Dietary Intake of Canadian Middle‐Aged Endurance Athletes

Data were collected for the present cross‐sectional study between January and August 2020. Participants were recruited via social media (Facebook) targeting endurance athlete communities across Canada, emails to friends and colleagues, and via snowball sampling. Inclusion criteria were middle‐aged (40–65 y) endurance athletes living in Canada and participating in ≥ 8 h of moderate‐vigorous aerobic training per week (e.g., long distance athletes such as marathon runners, ultra runners, triathletes, adventure racers, etc.). Exclusion criteria were any athletes that self‐disclosed their physical activity volume and/or dietary intake changed due to COVID‐19 induced restrictions that occurred in March of 2020. Additional exclusion criteria were women who were pregnant or breastfeeding, or anyone with a digestive disorder (e.g., celiac, irritable bowel syndrome, Crohn's, etc.). Informed consent and eligibility criteria were obtained using an online survey platform [Qualtrics] explaining the study with the following statement: “By clicking ‘I agree’ below, you acknowledge that you have read and understand the description provided, and as such consent to participate in this research study.” The study procedures were approved by the Research Ethics Board at the University of Regina (REB #2019‐212).

The online survey [Qualtrics] was used to collect demographic information (age, sex/gender, location of residence, self‐reported height and body mass), medical history (menopausal status for females, current or history of disease, current or history of smoking, medication use), current physical activity levels (International Physical Activity Questionnaire Short Form [IPAQ‐SF]) [23], and whether physical dietary intake changed due to COVID‐19‐induced restrictions: “Has the current COVID‐19‐induced restrictions changed the way you eat?” (with “how” and “why” follow‐up questions).

Eligible participants identified from the online survey were contacted and provided with instructions to complete a three‐day food intake record (FIR) on two non‐consecutive weekdays and one weekend day. Details including type of food and drink consumed, method of preparation, portion size consumed, and vitamin and mineral supplements were recorded. Written and verbal instructions on how to complete the FIR were provided via email and an unlisted YouTube video, respectively. If participants did not have access to a food scale, additional information on estimating portion size using a catalogue of pictures of individual food portions was provided. FIRs were reviewed by a trained research assistant [author O.M.] for clarity and detail; participants were contacted via email if additional information was required.

All food, beverage, and supplemented food and beverage items (e.g., bars or drinks with added micronutrients, protein powders, etc.) were entered by O.M. into Cronometer (v2.18.6), a freely available dietary assessment software that allows for analysis of up to 82 nutrients with information sourced from verified databases including the Canadian Nutrient File and the United States Department of Agriculture National Nutrient Database. Of note, vitamin and mineral supplements were not entered into the nutrient analysis software, and were assessed separately. A recent publication assessing the reliability and validity of Cronometer describes in more detail the standard operating procedure used by O.M. to ensure precision and accuracy of food and beverage input [24].

Data were exported to Excel where the 3‐day average intake for each participant was calculated for macronutrients and micronutrients. Estimated energy requirement (EER, using the Mifflin‐St Jeor equation and a physical activity coefficient of moderately active [1.55], very active [1.725], or extremely active [1.9]) was calculated [25] and compared to total energy intake (kcal) from the Cronometer output as “meeting,” or “not meeting” recommended intake. Macronutrient intakes were compared to dietary reference intakes (DRIs): recommended dietary allowance (RDA) (carbohydrate and protein), acceptable macronutrient distribution ranges (AMDR) (% of total intake for carbohydrate, protein, fat) [26], and sport nutrition recommendations (g/kg/day for carbohydrate and protein) [9] as “meeting,” “not meeting,” or “exceeding” recommended intakes. Water, fiber, omega‐3, and omega‐6 (mL/day or g/day) were compared to DRI Adequate Intake (AI), and micronutrient intakes were compared to DRI recommendations (RDA or AI), as “meeting,” “not meeting,” or “exceeding” recommended intakes [26].

Descriptive statistics were computed for demographics, medical history, and physical activity as mean ± standard deviation, median, and range, or as count (n, %). Average daily macronutrient and micronutrient intake parameters were calculated as mean ± standard deviation for the total cohort as well as for males and females separately; unpaired sample t‐tests were used to compare nutrient intake between males and females.

