Discrepancies between energy intake and expenditure in physically active women

Free-living competitive racewalkers and runners with energy availability estimates of <35 kcal·kg fat-free mass-1·day-1 exhibit peak serum progesterone concentrations indicative of ovulatory disturbances: a pilot study

Introduction

The release of luteinising hormone (LH) before ovulation is disrupted during a state of low energy availability (EA). However, it remains unknown whether a threshold EA exists in athletic populations to trigger ovulatory disturbances (anovulation and luteal phase deficiency) as indicated by peak/mid-luteal serum progesterone concentration (Pk-PRG) during the menstrual cycle.

Methods

We assessed EA and Pk-PRG in 15 menstrual cycles to investigate the relationship between EA and Pk-PRG in free-living, competitive (trained-elite) Guatemalan racewalkers (n = 8) and runners (n = 7) [aged: 20 (14-41) years; post-menarche: 5 (2-26) years; height: 1.53 ± 0.09 m; mass: 49 ± 6 kg (41 ± 5 kg fat-free mass "FFM")]. EA was estimated over 7 consecutive days within the follicular phase using food, training, and physical activity diaries. A fasted blood sample was collected during the Pk-PRG period, 6-8 days after the LH peak, but before the final 2 days of each cycle. Serum progesterone concentration was quantified using electrochemiluminescence immunoassay.

Results

Participants that reported an EA of <35 kcal·kg FFM-1·day-1 (n = 7) exhibited ovulatory disturbances (Pk-PRG ≤9.40 ng·mL-1). Athletes with EA ≥36 kcal·kg FFM-1·day-1 (n = 8) recorded "normal"/"potentially fertile" cycles (Pk-PRG >9.40 ng·mL-1), except for a single racewalker with the lowest reported protein intake (1.1 g·kg body mass-1·day-1). EA was positively associated with Pk-PRG [r(9) = 0.79, 95% confidence interval (CI): 0.37-0.94; p = 0.003; 1 - β = 0.99] after excluding participants (n = 4) that likely under-reported/reduced their dietary intake.

Conclusions

The result from the linear regression analysis suggests that an EA ≥ 36 kcal·kg FFM-1·day-1 is required to achieve "normal ovulation." The threshold EA associated with ovulatory disturbances in athletes and non-invasive means of monitoring the ovulatory status warrant further research.

Energy deficiency, menstrual disorders, and low bone mineral density in female athletes: a systematic review

PURPOSE

Low energy availability (LEA) may lead to menstrual disorders and low bone mineral density, predisposing to the female athlete triad. The primary aim of the present review was to systematically investigate the impact of chronic strenuous exercise on the energy status of professional female athletes compared to sedentary, recreationally active controls as concerns their menstrual status and bone mineral density (BMD). A secondary aim was evaluation of the combined prevalence of the components of the female athlete triad in athletes as compared to non-athletes.

METHODS

A systematic review was conducted from 2007 to February 2018. The inclusion and exclusion criteria of the studies were established in advance of the literature search according to the clinical inquiry and the study design.

RESULTS

Four studies were included in this systematic review. The female athlete triad was more prevalent in professional athletes compared to non-athletes. The same results were obtained for both LEA and menstrual disorders. However, BMD and Z-scores showed high heterogeneity among the studies.

CONCLUSION

Both female athletes and non-athletes are prone to LEA and subsequent menstrual disorders and low BMD or osteoporosis. Future studies are needed to examine energy availability in elite female athletes as well as in non-athletes.

Exertional sodium loss does not increase immediate salt appetite or dietary sodium intake in athletes

We tested whether salt preference increases immediately after exertion-induced Na⁺ loss in sweat, and whether this may generalise to an increase in habitual dietary Na⁺ intake. For the first aim, trained athletes (n = 20) exercised in 2 ambient temperatures and sweat Na⁺ loss related to immediate salt preference assessed by taste, intake and psychophysical tests. For the second aim, we compared dietary and urinary Na⁺, and salt preference, seasoning and hedonics in the athletes and sedentary men (n = 20). No relationship was found between sodium loss during exercise and immediate preference for salt or psychophysical responses, and no differences in comparison to sedentary men. However, athlete diet had fewer foods (29.4 ± 1.5 vs 37.8 ± 1.9, p < 0.001), less seasoning (19 vs 32. p = 0.011) and more athletes reported dietary limitations (31 vs 11, p < 0.05), although nutrient content did not differ. Together these might suggest athlete adherence to a healthy diet at the expense of variety and flavour and a dissociation between dietary reports and intake. Athletes, more than controls, liked foods rich in energy and K⁺ suggesting compensatory-driven hedonics, although overall their intake did not differ. The findings are consistent with the absence of a salt appetite responding to Na⁺ loss in humans, and specifically that trained athletes do not increase their preference for salt in immediate response to exertion-induced Na⁺ loss and are not at risk for increased dietary Na⁺ compared to sedentary men.

Accuracy of predictive equations for resting metabolic rate in Korean athletic and non-athletic adolescents

BACKGROUND/OBJECTIVES

Athletes generally desire changes in body composition in order to enhance their athletic performance. Often, athletes will practice chronic energy restrictions to attain body composition changes, altering their energy needs. Prediction of resting metabolic rates (RMR) is important in helping to determine an athlete's energy expenditure. This study compared measured RMR of athletic and non-athletic adolescents with predicted RMR from commonly used prediction equations to identify the most accurate equation applicable for adolescent athletes.

SUBJECTS/METHODS

A total of 50 athletes (mean age of 16.6 ± 1.0 years, 30 males and 20 females) and 50 non-athletes (mean age of 16.5 ± 0.5 years, 30 males and 20 females) were enrolled in the study. The RMR of subjects was measured using indirect calorimetry. The accuracy of 11 RMR prediction equations was evaluated for bias, Pearson's correlation coefficient, and Bland-Altman analysis.

RESULTS

Until more accurate prediction equations are developed, our findings recommend using the formulas by Cunningham (-29.8 kcal/day, limits of agreement -318.7 and +259.1 kcal/day) and Park (-0.842 kcal/day, limits of agreement -198.9 and +196.9 kcal/day) for prediction of RMR when studying male adolescent athletes. Among the new prediction formulas reviewed, the formula included in the fat-free mass as a variable [RMR = 730.4 + 15 × fat-free mass] is paramount when examining athletes.

CONCLUSIONS

The RMR prediction equation developed in this study is better in assessing the resting metabolic rate of Korean athletic adolescents.

Does increased exercise or physical activity alter ad-libitum daily energy intake or macronutrient composition in healthy adults? A systematic review

BACKGROUND

The magnitude of the negative energy balance induced by exercise may be reduced due to compensatory increases in energy intake.

OBJECTIVE

TO ADDRESS THE QUESTION: Does increased exercise or physical activity alter ad-libitum daily energy intake or macronutrient composition in healthy adults?

DATA SOURCES

PubMed and Embase were searched (January 1990-January 2013) for studies that presented data on energy and/or macronutrient intake by level of exercise, physical activity or change in response to exercise. Ninety-nine articles (103 studies) were included.

STUDY ELIGIBILITY CRITERIA

Primary source articles published in English in peer-reviewed journals. Articles that presented data on energy and/or macronutrient intake by level of exercise or physical activity or changes in energy or macronutrient intake in response to acute exercise or exercise training in healthy (non-athlete) adults (mean age 18-64 years).

