Hericium erinaceus (HE), also known as Lion’s Mane mushroom, has been found to enhance cognition and metabolic flexibility in various animal models. To date however, only four studies exist in humans and none have evaluated the effects of HE on markers of metabolic flexibility or cognitive performance. A single-blind, placebo controlled, parallel-longitudinal study was used to determine the effects of HE on markers of metabolic flexibility and cognition. Twenty-four participants completed a graded exercise test on a cycle ergometer to analyze substrate oxidation rates and markers of cardiorespiratory fitness. Additionally, two dual-task challenges consisting of a Stroop Word Challenge interspersed with a Mental Arithmetic Challenge were performed, pre-post the graded exercise test, to evaluate markers of cognition in a pre-post fatigued state. Participants were stratified into two groups, receiving either 10 g of HE per day or placebo for 4-weeks in the form of two muffins identical in taste and appearance. Repeated-measures analysis of variance were conducted to evaluate potential interactions or main effects. Although group differences were noted at baseline, there were no significant interactions or main effects observed from HE ingestion for any dependent variable (all p > 0.05). Our data suggest that ingesting 10 g of HE per day for 4-weeks had no impact on metabolic flexibility and cognition in a college-age cohort. Due to the limited research on HE supplementation, future research is needed to establish an effective supplement dose and duration for potential physiological changes to be observed in humans.
Fatigue is considered a multidimensional sensation, likely resulting from repeated physiological and psychological stressors, although no universal definition exists. In sport, various mechanisms have been detailed which might cause neural, cognitive, or muscular fatigue including inadequate motor command by the motor cortex (8), modulation of brain neurotransmitters (24), metabolite build-up (25), and depletion of endogenous carbohydrate stores (24). Moreover, it is common in sport for athlete’s to be exposed to multiple stressors (i.e., dual-task challenges; DTC) simultaneously, such as concurrent psychological and physiological stressors, which are known to elicit a greater stress and fatigue response compared to that noted from a single stressor alone (12, 29). Provided these findings, athletes have turned their attention to ingesting various dietary supplements prior to competition to improve cognitive and physical performance and potentially mitigate some aspects of fatigue.
One area of interest for athletes and sport nutritionists alike are the purported anti-fatigue properties offered by the regular consumption of edible mushrooms (9). Mushrooms of a wide variety have been ingested by athletes worldwide due to their bioactive constituents of polysaccharides, proteins, vitamins, and minerals. In the animal model, mushroom ingestion has been shown to inhibit blood lactate accumulation, increase glycogen storage in the liver and muscle, and improve the integrity of the mitochondria (16). In humans, current practices for mitigating fatigue are aimed primarily at delaying skeletal and liver glycogen depletion during competition either through exogenous carbohydrate consumption or through dietary manipulations to enhance fatty acid oxidation rates (i.e., low-carbohydrate diets; 17). Regardless of which dietary technique the athlete adopts, both practices arguably rely on a high-degree of metabolic flexibility and a robust mitochondrial environment (10). Interestingly, the regular consumption of mushrooms in the animal model has been found to improve the mitochondrial environment (e.g., increased biogenesis via an increase in peroxisome proliferator-activated receptor gamma coactivator 1-alpha) and should hypothetically, improve markers of metabolic flexibility and assist in fatigue management (14).
Hericium erinaceus (HE), also known as Lion’s Mane, is a popular medicinal mushroom that has been shown in a mouse model to improve markers of metabolic flexibility by shifting the cell’s reliance towards fatty acids (13) and reducing the oxidation of endogenous carbohydrate stores during exercise (16). Similar mushrooms (e.g., Cordyceps sinensis) have shown a strong capacity to modulate mitochondrial function via their upregulation of mitochondrial biogenesis and enzymes associated with long chain fatty acid β-oxidation (9). Although the metabolic effects of HE are still unclear, the neurological and cognitive aspects of HE are frequently highlighted within the literature (15, 19, 20). For example, HE has continuously demonstrated properties to stimulate nerve growth factor and brain-derived neurotropic factor production, both which are known to increase cognitive functioning through its neurotrophic properties (5, 19). Interestingly, only four studies to date have examined the psychological, gut microbiota, and neuroprotective effects of HE in humans and findings are mixed (19, 20, 27, 30). While data are limited in both animals and humans, discrepancies in findings likely reflect the incorporation of an absolute versus a relative HE dose (grams vs. mg/kg), the dose incorporated for HE consumption (~50 mg/kg – 4 g/day), and the duration of HE consumption (2–16 weeks), Additionally, no studies have yet examined HE consumption on markers of metabolic flexibility or cognitive performance in a human cohort. Therefore, the primary purpose of this study was to examine the effects of a 4-week HE supplementation period on markers of metabolic flexibility (i.e., changes to substrate oxidation rates) with a secondary aim to examine potential changes to markers of cognition, pre-post a fatiguing graded exercise test in a college-age cohort.
