Comparative Analysis of Circulating Metabolomic Profiles Identifies Shared Metabolic Alterations Across Distinct Multi-Stressor Military Training Operations.

Military training provides insight into metabolic responses under unique physiological demands that can be comprehensively characterized by global metabolomic profiling to identify potential strategies for improving performance. This study identified shared changes in metabolomic profiles across three distinct military training exercises varying in magnitude and types of stress. Blood samples collected before and after three real or simulated military training exercises were analyzed using the same untargeted metabolomic profiling platform. Exercises included a three-week survival school course (ST, n=36), a four-day arctic cross country ski march (AT, n=24), and a 28-day controlled diet- and exercise-induced energy deficit (CED, n=26). Log2-fold changes of >±1 in 191, 121 and 64 metabolites were identified in the ST, AT and CED datasets, respectively. Most metabolite changes were within lipid (57-63%) and amino acid metabolism (18-19%) pathways, and changes in 87 were shared across studies. The largest and most consistent increases in shared metabolites were found in acylcarnitine, fatty acid, ketone, and glutathione metabolism pathways, whereas the largest decreases were in diacylglycerol and urea cycle metabolism pathways. Multiple shared metabolites were consistently correlated with biomarkers of inflammation, tissue damage, and anabolic hormones across studies. These three studies of real and simulated military training revealed overlapping alterations in metabolomic profiles despite differences in environment and the stressors involved. Consistent changes in metabolites related to lipid metabolism, ketogenesis and oxidative stress suggest a potential common metabolomic signature associated with inflammation, tissue damage and suppression of anabolic signaling that may characterize unique physiological demands of military training.

Exogenous erythropoietin increases hematological status, fat oxidation, and aerobic performance in males following prolonged strenuous training.

This study investigated the effects of EPO on hemoglobin (Hgb) and hematocrit (Hct), time trial (TT) performance, substrate oxidation, and skeletal muscle phenotype throughout 28 days of strenuous exercise. Eight males completed this longitudinal controlled exercise and feeding study using EPO (50 IU/kg body mass) 3×/week for 28 days. Hgb, Hct, and TT performance were assessed PRE and on Days 7, 14, 21, and 27 of EPO. Rested/fasted muscle obtained PRE and POST EPO were analyzed for gene expression, protein signaling, fiber type, and capillarization. Substrate oxidation and glucose turnover were assessed during 90-min of treadmill load carriage (LC; 30% body mass; 55 ± 5% V̇O2peak) exercise using indirect calorimetry, and 6-6-[2H2]-glucose PRE and POST. Hgb and Hct increased, and TT performance improved on Days 21 and 27 compared to PRE (p < 0.05). Energy expenditure, fat oxidation, and metabolic clearance rate during LC increased (p < 0.05) from PRE to POST. Myofiber type, protein markers of mitochondrial biogenesis, and capillarization were unchanged PRE to POST. Transcriptional regulation of mitochondrial activity and fat metabolism increased from PRE to POST (p < 0.05). These data indicate EPO administration during 28 days of strenuous exercise can enhance aerobic performance through improved oxygen carrying capacity, whole-body and skeletal muscle fat metabolism.

Higher Expression of miR-15b-5p with Inclusion of Fresh, Lean Beef as Part of a Healthy Dietary Pattern Is Inversely Associated with Markers of Cardiometabolic Disease Risk.