STUDY APPRAISAL AND SYNTHESIS METHODS

Articles were grouped by study design: cross-sectional, acute/short term, non-randomized, and randomized trials. Considerable heterogeneity existed within study groups for several important study parameters, therefore a meta-analysis was considered inappropriate. Results were synthesized and presented by study design.

RESULTS

No effect of physical activity, exercise or exercise training on energy intake was shown in 59% of cross-sectional studies (n = 17), 69% of acute (n = 40), 50% of short-term (n = 10), 92% of non-randomized (n = 12) and 75% of randomized trials (n = 24). Ninety-four percent of acute, 57% of short-term, 100% of non-randomized and 74% of randomized trials found no effect of exercise on macronutrient intake. Forty-six percent of cross-sectional trials found lower fat intake with increased physical activity.

LIMITATIONS

The literature is limited by the lack of adequately powered trials of sufficient duration, which have prescribed and measured exercise energy expenditure, or employed adequate assessment methods for energy and macronutrient intake.

CONCLUSIONS

We found no consistent evidence that increased physical activity or exercise effects energy or macronutrient intake.

Obstacles in the optimization of bone health outcomes in the female athlete triad

Maintaining low body weight for the sake of performance and aesthetic purposes is a common feature among young girls and women who exercise on a regular basis, including elite, college and high-school athletes, members of fitness centres, and recreational exercisers. High energy expenditure without adequate compensation in energy intake leads to an energy deficiency, which may ultimately affect reproductive function and bone health. The combination of low energy availability, menstrual disturbances and low bone mineral density is referred to as the 'female athlete triad'. Not all athletes seek medical assistance in response to the absence of menstruation for 3 or more months as some believe that long-term amenorrhoea is not harmful. Indeed, many women may not seek medical attention until they sustain a stress fracture. This review investigates current issues, controversies and strategies in the clinical management of bone health concerns related to the female athlete triad. Current recommendations focus on either increasing energy intake or decreasing energy expenditure, as this approach remains the most efficient strategy to prevent further bone health complications. However, convincing the athlete to increase energy availability can be extremely challenging. Oral contraceptive therapy seems to be a common strategy chosen by many physicians to address bone health issues in young women with amenorrhoea, although there is little evidence that this strategy improves bone mineral density in this population. Assessment of bone health itself is difficult due to the limitations of dual-energy X-ray absorptiometry (DXA) to estimate bone strength. Understanding how bone strength is affected by low energy availability, weight gain and resumption of menses requires further investigations using 3-dimensional bone imaging techniques in order to improve the clinical management of the female athlete triad.

Prevalence of the female athlete triad in high school athletes and sedentary students

OBJECTIVE

To determine the prevalence of the female athlete triad (low energy availability, menstrual dysfunction, and low bone mineral density) in high school varsity athletes in a variety of sports compared with sedentary students/control subjects.

DESIGN

Prospective study.

SETTING

Academic medical center in the Midwest.

PARTICIPANTS

Eighty varsity athletes and 80 sedentary students/control subjects volunteered for this study.

INTERVENTION

Subjects completed questionnaires, had their blood drawn, and underwent bone mineral density testing.

MAIN OUTCOME MEASURES

Each participant completed screening questionnaires assessing eating behavior, menstrual status, and physical activity. Each subject completed a 3-day food diary. Serum hormonal, thyroid-stimulating hormone, and prolactin levels were determined. Bone mineral density and body composition were measured by dual-energy x-ray absorptiometry.

RESULTS

Low energy availability was present in similar numbers of athletes (36%) and sedentary/control subjects (39%; P = 0.74). Athletes had more menstrual abnormalities (54%) compared with sedentary students/control subjects (21%) (P < 0.001). Dual-energy x-ray absorptiometry revealed that 16% of the athletes and 30% of the sedentary/control subjects had low bone mineral density (P = 0.03). Risk factors for reduced bone mineral density include sedentary control student, low body mass index, and increased caffeine consumption.

CONCLUSIONS

A substantial number of high school athletes (78%) and a surprising number of sedentary students (65%) have 1 or more components of the triad. Given the high prevalence of triad characteristics in both groups, education in the formative elementary school years has the potential to prevent several of the components in both groups, therefore improving health and averting long-term complications.

The female athlete triad: components, nutrition issues, and health consequences

This paper, which was part of the International Association of Athletics Federations (IAAF) 2007 Nutritional Consensus Conference, briefly reviews the components of the female athlete triad (Triad): energy availability, menstrual status, and bone health. Each component of the Triad spans a continuum from health to disease, and female athletes can have symptoms related to each component of the Triad to different degrees. Low energy availability is the primary factor that impairs menstrual dysfunction and bone health in the Triad. We discuss nutritional issues associated with the Triad, focusing on intakes of macronutrients needed for good health, and stress fractures, the most common injury associated with the Triad. Finally, we briefly discuss screening and treatment for the Triad and the occurrence of the Triad in men.

The Effects of Exercise on Food Intake and Body Fatness: A Summary of Published Studies

Exercise has well-recognized health benefits, including reduction in risk factors for cardiovascular disease and type 2 diabetes. However, the extent to which exercise influences energy regulation and facilitates a reduction in body fat is less clear. This review summarizes published studies on the effects of different amounts of exercise on body fatness, energy intake, and food preferences in humans. The results show consistent effects of exercise on body fatness in the absence of prescribed dietary change, with a progressive loss of body fat associated with higher exercise energy expenditures in both men and women. In part, these effects appear to be mediated by a spontaneous reduction in hunger associated with participation in exercise. Insufficient data are available on whether there are changes in food preferences and taste perception that influence energy balance through macronutrient selection, so further studies in this area are needed.

Energy availability and infertility

PURPOSE OF REVIEW

To relate recent research on the dependence of reproductive function on energy availability in women to recent clinical experience in the treatment of anorexia nervosa.

RECENT FINDINGS

The dependence of luteinizing hormone pulsatility on energy availability declines during adolescence, but the responses of leptin and other peripheral signals of energy deficiency do not. This finding suggests that central sensitivity to these signals may decline during adolescence. Energy availability may be inadequate in anorexia nervosa patients whose menstrual cycles are not restored after weight recovery.

SUMMARY

Energy availability is a theoretically satisfying and operationally controllable concept for understanding, investigating, and managing the energy dependence of reproductive function. Nutritional intervention to restore menstrual cycles in anorexia nervosa patients might be more successful if it was guided by energy availability and ovarian volume rather than energy intake and body weight.

The Female Athlete Triad

The female athlete triad (Triad) refers to the interrelationships among energy availability, menstrual function, and bone mineral density, which may have clinical manifestations including eating disorders, functional hypothalamic amenorrhea, and osteoporosis. With proper nutrition, these same relationships promote robust health. Athletes are distributed along a spectrum between health and disease, and those at the pathological end may not exhibit all these clinical conditions simultaneously. Energy availability is defined as dietary energy intake minus exercise energy expenditure. Low energy availability appears to be the factor that impairs reproductive and skeletal health in the Triad, and it may be inadvertent, intentional, or psychopathological. Most effects appear to occur below an energy availability of 30 kcal.kg(-1) of fat-free mass per day. Restrictive eating behaviors practiced by girls and women in sports or physical activities that emphasize leanness are of special concern. For prevention and early intervention, education of athletes, parents, coaches, trainers, judges, and administrators is a priority. Athletes should be assessed for the Triad at the preparticipation physical and/or annual health screening exam, and whenever an athlete presents with any of the Triad's clinical conditions. Sport administrators should also consider rule changes to discourage unhealthy weight loss practices. A multidisciplinary treatment team should include a physician or other health-care professional, a registered dietitian, and, for athletes with eating disorders, a mental health practitioner. Additional valuable team members may include a certified athletic trainer, an exercise physiologist, and the athlete's coach, parents and other family members. The first aim of treatment for any Triad component is to increase energy availability by increasing energy intake and/or reducing exercise energy expenditure. Nutrition counseling and monitoring are sufficient interventions for many athletes, but eating disorders warrant psychotherapy. Athletes with eating disorders should be required to meet established criteria to continue exercising, and their training and competition may need to be modified. No pharmacological agent adequately restores bone loss or corrects metabolic abnormalities that impair health and performance in athletes with functional hypothalamic amenorrhea.

