Nutritional survey of highly trained women runners

Determination of Optimal Daily Magnesium Intake among Physically Active People: A Scoping Review

Little is known about the optimal daily magnesium (Mg) intake for individuals with high levels of physical activity. The aim of this study was to clarify the optimal dietary Mg intake for people with high levels of physical activity in a scoping review. In this review, we searched MEDLINE and Japan Medical Abstracts Society for studies published up to May 31, 2020. We conducted two searches, one for studies using gold standard measurement methods such as the balance method and factorial calculation (Search 1), and the other for studies using estimation from daily food intake (Search 2). We also performed a meta-analysis of studies that compared the Mg intake among physically active people with the Mg intake among controls. After the primary and secondary screening, 31 studies were included in the final review. All of the included studies examined professional or recreational athletes. We found no studies that examined the optimal intake of Mg using gold standard measurement methods. The Mg intake among physically active individuals was below the recommended dietary allowance in most studies. In five studies that conducted meta-analyses, physically active individuals had significantly higher intakes of Mg than controls, although these levels were still below the recommended dietary allowance. The present review revealed that evidence regarding the optimal daily magnesium intake is currently scarce, and further studies are needed.

Influence of physical training on intracellular and extracellular zinc concentrations

Background

Physical exercise affects zinc (Zn) homeostasis. This study aimed to analyze the influence of physical training on extracellular (serum, plasma, and urine) and intracellular (erythrocytes and platelets) concentrations of Zn.

Methods

Forty young men, divided into a training group (TG; n = 20; 18.15 ± 0.27 years; 68.59 ± 4.18 kg; 1.76 ± 0.04 m) and a control group (CG; n = 20; 19.25 ± 0.39 years; 73.45 ± 9.04 kg; 1.79 ± 0.06 m), participated in this study. The TG was formed by semiprofessional soccer players from a youth category with a regular training plan of 10 h/week. The CG was formed by healthy men who did not practice physical exercise and had not followed any specific training plan. Plasma, serum, urine, erythrocyte, and platelet samples of Zn were obtained and analyzed by inductively coupled plasma mass spectrometry.

Results

The TG showed elevated plasma Zn concentrations (p < 0.01) despite similar intakes. However, TG showed reduced absolute (p < 0.01) and relative (p < 0.05) Zn concentrations in erythrocytes.

Conclusions

Athletes who underwent regular physical training showed elevated plasma and reduced erythrocyte Zn concentrations despite similar intakes to the CG.

Prevalence of Dietary Supplement Use by Athletes: Systematic Review and Meta-Analysis

BACKGROUND

Dietary supplements (DSs) are commercially available products consumed as an addition to the usual diet and are frequently ingested by athletes.

OBJECTIVE

Our objective was to examine the prevalence of DS use by athletes.

DATA SOURCES

PubMed, Ovid MEDLINE, OVID Healthstar, and Cumulative Index to Nursing and Allied Health were searched for original research articles published up to August 2014. Search terms included specific sports, specific DSs, and other terms.

STUDY SELECTION

Studies were selected if they were written in English, involved athletes, and provided a quantitative assessment of the proportion of athletes using specific DSs. Percent of athletes using specific DSs.

SYNTHESIS OF DATA

Methodological quality of studies was assessed by three reviewers using an 8-point scale that included evaluations for sampling methods, sampling frame, sample size, measurement tools, bias, response rate, statistical presentation, and description of the participant sample. Where there were at least two investigations, meta-analysis was performed to obtain summary (pooled) prevalence estimates (SPEs) on (1) DS use prevalence by sport and sex, (2) DS use prevalence by elite versus non-elite athletic status, and (3) specific DS prevalence for all athletic groups combined. Meta-analyses included evaluations of homogeneity and publication bias.

RESULTS

A total of 159 unique studies met the review criteria. Methodological quality was generally low with an average ± standard deviation of 43 ± 16% of available rating points. There was low homogeneity for SPEs when compiled by sport, athletic status, and/or specific DSs. Contributing to the lack of homogeneity were differences in studies' objectives and types of assessments used (e.g., dietary surveys, interviews, questionnaires). Despite these limitations, the data generally indicated that elite athletes used DSs much more than their non-elite counterparts. For most DSs, use prevalence was similar for men and women except that a larger proportion of women used iron while a larger proportion of men used vitamin E, protein, and creatine. No consistent change in use over time was observed because even the earliest investigations showed relatively high use prevalence.

CONCLUSION

It was difficult to generalize regarding DS use by athletes because of the lack of homogeneity among studies. Nonetheless, the data suggested that elite athletes used dietary supplements far more than their non-elite counterparts; use was similar for men and women with a few exceptions; use appeared to change little over time; and a larger proportion of athletes used DSs compared with the general US population. Improvements in study methodology should be considered in future studies especially (1) defining DSs for participants; (2) querying for very specific DSs; (3) using a variety of reporting timeframes (e.g., daily, 2-6 times/week, 1 time/week and <1 time/week); (4) reporting the sampling frame, number of individuals solicited, and number responding; (5) reporting characteristics of volunteers (and non-volunteers, if available); and (6) using similar methods on several occasions to examine possible temporal trends among athletes.

