Suchergebnisse

INTRODUCTION: Respiratory tract infections (RTI), such as those caused by influenza viruses and, more recently, the severe acute respiratory syndrome coronavirus-2, pose a significant burden to military health care systems and force readiness. The gut microbiota influences immune function, is malleable, and may provide a target for interventions aiming to reduce RTI burden. This narrative review summarizes existing evidence regarding the effectiveness of probiotics, prebiotics, and synbiotics, all of which are gut microbiota-targeted interventions, for reducing the burden of RTI in military-relevant populations (i.e., healthy non-elderly adults). MATERIALS AND METHODS: A systematic search strategy was used to identify recent meta-analyses and systematic reviews of randomized controlled trials conducted in healthy non-elderly adults which examined effects of probiotics, prebiotics, or synbiotics on the incidence, duration, and/or severity of RTI, or on immune responses to vaccinations against viruses that cause RTI. Relevant randomized controlled clinical trials not included in those reports were also identified. RESULTS: Meta-analyses and multiple randomized controlled trials have demonstrated that certain probiotic strains may reduce the incidence, duration, and/or severity of RTI and improve immune responses to vaccination against RTI-causing pathogens in various populations including healthy non-elderly adults. Fewer randomized controlled trials have examined the effects of prebiotics or synbiotics on RTI-related outcomes in healthy non-elderly adults. Nevertheless, some studies conducted within that population and other populations have observed that certain prebiotics and synbiotics reduce the incidence, duration, and/or severity of RTI or improve immune responses to vaccinations against RTI-causing viruses. However, across all product classes, not all product formulations have shown benefit, and most have not been tested in multiple randomized controlled trials in military-relevant populations. CONCLUSION: ...

OBJECTIVES: The fecal metabolome provides a functional readout of interactions between host, diet and the gut microbiota that may help identify gut microbiota-derived compounds associated with health outcomes. This study aimed to determine associations between inter-individual variability in gut microbiota composition, diet-induced changes in the fecal metabolome and gastrointestinal symptoms in adults consuming a diet consisting solely of military rations. METHODS: Secondary analysis of a randomized-controlled trial in which 54 healthy adults (32 ± 14 yr, BMI 26 ± 3 kg/m(2)) were randomly assigned to consume their usual diet (Control) or a provided diet of Meal, Ready-to-Eat military rations (MRE) for 3wk. Fecal microbiota composition was measured by 16S rRNA sequencing and the fecal metabolome by untargeted UPLC-MS/MS at baseline and post-intervention. Self-reported gastrointestinal symptoms were measured weekly using the Irritable Bowel Severity Scoring System (IBSSS). RESULTS: Principal coordinates analysis of baseline gut microbiota composition separated MRE participants into two clusters determined primarily by ratio of Bacteroides to Prevotella (HIGH (n = 17) or LOW (n = 10)). Random Forest classification of changes in the fecal metabolome within Control, HIGH, and LOW produced error rates of 7%, 18% and 100%, respectively, suggesting a more discriminant metabolome response in HIGH than LOW. Between-group differences in 153 metabolites were detected by ANOVA (FDR <0.20). Among those, 39 identified and 20 unidentified metabolites demonstrated an association with the gut microbiota (HIGH vs. LOW, P < 0.05). Compounds within xenobiotic, peptide/amino acid, and lipid metabolism pathways comprised 29 of the microbiota-associated metabolites. Changes in microbiota-associated metabolites were not correlated with changes in IBSSS scores. CONCLUSIONS: Changes in the fecal metabolome of individuals consuming a short-term military ration diet are associated with inter-individual variability in gut microbiota ...