Energy balance and body composition in sports and exercise

Many athletes, especially female athletes and participants in endurance and aesthetic sports and sports with weight classes, are chronically energy deficient. This energy deficiency impairs performance, growth and health. Reproductive disorders in female athletes are caused by low energy availability (defined as dietary energy intake minus exercise energy expenditure), perhaps specifically by low carbohydrate availability, and not by the stress of exercise. These reproductive disorders can be prevented or reversed by dietary supplementation in compensation for exercise energy expenditure without any moderation of the exercise regimen. Energy balance is not the objective of athletic training. To maximize performance, athletes strive to achieve an optimum sport-specific body size, body composition and mix of energy stores. To pursue these objectives, athletes need to manage fat, protein and carbohydrate balances separately, but it is impractical for athletes to monitor these balances directly, and appetite is not a reliable indicator of their energy and macronutrient needs. To guide their progress, athletes need to eat by discipline and to monitor specific, reliable and practical biomarkers of their objectives. Skinfolds and urinary ketones may be the best biomarkers of fat stores and carbohydrate deficiency, respectively. Research is needed to identify and validate these and other markers.

Hematologic Disorders in the Athlete

Optimal athletic performance depends on proper function of many organs, including the blood. This is underscored by the focus of endurance athletes on increased hemoglobin through training at altitude or exogenous erythropoietin. Several other aspects of the hematologic system can also affect or be influenced by physical activity. In this article, the authors briefly discuss inherited abnormalities of the blood that can manifest themselves in athletes. We then discuss the effects of exercise on the blood, and acquired abnormalities of blood cells or coagulation parameters that occur in athletes, and that can influence performance or cause other symptoms.

Micronutrient requirements of physically active women: what can we learn from iron?

The health benefits of physical activity are well established and there is increasing recognition of the importance of fitness as a key modulator of chronic disease. The impact of physical activity on micronutrient requirements is a topic of tremendous interest to the lay public, but the interest is in sharp contrast to data from well-designed studies. Research in this area is poorly controlled for nutritional status of the participants, standardized exercise protocols, markers and cutoff points for measurement of micronutrient status, and variability in subject characteristics. The micronutrient status of women in the general population is of concern, but it is not clear that physical activity increases the requirement of most micronutrients. When dietary intake is adequate, the results of most studies are either equivocal or show no benefit to performance of supplementation. In the few instances where exercise does appear to increase an individual's requirement, the increase can be obtained within the additional calories required for energy balance. In the absence of consistent data, micronutrient supplementation is often indiscriminate without regard to nutrient status. Because iron is such a key nutrient for physical activity, and the status in women is often compromised, it serves as a useful example of how current research limits the ability to make recommendations regarding the impact of exercise on micronutrients requirements in women. With the recent recognition of the importance of physical activity to the prevention and treatment of chronic diseases through the life span, more attention should be focused on the impact of exercise on micronutrient requirements, especially in the context of weight loss regimens.

Human plasma ghrelin levels increase during a one-year exercise program

Weight loss resulting from decreased caloric intake raises levels of the orexigenic hormone, ghrelin. Because ingested nutrients suppress ghrelin, increased ghrelin levels in hypophagic weight loss may result from decreased inhibitory input by ingested food, rather than from lost weight. We assessed whether ghrelin levels increase in response to exercise-induced weight loss without decreased caloric intake. We randomized 173 sedentary, overweight, postmenopausal women to an aerobic exercise intervention or stretching control group. At baseline, 3 months, and 12 months, we measured body weight and composition, food intake, cardiopulmonary fitness (maximal oxygen consumption), leptin, insulin, and ghrelin. Complete data were available for 168 women (97%) at 12 months. Exercisers lost 1.4 +/- 0.4 kg (P < 0.05 compared with baseline; P = 0.01 compared with stretchers) and manifested a significant, progressive increase in ghrelin levels, whereas neither measure changed among stretchers. Ghrelin increased 18% in exercisers who lost more than 3 kg (P < 0.001). There was no change in caloric intake in either group and no effect on ghrelin of exercise per se independent of its impact on body weight. In summary, ghrelin levels increase with weight loss achieved without reduced food intake, consistent with a role for ghrelin in the adaptive response constraining weight loss and, thus, in long-term body weight regulation.

Non-exercise activity thermogenesis (NEAT)

Non-exercise activity thermogenesis (NEAT) is the energy expended for everything we do that is not sleeping, eating or sports-like exercise. NEAT can be measured by one of two approaches. The first approach is to measure or estimate total NEAT. Here, total daily energy expenditure is measured and from it, the basal metabolic rate-plus-thermic effect of food is subtracted. The second approach is the factoral approach whereby the components of NEAT are quantified and total NEAT calculated by summing these components. The amount of NEAT that humans perform represents the product of the amount and types of physical activities and the thermogenic cost of each activity. The factors that impact a human's NEAT are readily divisible in biological factors such as weight, gender and body composition and environmental factors such occupation or dwelling within a "concrete jungle." The impact of these factors combined explains the substantial variance in human NEAT. The variability in NEAT might be viewed as random and unprogrammed but human data contradict this thesis. It appears that changes in NEAT accompany experimentally induced changes in energy balance and may be important in the physiology of weight change. NEAT and a sedentary lifestyle may thus be of profound importance in obesity.

Influência do treinamento aeróbio e anaeróbio na massa de gordura corporal de adolescentes obesos

O objetivo deste estudo foi verificar as influências do exercício aeróbio e anaeróbio na composição corporal de adolescentes obesos do sexo masculino. A amostra foi constituída de 28 adolescentes com idades entre 15 e 19 anos, que apresentavam obesidade grave. Os voluntários foram distribuídos aleatoriamente em três grupos: grupo I: exercício anaeróbio; grupo II: exercício aeróbio; e grupo III: controle. O grupo I realizou treinamento intervalado em cicloergômetro que consistiu de 12 "tiros" de 30" com máxima força e velocidade, pedalando com carga alta (0,8% do massa corporal x 25 watts) e recuperação ativa de 3'; o grupo II realizou treinamento aeróbio em cicloergômetro pedalando com carga relativa ao limiar ventilatório por 50 minutos. Já o terceiro grupo funcionou como controle, sem atividade física. Todos os grupos tiveram orientação nutricional e o período de intervenção foi de 12 semanas (três meses). Os voluntários realizaram densitometria óssea com análise da composição corporal (DEXA) e avaliações médicas e de aptidão física. Quando comparados os períodos inicial e final de intervenção foram observadas reduções nas variáveis massa corporal, IMC, na massa de gordura corporal total e de membros inferiores e na percentagem de gordura corporal de tronco nos grupos de exercício. Diferenças foram observadas entre os grupos I e III para os deltas percentuais de massa de gordura corporal total e de membros inferiores e na percentagem de gordura de membros inferiores. Os dados sugerem que o exercício físico, tanto aeróbio como anaeróbio, aliado à orientação nutricional, promove maior redução ponderal, quando comparado com a orientação nutricional somente, e que, neste estudo, o exercício anaeróbio foi mais eficiente para promover a diminuição da gordura corporal e da percentagem de gordura e o exercício aeróbio foi mais eficaz no sentido de preservar e/ou aumentar a massa magra e a massa livre de gordura.