Fisher's Exact Test was used to compare the proportion of male and female endurance athletes that were meeting and exceeding the energy, macronutrient, and micronutrient recommendations. Shortfall nutrients were defined as < 75% of the total cohort meeting the recommended intakes (DRI RDA or AI), loosely based off similar previous work [27]. When inadequate micronutrient intake was observed (i.e., shortfall nutrients), vitamin and mineral supplements were considered, and Fisher's Exact Test was used to compare the proportion of male and female endurance athletes that were meeting the recommendations (i.e., food intake plus vitamin and mineral supplement(s)). Data were analyzed using IBM SPSS version 28.0.1.0 (IBM Inc., Armonk, NY), and figures were generated using GraphPad Prism version 9.0 (GraphPad Software, La Jolla, CA).

Findings of inadequate total kcal and water intake in the present cohort of both male and female middle‐aged endurance athletes align with several previous studies among collegiate and young elite endurance athletes [33, 34, 35, 36] and a more recent study among non‐elite endurance athletes (age: 34.9 ± 12.9 y) [10]. Consuming adequate total kcal and water are important for middle‐aged endurance athletes not only for optimal athletic performance, but also for muscle maintenance and recovery, bone health, hormonal regulation, immune function, hydration, and overall healthy aging [14].

Similar to previous literature among young high‐performance [19, 35, 37] and non‐elite endurance athletes [38, 39], middle‐aged endurance athletes in the present study did not meet the recommended intake of CHO [9]. Since CHO are essential for energy, recovery, and overall health, inadequate intake can be detrimental particularly among middle‐aged endurance athletes due to their high energy needs and age‐related physiological changes [14]. Conversely, and similar to previous findings [10, 19], 54.5% (n = 24) of the total cohort exceeded the AMDR for total FAT intake (20%–35% of total kcal intake). Of important consideration is the increased popularity of low CHO high FAT, or ketogenic, diets among athletes [40]. While athletes in the present study were not asked if they were intentionally adhering to a ketogenic diet, n = 4 (2 M/2 F) were at or below the DRI RDA for CHO (< 130 g/day), including n = 1 male at the definition of a ketogenic diet [approximately 10% CHO, 20% PRO and 70% FAT] [41]. While some evidence supports the use of these diets for enhanced performance [42], much of the literature suggests no change or impaired performance [40, 43, 44]. Regarding saturated fat, over 65% of the athletes exceeded recommended intakes (< 10% of total kcal intake), similar to previous findings [37, 45]. Increased saturated fat intake is associated with increased risk of obesity and cardiovascular disease [46, 47].

Some encouraging findings from the present cohort were related to dietary fiber and essential fatty acids intake. That is, most athletes met the DRI AI for daily fiber intake (M 71.4% and F 75.0%), a critical nutrient for gastrointestinal health including gut microbiota composition and function [48], and microbial byproducts (e.g. short chain fatty acids) that can subsequently impact athletic performance [49, 50]. Further, contrary to previous work reporting low adherence to omega‐3 intake [10, 19], > 75% of the present cohort met the recommended intakes in the present study. Sufficient omega‐3 intake decreases exercise‐induced inflammatory markers that promotes health and performance. The balance of omega‐6 to omega‐3 is important to optimize performance and recovery; typical Western diets have excess omega‐6 and are deficient in omega‐3 resulting in an increased ratio of omega‐6 to omega‐3 that promotes an inflammatory environment [51]. The ratio in the present study was 9.5 ± 6.9:1, higher than the ideal ratio of 4:1, but less than the reported typical Western diet ratio of 15:1–16.7:1 [51].

One hundred percent of the present cohort met the AMDR for PRO (n = 44), and 86.4% (n = 38) met the sport nutrition guidelines of 1.2–2.0 g/kg/day [9] with no difference between sexes; these findings are particularly encouraging considering age‐related decreases in muscle mass [14]. Previous studies have similarly reported sufficient PRO intakes among endurance athletes, but further reported females do not meet PRO intake guidelines compared to males [10, 19]. It has been recommended that masters endurance athletes increase their PRO intake to 1.6 g/kg/day to promote optimal post‐exercise recovery and prevent muscle mass and bone density losses associated with the aging process [14]; in the present cohort 64.3% (n = 18) males and 43.8% (n = 7) females met the 1.6 g PRO/kg/day intake guideline (p = 0.220). Of note, intake of leucine in the present cohort (M 99.3 ± 27.7 and F 92.7 ± 47.6 mg/kg/day) was above the 55 mg/kg/day recommended levels for those engaging in intensive training [14, 52] for most of the present cohort (M 89.3% [n = 25] v F 81.3% [n = 13]; p = 0.652). This is an important finding as leucine is an essential amino acid that cannot be synthesized by the human body, and is responsible for muscle growth, strength and enhanced athletic performance [14, 52, 53].