OBJECTIVES: Acute bouts of sleep restriction (SR) are unavoidable in certain populations (e.g., military personnel and first responders), and impairs immune function as evidenced by delays in skin barrier recovery of experimental wounds by ∼1 day. To what extent this impairment can be mitigated by nutritional supplementation is less clear. We tested the efficacy of a multi-nutrient beverage and additional protein on wound healing in response to acute SR. METHODS: In this single-blind, cross-over study, wounds were created in healthy adults by removing the top layer of ≤ 8 forearm blisters (∼30 mm(2)) induced via suction on Day 2 of 72-h SR (lab monitored, 2-h nightly sleep). A controlled, isocaloric diet was provided during SR with either 0.9 g · kg(−1) · d(−1) protein plus placebo (PLA) or 1.5 g · kg(−1) · d(−1) protein plus multi-nutrient beverage (NUT; L-arginine: 20 g · d(−1), L-glutamine: 30 g · d(−1), omega-3 fatty acids: 1 g · d(−1), zinc sulfate: 24 mg · d(−1), vitamin D3: 800 IU · d(−1) and vitamin C: 400 mg · d(−1)). For 4 days following SR, participants were instructed to continue with the respective PLA or NUT treatment. Protein prescription and beverage components were based on data from clinical settings that have shown benefits related to postsurgical infectious complications and wound healing disorders. Skin barrier restoration was assessed by transepidermal water loss, measured daily until values were within 90% of unbroken skin. RESULTS: Twenty participants completed PLA and NUT (18 M/2F; 19.7 ± 2.3 years [mean ± SD]), Body weight change was not different during PLA and NUT (–0.06 ± 0.88 kg and −0.12 ± 1.54 kg, respectively, P = 0.90) and dietary protein intake during and after SR was 1.08 ± 0.28 g · kg(−1) · d(−1) and 1.44 ± 0.27 g · kg(−1) · d(−1), respectively. Compliance with study beverages was ∼95%. Skin barrier recovery time was shorter for NUT (4.29 ± 1.17 days) compared to PLA (5.48 ± 1.30 days) (P = 0.001). CONCLUSIONS: Supplemental nutrition may be beneficial for mitigating delays in ...

OBJECTIVES: Recent studies have reported altered fecal microbiota composition together with increased intestinal permeability (IP) and inflammation in individuals consuming military food rations in austere environments, but could not separate effects of the highly processed, commercially sterile ration-based diets from environmental factors. This study aimed to determine how the U.S. Meal, Ready-to-Eat (MRE) food ration affects fecal microbiota composition and IP. METHODS: In this parallel-arm trial, 60 adults (95% male, 18–61 yr) were randomly assigned to consume their usual diet for 31d (CON), or a strictly controlled MRE-only diet for 21d then their usual diet for 10d (MRE). Fecal samples were collected at baseline (BL, days -8–0), and during (INT, days 1–21) and after (POST, days 22–31) the intervention period to measure microbiota composition by 16S rDNA sequencing. On days 0, 10, 21 and 31 IP was measured by dual-sugar absorption test, and circulating markers of bacterial translocation from the gut lumen (LPS-binding protein (LBP)) and inflammation (hsCRP) were measured. RESULTS: During INT, carbohydrate (CON vs MRE: 44% vs 50% energy) and fiber (19 vs 26 g/d) intakes were lower in CON relative to MRE, whereas protein intake was higher (18% vs. 13% energy) (P ≤ 0.01). Body weight increased over time in CON, but transiently decreased during INT in MRE (P = 0.001). Changes in fecal microbiota composition differed over time between groups (P ≤ 0.01), with random forest models discriminating the fecal microbiota of MRE and CON samples during INT with 88% accuracy. The most discriminant genera included multiple bacteria used in food production (Lactobacillus, Lactococcus, Streptococcus, Leuconostoc) which were less abundant in MRE, and the inflammation-associated genus Sutterella which transiently increased in MRE during INT. IP and hsCRP were both lower (25% and 16%, respectively) in MRE relative to CON on day 21 (P < 0.05), but did not differ before or after. LBP did not differ between groups at any time. ...

OBJECTIVES: The Dietary Guidelines for Americans 2015–2020 indicate that potassium, choline, magnesium, calcium, vitamins A, D, E, and C are underconsumed (i.e., shortfall) micronutrients. Intakes of specific performance-related micronutrients (i.e., calcium, magnesium, folate, choline, iron, zinc, and vitamins A, D, E, B1, B2, B3, and B12), may also be a concern, as suboptimal intakes may limit adaptations to unaccustomed physical training, such as initial military training (IMT). Protein-containing foods are nutrient-dense; therefore, dietary protein intake may alter the amount of shortfall and performance-related micronutrients habitually consumed. This study explored associations between dietary protein (PRO) intake and shortfall or performance-related micronutrient intakes at IMT accession. METHODS: A 3-month food frequency questionnaire was used to estimate habitual dietary intake in male (n = 276, age: Mean (SD), 21.1 (3.8)) and female (n = 254, age: 21.2 (3.7)) recruits. Multivariate-adjusted MANCOVA and ANCOVA models were used to identify associations between quartiles of PRO intake and shortfall micronutrients or performance-related micronutrients. Models were adjusted for age, sex, ethnicity, race, physical activity, energy density, and total energy intake. RESULTS: Mean (SE) energy-adjusted PRO intakes were 29.3 (3.2), 36.0 (1.4), 40.8 (1.3), and 47.7 (3.9) g/1000 kcal for quartiles 1–4, respectively. Composite shortfall micronutrient intake differed (P < 0.001) by PRO quartile, as intake of each micronutrient, except vitamin C, progressively increased (all, P < 0.05) with increasing PRO quartiles. Similarly, composite (P < 0.001), and most individual (all, P < 0.05) performance-related micronutrient intakes, except calcium, were different across PRO quartiles. Calcium intake only differed for PRO quartile 1 and was lower than all other quartiles (P < 0.00). CONCLUSIONS: These cross-sectional data suggest that habitually consuming more protein is associated with greater intakes of ...