Nonexercise activity thermogenesis (NEAT): environment and biology

Nonexercise activity thermogenesis (NEAT) is the energy expended for everything that is not sleeping, eating, or sports-like exercise. It includes the energy expended walking to work, typing, performing yard work, undertaking agricultural tasks, and fidgeting. NEAT can be measured by one of two approaches. The first is to measure or estimate total NEAT. Here, total daily energy expenditure is measured, and from it "basal metabolic rate-plus-thermic effect of food" is subtracted. The second is the factoral approach, whereby the components of NEAT are quantified, and total NEAT is calculated by summing these components. The amount of NEAT that humans perform represents the product of the amount and types of physical activities and the thermogenic cost of each activity. The factors that impact a human's NEAT are readily divisible into environmental factors, such as occupation or dwelling within a "concrete jungle," and biological factors such as weight, gender, and body composition. The combined impact of these factors explains the substantial variance in human NEAT. The variability in NEAT might be viewed as random, but human and animal data contradict this. It appears that changes in NEAT subtly accompany experimentally induced changes in energy balance and are important in the physiology of weight change. Inadequate modulation of NEAT plus a sedentary lifestyle may thus be important in obesity. It then becomes intriguing to dissect mechanistic studies that delineate how NEAT is regulated into neural, peripheral, and humoral factors. A scheme is described in this review in which NEAT corresponds to a carefully regulated "tank" of physical activity that is crucial for weight control.

Non-exercise activity thermogenesis

Non-exercise activity thermogenesis (NEAT) is the energy expended that is not from sleeping, eating or sports-like exercise. It ranges from the energy expended walking to work, typing, performing yard work, undertaking agricultural tasks and fidgeting. NEAT can be measured by one of two approaches. The first approach is to measure or estimate total NEAT. Here, total daily energy expenditure is measured and from it is subtracted BMR + thermic effect of food. The second is the factoral approach whereby the components of NEAT are quantified and total NEAT calculated by summing these components. The amount of NEAT that human subjects perform represents the product of the amount and types of physical activities and the thermogenic cost of each activity. The factors that affect the NEAT of a human subject are readily divisible into biological factors, such as weight, gender and body composition, and environmental factors, such as occupation or dwelling within a 'concrete jungle'. The combined impact of these factors explains the substantial variance in human NEAT. The variability in NEAT might be viewed as random but human data contradict this perception. It appears that changes in NEAT subtly accompany experimentally-induced changes in energy balance and are important in the physiology of weight change. NEAT and sedentariness may thus be important in obesity. It then becomes intriguing to dissect mechanistic studies that delineate how NEAT is regulated by neural, peripheral and humoral factors. NEAT may be a carefully-regulated 'tank' of physical activity that is crucial for weight control.

Diurnal profiles of testosterone and pituitary hormones suggest different mechanisms for menstrual disturbances in endurance athletes

The aim of this study was to evaluate the diurnal pattern of testosterone and pituitary hormones in endurance female athletes with different types of menstrual disorder. Age- and body mass index-matched groups of endurance athletes with amenorrhea (n = 10) and oligomenorrhea (n = 6), regularly cycling athletes (n = 8), and sedentary controls (n = 8) were compared with respect to 24-h hormonal profiles of testosterone, LH, prolactin (PRL), GH, insulin, IGF binding protein 1 (IGFBP-1), and cortisol. The 24-h hormone profiles in amenorrheic athletes were characterized by decreased LH pulsatility and peak amplitude of PRL and increased baseline levels of GH and cortisol. However, oligomenorrheic athletes displayed a significantly different pattern with higher diurnal testosterone secretion than all other groups. Furthermore, LH, PRL, GH, and cortisol secretions were comparable with regularly menstruating subjects. In the combined group of athletes with menstrual disturbances, diurnal secretions of testosterone, LH, and PRL were positively, whereas cortisol was negatively correlated with the number of menstruations the last year. Although this could be explained by a gradual inhibition of the hypothalamic-pituitary-gonadal axis, our results indicate that the symptoms of amenorrhea and oligomenorrhea may reflect two hormonally distinct conditions. Thus, amenorrheic athletes displayed a hormonal pattern in agreement with hypothalamic inhibition due to energy deficiency, whereas oligomenorrheic athletes demonstrated increased diurnal secretion of testosterone, suggesting a different mechanism, e.g. essential hyperandrogenism.

Methodology of dietary assessment in athletes: concepts and pitfalls

PURPOSE OF REVIEW

Evaluation of an athlete's diet is important in both clinical practice and research. The main purpose of this review is to provide health professionals with guidance regarding the special issues that are likely to be encountered when assessing the dietary intake of sportspersons.

RECENT FINDINGS

A number of methods may be used for the dietary assessment of individuals and/or groups of athletes, including retrospective (diet recall, food-frequency questionnaire, and diet history) and prospective (diet record, duplicate portion) techniques. A 3-4-day estimated diet record is the most widely used approach, but collection of single or multiple diet recalls is also common. Care must be taken, however, to ensure that days of diet monitoring accurately reflect usual food consumption during the period of interest. Under-reporting of habitual energy intake is widespread among athletes, and its magnitude should be carefully addressed when interpreting the results of dietary assessment. Other issues, specifically related to sportspersons, that are often neglected include adequacy of standard portion sizes, frequency of snacking, fluid intake, supplement use, weight-control practices, and seasonality of sport activities and food consumption.

SUMMARY

There are subtle methodological differences in the dietary assessment of athletes and non-athletes, which, when taken into consideration, may substantially increase the quality of intake data and optimise the outcome of dietary intervention.

Non-exercise activity thermogenesis (NEAT)

Non-exercise activity thermogenesis (NEAT) is the energy expended for everything we do that is not sleeping, eating or sports-like exercise. It ranges from the energy expended walking to work, typing, performing yard work, undertaking agricultural tasks and fidgeting. Even trivial physical activities increase metabolic rate substantially and it is the cumulative impact of a multitude of exothermic actions that culminate in an individual's daily NEAT. It is, therefore, not surprising that NEAT explains a vast majority of an individual's non-resting energy needs. Epidemiological studies highlight the importance of culture in promoting and quashing NEAT. Agricultural and manual workers have high NEAT, whereas wealth and industrialization appear to decrease NEAT. Physiological studies demonstrate, intriguingly, that NEAT is modulated with changes in energy balance; NEAT increases with overfeeding and decreases with underfeeding. Thus, NEAT could be a critical component in how we maintain our body weight and/or develop obesity or lose weight. The mechanism that regulates NEAT is unknown. However, hypothalamic factors have been identified that specifically and directly increase NEAT in animals. By understanding how NEAT is regulated we may come to appreciate that spontaneous physical activity is not spontaneous at all but carefully programmed.