Exercise and Obesity

This paper reviews succinctly the evidence for a role of regular exercise in the prevention and the treatment of obesity and of its metabolic complications. Seventeen propositions relevant to an understanding of the topic are considered. The evidence suggests that regular exercise can be an important factor in the development of sustained negative energy balance conditions provided the volume of activity is high. This implies a program of low to moderate intensity exercise performed on an almost daily basis for at least one hour per session. To induce significant weight and fat losses and to treat overweight and obese patients, compliance to the program for several years becomes a necessity. Exercise increases lipid substrate oxidation and may favor carbohydrate intake for the same amount of energy intake. The acute effects of exercise on resting metabolic rate are well documented, but the long-term influences of exercise training seem to be small and are rapidly suppressed with the cessation of training. The obese benefits also from a regular exercise regimen in terms of improved insulin sensitivity, lipid and lipoprotein profile, and blood pressure, as well as reduced risk of death. Regular exercise, such as walking, is a healthy course of action for the overweight or the obese patients.

Dietary protein requirements and adaptive advantages in athletes

Dietary guidelines from a variety of sources are generally congruent that an adequate dietary protein intake for persons over the age of 19 is between 0·8–0·9 g protein/kg body weight/d. According to the US/Canadian Dietary Reference Intakes, the RDA for protein of 0·8 g protein/kg/d is “…the average daily intake level that is sufficient to meet the nutrient requirement of nearly all [~98 %]… healthy individuals…” The panel also states that “…no additional dietary protein is suggested for healthy adults undertaking resistance or endurance exercise.” These recommendations are in contrast to recommendations from the US and Canadian Dietetic Association: “Protein recommendations for endurance and strength trained athletes range from 1·2 to 1·7 g/kg/d.” The disparity between those setting dietary protein requirements and those who might be considered to be making practical recommendations for athletes is substantial. This may reflect a situation where an adaptive advantage of protein intakes higher than recommended protein requirements exists. That population protein requirements are still based on nitrogen balance may also be a point of contention since achieving balanced nitrogen intake and excretion likely means little to an athlete who has the primary goal of exercise performance. The goal of the present review is to critically analyse evidence from both acute and chronic dietary protein-based studies in which athletic performance, or correlates thereof, have been measured. An attempt will be made to distinguish between protein requirements set by data from nitrogen balance studies, and a potential adaptive ‘advantage’ for athletes of dietary protein in excess of the RDA.

Symposium on ‘Performance, exercise and health’ Practical aspects of nutrition in performance

The importance of nutrition in sport has been recognised since the ancient Olympians, and its role in improving both health and sports performance has widespread acceptance. However, in sporting circles nutritional knowledge, beliefs and practices are extremely varied. Within any sporting organisation the sports dietitian or nutritionist must be able to work with athletes, their family, coaches and other support staff to develop and monitor realistic and practical strategies that work best for each performer, contributing to a positive and sustained outcome on performance. The present review examines the practical application of current key issues in performance nutrition, highlighting the advantages of early intervention in youth development and comprehensive and integrated nutrition services.

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.

Effect of magnesium supplementation on some plasma elements in athletes at rest and exhaustion

The effects of magnesium supplementation on plasma magnesium, zinc, and copper levels were determined in young adult tae-kwon-do athletes and sedentary controls at rest and exhaustion. After a 4-week supplementation period with 10 mg/day/kg Mg, the plasma magnesium, copper, and zinc levels significantly increased in sedentary and training (90-120 min training 5 days a week) subjects when compared to nonsupplemented controls (p < 0.05).

Protein and amino acids for athletes

The main determinants of an athlete's protein needs are their training regime and habitual nutrient intake. Most athletes ingest sufficient protein in their habitual diet. Additional protein will confer only a minimal, albeit arguably important, additional advantage. Given sufficient energy intake, lean body mass can be maintained within a wide range of protein intakes. Since there is limited evidence for harmful effects of a high protein intake and there is a metabolic rationale for the efficacy of an increase in protein, if muscle hypertrophy is the goal, a higher protein intake within the context of an athlete's overall dietary requirements may be beneficial. However, there are few convincing outcome data to indicate that the ingestion of a high amount of protein (2-3 g x kg(-1) BW x day(-1), where BW = body weight) is necessary. Current literature suggests that it may be too simplistic to rely on recommendations of a particular amount of protein per day. Acute studies suggest that for any given amount of protein, the metabolic response is dependent on other factors, including the timing of ingestion in relation to exercise and/or other nutrients, the composition of ingested amino acids and the type of protein.

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.

Protein requirements for endurance athletes

Acute endurance exercise results in the oxidation of several amino acids. The total amount of amino acid oxidation during endurance exercise amounts to only 1-6% of the total energy cost of exercise. The branched chain amino acid, leucine, has been most often studied in relation to endurance exercise. Leucine is oxidized by the enzyme, branched-chain oxo-acid dehydrogenase (BCOAD). BCOAD is relatively inactive at rest ( approximately 4-7%) and is activated at the onset of exercise by dephosphorylation (to about 25%). After a period of endurance exercise training, the activation of BCOAD and amino acid oxidation are attenuated, however the total amount of BCOAD enzyme is up-regulated. A low energy and/or carbohydrate intake will increase amino acid oxidation and total protein requirements. With adequate energy and carbohydrate intake, low to moderate intensity endurance activity has little impact on dietary protein requirements and 1.0 gPRO/kg/d is sufficient. The only situation where dietary protein requirements exceed those for relatively sedentary individuals is in top sport athletes where the maximal requirement is approximately 1.6 gPRO/kg/d. Although most endurance athletes get enough protein to support any increased requirements, those with low energy or carbohydrate intakes may require nutritional advice to optimize dietary protein intake.

