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Invited Commentary

Nutrition Assessment of the Athlete

Larson-Meyer, D. Enette PhD, RD, FACSM

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Current Sports Medicine Reports: April 2019 - Volume 18 - Issue 4 - p 105-108
doi: 10.1249/JSR.0000000000000586
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Nutrition assessment is the first step in advising athletes on dietary strategies including supplement use. The complete assessment should ideally include dietary evaluation, anthropometry and body composition analysis, biochemical testing, and nutrition-focused clinical examination (1,2). This commentary provides a brief summary of the comprehensive assessment of an individual athlete’s nutritional status (3), using the “A–E” model of Anthropometric, Biochemical, Clinical, Dietary, and Environmental assessment (4) as the framework. The article also highlights assumptions and possible errors in the collection of assessment data that should be considered in the assessment process (3).

D — Dietary Assessment

Assessment of dietary intake — including nutrients and other food components — is the cornerstone of the nutrition assessment process (5,6) and is discussed first (out of alphabetical order of the A–E Framework). The objective of dietary assessment is to evaluate what an athlete eats, either over a specific period or in a typical day. Outcomes typically include quantification of total energy, macronutrient or micronutrient intake, and/or estimation of diet quality (e.g., adequacy of fruit and vegetable intake or timing of intake around training/competition).

Dietary assessment methodologies include retrospective methods, such as dietary recalls (typically the 24-h recall) and food frequency questionnaires (FFQ), and prospective methods that include food records (or diaries) and direct observation (e.g., at a training table). Although the specific methodology used should match the intent of the assessment, staffing constraints, availability of resources (e.g., food models, portable food scales, dietary software programs, etc.), and perceived athlete burden may impact which methodology is used (3).

Retrospective Methodology

The 24-h recall is a well-known procedure that is relatively quick to administer. It, however, does not provide a valid estimate of usual intake and tends to underestimate energy intake when compared with direct measurement by doubly labeled water analysis of energy expenditure (7,8). Omission of condiments, beverages, and snacks contributes to underreporting. Employment of systematic methodology, such as the USDA five-step multiple-pass method (9,10) may reduce reporting error; whereas use of multiple recalls spaced over various seasons may provide a reasonable estimate of nutrient intake. Single 24- or 48-h recalls, however, are useful when evaluating timing of food/beverage intake in relation to exercise, gastrointestinal distress, or food allergy. In contrast, FFQ focus on identifying how frequently a specific list of food categories or individual foods/beverages are consumed and may be more representative of usual intake than a few days of collected data. FFQ are particularly useful when assessing intake of nutrients with limited dietary sources, including vitamin D (11), calcium (12), and antioxidants (13). FFQs tend to underestimate energy intake (7,8,14) but progression to the mean (overestimation with low intake and underestimation with high intake) of nutrients has been reported. FFQ methodology, however, does not collect information on meal patterns or timing of food/beverage intake (5). Although retrospective techniques are challenged by the athlete’s ability to accurately describe typical portion sizes of foods/beverages consumed, tools, such as food models, pictures of food, geometric shapes, and standard household measures and/or dishes, can assist the athlete to better describe quantities consumed (5).

Prospective Methodology

Food records can provide detailed information about eating habits and timing of intake and are thought to be reflective of usual intake if enough days are collected. While collection of more days is thought to increase the probability of obtaining a “true” picture of usual intake, it also increases athlete burden and the likelihood of recording fatigue (8). Additionally, due to day-to-day variability in food intake, the number of recording days needed to truly represent an individual’s mean intake for energy and various nutrients is longer than the 3- to 14-d records are typically kept. A study in healthy nonathletes, for example, found that 21 d were needed to accurately estimate protein intake, whereas more than 200 d were needed for vitamin C. Like the 24-h recall, food records tend to underestimate energy intake compared with doubly labeled water (8,15,16). Underreporting is estimated to range from 10% to 45% of total energy expenditure among athlete (16), with the degree of underreporting dependent on personal characteristics, including body dissatisfaction/weight consciousness, sex, age, and absolute daily energy expenditure (8,15,16). Reporting accuracy also may be selective to certain foods/nutrients; sodium, potassium, and calcium intakes are commonly underreported and fiber commonly overreported (17).