OBJECTIVES: Sustained negative energy balance during military operations contributes to degradations in physical and cognitive performance. Characterizing the diet-related behaviors and nutrition knowledge of Soldiers who self-select higher energy intakes during military operations may identify strategies for promoting energy balance. This study aimed to identify diet-related behaviors of Soldiers who self-selected higher energy intakes during a simulated military operation. METHODS: Dietary intake and body weight were measured daily in 54 Soldiers (91% male, BMI 25 ± 4 kg/m(2), 25 ± 4 yr) participating in a 3-d military exercise. During the exercise, Soldiers were provided with military rations (2787–3003 kcal/d), and in some cases consumed items from home or mobile catering. Food frequency and nutrition knowledge questionnaires were completed before the exercise to assess diet quality by HEI-2010 total score and nutrition knowledge, respectively, and questionnaires assessing eating behaviors during the exercise were completed daily and after the exercise. Associations between diet quality, nutrition knowledge, and diet-related behaviors with 1) daily energy intake (EI) and 2) weight loss (∆BW) were determined by backwards elimination multiple linear regression. RESULTS: EI (mean ± SD: 1947 ± 627 kcal/d) and ∆BW (−1.4 ± 1.2%) during the exercise were not correlated. After adjusting for baseline BMI, EI was associated with diet quality (β ± SE: 17 ±9 kcal/d, P = 0.07) and eating frequency (170 ± 86 kcal/d, P = 0.06) and more often intentionally eating foods to improve performance (−389 ± 207 kcal/d, P = 0.07) during the exercise (R(2) = 0.27, P = 0.03). In contrast, greater ∆BW was associated only with more often "not allowing myself to eat" certain foods during the exercise (R(2) = 0.11; −0.8 ± 0.4%, P = 0.04). Nutrition knowledge was not a significant predictor in either model. CONCLUSIONS: Findings suggest that self-selected energy intake and body weight loss during military operations may be associated with ...

OBJECTIVES: From a military perspective, the gut microbiome serves as an ideal tool to enhance Soldier gut and immune health and to improve survivability and performance. Our work employs in vitro tools as a means to elucidate systematic processes of colonic bacterial metabolism of dietary inputs under native and stressed conditions. This talk will focus on the use of in vitro fermentation to investigate both the prebiotic potential of cranberry proanthocyanidins (PAC) within a healthy microbiome and stress-induced alterations in microbial inter-species competition for fermentable fiber. METHODS: Fermentations were performed in triplicate, utilizing fecal inocula derived from at least three individuals, in a nutrient-rich anaerobic medium with sampling at 0 and 24 hrs. Within PAC supplementation studies, samples were analyzed for bacterial identification (16 s rRNA sequencing) and metabolite content (GC-FID and GC/MS). Stressed metabolism studies, which utilized fecal samples before and after a 21-day change in diet challenge (habitual vs. Meal Ready-to-Eat), employed media supplemented with resistant starch under ascending colon domain-specific conditions; samples taken were analyzed for bacterial identification (16 s rRNA) and enumeration of select organisms (qPCR). RESULTS: Bacterial population dynamics within PAC supplementation studies indicated a dose-dependent increase in several beneficial taxa, including Ruminococcus spp (P < 0.05). Phenolic metabolite generation as a function of PAC dosage identified several compounds associated with anti-inflammatory activity, including 3-(4-OH-phenyl) propionic acid (P < 0.001). Within stressed metabolism studies, Lactobacillus spp. growth was attenuated as a function of sudden change in diet (P ≤ 0.001), whereas growth of R. bromii was enhanced (P ≤ 0.05), indicating potential for an acute stressor to impact gut bacteria functional metabolism. CONCLUSIONS: In vitro fermentation elucidated both a potential prebiotic effect of cranberry PAC on gut microbiota and ...