Nitric oxide and changes of iron metabolism in exercise

Accumulated data imply that exercise itself might not lead to a true iron deficiency or 'sport anaemia' in a healthy athlete who has adequate iron intake. The higher prevalence of iron deficiency anaemia in younger female athletes might be not due to exercise itself, but probably results from dietary choices, inadequate iron intake and menstruation. These factors can also induce iron deficiency or anaemia in the general population. However, exercise does affect iron metabolism, leading to low or sub-optimal iron status. The underlying mechanism is unknown. In this review, recent advances in the study of the effect of exercise on iron metabolism and nitric oxide, and the relationship between nitric oxide and iron status in exercise are discussed. A hypothesis that increased production of nitric oxide might contribute to sub-optimal iron status in exercise is proposed.

Energy needs of athletes

Each athlete has unique energy requirements, which underpin their ability to meet total nutritional goals. For everyday dietary planning and evaluation, energy requirements can be predicted via estimations of RMR and activity levels. Research methods such as indirect calorimetry and DLW allow energy requirements to be measured, and may be useful to confirm situations in which an athlete has a true energy balance anomaly. There is some evidence that individual athletes may have reduced energy requirements, although this occurs less frequently than is reported. Most self-reports of food intake substantially under-estimate energy intake, due to under-reporting or under-eating during the period of record keeping. Many athletes are over-focused on reducing body mass and body fat below levels that are consistent with long-term health and performance. Restrained eating can cause significant detrimental outcomes to body function. Leptin may be involved in modulating or mediating some of these changes. Athletes should use their energy budget to choose foods that provide macronutrient and micronutrient needs for optimal health and performance. Practical advice may help athletes to achieve energy intake challenges.

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.

Guidelines for daily carbohydrate intake: do athletes achieve them?

Official dietary guidelines for athletes are unanimous in their recommendation of high carbohydrate (CHO) intakes in routine or training diets. These guidelines have been criticised on the basis of a lack of scientific support for superior training adaptations and performance, and the apparent failure of successful athletes to achieve such dietary practices. Part of the problem rests with the expression of CHO intake guidelines in terms of percentage of dietary energy. It is preferable to provide recommendations for routine CHO intake in grams (relative to the body mass of the athlete) and allow flexibility for the athlete to meet these targets within the context of their energy needs and other dietary goals. CHO intake ranges of 5 to 7 g/kg/day for general training needs and 7 to 10 g/kg/day for the increased needs of endurance athletes are suggested. The limitations of dietary survey techniques should be recognised when assessing the adequacy of the dietary practices of athletes. In particular, the errors caused by under-reporting or undereating during the period of the dietary survey must be taken into account. A review of the current dietary survey literature of athletes shows that a typical male athlete achieves CHO intake within the recommended range (on a g/kg basis). Individual athletes may need nutritional education or dietary counselling to fine-tune their eating habits to meet specific CHO intake targets. Female athletes, particularly endurance athletes, are less likely to achieve these CHO intake guidelines. This is due to chronic or periodic restriction of total energy intake in order to achieve or maintain low levels of body fat. With professional counselling, female athletes may be helped to find a balance between bodyweight control issues and fuel intake goals. Although we look to the top athletes as role models, it is understandable that many do not achieve optimal nutrition practices. The real or apparent failure of these athletes to achieve the daily CHO intakes recommended by sports nutritionists does not necessarily invalidate the benefits of meeting such guidelines. Further longitudinal studies of training adaptation and performance are needed to determine differences in the outcomes of high versus moderate CHO intakes. In the meantime, the recommendations of sports nutritionists are based on plentiful evidence that increased CHO availability enhances endurance and performance during single exercise sessions.

Chronic fatigue syndrome: an update

The chronic fatigue syndrome is characterised by a fatigue that is disproportionate to the intensity of effort that is undertaken, has persisted for 6 months or longer, and has no obvious cause. Unless there has been a long period of patient- or physician-imposed inactivity, objective data may show little reduction in muscle strength or peak aerobic power, but the affected individual avoids heavy activity. The study of aetiology and treatment has been hampered by the low disease prevalence (probably <0.1% of the general population), and (until recently) by a lack of clear and standardised diagnostic criteria. It is unclear how far the aetiology is similar for athletes and nonathletes. It appears that in top competitors, overtraining and/or a negative energy balance can be precipitating factors. A wide variety of other possible causes and/or precipitating factors have been cited in the general population, including psychological stress, disorders of personality and affect, dysfunction of the hypothalamic-pituitary-adrenal axis, hormonal imbalance, nutritional deficits, immune suppression or activation and chronic infection. However, none of these factors have been observed consistently. The prognosis is poor; often disability and impairment of athletic performance are prolonged. Prevention of overtraining by careful monitoring seems the most effective approach in athletes. In those where the condition is established, treatment should aim at breaking the vicious cycle of effort avoidance, deterioration in physical condition and an increase in fatigue through a combination of encouragement and a progressive exercise programme.