Regardless of collection method, the subsequent estimation of energy and nutrient intake from reported/recorded food intake and comparison to standard intake references introduce additional issues of reliability and validity (3). These include coding of data (matching of described foods/beverages to the closest in the food composition database), estimation of nutrient composition using dietary software programs, systematic bias associated with food products missing from the USDA (18) and other databases (which often includes sports foods), error in the chemical analysis of food (19), and the variability of nutrient content of food based on variety, season, growing conditions, storage, and cooking procedures. While these errors are difficult to assess, Braakhuis and colleagues (20) estimated that daily energy and nutrient intakes due to coding decisions by sports dietitians was greater than the athletes’ day-to-day variability for a single day’s record but similar to the variability in an average 7-d record. Differences in the variability of nutrients also were observed with almost a three-fold higher day-to-day variability for cholesterol, vitamin C, and vitamin A compared with energy, carbohydrate, and magnesium. Error associated with comparison of the athlete’s intake to reference standards including food guidance models (such as USDA’s MyPlate), the Dietary Reference Intake (DRI), or specific guidelines for athletes also is unknown but may be reduced by using intake standards specific to athletes when available. Currently, athlete-specific recommendations are available for carbohydrate and protein (21–23). The DRI (6) are appropriate for assessing micronutrient intake adequacy (24). However, it should be noted that comparing a single day’s intake with the recommended daily allowance is of little use for assessing an athlete’s micronutrient status (25) due to the number of days of intake data needed to estimate “usual” intake (25). Nevertheless, the DRI are still the best reference for evaluation of nutrient sufficiency and deficiency. An athlete’s intake data averaged over a 5- to 8-d period is a reasonable reference point, and should not fall below the estimated average intake or suggested adequate intake (indicating a high probability intake is inadequate), or above the upper limit (indicating possible risk for adverse effects from excessive intake).

A — Anthropometrics

In athletic populations, anthropometrics commonly includes measurement of height, weight, body circumferences (waist, hip, mid-thigh, calf, bicep), and subcutaneous (“skinfold”) fat thickness. Assessment of body size and body composition can be a useful part of a general assessment but is particularly useful in athletes participating in weight class, gravitational, and esthetic sports where these factors may influence competition qualification, performance, or adjudication (26). Caution should be taken when performing body composition measurements in athletes uncomfortable with physique assessment or with body image concerns.

Although there are a variety of techniques for assessing body composition, the International Olympic Committee ad hoc research working group on body composition, health, and performance (26) recommends the procedures established by the International Society for the Advancement of Kinanthropometry (ISAK) (27) or those published in the Anthropometric Standardization Reference Manual (28). The ISAK procedures focus on performing standardized anthropometric profiling and skinfold measurements at specific anatomical sites and expressing body composition as a sum of skinfolds rather than as a regression-converted estimate of body fat percentages because it introduces additional errors of assumption and validity. While other more “technical” methods of monitoring body composition are available, including plethysmography (BodPod) and dual energy x-ray absorptiometry, these techniques are not always practical or affordable and have inherent limitations (19,29). In fact, these techniques may be no better than anthropometry for accurate and reliable assessment of body composition in athletes (3,30). Bioelectrical impedance, for example, is sensitive to hydration status and dehydration overestimates body fat percentage.