Validity of methods for analyzing urinary steroid data to detect ovulation in athletes

PURPOSE

The purpose of this study was to determine whether the accuracy of ovulation detection algorithms is compromised when applied to menstrual cycles exhibiting subclinical hormonal abnormalities, which are particularly prevalent in female athletes.

METHODS

The validity of five ovulation detection algorithms was compared between 25 regularly exercising women and 15 sedentary controls. Subjects collected daily urine samples for an entire menstrual cycle for analysis of estrone-3-glucuronide (E1G), pregnanediol-3-glucuronide (PDG), and luteinizing hormone (LH). The algorithms were applied to determine their sensitivity (% of true ovulatory cycles), specificity (% of true anovulatory cycles), and the deviation from the reference day of ovulation (difference scores).

RESULTS

The sensitivity was > 80% in all algorithms except Baird's E1G/PDG ratio algorithm (74%) and Kassam's PDG ratio algorithm (78%). All algorithms, except Kassam's PDG ratio algorithm (80%), were found to exhibit specificities < 70%. Baird's E1G/PDG ratio algorithm was the most accurate in estimating the day of ovulation by deviating only -0.2 +/- 0.3 d from the reference day in the exercising female cycles and -0.5 +/- 0.3 d in the controls. No statistical differences in the sensitivities of the algorithms were found between the exercising and control cycles. When comparing the deviation from the reference day of ovulation between subject groups, no statistical difference was found.

CONCLUSION

The algorithms display similar validity in determining the presence and day of ovulation between subject groups, and thus may be applied to cycles exhibiting subclinical hormonal abnormalities as commonly observed in exercising women.

Sub-clinical eating disorder characteristics among male and female triathletes

The characteristics of sub-clinical eating disorders were assessed in 583 male and female triathletes. We found that 28% of the females and 11% of the males scored below the mid-point of the range for the Eating Attitude Test-26 (EAT-26) construct Preoccupation with Food and Weight, and respectively 39% and 23% scored below the mid-point of the range for the construct Calorie Control. All of the subjects indicated dissatisfaction with their actual body mass index (BMI). The study participants revealed attempts to reduce body weight by means of energy restriction, severe limitation of food groups and excessive exercise, in addition to controlling their food intake on the basis of strict dietary rules. The triathlon seems to be a sport that is susceptible to a higher prevalence of disordered eating. Further studies are needed to investigate its real prevalence and the factors contributing to it.

Effect of dietary intake on immune function in athletes

Athletes are exposed to acute and chronic stress that may lead to suppression of the immune system and increased oxidative species generation. In addition, the tendency to consume fewer calories than expended and to avoid fats may further compromise the immune system and antioxidant mechanisms. The exercise stress is proportional to the intensity and duration of the exercise, relative to the maximal capacity of the athlete. Muscle glycogen depletion compromises exercise performance and it also increases the stress. Glycogen stores can be protected by increased fat oxidation (glycogen sparing). The diets of athletes should be balanced so that total caloric intake equals expenditure, and so that the carbohydrates and fats utilised in exercise are replenished. Many athletes do not meet these criteria and have compromised glycogen or fat stores, have deficits in essential fats, and do not take in sufficient micronutrients to support exercise performance, immune competence and antioxidant defence. Either overtraining or under nutrition may lead to an increased risk of infections. Exercise stress leads to a proportional increase in stress hormone levels and concomitant changes in several aspects of immunity, including the following: high cortisol; neutrophilia; lymphopenia; decreases in granulocyte oxidative burst, nasal mucociliary clearance, natural killer cell activity, lymphocyte proliferation, the delayed-type sensitivity response, the production of cytokines in response to mitogens, and nasal and salivary immunoglobulin A levels; blunted major histocompatibility complex II expression in macrophages; and increases in blood granulocyte and monocyte phagocytosis, and pro- and anti-inflammatory cytokines. In addition to providing fuel for exercise, glycolysis, glutaminlysis, fat oxidation and protein degradation participate in metabolism and synthesis of the immune components. Compromising, or overusing, any of these components may lead to immunosuppression. In some cases, supplementation with micronutrients may facilitate the immune system and compensate for deficits in essential nutrients. In summary, athletes should eat adequate calories and nutrients to balance expenditure of all nutrients. Dietary insufficiencies should be compensated for by supplementation with nutrients, with care not to over compensate. By following these rules, and regulating training to avoid overtraining, the immune system can be maintained to minimise the risk of upper respiratory tract infections.

Using an exercise-based instrument to detect signs of an eating disorder

The study employed an innovative exercise-based instrument to identify individuals at risk for eating disorder (ED). The Exercise Orientation Questionnaire (EOQ), a reliable and valid instrument, was used to compare 80 ED patients, 74 obese patients, 99 elite runners, and 214 controls from a previous study. Runners resembled ED patients in scoring high on total EOQ and exercise intensity but differed in that the athletes scored low on self-loathing (SLSS), a sub-scale of the EOQ. SLSS scores clearly distinguished clinical (ED, obese) from non-clinical groups, while other sub-scales (self-control, weight loss, and identity) did not. The study suggests that it is feasible to detect ED risk through assessment of exercise attitudes and behaviors. The SLSS subscale of the EOQ can differentiate clinical from non-clinical groups and anorexic patients from healthy individuals with body mass index within the anorexic range. The SLSS could provide a theoretical bridge between compulsive athleticism and ED.

Dietary intakes of elite female athletes in Greece

BACKGROUND

Although there is a great interest in sports in Greece, there are very few data regarding dietary intakes and habits of Greek elite female athletes. The present study assesses the dietary intakes and the energy balance of elite female athletes of four different sports (volleyball, middle distance running, ballet dancing, and swimming) and a non-athletic control group.

METHODS

Data were collected over two seasons, the training and the competitive, using 7-day weighed dietary records. Energy expenditure was calculated from 7-day activity records. Anthropometric measurements were also taken for all athletes.

RESULTS

Athletes and controls had similar BMI values. Per cent body fat was lower for athletes compared with controls. Between sports, middle distance runners had the lowest per cent body fat. No significant differences were found between mean energy intake of athletes and controls. Mean energy intake was found lower than calculated energy expenditure, for all four teams. Macronutrient and micronutrient intakes of the athletes were not statistically different from those of the non-athletic control group. Mean micronutrient intakes were found above the recommended values with the exception of iron. Both athletes and controls had a high intake of vitamin C that is a characteristic of the population of the Mediterranean countries.

CONCLUSIONS

Energy intakes varied between sports and between athletes of the same sport. Calculated energy expenditure was higher from the reported energy intake for most athletes. Athletes with the lowest energy intakes reported menstrual abnormalities.

Effects of habitual physical activity on the resting metabolic rates and body compositions of women aged 35 to 50 years

OBJECTIVE

To examine the effect habitual physical activity has on resting metabolic rate (RMR) and body composition (fat-free mass[FFM], fat mass, and percent body fat) in active compared to sedentary adult women.

DESIGN

RMR was measured (by indirect calorimetry) twice after a 12-hour fast at the same point of the menstrual cycle and 48 hours after exercise. FFM, fat mass and percent body fat were measured using whole body air displacement plethysmography. Energy intake and expenditure were determined using 7-day weighed-food records and activity logs.

SUBJECTS

Healthy, weight-stable premenopausal women aged 35 to 50 years classified as either active (approximately 9 hours per week of physical activity for 10 or more years) (n= 18) or sedentary (approximately 1 hour per week of physical activity) (n= 14).