Objective: This study characterized habitual dietary protein intake in healthy young adults entering military service and explored whether diet protein density is associated with diet quality and micronutrient intake. Methods: An FFQ was used to estimate habitual dietary intake and calculate HEI scores in 276 males [mean(SD), age:21.1y(3.8)] and 254 females [age:21.2y(3.7)]. Multivariate-adjusted MANCOVA and ANCOVA models were used to identify associations between protein density quartiles and HEI scores and micronutrient intake. Higher HEI components scores for sodium, refined grains, and empty calories indicate lower intake; higher scores for all other components indicate higher intakes. Results: Mean(SD) energy-adjusted protein intakes were 29.3(3.2), 36.0(1.4), 40.8(1.3), and 47.9(3.9) g/1,000 kcal for protein density quartiles 1–4, respectively. For males, empty calorie scores as well as dark green and orange vegetable scores were higher in quartiles 3 and 4 than 1 and 2 (all, p < 0.05). Scores for total vegetable, dairy, and total protein foods were lower in quartile 1 vs. quartiles 2, 3, and 4 (all, p < 0.05). Sodium scores decreased as quartiles increased (p < 0.001). Total HEI, fruit, whole grains, seafood and plant protein, fatty acids, and refined grain scores did not differ. For females, total HEI, vegetable, and total protein foods scores were higher in quartiles 3 and 4 than 1 and 2 (all, p < 0.05). Empty calorie scores increased as quartile increased (p < 0.05). Dairy scores were higher in quartiles 2, 3, and 4 than 1 (p < 0.05). Whole fruit scores were lowest in quartile 1 (p < 0.05). Whole grain as well as seafood and plant protein scores were higher in quartile 4 vs. 1 (both, p < 0.05). Sodium scores decreased as quartile increased (p < 0.001). Fatty acids scores did not differ. For males and females, micronutrient intakes progressively increased across quartiles with the exception of calcium and vitamin C, (all, p < 0.05). Intakes remained nearly the same when ...

OBJECTIVES: US Army Soldiers must comply with body composition (BC) and physical fitness (PF) standards as a condition for military entry and retention. Whether eating behaviors are associated with meeting these standards is unknown. This cross-sectional study aimed to determine the specific eating behaviors associated with failing BC and PF standards, and to characterize the eating behaviors and other habits of Soldiers who are high performers as defined by high PF scores and consistently meeting BC standards. METHODS: Soldiers (N = 1460, 93% enlisted, 83% male, 23.5 ± 5.2 years of age with 3.5 ± 4.0 years of service) completed a questionnaire to assess their eating behaviors and history of compliance with BC and PF standards. Multivariate adjusted logistic regression models using maximum likelihood estimation were used to examine relationships between Soldiers' eating behaviors and failing standards. Bivariate analysis was used to test differences between high (HP) and low performers (LP). RESULTS: Eating mostly (>50% of meals in last 7 days) at a dining facility lowered the odds of BC failure by 2.63 times (OR: 0.38, 95% CI: 0.22, 0.64); whereas, eating mostly Meals, Ready-to-Eat (MRE), eating at a fast rate, and ignoring fullness cues raised the odds by 2.23 times (95% CI: 1.15, 4.35), 2.65 times (95% CI: 1.18, 5.94) and 1.90 times (95% CI: 1.16, 3.11), respectively. Eating mostly at restaurants, being distracted while eating, and extreme hunger prior to meals, raised the odds of PF failure by 1.70 times (95% CI: 1.17, 2.48), 1.68 times (95% CI: 1.13, 2.51), and 1.55 times (95% CI: 1.08, 2.24), respectively. HP were significantly less likely than LP to eat mostly at restaurants (25% HP, 39% LP) and were significantly more likely than LP to report longer work hours (33% HP, 28% LP) (P < 0.05). CONCLUSIONS: Findings suggest that specific eating behaviors of Soldiers are associated with failing BC and PF standards. As eating behaviors may be modifiable, these findings could identify opportunities for ...