BACKGROUND: Considerable controversy exists surrounding the consumption of red meat and its impacts on cardiometabolic health and if it may further impact risk factors at the molecular level. OBJECTIVE: The purpose of this study was to examine the acute effects of dietary patterns, varying in red meat quantity, on the expression of circulating microRNAs (miRNAs), which are emerging biomarkers of metabolic dysfunction and chronic disease severity. METHODS: Secondary analyses were performed on plasma samples collected within a randomized, crossover design study in 16 women with overweight (mean ± standard deviation, age = 33 ± 9.89 y; body mass index = 27.9 ± 1.66 kg/m2). Participants were provided with eucaloric, isonitrogenous diets (15% of daily intake as protein) containing either 2 servings of fresh, lean beef/day (BEEF) or 0 servings of fresh, lean beef/day (PLANT) for 7 d/pattern. Fasting blood samples were collected at the end of each dietary pattern for the assessment of 12 circulating metabolic miRNA expression levels (determined a priori by quantitative reverse transcriptase-polymerase chain reaction), plasma glucose, insulin, interleukin-6, tumor necrosis factor-α, C-reactive protein (CRP), adiponectin, glucagon-like peptide-1, and branched-chain amino acids. RESULTS: Of the 12 miRNAs, miR-15b-5p expression was higher following BEEF versus PLANT (P = 0.024). Increased miR-15b-5p expression correlated with decreased fasting CRP (r = -0.494; P = 0.086) and insulin concentrations (r = -0.670; P = 0.017). miR-15b-5p was inversely correlated with insulin resistance (r = -0.642; P = 0.024) and ß cell function (r = -0.646; P = 0.023) and positively correlated with markers of insulin sensitivity (r = 0.520; P = 0.083). However, the correlations were only observed following BEEF, not PLANT. CONCLUSIONS: These data indicate that the short-term intake of fresh, lean beef as part of a healthy dietary pattern impacts potential biomarkers of cardiometabolic health that are associated with cardiometabolic risk factors in women with overweight. This study was registered at clinicaltrials.gov as NCT02614729.

Pioglitazone does not enhance exogenous glucose oxidation or metabolic clearance rate during aerobic exercise in men under acute high altitude exposure.

Insulin insensitivity decreases exogenous glucose oxidation and metabolic clearance rate (MCR) during aerobic exercise in unacclimatized lowlanders at high altitude (HA). Whether use of an oral insulin sensitizer prior to acute HA exposure enhances exogenous glucose oxidation is unclear. This study investigated the impact of Pioglitazone (PIO) on exogenous glucose oxidation and glucose turnover compared to placebo (PLA) during aerobic exercise at HA. Using a randomized, crossover design, native lowlanders (n=7 males, mean±SD, age: 23±6 yr, body mass: 84±11 kg) consumed 145 g (1.8 g/min) glucose while performing 80-min of steady-state (1.43±0.16 V̇O2 L/min) treadmill exercise at HA (460 mmHg) following short-term (5 days) use of PIO (15 mg oral dose per day) or PLA (microcrystalline cellulose pill). Substrate oxidation and glucose turnover were determined using indirect calorimetry and stable isotopes (13C-glucose and [6,6-2H2]-glucose). Exogenous glucose oxidation was not different between PIO (0.31±0.03 g/min) and PLA (0.32±0.09 g/min). Total carbohydrate oxidation (PIO: 1.65±0.22 g/min, PLA: 1.68±0.32 g/min) or fat oxidation (PIO: 0.10±0.0.08 g/min, PLA: 0.09±0.07 g/min) were not different between treatments. There was no treatment effect on glucose rate of appearance (PIO: 2.46±0.27, PLA: 2.43±0.27 mg/kg/min), disappearance (PIO: 2.19±0.17, PLA: 2.20 ± 0.22 mg/kg/min), or MCR (PIO: 1.63±0.37, PLA: 1.73±0.40 mL/kg/min). Results from this study indicate that PIO is not an effective intervention to enhance exogenous glucose oxidation or MCR during acute HA exposure. Lack of effect with PIO suggests the etiology of glucose metabolism dysregulation during acute HA exposure may not result from insulin resistance in peripheral tissues.

High-fat ketogenic diets and ketone monoester supplements differentially affect substrate metabolism during aerobic exercise.

Chronically adhering to high-fat ketogenic diets or consuming ketone monoester supplements elicits ketosis. Resulting changes in substrate metabolism appear to be drastically different between ketogenic diets and ketone supplements. Consuming a ketogenic diet increases fatty acid oxidation with concomitant decreases in endogenous carbohydrate oxidation. Increased fat oxidation eventually results in an accumulation of circulating ketone bodies, which are metabolites of fatty acids that serve as an alternative source of fuel. Conversely, consuming ketone monoester supplements rapidly increases circulating ketone body concentrations that typically exceed those achieved by adhering to ketogenic diets. Rapid increases in ketone body concentrations with ketone monoester supplementation elicit a negative feedback inhibition that reduces fatty acid mobilization during aerobic exercise. Supplement-derived ketosis appears to have minimal impact on sparing of muscle glycogen or minimizing of carbohydrate oxidation during aerobic exercise. This review will discuss the substrate metabolic and associated aerobic performance responses to ketogenic diets and ketone supplements.