STATISTICAL ANALYSES

Analysis of covariance was used to investigate differences in mean RMR (kcal/day) between the groups adjusted for FFM, and independent t tests were used to determine differences in demographic, energy expenditure, and diet variables.

RESULTS

Percent body fat and fat mass were lower (P<.0005) and RMR (adjusted for FFM) was significantly higher in the active women (P=.045) compared with sedentary controls. In the active and sedentary groups respectively, mean adjusted RMR was 1,510 kcal/day and 1,443 kcal/day, body fat was 18.9% and 28.8%, and fat mass was 11.1 kg and 18.8 kg. Groups were similar in body mass, FFM, body mass index, and age. Mean energy balance appeared to be more negative in the active group (P=.0059) due to significantly higher mean self-reported energy expenditures (P=.0001) and similar mean self-reported energy intakes (P=.52) compared with sedentary controls. These data indicate that active women who participate in habitual physical activity can maintain lower body fat and a higher RMR than sedentary controls with similar body mass, FFM, and body mass index.

APPLICATIONS/CONCLUSIONS

This research supports and emphasizes the benefits of habitual physical activity in maintaining RMR and lower body fat levels in middle-aged women.

Relationship between self-reported food and fluid intake and menstrual disturbance in female recreational runners

A 1 year prospective study was conducted in France in 1993-1994 to examine the extent of menstrual cycle impairment in a sample of recreational French runners, and to relate the extent of impairment to dietary characteristics. The runners provided 7-day weighed food and fluid intake at intervals of 3 months during the year, as well as full details of their menstrual cycles and training schedules. The food survey commenced with 34 runners and 21 provided information on all four occasions. About 6% of the women, at any session, unrealistically report their dietary intakes. However, there was no evidence of any relationship between extent of under-reporting and menstrual status. The sample was divided into three menstrual cycle groups of eumenorrhoeic, irregular and amenorrhoeic (including oligomenorrhoeic). No significant differences in mean energy intake, carbohydrate, fat and protein intakes were found between groups. However, there were very marked differences in fluid and fibre intake, with amenorrhoeic and oligomenorrhoeic runners consuming about twice the mean daily fluid intake of eumenorrhoeic or irregularly menstruating groups.

The validity of self-reported energy intake as determined using the doubly labelled water technique

In the 1980s the development of the doubly labelled water (DLW) technique made it possible to determine the validity of dietary assessment methods using external, independent markers of intake in free-living populations. Since then, the accuracy of self-reported energy intake (EI) has been questioned on a number of occasions as under-reporting has been found to be prevalent in many different populations. This paper is a review of investigations using the DLW technique in conjunction with self-reported EI measures in groups including adults, children and adolescents, obese persons, athletes, military personnel and trekking explorers. In studies where a person other than the subject is responsible for recording dietary intake, such as parents of young children, EI generally corresponds to DLW determined energy expenditure. However, in instances where the subjects themselves report their intake, EI is generally under-reported when compared with energy expenditure. It was originally believed that this phenomenon of under-reporting was linked to increased adiposity and body size, however, it is now apparent that other factors, such as dietary restraint and socio-economic status, are also involved. This paper therefore aims to present a more comprehensive picture of under-reporting by tying in the findings of many DLW studies with other studies focusing particularly on the characteristics and mechanisms for under-reporting. Awareness of these characteristics and mechanisms will enable researchers to obtain more accurate self-reports of EI using all dietary recording techniques.

Relationship between energy deficits and body composition in elite female gymnasts and runners

PURPOSE

The purpose of this study was to evaluate energy balance and body composition in 42 gymnasts (mean age = 15.5 yr) and 20 runners (mean age = 26.6 yr), all of whom were on national teams or were nationally ranked.

METHODS

Athletes were assessed for body composition using DEXA and skinfolds, and energy balance was determined with a Computerized Time-Line Energy Analysis (CTLEA) procedure.

RESULTS

Results from the CTLEA were assessed as the number of within-day energy deficits (largest and frequency) and within-day energy surpluses (largest and frequency). There was a significant difference (P = 0.000) in the mean number of hourly energy deficits > 300 kcal experienced by gymnasts (9.45 +/- 6.00) and runners (3.70 +/- 5.34). There was also a significant difference (P = 0.001) in the mean number of hourly energy surpluses > 300 kcal experienced by gymnasts (1.40 +/- 3.04) and runners (6.20 +/- 5.50). The mean largest daily energy deficit was 743 (+/- 392) kcal for gymnasts and 435 (+/- 340) kcal for runners. The mean largest daily energy surplus was 239 (+/- 219) kcal for gymnasts, and 536 (+/- 340) kcal for runners. There was a significant relationship between the number of daily energy deficits > 300 kcal and DEXA-derived body fat percent for gymnasts (r = 0.508; P = 0.001) and for runners (r = 0.461; P = 0.041). There was also a negative relationship between the largest daily energy surplus and DEXA-derived body fat percentage for gymnasts (r = -0.418; P = 0.003). Using the energy balance variables, age, and athlete type (artistic gymnast, rhythmic gymnast, middle-distance runner, long-distance runner) as independent variables in a forward stepwise regression analysis, a small but significant amount of variance was explained in DEXA-derived (P = 0.000; R2 = 0.309) and skinfold-derived (P = 0.000; R2 = 0.298) body fat percent by the number of energy deficits > 300 kcal and age.

CONCLUSIONS

These data suggest that within-day energy deficits (measured by frequency and/or magnitude of deficit) are associated with higher body fat percentage in both anaerobic and aerobic elite athletes, possibly from an adaptive reduction in the REE. These data should discourage athletes from following restrained or delayed eating patterns to achieve a desired body composition.

The effects of varying dietary fat on the nutrient intake in male and female runners

OBJECTIVE

The present study examined the effects of varying dietary fat levels on nutrients in female and male endurance runners.

METHODS

Three diets (low, medium and high fat) were designed for each subject using their food preferences and three-day food records. Each diet was eaten for 28 to 31 days. The diets were self-selected from seven-day sample menus. Twelve male and 13 female runners between 18 and 55 years of age who averaged 42 miles/week participated in the study. Daily food intakes, activity records and weekly palatability/hunger scales were completed.

RESULTS

Dietary fat intakes, as a percent of total energy intake (%E), averaged 17%E, 31%E, and 44%E on the low, medium and high fat diets, respectively. Energy consumption was less than their estimated energy expenditure (EEE) on all diets. On the low fat diet, the female runners were consuming approximately 60% of their EEE. As dietary fat increased, the difference between calorie intake and estimated energy expenditure became less and the subjects were less hungry on the two higher fat diets. For all subjects, as energy intakes increased, so did carbohydrate intake. Therefore, carbohydrate intake was not different on the two lower fat diets. Irrespective of gender, calcium and zinc intakes, which were below 1989 RDAs, increased with increasing fat intakes, between the low and medium fat diets. Zinc intake was also higher on the highest fat diet. Essential fatty acid intakes for females on the low fat diet were less than 2.5%E. Half of the female runners ate less than the RDA of calcium and zinc on the low fat diet and Fe on the medium fat diet.

CONCLUSION

This study suggests that endurance runners may not be consuming enough calories on a low fat diet and that increasing dietary fat increased energy consumption. On the low fat diet, essential fatty acids and some minerals (especially zinc) may be too low. A low fat diet could compromise health and performance.