OBJECTIVES: Vitamin D deficiency (VDD) and iron deficiency (ID) are associated with injury risk and performance, respectively, in military recruits during initial military training (IMT). Breakfast skipping is prevalent among young adults and contributes to decreased intakes of vitamin D and iron. However, whether breakfast skipping is associated with VDD and ID in military recruits, and whether the mandatory breakfast attendance required in IMT mitigates VDD and ID is unknown. METHODS: Army, Air Force, and Marine recruits (N = 2117, 42% male, mean ± SD age 21 ± 4y) completed a food frequency questionnaire pre-IMT, and provided blood samples pre- and post-IMT. Breakfast skipping was self-reported and defined as skipping breakfast ≥3 d/wk pre-IMT. Diet quality was determined by Healthy Eating Index. ID was defined as meeting ≥2 of the following: serum ferritin 15%. VDD was defined as serum 25-hydroxyvitamin D (25OHD) <20 ng/mL. Associations between breakfast skipping, VDD, ID, vitamin D intake, and diet quality were determined by multivariate-adjusted logistic and linear regression. Mediation models tested whether diet quality and vitamin D intake mediated associations between breakfast eating and VDD. RESULTS: 50% of military recruits were classified as breakfast skippers pre-IMT. Breakfast skipping was associated with increased odds of VDD pre-IMT (OR 1.6, 95% CI 1.1–2.2). Diet quality and vitamin D intake were partial mediators, with breakfast skipping indirectly increasing odds of VDD through lower diet quality and lower vitamin D intake pre-IMT (OR 1.1, 95% CI 1.0–1.2; OR 1.2, 95% CI 1.1–14, respectively). There were no associations between habitual breakfast skipping and pre-IMT ID or pre- to post-IMT change in VDD, 25OHD concentrations, diet quality, or vitamin D intake. CONCLUSIONS: Breakfast skipping is prevalent among incoming military recruits and is associated with increased odds of VDD due in part to lower diet ...

Stress, a ubiquitous part of daily human life, has varied biological effects which are increasingly recognized as including modulation of commensal microorganisms residing in the gastrointestinal tract, the gut microbiota. In turn, the gut microbiota influences the host stress response and associated sequelae, thereby implicating the gut microbiota as an important mediator of host health. This narrative review aims to summarize evidence concerning the impact of psychological, environmental, and physical stressors on gut microbiota composition and function. The stressors reviewed include psychological stress, circadian disruption, sleep deprivation, environmental extremes (high altitude, heat, and cold), environmental pathogens, toxicants, pollutants, and noise, physical activity, and diet (nutrient composition and food restriction). Stressors were selected for their direct relevance to military personnel, a population that is commonly exposed to these stressors, often at extremes, and in combination. However, the selected stressors are also common, alone or in combination, in some civilian populations. Evidence from preclinical studies collectively indicates that the reviewed stressors alter the composition, function and metabolic activity of the gut microbiota, but that effects vary across stressors, and can include effects that may be beneficial or detrimental to host health. Translation of these findings to humans is largely lacking at present. This gap precludes concluding with certainty that transient or cumulative exposures to psychological, environmental, and physical stressors have any consistent, meaningful impact on the human gut microbiota. However, provocative preclinical evidence highlights a need for translational research aiming to elucidate the impact of stressors on the human gut microbiota, and how the gut microbiota can be manipulated, for example by using nutrition, to mitigate adverse stress responses.

Objective: This study investigated whether a stressful military training program, the 9- to 10-week U.S. Army basic combat training (BCT) course, alters the cognitive performance and mood of healthy young adult females. Background: Structured training programs including adolescent boot camps, sports training camps, learning enrichment programs, and military basic training are accepted methods for improving academic and social functioning. However, limited research is available on the behavioral effects of structured training programs in regard to cognitive performance and mood. Method: Two separate, within-subject studies were conducted with different BCT classes; in total 212 female volunteers were assessed before and after BCT. In Study 1, Four-Choice Reaction Time, Match-to-Sample, and Grammatical Reasoning tests were administered. The Psychomotor Vigilance Test (PVT) was administered in Study 2. The Profile of Mood States (POMS) was administered in both studies. Results: In Study 1, reaction time to correct responses on all three of the performance tests improved from pre- to post-BCT. In Study 2, PVT reaction time significantly improved. All POMS subscales improved over time in the second study, whereas POMS subscales in the first study failed to meet criteria for statistically significant differences over time. Conclusion: Cognition and mood substantially improved over military basic training. These changes may be a result of structured physical and mental training experienced during basic training or other factors not as yet identified. Application: Properly structured training may have extensive, beneficial effects on cognitive performance and mood; however, additional research is needed to determine what factors are responsible for such changes.