The effects of magnesium supplementation on exercise performance

OBJECTIVES

Magnesium (Mg) status, although difficult to assess, is suspected to be marginal in many individuals, especially athletes, and this has led to the common use of Mg supplements. The purpose of this article is to critique research that has addressed Mg supplementation in athletes.

DATA SOURCES

The primary database was Medline, which was searched for English articles from 1966 to June 1999 using the words "magnesium" and "supplementation."

STUDY SELECTION

Only experimental studies dealing with human subjects, Mg supplementation, and exercise performance were critiqued (n = 12).

DATA EXTRACTION

Quality of critiqued articles was based on 1) use of cross-over designs, 2) how and if Mg status was assessed, 3) whether treatment was solely Mg supplementation, 4) duration of supplementation, 5) subject number, and 6) degree of experimental control. Articles were classified into "no effect" and "positive effect," and also were examined in regard to the type of performance outcome (strength, anaerobic-lactacid, and aerobic).

DATA SYNTHESIS

Mg is a cofactor to over 325 enzymatic reactions, and a deficiency of the mineral therefore has many physiological and exercise performance implications. Low dietary intakes, as found in many female athletes, coupled with increased urinary losses with exercise, may eventually lead to an Mg deficiency. Strength of evidence favors those studies finding no effect of Mg supplementation, regardless of whether the performance outcome was strength, anaerobic-lactacid, or aerobic. Analysis was confounded due to: 1) variable exercise modes, intensities, and durations, 2) variable training states and ages of subjects, 3) subject selection favoring males and gender differences has not been probed, 4) Mg dosage has ranged from 1 day to 3 months and from 116 mg/day to 500 mg/day, 5) multivitamins/minerals have been ingested with the Mg, 6) with one exception, Mg status was either not reported or reliant on total Mg (TMg), 7) lack of a cross-over design, 8) only one study made note of controlling exercise prior to exercise testing and blood assay, and 9) typical Mg intake measured was only measured in three of the studies.

CONCLUSIONS

Most evidence indicates no effect of Mg supplementation on performance (strength, anaerobic-lactacid, and aerobic). When only peak treadmill speed during a VO2 max test is examined, the strength of evidence is equivocal. Trained subjects appear to benefit less than untrained subjects, but this observation requires further study. Little research has focused on physically active females who may be at the highest risk for Mg deficiency. Research has been confounded by numerous factors.

Dietary carbohydrate, muscle glycogen content, and endurance performance in well-trained women

This study examined the ability of well-trained eumenorrheic women to increase muscle glycogen content and endurance performance in response to a high-carbohydrate diet (HCD; approximately 78% carbohydrate) compared with a moderate-carbohydrate diet (MD; approximately 48% carbohydrate) when tested during the luteal phase of the menstrual cycle. Six women cycled to exhaustion at approximately 80% maximal oxygen uptake (VO(2 max)) after each of the randomly assigned diet and exercise-tapering regimens. A biopsy was taken from the vastus lateralis before and after exercise in each trial. Preexercise muscle glycogen content was high after the MD (625.2 +/- 50.1 mmol/kg dry muscle) and 13% greater after the HCD (709.0 +/- 44.8 mmol/kg dry muscle). Postexercise muscle glycogen was low after both trials (MD, 91.4 +/- 34.5; HCD, 80.3 +/- 19.5 mmol/kg dry muscle), and net glycogen utilization during exercise was greater after the HCD. The subjects also cycled longer at approximately 80% VO(2 max) after the HCD vs. MD (115:31 +/- 10:47 vs. 106:35 +/- 8:36 min:s, respectively). In conclusion, aerobically trained women increased muscle glycogen content in response to a high-dietary carbohydrate intake during the luteal phase of the menstrual cycle, but the magnitude was smaller than previously observed in men. The increase in muscle glycogen, and possibly liver glycogen, after the HCD was associated with increased cycling performance to volitional exhaustion at approximately 80% VO(2 max).

Protein and physical performance

Important advances have been made in the understanding of the regulation of protein metabolism, which are of relevance to those interested in maximizing muscle performance in sport and aging. The use of 24 h amino acid infusion studies, the development of methods to measure skeletal muscle fractional breakdown rate and the fractional synthetic rate of specific proteins have and will continue to enhance our understanding of protein metabolism in exercise. Recent studies have demonstrated potentially beneficial effects upon protein metabolism by altering the composition and timing of nutrient delivery. Exercise and nutritional interventions may positively influence the negative effects of aging upon protein metabolism.