B — Biochemical

Biochemical tests can provide objective and quantitative assessment of an athlete’s current nutrition status or recent nutrient intake, and often detect nutrient deficiency long before clinical signs and symptoms appear. They are particularly useful when performed along with other assessment components including dietary assessment (6). In general, nutrient concentration in serum and plasma reflects recent dietary intake (or acute status) unless the nutrient is homeostatically regulated (e.g., calcium or sodium) or buffered by extravascular sources (e.g., zinc). Nutrient content of erythrocytes, on the other hand, reflects longer-term status. Additionally, urinary analysis can be useful when there is a consistent relationship between nutrient intake/status and urinary excretion whereas hair analysis may eventually prove useful for assessment of specific trace minerals (31) including zinc (6). Nutrients that have specific biochemical markers include folate, iron, magnesium, iodine, folate and vitamins A, B12, C, and D (see Larson-Meyer et al. (18)). Limitations of use of biochemical markers in the sports setting must be considered along with cost-benefit analysis. The cost-benefit analysis should consider practicality of sample collection (19) in the athlete during training (i.e., feasibility of fasting blood or 24-hour urine collection) and whether the test has the potential to be altered by exercise, exercise-induced inflammation, or circadian variation. Some biochemical markers for example are altered by acute or chronic exercise, or due to hemoconcentration from dehydration or hemodilution from plasma volume expansion associated with endurance training or heat acclimatization. Non-specificity and poor sensitivity are limitations to many biochemical tests as are lack of specific reference ranges for well-trained athletes. For example, the mean cell volume may suggest the presence of compromised nutritional status but lack specificity to determine the underlying cause (nutritional or pathophysiological) and/or pinpoint the deficient nutrient (folate or B12). Biomarkers, such as serum retinol or zinc concentration, may not decline until overt deficiency is present, lacking sensitivity as an early nutrition marker.

C — Clinical

Clinical assessment involves collection of a detailed history, a physical examination, and the interpretation of signs and symptoms that may be related to compromised nutrition status or excess nutrient intake (6,19). A systems approach is recommended to ensure efficiency and thoroughness (32), with the eyes, mouth, lips, tongue, scalp/hair, neck, hands, fingernails, skin, muscles, and joints assessed for signs of nutrient deficiency (1). Ideally, the examination should be tailored to the individual athlete and guided by data obtained in the diet and biochemical assessments (32). Information on general well-being, appetite, chewing, swallowing, taste sensation, gastrointestinal health (nausea, vomiting, bowel regularity, stool consistency), menstrual cycle (in females), sleep patterns, and perceived metabolic/physiological improvement in response to training should be collected. The physical examination, however, may be unremarkable; overt deficiencies are rare in the healthy athlete, and subclinical deficiencies are difficult to detect from examination alone. Exceptions include iron deficiency, disordered eating, or long-term consumption of nutrient-poor fad diets. Many clinical signs and symptoms also are nonspecific, that is, fatigue, weakness, and anorexia, and could result from nonnutritional factors or compromised status of a variety of nutrients.

Collection of information on current prescription and over-the-counter medication and dietary supplement use (vitamins, minerals, herbal, and sport supplement) and possible food-drug (supplement-drug) interactions also is essential even in the healthy athlete who may be taking medications for an acute illness or chronic condition (3). Examples include tetracycline for acne (chelates with dietary calcium) and corticosteroid for musculoskeletal injury (decreases vitamin D status) (33).

E — Environment

Collection of data on environmental, social, and lifestyle factors including the athlete’s socioeconomic status, living arrangements, grocery shopping and cooking abilities, transportation, training regimen, education, culture, psychosocial support system, religious practices, and personal belief system are important because they may influence nutritional status or impact treatment. This includes cultural or religious practices and personal beliefs that dictate fasting (Buddhists, Hindu, Jewish Orthodox, Muslim, Eastern Orthodox) or restricting food choices such as following plant-based diets (Buddhists, Hindu, Seventh Day Adventists, vegans, vegetarians, animal rights activists) (34). Additionally, collecting information on desire/ability to change and barriers to change (i.e., the trans-theoretical model of health behavior change) (35), is useful because an athlete not yet considering the benefits of diet on health or performance requires a different approach than another who desires dietary change but needs strategies to do so. An athlete’s stage of change may be determined by careful listening during the assessment (i.e., why is the athlete there) or by providing the athlete with a “readiness to change ruler” (35) or formal questionnaire (36).

Conclusions

Nutritional assessment is an important first step in advising athletes on dietary strategies. Although dietary assessment is the cornerstone of nutrition assessment, it should be performed within the context of a complete evaluation of anthropometric, biochemical, clinical, and environmental components. Collection of dietary intake data can be challenging with the potential for significant error of validity and reliability, including the dietary recall and food recording by athletes, coding of data by clinicians, estimation of nutrient composition using dietary software programs and expression of data relative to reference standards. There also are limitations in anthropometric and biochemical assessment methodologies, as not all nutrients have practical and reliable markers of nutritional status and few have reference norms for the well-trained athlete. An assessment of clinical signs, potential food-drug interactions, and environmental factors completes the task.

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