Numerous previous studies have reported findings of inadequate intakes of most micronutrients among young elite athletes [19, 37, 54, 55, 56, 57]. A recent systematic review assessing dietary intake among master's athletes (> 35 y of age) showed eight of the 26 included studies reported on five key micronutrients: they found higher iron, calcium, and sodium intakes among the athletes compared to the general Australian population [21]. When comparing intakes from the present study to average intakes of middle‐aged Canadians [32], similar findings of higher iron, calcium, and sodium intakes among the athletes were observed. However, when assessing the proportion of athletes in the present study meeting the DRIs (RDA or AI), the athletes were not meeting the micronutrient intake recommendations for iron (females only) or calcium, as well as additional micronutrients of vitamins A, D, E, K, B9, potassium, or magnesium. As athletes age, prioritizing recovery, muscle preservation, and bone health become more important; fat‐soluble vitamins, vitamin B9, calcium, potassium and magnesium work together to enhance endurance, prevent injury, and support performance. Promisingly, several athletes in the present cohort reported taking vitamin D and calcium supplements (and/or multivitamins that typically contain these micronutrients), particularly important in this Canadian cohort who do not get enough vitamin D from sunlight between October and March [58]. Regarding sodium, most of the participants in the present study exceeded the recommended intake from their diet (DRI CDRR 2300 mg/day). Of note, the CDRR (formerly UL) was derived for the general population with the primary goal of reducing chronic disease risk and do not account for the higher sodium losses incurred during prolonged endurance exercise. While there are no specific sodium intake guidelines for athletes, a recent review suggested sodium intake should be individualized based on sweat rate, sweat sodium concentration, environment, and the athlete's health history [59]. Importantly, overconsumption of sodium among athletes does not confer performance benefits [60] and may pose health risks [61].

Regarding sex differences, males were at a greater risk compared to females for not meeting the recommended intake of Vitamin A, contrary to a recent study reporting the opposite among younger non‐elite endurance athletes (average age 34.9 y) [10]. In the present cohort, females were at a greater risk compared to males for not meeting the recommended intakes of vitamin E, vitamin B1, vitamin B9, vitamin B12, calcium, potassium, iron, and selenium. Females have different nutrient needs due to fluctuations in sex hormones, substrate reliance, and increased energy demand during exercise, and females may have deficiencies in certain nutrients due to factors like menstrual losses, bioavailability, and dietary habits [15, 62, 63, 64]. Female athletes who to not consume enough B vitamins or iron may influence their ability to convert macronutrients into energy during exercise as well as increase the risk of anemia, increasing fatigue and decreasing endurance [55, 65]. Female athletes reported taking B vitamins (31.3%, n = 5), iron (12.5%, n = 2), and multivitamin (18.8%, n = 3) supplements; the two female athletes that took iron supplements were already meeting the DRIs. As female athletes transition through perimenopause and post menopause, hormonal changes impact bone density, muscle mass, energy metabolism, and cardiovascular health [66]. Unfortunately, the sample size of females in the present study was too small to evaluate differences in nutrient intake by menopause status, a research area of great importance for future research.

A strength of the present study was the comprehensive nature of evaluating both macronutrients and micronutrients among the under‐represented cohort of middle‐aged endurance athletes. A methodological strength was the utilization of a three‐day non‐consecutive (two weekdays and one weekend day) FIR; while this method of nutrient intake data collection has limitations including potential for reactivity (i.e., changing eating habits) and underreporting, its validity is higher than food frequency questionnaires [67]. Further, participants were given instructions reiterating the importance of reporting accurate intake quantities, and participants were contacted when additional information on a food entry was required. The use of a reliable and valid nutrient assessment software–Cronometer [24] – is another methodological strength. Limitations include the relatively small sample size and cross‐sectional design that may not reflect long‐term consumption patterns. As nutrient recommendations are typically expressed relative to body mass, reliance on self‐reported body mass represents a limitation. Further, athletes were not asked to record training volume or intensity on the days they recorded food intake, which could influence dietary needs and intake patterns. Lastly, protein intake across the day was not considered; research suggests distributed protein intake leads to greater lean‐mass gains and recovery from exercise for master athletes [68].