Nutritional aspects of immunosuppression in athletes

The literature suggests that a heavy schedule of training and competition leads to immunosuppression in athletes, placing them at a greater risk of opportunistic infection. There are many factors which influence exercise-induced immunosuppression, and nutrition undoubtedly plays a critical role. Misinterpretation of published data and misleading media reports have lead many athletes to adopt an unbalanced dietary regimen in the belief that it holds the key to improved performance. Some sports have strict weight categories, whilst in others low body fat levels are considered to be necessary for optimal performance or seen as an aesthetic advantage. This leads some athletes to consume a diet extremely low in carbohydrate content which, whilst causing rapid weight loss, may have undesirable results which include placing the athlete at risk from several nutrient deficiencies. Complete avoidance of foods high in animal fat reduces the intake of protein and several fat-soluble vitamins. On the other hand, diets with a very high carbohydrate content are usually achieved at the expense of protein. In addition, anecdotal and media reports have often promoted the supposed performance benefits of certain vitamins and minerals, yet most athletes do not realise that micronutrient supplementation is only beneficial when correcting a deficiency, and to date there is little scientific evidence to substantiate claims that micronutrients act as an ergogenic aid. Moreover, excessive intakes of micronutrients can be toxic. Deficiencies or excesses of various dietary components can have a substantial impact on immune function and may further exacerbate the immunosuppression associated with heavy training loads. This review examines the role of nutrition in exercise-induced immunosuppression and the effect of both excessive and insufficient nutrient intake on immunocompetence. As much of the present literature concerning nutrition and immune function is based on studies with sedentary participants, the need for future research which directly investigates the relationship between exercise, training, immunity and nutrition is highlighted.

Nutritional status of female athletes with subclinical eating disorders

OBJECTIVE

To assess the energy and nutritional status of female athletes with subclinical eating disorders and compare them with that of control subjects and standard norms.

DESIGN

Group classification (subclinical eating disorder or control) was based on responses to a health and diet history questionnaire, a battery of self-report eating disorder questionnaires, and an in-depth interview. Energy and nutrient intakes and energy expenditure were determined by means of 7-day weighed food records and 7-day activity logs. Micronutrient status was assessed for iron, zinc, magnesium, vitamin B-12, and folate.

SUBJECTS

Twenty-four female athletes with subclinical eating disorders and 24 female control athletes.

STATISTICAL ANALYSES

Descriptive statistics were used to analyze demographic data. One-way analysis of variance was used to determine group differences in energy and nutrient intakes, energy balance, and blood values.

RESULTS

Groups were similar in age, height, weight, fat-free mass, and body mass index. Mean energy intake was lower in the group with subclinical eating disorders (1,989 kcal/day) than in the control group (2,300 kcal/day; P=.004), whereas mean energy expenditures were similar (2,405 and 2,293 kcal/day, respectively). The group with subclinical eating disorders had significantly (P<.05) lower mean protein and fat intakes compared with the control group; mean micronutrient intakes were not significantly different. Mean status measures for iron, zinc, magnesium, vitamin B-12, and folate were within the normal ranges for both groups and no differences were noted between the groups. A similar number of athletes within each group used vitamin/mineral supplements < or = 4 times per week.

CONCLUSION

Although female athletes with subclinical eating disorders had dietary intakes of energy, protein, carbohydrate, and certain micronutrients that were below recommended levels, micronutrient status appeared relatively unaffected, probably due to their use of supplements.

Postexercise protein-carbohydrate and carbohydrate supplements increase muscle glycogen in men and women

We have previously demonstrated that women did not increase intramuscular glycogen in response to an increased percent of dietary carbohydrate (CHO) (from 60 to 75% of energy intake) (M. A. Tarnopolsky, S. A. Atkinson, S. M. Phillips, and J. D. MacDougall. J. Appl. Physiol. 78: 1360-1368, 1995). CHO and CHO-protein (Pro) supplementation postexercise can potentiate glycogen resynthesis compared with placebo (K. M. Zawadzki, B. B. Yaspelkis, and J. L. Ivy. J. Appl. Physiol. 72: 1854-1859, 1992). We studied the effect of isoenergetic CHO and CHO-Pro-Fat supplements on muscle glycogen resynthesis in the first 4 h after endurance exercise (90 min at 65% peak O2 consumption) in trained endurance athletes (men, n = 8; women, tested in midfollicular phase, n = 8). Each subject completed three sequential trials separated by 3 wk; a supplement was provided immediately and 1-h postexercise: 1) CHO (0.75 g/kg) + Pro (0.1 g/kg) + Fat (0.02 g/kg), 2) CHO (1 g/kg), and 3) placebo (Pl; artificial sweetener). Subjects were given prepackaged, isoenergetic, isonitrogenous diets, individualized to their habitual diet, for the day before and during the exercise trial. During exercise, women oxidized more lipid than did men (P < 0.05). Both of the supplement trials resulted in greater postexercise glucose and insulin compared with Pl (P < 0.01), with no gender differences. Similarly, both of these trials resulted in increased glycogen resynthesis (37.2 vs. 24. 6 mmol . kg dry muscle-1 . h-1, CHO vs. CHO-Pro-Fat, respectively) compared with Pl (7.5 mmol . kg dry muscle-1 . h-1; P < 0.001) with no gender differences. We conclude that postexercise CHO and CHO-Pro-Fat nutritional supplements can increase glycogen resynthesis to a greater extent than Pl for both men and women.

