining peak bone mass during adolescence and early adulthood and maintaining skeletal mass after that time (Heaney, 1996). Military women have the advantage of an active lifestyle. A recent review of 17 studies with mostly peri- and postmenopausal women concluded that a positive effect of physical activity

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--> on bone density appeared to exist only at calcium intakes greater than 1,000 mg/d and that the beneficial effect of high calcium intake only appears to be present when there is physical activity (Specker, 1996). It is not clear whether this association is also true in younger women. The MRDA for calcium is set at 800 to 1,200 mg to reflect the range of ages of active-duty women. In comparison, the adequate intakes (AIs) reported by the Institute of Medicine for women aged 19 to 50 years are 1,000 mg/d, with AIs for girls aged 14 to 18 years set at 1,300 mg/d (IOM, 1997). While it appears that the MRDA level of calcium intake should be adequate to meet the needs of most military women, many women relying on operational rations as well as those consuming their meals in military dining facilities are at risk for inadequate calcium intakes unless they choose their foods carefully. Folate Randomized control trials have shown clear evidence that periconceptional supplementation with folic acid can lower the risk of neural tube defects in the offspring of women who have had previous pregnancies with neural tube defects. These data have led to the recommendation that (1) women of childbearing age take 400 µg/d of supplemental folic acid and (2) that food processors add folic acid to some staple food ingredients (grains). Although the MRDA for folic acid is 400 µg/d, which is the amount supplied by operational rations, the results of food intake surveys have shown that many active-duty women do not consume a full day's rations or dining hall meals. In view of these practices and the relatively high incidence of unplanned pregnancy among active-duty women (Thomas and Edwards, 1989), additional measures are necessary to ensure that these women receive adequate folate. Protein The tenth edition of the RDAs states, ''There is little evidence that muscular activity increases the need for protein, except for the small amount required for the development of muscles during physical conditioning … In view of the margin of safety in the RDA, no increment is added for work or training" (NRC, 1989, pp. 70–71). However, in a recent review, Lemon (1997) summarizes pertinent studies, and he suggests that the RDA for protein for active individuals may be 1.5 to 2.2 times the current RDA; that is, he concludes that the RDA for endurance athletes should be about 1.2 to 1.4 g protein/kg/d and the RDA for strength athletes should be 1.7 to 1.8 g protein/kg/d. He notes that with sufficient energy intake, these intakes can be obtained without difficulty from diets that provide 10 percent energy as protein (Lemon, 1997). The MRDA for protein for women is 80 g/d, which for women in the weight range 46 to 63 kg allows 1.74 to 1.27 g/kg/d, respectively. This intake is higher than the RDA for protein and appears to be more than adequate for women engaging in moderate activity. The issue of protein requirements and intakes of both male and female military personnel will be considered in depth in a forthcoming report by the BCNH committee and the CMNR.