Women at altitude: energy requirement at 4,300 m

To test the hypotheses that prolonged exposure to moderately high altitude increases the energy requirement of adequately fed women and that the sole cause of the increase is an elevation in basal metabolic rate (BMR), we studied 16 healthy women [21.7 +/- 0.5 (SD) yr; 167.4 +/- 1.1 cm; 62.2 +/- 1.0 kg]. Studies were conducted over 12 days at sea level (SL) and at 4,300 m [high altitude (HA)]. To test that menstrual cycle phase has an effect on energetics at HA, we monitored menstrual cycle in all women, and most women (n = 11) were studied in the same phase at SL and HA. Daily energy intake at HA was increased to respond to increases in BMR and to maintain body weight and body composition. Mean BMR for the group rose 6.9% above SL by day 3 at HA and fell to SL values by day 6. Total energy requirement remained elevated 6% at HA [ approximately 670 kJ/day (160 kcal/day) above that at SL], but the small and transient increase in BMR could not explain all of this increase, giving rise to an apparent "energy requirement excess." The transient nature of the rise in BMR may have been due to the fitness level of the subjects. The response to altitude was not affected by menstrual cycle phase. The energy requirement excess is at present unexplained.

Ovarian impairments of female recreational distance runners during a season of training

This study was carried out to investigate the relationship between the level of training and the impairment of ovarian function among female recreational distance runners, and its reversibility. Thirty-six female distance runners self-recorded, for 7 consecutive days each month, the duration and distance of daily running from October 1989 to May 1990 in Great Britain. During the last 3 months of the survey, saliva samples were taken for progesterone assay and a subsample was measured for body composition. No trend in weight loss was observed over the season of training. Amenorrheic (AM) and oligomenorrheic (Oligo) runners had a significantly lower body mass index than eumenorrheic (EU) and irregularly menstruating (IM) runners. The amenorrheic and oligomenorrheic subjects did not show any rise in progesterone, at any time, during the 3 months of sampling. The eumenorrheic subjects showed evidence of a rise in progesterone, though the mean level was always significantly lower than that of sedentary controls. The most severely impaired runners (AM and Oligo) ran more than EU or irregularly menstruating runners in this sample, had lower body weight, a younger age and had a significantly lower body mass index (BMI). They tended to run faster during training sessions than those with apparently normal menstrual cycle or just irregular periods. It is suggested that low BMI, which is an indicator of body energy stores, reflects the intensity of regular training runs among female athletes with a stable body weight. It is possible that repeated elevations of beta-endorphins or other suppressors of gonadotropin release, secreted above a level of training commonly exceeded by long distance runners, when concurrent with energy restriction, could contribute to impairment of menstrual cycle.

Sex steroid metabolism and menstrual irregularities in the exercising female. A review

This article aims to clarify why, and by which mechanisms, exercise may influence the normal menstrual cycle. Therefore, the vast amount of literature on this subject is reviewed and a critical appraisal of the most widespread hypotheses if offered. The strikingly low body mass which frequently accompanies exercise-related menstrual irregularities (ERMI) has led some authors to develop a hypothesis which postulates that a critical percentage of body fat is essential to trigger normal menstruation. The relevance of any reference to anorexia nervosa to support this view lacks consistency: female athletes differ in many ways from patients with anorexia nervosa, not least in their excellent physical status which is essential to deliver first-class performances. ERMI is not identical to the so-called female athlete triad, a complicated pathology that involves ERMI, premature osteoporosis and disordered eating. ERMI itself does not seem to have any substantial pathological effects as long as attention is paid to preventing osteoporosis or stress fractures which may result from prolonged hypo-estrogenaemia. In the female athlete with ERMI who wishes to conceive, the accompanying subfertility may necessitate a response other than a prompt reduction in training intensity, as this is hardly a first choice for any top athlete. During recent years, a number of prospective studies have greatly contributed to our understanding of the complexity of the mechanisms involved in ERMI. Older hypotheses, such as those considering hyperprolactinaemia as the cornerstone of ERMI, have now been firmly rejected. The present hypotheses emphasise the importance of caloric deficiency and limited energy availability, although they still fail to identify the actual mechanism that causes ERMI. There is, however, evidence that ERMI is produced by a disturbance of the hypothalamic gonadotrophin-releasing hormone oscillator. This disturbance is caused by either an insufficient estrogen or progesterone feedback or by an imbalance of local opioid peptide and catecholamine activities mediated by gamma-aminobutyric acid (GABA), corticotrophin-releasing hormone and insulin-like growth factor-1. More recent experiments have also linked ERMI with changes in steroid metabolism, in particular, an increasing activity of catecholestrogens possibly leading to enhanced intracerebral noradrenaline (norepinephrine) levels that may interfere with normal gonadotrophin release. This article demonstrates that the outcome of the many studies of ERMI is characterised by much controversy and numerous methodological flaws. The importance and complexity of some recent findings necessitate a comprehensive study which links older and newer findings within a critical perspective.

Effects of human growth hormone, insulin-like growth factor I, and diet and exercise on body composition of obese postmenopausal women

To determine the effects of GH and insulin-like growth factor I (IGF-I) administration, diet, and exercise on weight loss, body composition, basal metabolic rate (BMR), muscle strength, and psychological status, 33 moderately obese postmenopausal women (67.1 +/- 5.2 yr) participated in a 12-week randomized, double blind study. Participants were placed on a diet that provided 500 Cal/day less than that needed for weight maintenance, and they walked 3 days and strength trained 2 days each week. Subjects also self-injected GH (0.025 mg/kg BW.day), IGF-I (0.015 mg/kg BW.day), a combination of these doses of GH and IGF-I, or placebo (P). Twenty-eight women completed the study, as five subjects dropped out due to intolerable side-effects (e.g. edema). Weight loss occurred in all groups, with the largest decrease occurring in the GH plus IGF-I group (5.6 +/- 1.4 kg). Fat mass significantly decreased in all groups, with the largest losses observed in GH and GH plus IGF-I groups (6.3 +/- 1.8 and 8.4 +/- 2.8 kg, respectively). Despite weight loss, BMR was maintained in all groups. Muscle strength increased with training for all groups, and depression and anxiety scores decreased in groups receiving IGF-I. These data show that obese postmenopausal women can lose weight and fat without compromising fat free mass, BMR, or gains in muscle strength, and that GH and IGF-I given together may enhance fat loss over either given alone.

Daily exercise reduces fat, protein and body mass in male but not female rats

This study was designed to compare the estimated energy balance, linear growth (body and bone lengths) and body composition (all components including body mass, total body water, fat, protein and ash) response to daily spontaneous running (DSR) in young male and female rats. We tested the hypothesis that due to gender differences in energy efficiency, DSR would reduce linear growth and body composition more in male rats. Fourteen male and sixteen female weanling Sprague-Dawley rats were randomly assigned to either a sedentary (SED) control (male 7, female 8) or DSR (male 7, female 8) group. The DSR rats were allowed to run spontaneously in running wheels while SED rats remained in standard rat cages for 9 weeks. Body mass, running distance and food intake were measured over the nine week period. Subsequently, chemical analysis was performed to measure carcass content of water, protein, fat and ash. Linear growth was assessed by measures of body and bone lengths. The estimated energy balance of the DSR rats was computed and compared between genders. Estimated energy balance was significantly more negative in females than males due to significantly greater DSR distance. Body and bone lengths were similar among the SED and DSR female and SED and DSR male rats. However, whole body mass, fat mass and protein mass were significantly lower only in DSR males. These results demonstrate that DSR reduced body mass, body fat and protein mass in male rats but not in female rats despite a more negative estimated energy balance in female rats. These findings suggest that females are better protected from an energy deficit due to DSR. Possible mechanisms include gender-specific hormonal responses.