Evaluation of the influence of physical activity on the plasma concentrations of several trace metals

Our study was carried out with the aim of evaluating the influence that the degree of physical activity may have on plasma concentrations of essential and toxic elements. Copper and zinc, elements of known importance in basic cellular processes, have been analysed as essential, and cadmium and lead as toxic for the body in abnormal doses. The study was performed on a total population of 50 healthy individuals, 34 of them professional sportsmen and the rest who undertook moderate physical activity (control group), all of them living in a polluted environment (Madrid, Spain). Sampling was conducted at the beginning of the season (October). Electro-analytical techniques of proved reliability and accuracy were used for the determination of the metals. The results were related to data obtained using graphite furnace atomic absorption spectrophotometry and by use of biological reference materials. We found significantly higher zinc plasma concentrations in the sportsmen involved in anaerobic-type training (judo, fencing) compared to those undertaking aerobic activities (endurance, cycling) (P < 0.05). The values in both cases were higher than those found in the control group. Our study showed an increase of plasma copper concentrations in professional sportsmen, especially in those performing anaerobic activities, compared to those subjects undertaking moderate activity (control group) (P < 0.05). In summary, our results showed that there were no deficiencies of copper and zinc in the athletes studied at the beginning of the season. The levels were higher than those of the control population. As for the toxic metals, cadmium and lead, we observed lower levels in the athletes than in the control group (cadmium P < 0.005, lead P < 0.05). These results may indicate the existence of possible elimination systems for these metals in athletes, when they are training in a polluted environment.

Iron nutritional status in female karatekas, handball and basketball players, and runners

The iron nutritional status was studied in 84 sportswomen (19 karatekas, 20 handball players, 20 basketball players, and 25 middle and long distance runners) and in 82 nonathletic females of similar characteristics (control group). After a 7-day nutritional survey by means of the food weighing method, it was found that iron intake was significantly higher in the handball players (p < 0.05), basketball players (p < 0.01), and runners (p < 0.01) with regard to the control group; the basketball players were the only ones to cover the recommended minimum intake (15 mg/day). The heme iron intake was significantly greater in the handball and basketball players (p < 0.01), who, together with the runners, reached the value of 1.5 mg/day, which is considered to be optimal. In relation to the control group, the karatekas and handball and basketball players had lower levels of serum ferritin, although their iron intake was greater, whereas the runners had higher values that were very similar to those of the control group, due to the iron supplementation they had received. Despite finding a marked prevalence of inadequate iron intake, both in the sportswomen and in the control group, the manifest cases of anemia are relatively scarce. The organic iron stores do not seem to depend exclusively on the iron intake but also on intimate mechanisms of intestinal absorption and diverse causes of iron loss.

An assessment of carbohydrate intake in collegiate distance runners

To determine the extent to which well-trained endurance athletes practice the dietary recommendations for maximizing muscle glycogen resynthesis, collegiate cross-country runners (14 males and 10 females) kept 4-day dietary and activity records during a training period and a competitive period in the regular cross-country season. The mean running mileages for men and women were 16.0 +/- 1.0 and 10.7 +/- 0.6 km/day during the training period and 14.6 +/- 0.8 and 8.7 +/- 0.5 km/day during the competitive period, respectively. Males reported adequate energy intake in both phases, whereas females fell short of the RDA. However, the percentage of calories from carbohydrate was found to be inadequate (< 60%) for male runners. Although female runners derived 65-67% of calories from carbohydrate, the daily amount of carbohydrate taken was insufficient (< 10 g/kg body weight). Carbohydrate was ingested immediately postexercise approximately 50% of the time or less, with even far less taken in suggested quantities (approximately 1 g carbohydrate/kg body weight). There were no significant differences in dietary trends between training and competitive phases. The results suggest that these endurance athletes were not practicing the recommended feeding regimen for optimal muscle glycogen restoration.

Measurement of the daily dietary calcium and magnesium intake in Belgium, using duplicate portion sampling

The daily dietary calcium and magnesium intakes in Belgium were evaluated by sampling duplicate portions of food, destruction in a microwave oven and their calcium and magnesium contents determined by atomic absorption spectroscopy. The mean intake value for calcium (618 +/- 125 mg/day) was found to be less than those values measured in most other countries and was below the recommended daily allowance (RDA). The mean intake value for magnesium (271 +/- 44 mg/day) was similar to levels found in most other countries, but was below the RDA value for healthy adult men (350 mg/day) whilst being adequate for healthy women (280 mg/day).

Nutritional practices of athletes: are they sub-optimal?

Athletes' nutritional needs are principally determined by their training load (the intensity x frequency x duration of daily workouts) and body mass. Analyses of the diets of track and field competitors and marathon runners reveal a macronutrient composition similar to that of weight-matched, inactive individuals. Male athletes generally ingest adequate dietary energy to meet their daily energy expenditure and all vitamin and mineral needs. However, the energy intake of most female athletes is less than might be anticipated based on their training load. As a result, intakes of iron, calcium, vitamin B12 and zinc are often below the recommended daily allowances. Compared with the recommendations of sports nutritionists and exercise physiologists, the majority of athletes consume a diet which might be considered significantly deficient in carbohydrate (CHO). Although there is currently little scientific support for increasing the proportion of daily energy intake from CHO above the 45-55% (approximately 5 g kg BM-1 day-1) chronically consumed by most athletes, such a regimen would probably improve an athlete's training capacity, especially when rapid recovery from intense activity is required.

Daily dietary copper intake in Belgium, using duplicate portion sampling

Daily dietary copper intake in Belgium has been evaluated by duplicate portion sampling, heating in a microwave oven and atomic absorption spectrometric determination of this element. The mean intake value (1.5 +/- 0.4 mg/day) is similar to levels found for most other countries, but is situated at the lower end of the recommended range for a safe and adequate daily dietary intake.