A total of twenty-four (N = 24; HE: 4 males, 8 females; PLA: 6 males, 6 females; height: 173.5 ± 8.6 cm; body mass: 73.3 ± 15. 4 kg; body fat: 20.3 ± 8.1%; age: 22 ± 2.9 years) apparently healthy, college-age adults participated in this study (Table 1). In brief, participants were allowed to participate in this study if they: (a) met the American College of Sports Medicine qualifications for aerobic activity per week (i.e., 150 min of moderate-intensity or 60 min of vigorous-intensity; American College of Sports Medicine, 2021), (b) had not consumed HE in the previous two weeks in any form, and (c) were currently weight stable (± 2.5 kg) for at least one month prior to the start of the study. Following inclusion criteria, each participant then completed a medical health questionnaire, a physical activity readiness questionnaire, and gave written informed consent. Approval from the University of North Alabama’s Institutional Review Board (IRB #: 21-22-088) was obtained prior to recruitment and all participants were informed that they may terminate participation at any time. All procedures in the present study conformed to the standards set by the Declaration of Helsinki and this research was conducted in accordance with the ethical standards of the International Journal of Exercise Science.
A placebo (PLA) controlled, single-blinded, parallel-longitudinal design was employed to examine the effects of ingesting 10 g/day HE supplement for 4-weeks on markers of metabolic flexibility and cognitive function following a fatiguing graded-exercise test (GXT). Since potential changes to markers of metabolic flexibility were a primary dependent variable, participants were stratified into PLA or the HE group following visit 2 based on absolute fat oxidation rates (g·min−1) across the GXT. Each participant was then provided 2 muffins (1 muffin: carbohydrates = 14 g, protein = 3 g, fat = 30 g, total caloric load = ~340 kcals) to consume daily, one in the morning and one at night, for a total of 4-weeks. For the HE group, an additional 10 g of HE (5 g per muffin) were included in the muffins. Pilot testing prior to the initiation of the present study determined that the PLA and HE muffins were identical in taste and appearance. All muffins were baked by the lead investigator prior to distribution to the participants every week. HE was provided by Nammex Organic Mushroom Extracts (Gibsons, BC) and Nammex provided guidance for the chosen dose (10 g/day) and duration (4-weeks) incorporated in the present study. Third party testing validated that the present HE sample included a 1 : 1 ratio of dried mushroom : extract supplement containing a 33.69% volume of β-(1,3) (1,6)-glucans.
Participants completed a total of three visits comprised of a familiarization (Visit 1), and two experimental trials (Visits 2 and 3). During visit 1, preliminary data of age, height (Detecto, Webb City, MO, USA), body mass (BWB-800, Tanita Inc. Tokyo, Japan), and body composition via three-site skinfold for respective sex (male: chest, abdominal, and thigh; female: tricep, suprailiac, and thigh; Lange Skinfold Calipers, Cambridge Scientific Industries, Inc., Cambridge, Maryland) were collected. All visits consisted of a DTC, pre-post-GXT on a Velotron cycling ergometer (RacerMate, Seattle, WA, USA). However, only variables collected during visit 2 (baseline) and visit 3 (post-supplement) were included in statistical analysis.
Prior to visit 2, participants provided the principle investigator with their previous 24-h dietary food log and were reminded to replicate this diet in the 24-h period before returning for visit 3. Moreover, participants provided the primary investigator with a 3-day (Thursday, Friday, Saturday) food log to examine possible dietary changes pre-post intervention during visits 2 and 3, which might impact markers of body composition or metabolic flexibility. Statistical analyses showed no significant differences in macronutrients or overall caloric load pre-post intervention for either group (p > 0.05.
Provided the evidence demonstrating a DTC as a greater stressor and inducer of fatigue than a physical or mental stressor alone (12, 29), we chose to adopt a DTC for the present investigation to see if HE had any impact on markers of cognitive performance while participants simultaneously completed a physical challenge. Prior to the start of and following the GXT, a computer screen (MacBook Pro, 13-inch, 2020, Apple California) was placed 2 m in front of the participants at eye level for the completion of the DTC. The DTC consisted of three consecutive 15-s segments composed of two visual-verbal modified Stroop Color Word (SCW; 11) interposed by a mental arithmetic task (MAT). Participants simultaneously completed a Y-Balance Test (YBT) during the DTC (27). The cognitive component of this protocol (i.e., SCW and MAT) was adopted from previous investigations (1, 17, 28) and modified to be performed during the YBT. At the initiation of the SCW protocol, 27 words in various colors (e.g., red, blue, black, green, etc.) would appear simultaneously on the computer screen. The participants were asked to ignore the conflicting color text and as quickly as possible, verbally identify the font color in which each word was presented. Following the completion of the first SCW, participants then completed the MAT which consisted of addition and subtraction problems using single and double-digit numbers, such as “11 minus 1” or “3 plus 10”. The MAT included a total of 10 arithmetic problems. To control for a potential learning effect, participants were never exposed to repeating SCW patterns or identical arithmetic problems during the experimental sessions. Further, the variables recorded and used for analysis include the total number of correct and incorrect responses for both the SCW and MAT, as well as the number of unanswered questions during the DTC.