Bone density and cyclic ovarian function in trained runners and active controls

This study was conducted to determine whether rigorous exercise training adversely affects ovarian hormone levels and bone health in cyclically menstruating trained runners. Ovarian hormones, bone mineral density (BMD), body composition, 3-d diet records, 3-d estimated energy expenditure, and menstrual histories were evaluated in 10 trained collegiate runners and 10 moderately active controls. The trained runners had lower total body calcium per kg of soft lean tissue measured by DEXA (P = 0.045). Half of the trained runners had experienced stress fractures compared with only one of the moderately active controls. The trained runners' lumbar (L2-L4) BMD (1.178 g.cm-2) was not significantly different from that of the active controls (1.283 g.cm-2) (P = 0.074) but, for all subjects combined, there wasa significant inverse relation between L2-L4 BMD and distance run per week (P = 0.036). Further, adding age, body weight, percent body fat, daily energy intake, and daily calcium intake to a stepwise multiple regression analysis did not significantly improve predictive precision. The trained runners consumed nearly twice the amount of calcium (1089 mg.d-1 vs 641 mg.d-1, respectively; P = 0.036), while intake of other nutrients did not differ significantly between groups. Urinary estrone conjugates (E1C) were lower in the trained runners during the early follicular phase (P = 0.028), while pregnanediol-3-glucuronide (PdG) was not significantly different between groups during the luteal phase (P = 0.213). Thus, it appears that lower estrogen production, especially during the early follicular phase, and not progesterone, is associated with lower whole body calcium per kg of soft lean tissue and, probably, L2-L4 BMD. Results of this study also suggest that regular menstrual cycles do not imply normal ovarian hormone function in young women who are engaged in either recreational or competitive running.

Predicted and measured resting metabolic rate of male and female endurance athletes

OBJECTIVE

To measure the resting metabolic rate (RMR) of a group of endurance-trained male and female athletes and to compare it with values predicted using published equations.

DESIGN

RMR was measured twice: 1 week apart for the men and approximately 1 month apart for the women. RMR was predicted using equations of Harris and Benedict, Owen et al, Mifflin et al, and Cunningham.

SUBJECTS/SETTING

Subjects were 37 trained endurance athletes (24 men, 13 women) who had participated in studies previously completed in our laboratory.

MAIN OUTCOME MEASURES

The primary outcome measure was the comparison of predicted RMR with measured RMR. An exploratory procedure for the determination of predictive variables in these athletes was also performed.

STATISTICAL ANALYSES PERFORMED

The Root Mean Squared Prediction Error method was used to compare predicted RMR with measured RMR. The maximum R2 procedure method was used to determine the best possible combination of four variables that explained the largest amount of variance in RMR.

RESULTS

The Cunningham equation was found to predict measured RMR most accurately (within 158 kcal/d for men and 103 kcal/d for women). Fat-free mass was the best predictor of RMR in men, whereas energy intake was the best predictor in women.

APPLICATIONS/CONCLUSIONS

The Cunningham equation provides an accurate estimate of RMR when determining energy needs of highly active people. Equations specific to athletes need to be developed. Factors in addition to body weight, height, and age should be investigated as possible predictor variables in athletes.

Do highly physically active females have a lowered basal metabolic rate?

In several studies estimated energy intake has been found to be low compared with estimated energy expenditure in female athletes. It has therefore been suggested that female athletes may have a depressed basal energy expenditure (BMR). The main purpose of the present study was to explore this possibility by measuring BMR in physically extremely active females. Eight female dancers and 7 controls with low physical activity, all musicians, were studied; the variables measured included body weight, height, skinfold thickness and total body potassium. BMR was measured by indirect calorimetry. In conclusion, the present study lends no support to the idea of a lowered basal metabolic rate in female athletes as an explanation of the general finding of a lower estimated energy intake than energy expenditure in this type of subjects.

Energy metabolism in free-living, 'large-eating' and 'small-eating' women: studies using 2H2(18)O

The doubly-labelled water (2H2(18)O) technique was used to assess the long-term rates of energy expenditure and, after accounting for any changes in body composition, the derived rates of energy intake in weight-stable 'large-eating' (n 6) and 'small-eating' (n 6) women. The self-reported energy intakes (approximately 11.2 v. 5.6 MJ/d) and energy expenditures (approximately 8.5 v. 12.4 MJ/d) for the 'large-eating' and 'small-eating' groups respectively, should not be sustainable without significant body-weight changes. 2H2(18)O-assessed rates of energy expenditure for the 'large-eaters' (approximately 8.5 MJ/d) and 'small-eaters' (approximately 11.3 MJ/d) were in close agreement with the results obtained using 5 d, self-reported activity diaries but the derived rates of energy intake for the 'large-' (approximately 8.5 MJ/d) and 'small-eaters' (approximately 10.8 MJ/d) were markedly different from those obtained using self-reported, weighed food diaries. When two 'small-eaters' were supplied with their self-reported energy intakes (approximately 5 MJ/d) for up to 28 d both subjects lost about 0.75 kg body-weight/week. These results provide no support for the existence of 'metabolically efficient' women in the community.

Exercise-induced menstrual cycle changes. A functional, temporary adaptation to metabolic stress

Chronic exercise is now known to alter the menstrual cycle. Yet, we do not yet know the true incidence of menstrual cycle alterations in athletes, because good normative data do not exist and the metabolic cost of training has not been considered in many studies. Secondary amenorrhoea is not easily induced by exercise training alone but seems to require additional metabolic stressors. Induction of secondary amenorrhoea in prospective exercise studies has not occurred, although the onset of short luteal or inadequate luteal phase cycles may occur in women even when running distances are not extensive. Such menstrual cycles may cause infertility, but this is only a temporary phenomenon since pregnancy, if desired, will usually occur upon cessation of training. Exercise-related changes in the menstrual cycle can be viewed as a functionally adaptive rather than a maladaptive dysfunction. A strong case can be made that the changes in the menstrual cycle as a result of exercise are an energy conserving strategy to protect more important biological processes. This hypothesis is consistent with the theory of metabolic arrest that has been identified in lower organisms and hibernating mammals.

Dietary iron deficiency and sports anaemia

In order to determine whether dietary inadequacies can explain the sub-optimal iron status widely documented in endurance-trained athletes, the food intake records of Fe-deficient and Fe-replete distance runners and non-exercising controls of both sexes were analysed. In all the male study groups the mean dietary Fe intake met the recommended dietary allowances (RDA; > 10 mg/d (US) Food and Nutrition Board, 1989). However, both female athletes and controls failed to meet the RDA with regard to Fe (< 15 mg/d) and folate (< 200 micrograms/d). There was no difference in the total Fe intakes of Fe-deficient and Fe-replete athletes and the controls of each sex. However, Fe-deficient male runners, but not female runners, consumed significantly less haem-Fe (P = 0.048) than their comparative groups. This suggests that the habitual consumption of Fe-poor diets is a factor in the aetiology of athletes' Fe deficiency.