Vitamin/mineral supplement use among athletes: a review of the literature

Vitamin/mineral supplements are often used by athletes as ergogenic aids to improve performance. This paper reviews studies of the prevalence, patterns, and explanations for vitamin/mineral supplement use among athletes. Fifty-one studies provided quantitative prevalence data on 10,274 male and female athletes at several levels of athletic participation in over 15 sports. The overall mean prevalence of athletes' supplement use was 46%. Most studies reported that over half of the athletes used supplements (range 6% to 100%), and the larger investigations found lower prevalence levels. Elite athletes used supplements more than college or high school athletes. Women used supplements more often than men. Varying patterns existed by sport. Athletes appear to use supplements more than the general population, and some take high doses that may lead to nutritional problems. Sport nutritionists should include a vitamin/mineral supplement history as part of their dietary assessment so they can educate athletes about vitamin/mineral supplements and athletic performance.

Consequences of magnesium deficiency on the enhancement of stress reactions; preventive and therapeutic implications (a review)

Stress intensifies release of catecholamines and corticosteroids that increase survival of normal animals when their lives are threatened. When magnesium (Mg) deficiency exists, stress paradoxically increases risk of cardiovascular damage including hypertension, cerebrovascular and coronary constriction and occlusion, arrhythmias and sudden cardiac death (SCD). In affluent societies, severe dietary Mg deficiency is uncommon, but dietary imbalances such as high intakes of fat and/or calcium (Ca) can intensify Mg inadequacy, especially under conditions of stress. Adrenergic stimulation of lipolysis can intensify its deficiency by complexing Mg with liberated fatty acids (FA), A low Mg/Ca ratio increases release of catecholamines, which lowers tissue (i.e. myocardial) Mg levels. It also favors excess release or formation of factors (derived both from FA metabolism and the endothelium), that are vasoconstrictive and platelet aggregating; a high Ca/Mg ratio also directly favors blood coagulation, which is also favored by excess fat and its mobilization during adrenergic lipolysis. Auto-oxidation of catecholamines yields free radicals, which explains the enhancement of the protective effect of Mg by anti-oxidant nutrients against cardiac damage caused by beta-catecholamines. Thus, stress, whether physical (i.e. exertion, heat, cold, trauma--accidental or surgical, burns), or emotional (i.e. pain, anxiety, excitement or depression) and dyspnea as in asthma increases need for Mg. Genetic differences in Mg utilization may account for differences in vulnerability to Mg deficiency and differences in body responses to stress.

The prevalence and consequences of subclinical eating disorders in female athletes

A growing body of evidence suggests that the prevalence of eating disorders and excessive concerns regarding body weight in certain subpopulations of female athletes are increasing. The pressure on female athletes to improve their performances and physiques, coupled with the general sociocultural demand placed on all women to be thin, often results in attempts to achieve unrealistic body size and body weight goals. For some female athletes the pressure to achieve and maintain a low body weight leads to potentially harmful patterns of restrictive eating or chronic dieting. This paper seeks to further delineate the characteristics of a recently identified subclinical eating disorder in female athletes: anorexia athletica. Research studies that support the existence of subclinical eating disorders will be reviewed. In addition, the possible physiological and psychological consequences of subclinical eating disorders will be explored.

Nutritional practices of elite athletes. Practical recommendations

The nutritional intake of elite athletes is a critical determinant of their athletic performance and ability to compete both physically and mentally. However, their demanding training and travel schedules in addition to a possible lack of nutritional knowledge may prohibit them from maintaining an optimal dietary intake. Sound scientific data about the nutritional habits of elite athletes are limited and, therefore, it is not clear as to whether elite athletes are following nutritional recommendations and maintaining nutritionally sound diets. This review takes a comprehensive look at 22 recent dietary intake studies, including 50 groups of elite athletes. The time period for food record collection ranged from 3 to 7 days except for 2 studies which collected records for 21 and 22 days. Energy intakes of > 50 kcal/kg/day for male athletes who train for > 90 min/day and 45 to 50 kcal/kg/day for female athletes training for > 90 min/day are recommended. Bodyweight should be monitored frequently as a check on calorie intake. With a sufficient calorie intake (1.2 to 2.0 kg/kg/day) protein supplementation is not necessary. Ingested carbohydrate stored as glycogen serves as the primary fuel for muscle performance. Athletes in training should consume 70% of total calories as carbohydrate. Athletes on low energy diets (< 2200 kcal/day) should have a diet of < 25% fat, and athletes with large energy needs should consume 30% fat in their diet. In general, fat intakes should be reduced and carbohydrate intakes increased. Athletes should also restrict alcohol intake during training and competition periods. Athletes with low calorie intakes should consume foods with high contents of iron, calcium, magnesium, zinc and vitamin B12. Athletes with high calorie intakes should consume foods that are naturally high in or fortified with B-group vitamins. Fluid, electrolyte and energy supplementation is desirable to support circulatory, metabolic and thermoregulatory functions. There is no special food that will help elite athletes perform better; the most important aspect of the diet of elite athletes is that it follows the basic guidelines for healthy eating.

