Validity and reliability evidence of a point of care assessment of salivary cortisol and a-amylase: a pre-registered study

Purpose The iPro Cube is a small portable point-of-care device designed to analyse salivary markers of stress in a user-friendly manner (e.g., fast, convenient). Our aim was to test the reliability and validity of the iPro Cube to measure salivary cortisol and α-amylase as compared to the common laboratory standard method (ELISA immunoassay) prior to and after moderate intensity exercise. Methods The study was a repeated measures, pre-registered design, and statistical framework that incorporated prior knowledge directly into the estimation process. Twenty-nine individuals (age = 27.4 ± 6.6 y; body-mass = 70.8 ± 11.3 kg; height = 1.74 ± 0.92 m; 18 males) completed a single PWC75%HRmax, with repeated measures of salivary cortisol and -amylase pre, immediately post, and 30 min post-exercise. Results Correlation between the iPro Cube and laboratory-based assessments of salivary cortisol was moderate-to-large (0.53 > r r r r < 0.77). Conclusions The iPro Cube is capable of taking measures of salivary cortisol that are moderately correlated to values obtained via ELISA immunoassay, however the unit underestimates salivary cortisol and overestimates salivary -amylase at rest and post-moderate intensity exercise. It is recommended that researchers continue using standard laboratory techniques to assess these salivary stress markers

Six Days of Low Carbohydrate, Not Energy Availability, Alters the Iron and Immune Response to Exercise in Elite Athletes

Purpose To quantify the effects of a short-term (6-d) low carbohydrate (CHO) high fat (LCHF), and low energy availability (LEA) diet on immune, inflammatory, and iron-regulatory responses to exercise in endurance athletes. Methods Twenty-eight elite male race walkers completed two 6-d diet/training phases. During phase 1 (Baseline), all athletes consumed a high CHO/energy availability (CON) diet (65% CHO and ~40 kcal·kg−1 fat-free mass (FFM)·d−1). In phase 2 (Adaptation), athletes were allocated to either a CON (n = 10), LCHF (n = 8; <50 g·d−1 CHO and ~40 kcal·kg−1·FFM−1·d−1), or LEA diet (n = 10; 60% CHO and 15 kcal·kg−1·FFM−1·d−1). At the end of each phase, athletes completed a 25-km race walk protocol at ~75% V˙O2max. On each occasion, venous blood was collected before and after exercise for interleukin-6, hepcidin, cortisol, and glucose concentrations, as well as white blood cell counts. Results The LCHF athletes displayed a greater IL-6 (P = 0.019) and hepcidin (P = 0.011) response to exercise after Adaptation, compared with Baseline. Similarly, postexercise increases in total white blood cell counts (P = 0.026) and cortisol levels (P 0.05). No differences between CON and LEA were evident for any of the measured biological markers (all P > 0.05). Conclusions Short-term adherence to a LCHF diet elicited small yet unfavorable iron, immune, and stress responses to exercise. In contrast, no substantial alterations to athlete health were observed when athletes restricted energy availability compared with athletes with adequate energy availability. Therefore, short-term restriction of CHO, rather than energy, may have greater negative impacts on athlete health

Influence of periodizing dietary carbohydrate on iron regulation and immune function in elite triathletes

Sleeping with low carbohydrate (CHO) availability is a dietary strategy that may enhance training adaptation. However, the impact on an athlete’s health is unclear. This study quantified the effect of a short-term “sleep-low” dietary intervention on markers of iron regulation and immune function in athletes. In a randomized, repeated-measures design, 11 elite triathletes completed two 4-day mixed cycle run training blocks. Key training sessions were structured such that a high-intensity training session was performed in the field on the afternoon of Days 1 and 3, and a low-intensity training (LIT) session was performed on the following morning in the laboratory (Days 2 and 4). The ingestion of CHO was either divided evenly across the day (HIGH) or restricted between the high-intensity training and LIT sessions, so that the LIT session was performed with low CHO availability (LOW). Venous blood and saliva samples were collected prior to and following each LIT session and analyzed for interleukin-6, hepcidin 25, and salivary immunoglobulin-A. Concentrations of interleukin-6 increased acutely after exercise (p < .001), but did not differ between dietary conditions or days. Hepcidin 25 increased 3-hr postexercise (p < .001), with the greatest increase evident after the LOW trial on Day 2 (2.5 ± 0.9 fold increase ±90% confidence limit). The salivary immunoglobulin-A secretion rate did not change in response to exercise; however, it was highest during the LOW condition on Day 4 (p = .046). There appears to be minimal impact to markers of immune function and iron regulation when acute exposure to low CHO availability is undertaken with expert nutrition and coaching input

Chronic Adherence to a Ketogenic Diet Modifies Iron Metabolism in Elite Athletes

Purpose The short-term restriction of carbohydrate (CHO) can potentially influence iron regulation via modification of postexercise interleukin-6 (IL-6) and hepcidin levels. This study examined the effect of a chronic ketogenic low-CHO high-fat (LCHF) diet on iron status and iron-regulatory markers in elite athletes. Methods International-level race walkers (n = 50) were allocated to one of three dietary interventions: (i) a high-CHO diet (n = 16), (ii) a periodized CHO availability (n = 17), or (iii) an LCHF diet (n = 17) while completing a periodized training program for 3 wk. A 19- to 25-km race walking test protocol was completed at baseline and after adaptation, and changes in serum ferritin, IL-6, and hepcidin concentrations were measured. Results from high-CHO and periodized CHO were combined into one group (CHO; n = 33) for analysis. Results The decrease in serum ferritin across the intervention period was substantially greater in the CHO group (37%) compared with the LCHF (23%) group (P = 0.021). After dietary intervention, the postexercise increase in IL-6 was greater in LCHF (13.6-fold increase; 95% confidence interval [CI] = 7.1–21.4) than athletes adhering to a CHO-rich diet (7.6-fold increase; 95% CI = 5.5–10.2; P = 0.033). Although no significant differences occurred between diets, CI values indicate that 3 h postexercise hepcidin concentrations were lower after dietary intervention compared with baseline in CHO (β = −4.3; 95% CI = −6.6 to −2.0), with no differences evident in LCHF. Conclusion Athletes who adhered to a CHO-rich diet experienced favorable changes to the postexercise IL-6 and hepcidin response, relative to the LCHF group. Lower serum ferritin after 3 wk of additional dietary CHO might reflect a larger more adaptive hematological response to training