OBJECTIVES: Iron status declines with military training; however, the reason for the decline is not known. The objective of this study was to determine whether dietary iron absorption is reduced following military training and whether energy deficit during training modifies the effect. METHODS: This was a randomized, cross-over, controlled-feeding trial in healthy, active duty military males (n = 10, age 22.4 ± 5.4 y, weight 87.3 ± 10.9 kg) with normal iron status (serum ferritin 77.0 ± 36.7 ng/mL). Following a rest day (no exercise), participants completed a 72-h simulated sustained military operations (SUSOPS) followed by a 7-d recovery period. SUSOPS was comprised of military tasks designed to elicit high energy expenditures, muscle damage, and sleep deprivation. During SUSOPS, participants were randomized to consume ± 10% of estimated total daily energy expenditure (BAL) or 45% of total daily energy expenditure to induce severe negative energy balance (NEG BAL), but an equivalent amount of dietary iron. Two hours after rest, BAL, and NEG BAL participants consumed a beverage containing 3.8 mg of a stable iron isotope and plasma isotope appearance and hepcidin were determined 0, 20, 40, 60, 120, 240, and 360 min later. RESULTS: BAL maintained weight (−0.03 ± 0.8 kg) and muscle glycogen (4.1 ± 68.1% change), while NEG BAL lost weight (−2.38 ± 1.7 kg, P < 0.01) and muscle glycogen (−47.6 ± 17.8% change, P = 0.08) during SUSOPS. C-reactive protein (rest 1.2 ± 0.9, BAL 4.7 ± 3.6, NEG BAL 4.8 ± 3.5 mg/L, P(phase) < 0.001) increased with SUSOPS compared to rest regardless of energy balance. Peak plasma isotope appearance at 120 min was 49% lower with BAL (116.9 ± 81.4% change from 0 min) and 74% lower with NEG BAL (58.9 ± 38.1%) compared to rest (229.7 ± 97.3%, P < 0.01 for all comparisons). Plasma hepcidin was not different at 0 min (rest 7.2 ± 1.6, BAL 6.7 ± 2.4, NEG BAL 6.8 ± 1.7 ng/mL, P = 0.79) and peaked at 360 min (rest 19.4 ± 9.5, BAL 9.5 ± 4.7, NEG BAL 13.7 ± 8.9 ng/mL, P = 0.03). CONCLUSIONS: ...

The probiotic industry continues to grow in both usage and the diversity of products available. Scientific evidence supports clinical use of some probiotic strains for certain gastrointestinal indications. Although much less is known about the impact of probiotics in healthy populations, there is increasing consumer and scientific interest in using probiotics to promote physical and psychological health and performance. Military men and women are a unique healthy population that must maintain physical and psychological health in order to ensure mission success. In this narrative review, we examine the evidence regarding probiotics and candidate probiotics for physical and/or cognitive benefits in healthy adults within the context of potential applications for military personnel. The reviewed evidence suggests potential for certain strains to induce biophysiological changes that may offer physical and/or cognitive health and performance benefits in military populations. However, many knowledge gaps exist, effects on health and performance are generally not widespread among the strains examined, and beneficial findings are generally limited to single studies with small sample sizes. Multiple studies with the same strains and using similar endpoints are needed before definitive recommendations for use can be made. We conclude that, at present, there is not compelling scientific evidence to support the use of any particular probiotic(s) to promote physical or psychological performance in healthy military personnel. However, plausibility for physical and psychological health and performance benefits remains, and additional research is warranted. In particular, research in military cohorts would aid in assessing the value of probiotics for supporting physical and psychological health and performance under the unique demands required of these populations.

Gut microbiome community dynamics are maintained by complex microbe-microbe and microbe-host interactions, which can be disturbed by stress. In vivo studies on the dynamics and manipulation of those interactions are costly and slow, but can be accelerated using in vitro fermentation. Herein, in vitro fermentation was used to determine how an acute stressor, a sudden change in diet, impacts inter-bacterial species competition for resistant starch-supplemented medium (RSM). Fermentation vessels were seeded with fecal samples collected from 10 individuals consuming a habitual diet or U.S. military rations for 21 days. Lactobacillus spp. growth in response to RSM was attenuated following ration consumption, whereas growth of Ruminococcus bromii was enhanced. These differences were not evident in the pre-fermentation samples. Findings demonstrate how incorporating in vitro fermentation into clinical studies can increase understanding of stress-induced changes in nutrient-microbiome dynamics, and suggest that sudden changes in diet may impact inter-species competition for substrates.