Exercise training and nutrient intake in elderly women

This study examined the relationship between moderate exercise training (five 30- to 40-minute sessions per week for 12 weeks at 60% of heart rate reserve) and changes in nutrient intake in a group of 30 sedentary elderly women aged 67 to 85 years. Subjects were placed randomly into two groups (those who walked and those who did calisthenics) and were followed for 12 weeks. Measurements were done at three times (baseline, 5 weeks, and 12 weeks). Dietary intake was based on 7-day food records. The 12-week walking program resulted in a significant (12.6%) improvement in maximum oxygen consumption (VO2max) but no change in body weight or skinfold thicknesses compared with the calisthenics program. Despite the improvement in cardiorespiratory fitness, no significant group x time interaction effects were observed for most of the nutrient intake variables tested. To test the effects of high levels of physical activity on nutrient intake, cross-sectional comparisons were made at baseline between highly conditioned and sedentary elderly women. The highly conditioned elderly women had higher energy and nutrient intakes, especially when expressed on a weight-adjusted basis. However, no differences in measures of dietary quality were found. Dietitians should not expect spontaneous improvement in either the quantity or quality of nutrient intake by elderly women who adopt a moderate exercise program. Although nutrient intake was greater in highly conditioned elderly women, their level of fitness and physical activity may be beyond the reach of many elderly women.

Practices and recommendations of sports nutritionists

A three-part questionnaire was used to identify professionals in sports nutrition and survey their recommendations on various aspects of sports nutrition. The majority of respondents were women. Over half of the sample reported working in sports nutrition for 6 years or less, and 72% indicated that 40% or less of their job is dedicated to sports nutrition. A portion of the questionnaire assessed the subjects' opinions on various sports nutrition topics. Statements on water and electrolytes generated the most agreement while statements on protein generated the least agreement. There was a positive correlation (p < 0.004) between level of education and whether or not the respondents recommended glycogen loading, and a positive correlation (p < 0.008) between the subjects' use of dietary supplements and the fact that they recommended supplements to the athletes they counseled. The majority of professionals in this study worked with recreational athletes and were more concerned about encouraging a healthy diet than improving athletic performance.

Vitamin-mineral supplement use and nutritional status of athletes

Dietary, anthropometric, and chronic disease risk factors (CDRF) including blood lipids and blood pressure (BP), were measured in 91 vitamin-mineral supplement users (SU) and nonusers (NU) representing a wide range of athletic interests. Supplements were used by 46 (51%) subjects; 100% of female athletes and 51% of male athletes used supplements while none of a group of 15 control female subjects currently used supplements. Both dietary intake and energy expenditure were measured using 7-day records. Adiposity was determined from body weight, body mass index, and skinfolds. Total cholesterol, high-density lipoprotein cholesterol, serum ferritin, hemoglobin, hematocrit, zinc, copper, and vitamin C were based on 12-hour fasting blood samples. Dietary intake (excluding supplements) for SU tended to be greater than NU for vitamin C, thiamin, riboflavin, niacin, B6, B12, folate, calcium, iron and magnesium. Plasma vitamin C levels were significantly higher among SU than NU of both gender groups (p < 0.05). Although SU may exhibit additional healthy lifestyle practices, lipid profiles for many of these athletes were unfavorable with regard to CDRF.

Dietary intake and thiamin, iron, and zinc status in elite Nordic skiers during different training periods

This study evaluated how different training periods affect dietary intake and biochemical indices of thiamin, iron, and zinc status in elite Nordic skiers. Subjects were 17 skiers and 39 controls, ages 18-38 yrs. Dietary data were collected by 7-day food records at 3-month intervals. Coefficient of variation (CV) was used to indicate magnitude of seasonal changes. Energy intake for the year (28 food record days) was 3,802 kcal/day (CV 19.1%) in male skiers, 2,754 kcal/day (CV 3.7%) in male controls, 2,812 kcal/day (CV 9.1%) in female skiers, and 2,013 kcal/day (CV 5.9%) in female controls. CVs for thiamin, riboflavin, vitamin C, calcium, magnesium, iron, and zinc intake were 14.1-23.9% (male skiers), 2.9-15.0% (male controls), 4.8-24.5% (female skiers), and 4.3-11.5% (female controls). Seasonal changes in energy, carbohydrate, and micronutrient intakes reflected energy expenditure in male endurance athletes particularly. Erythrocyte transketolase activation coefficients and serum ferritin and zinc concentrations did not differ between skiers and controls. Seasonal variations in these biochemical indices of nutritional status were of the same magnitude in skiers and controls, despite large changes in skiers' physical activity.

Non-exercise daily energy expenditure and physical activity pattern in male endurance athletes

The present study was performed to determine whether differences in non-exercise daily energy expenditure (Md,ne) exist between trained and untrained individuals. The data from seven cross-country skiers were compared with those from eight sedentary men. Daily energy expenditure (Md) was determined using the heart rate-oxygen consumption relationship; resting metabolic rate (Mr) was measured using indirect calorimetry. A physical activity questionnaire and ratios of Md or Md,ne to Mr were used as indices of physical activity. Md and Mr were significantly higher in the trained subjects whereas Md,ne was identical in the two groups. The ratio of Md,ne to Mr and the data from the physical activity questionnaire showed that there was no significant difference in daily energy expenditure and physical activity pattern during the non-exercise time. These results suggest that the exercise-induced increase in daily energy requirements is not compensated by a more sedentary life during the other daily activities in these trained men.