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--> Energy MRDA allowances for energy reflect moderate activity levels. Military occupational specialties requiring greater strength do not necessarily have higher energy requirements, and the frequency and duration of strength-requiring activities will influence energy expenditure. Fluids Research has shown that dehydration resulting from insufficient fluid intake and exposure to environmental extremes can impair physiological function and may affect cognitive function by impairing balance (IOM, 1996b). Results of a survey conducted by the Air Force (Voge and King, 1996) suggest that active-duty women in positions that involve air flight may restrict fluid intake to avoid the need to eliminate the fluids while in flight. In addition, anecdotal evidence presented at the 1996 workshop held in Irvine, California, suggested that women in field operations restrict fluid when private facilities are unavailable or difficult to reach. In response to a recommendation that appeared in a CMNR report on fluid intake (IOM, 1994), a water doctrine was established by the Army emphasizing the need to enforce adequate fluid intake. Summary Only a small number of military nutrition studies have included women, and of those that have, nearly all have studied dietary intake or nutrient status of soldiers in brief field training sessions, cadets enrolled at military academies, or new recruits in BCT. Operational rations and dining hall menus are formulated based on the MRDAs for male soldiers. Thus, nutrient analysis has shown that the density of several key nutrients is low compared to nutrient density standards of the MRDAs; that is, women who limit their food consumption in these situations to balance energy intake and expenditure may experience inadequate intakes of calcium, iron, and folate unless careful choices are made. Nevertheless, intake analysis in a study of women in BCT indicated that, on average, at least two-thirds of the MRDAs of these nutrients were consumed. Except for folate and iron, nutrient status improved or did not change during the course of the training period; the prevalence of iron deficiency increased from 15 percent at baseline to 19 percent at completion. No studies could be identified that assessed the nutritional status of active-duty women in situations other than training and brief field exercises. The majority of active-duty women reside in military or private quarters and consume the majority of their meals in the same settings as civilian women, and while it is impossible at this time to evaluate their nutritional status, there is little reason to believe that it is significantly different than that of civilian women of comparable age, socioeconomic status, educational achievement, and activity level. National surveys have suggested that many civilian women consume diets that place them at risk for low calcium and iron intake. A large-scale survey of nutritional knowledge and attitudes and food intake practices of active-duty female Army personnel has recently been completed. It is not clear whether the information gathered will permit an assessment of the actual nutritional status of active-duty women in garrison.

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--> Studies in the civilian sector on the impact of prolonged inadequate intake of iron have shown effects on physical and cognitive task performance and depressed immune function. In addition, strenuous exercise increases iron losses. Inadequate calcium intake during young adulthood may inhibit attainment of peak bone mass and later maintenance of skeletal mass. Physical activity exerts a positive effect on bone density in peri- and postmenopausal women when daily calcium intake is adequate; it is unknown if this association is true for younger women. Periconceptional folate supplementation may decrease the risk of neural tube defects among the offspring of women who have given birth to an infant with a neural tube defect. This has led to the recommendation that all women of childbearing age take 400 µg/d of supplemental folic acid. Although recent recommendations for higher intakes of protein among physically active individuals are controversial, the MRDA for protein appears to be more than adequate. This issue will be considered further in an upcoming report by the CMNR. MRDA allowances for energy reflect moderate activity levels. Although little attention has been given to active-duty women of very low BMI, the additional energy sources available in operational rations and supplemental ration components allow for increased needs. Finally, evidence suggests that increased emphasis must be placed on adequate fluid consumption, particularly among women whose military occupational specialties involve airborne operations. Concluding Remarks The average active-duty woman appears to face the same nutritional risks as her civilian counterparts. Military service creates the added pressure for many women of needing to practice weight control, although like their civilian counterparts, the number of active-duty women who perceive themselves as overweight and who are restricting intake exceeds the number who in fact need to lose weight. The only information currently available on the nutritional status of active-duty women is based on studies of women who are in temporary training situations and suggests that their intake of calcium, iron, and folic acid during these periods may be inadequate. Research suggests that this may have immediate negative consequences for their ability to perform both physically and cognitively. The long-term consequences, if any, of these periods of inadequate intake as well as the effects of more prolonged subsistence on rations during deployment are unknown. In addition, the effects of exposure to the environmental extremes encountered during deployment on active-duty women's health and nutritional status have not been explored. References ACSM (American College of Sports Medicine). 1997. ACSM position stand. The female athlete triad. Med. Sci. Sports. Exerc. 29:i–ix. Anderson, I.M., M. Parry-Billings, E.A. Newsholme, C.G. Fairburn, and P.J. Cowen. 1990. Dieting reduces plasma tryptophan and alters brain 5-HT function in women. Psychol. Med. 20:785–791. AR (Army Regulation) 40-25. 1985. See U.S. Departments of the Army, the Navy, and the Air Force, 1985. Bagga, D., J.M. Ashley, S.P. Geffrey, H.J. Wang, R.J. Barnard, S. Korenman, and D. Heber. 1995. Effects of a very low fat, high fiber diet on serum hormones and menstrual function. Implications for breast cancer prevention. Cancer 76:2491–2496.

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