The YBT was conducted on the participant’s dominant limb and consisted of a single leg reach in the anterior, posterolateral, and posteromedial directions, respectively. Participants were instructed to place their hands on their hips and tap the distal portion of the foot to the furthest possible point without placing weight on the extended foot for assistance with balance. Prior to the start of the DTC, participants completed three rounds of the YBT without interference from the SCW to gather a baseline reach distance for the trial. The baseline measurement was then taken as the furthest of the three reach distances (cm). During each trial, participants were instructed to reach as far as possible and complete as many rotations as possible before they finished the SCW and MAT assessment.
Following completion of the first DTC, participants then completed a GXT on a cycle ergometer. Participants first had a heart rate (HR) monitor (T31 Transmitter, Polar Electro, Kempele, Finland) fixed across their chest and then donned metabolic headgear for the collection of cardiorespiratory measures using a metabolic cart (Parvo Medics TrueOne 2400, Sandy, UT, USA) to record oxygen consumption (VO2), carbon dioxide production (VCO2), and respiratory exchange ratio (RER). Additionally, rating of perceived exertion (RPE) was gathered in the final 30-s of each stage using the modified cycling Borg 0–10 scale (4). The present GXT was adopted as a valid protocol for measuring an individual’s substrate oxidation rates and modified by the present investigative team to start at a lighter intensity since the current study did not require participants to be well-trained (2).
Following connection to the metabolic cart, participants were asked to sit quietly for 5 min to gather resting cardiorespiratory measures. After the resting period, participants were instructed to straddle the cycle ergometer and begin pedaling at 50 W for men and 35 W for females for 5 min (Stage 1). Resistance then increased by 25 W for males and 15 W for females every 3 min until a total of 5 stages had been completed. Following each participant completing 5 stages, resistance then increased by 15 W every minute, until volitional exhaustion was achieved to obtain a VO2peak. Participants were assumed by the investigative team to be in a fatigued state following termination of the VO2peak, as evident by a final VO2peak RPE of 9 ± 1 for both visits 2 and 3.
All cardiorespiratory variables (VO2, VCO2, and RER) were averaged from steady-state expired gas and used to calculate substrate oxidation rates. The first 4 min of each stage were excluded and the last 60 s were averaged in two, 30 s cycles from breath-by-breath data. HR, RPE and blood lactate concentrations were also collected during the final 30 s of each stage. Stoichiometric equations were used to evaluate fat and carbohydrate oxidation rates during the GXT and ignored rates of protein oxidation (6).
During the experimental sessions, blood lactate concentrations (5 μl) were assessed via a finger stick at a lateral side of the nondominant index finger using a 26-gauge Dynarex (1.8 mm lancet; Orangeburg, NY) self-withdrawing safety lancet and a lactate meter (Nova Biomedical Corporation, Waltham, MA, USA) at the end of each stage during the GXT.
Data are presented at means ± SD. An alpha level of p ≤ 0.05 was determined a priori to be considered statistically significant. Data were tested for normality using the Shapiro-Wilk’s test prior to proceeding with the parametric tests as described. Sphericity was evaluated using Mauchly’s test. A 2-way (group [PLA vs. HE] × condition [PRE vs. POST]) repeated-measures analysis of variance (ANOVA) was used to assess changes in BM, BF%, as well as VO2peak. A mixed model (group [PLA vs. HE] × stage [1–5] × condition [PRE vs. POST]) repeated measures ANOVA was conducted to assess VO2, VCO2, fat oxidation, carbohydrate oxidation, and blood lactate levels. Regarding cognitive data, DTC (SCW and MAT: correct and incorrect responses, unanswered questions) and YBT data (number of rotations) were analyzed using a 3-way ANOVA (group [PLA vs. HE] × condition [PRE vs. POST] × test [Pre-GXT vs. Post-GXT]). A mixed model (group [PLA vs. HE] × condition [PRE vs. POST]) ANOVA was conducted to evaluate reach distance measures (cm). Note the term “group” refers to HE vs. PLA and “condition” refers to pre- or post-supplementation. When significance occurred, partial eta square (η2p: .01 = small effect; .09 = moderate effect; and .25 = large effect) were calculated and reported to provide effect sizes for an interpretation of meaningful differences (7). All data were analyzed using SPSS (Version 28; IBM, Chicago, IL).