Low carbohydrate availability impairs hypertrophy and anaerobic performance.

PURPOSE OF REVIEW: Highlight contemporary evidence examining the effects of carbohydrate restriction on the intracellular regulation of muscle mass and anaerobic performance. RECENT FINDINGS: Low carbohydrate diets increase fat oxidation and decrease fat mass. Emerging evidence suggests that dietary carbohydrate restriction increases protein oxidation, thereby limiting essential amino acid availability necessary to stimulate optimal muscle protein synthesis and promote muscle recovery. Low carbohydrate feeding for 24 h increases branched-chain amino acid (BCAA) oxidation and reduces myogenic regulator factor transcription compared to mixed-macronutrient feeding. When carbohydrate restriction is maintained for 8 to 12 weeks, the alterations in anabolic signaling, protein synthesis, and myogenesis likely contribute to limited hypertrophic responses to resistance training. The blunted hypertrophic response to resistance training when carbohydrate availability is low does not affect muscle strength, whereas persistently low muscle glycogen does impair anaerobic output during high-intensity sprint and time to exhaustion tests. SUMMARY: Dietary carbohydrate restriction increases BCAA oxidation and impairs muscle hypertrophy and anaerobic performance, suggesting athletes who need to perform high-intensity exercise should consider avoiding dietary strategies that restrict carbohydrate.

Sex differences in body composition and serum metabolome responses to sustained, physical training suggest enhanced fat oxidation in women compared with men.

Sex differences in energy metabolism during acute, submaximal exercise are well documented. Whether these sex differences influence metabolic and physiological responses to sustained, physically demanding activities is not well characterized. This study aimed to identify sex differences within changes in the serum metabolome in relation to changes in body composition, physical performance, and circulating markers of endocrine and metabolic status during a 17-day military training exercise. Blood was collected, and body composition and lower body power were measured before and after the training on 72 cadets (18 women). Total daily energy expenditure (TDEE) was assessed using doubly labeled water in a subset throughout. TDEE was greater in men (4,085 ± 482 kcal/d) than in women (2,982 ± 472 kcal/d, P < 0.001), but not after adjustment for dry lean mass (DLM). Men tended to lose more DLM than women (mean change [95% CI]: -0.2[-0.3, -0.1] vs. -0.0[-0.0, 0.0] kg, P = 0.063, Cohen's d = 0.50) and have greater reductions in lower body power (-244[-314, -174] vs. -130[-209, -51] W, P = 0.085, d = 0.49). Reductions in DLM and lower body power were correlated (r = 0.325, P = 0.006). Women demonstrated greater fat oxidation than men (Δfat mass/DLM: -0.20[-0.24, -0.17] vs. -0.15[-0.17, -0.13] kg, P = 0.012, d = 0.64). Metabolites within pathways of fatty acid, endocannabinoid, lysophospholipid, phosphatidylcholine, phosphatidylethanolamine, and plasmalogen metabolism increased in women relative to men. Independent of sex, changes in metabolites related to lipid metabolism were inversely associated with changes in body mass and positively associated with changes in endocrine and metabolic status. These data suggest that during sustained military training, women preferentially mobilize fat stores compared with men, which may be beneficial for mitigating loss of lean mass and lower body power.NEW & NOTEWORTHY Women preferentially mobilize fat stores compared with men in response to sustained, physically demanding military training, as evidenced by increased lipid metabolites and enhanced fat oxidation, which may be beneficial for mitigating loss of lean mass and lower body power.

Ketone Monoester Plus Carbohydrate Supplementation Does Not Alter Exogenous and Plasma Glucose Oxidation or Metabolic Clearance Rate During Exercise in Men Compared with Carbohydrate Alone.

BACKGROUND: Increasing ß-hydroxybutyrate (ßHB) availability through ketone monoester (KE) plus carbohydrate supplementation is suggested to enhance physical performance by sparing glucose use during exercise. However, no studies have examined the effect of ketone supplementation on glucose kinetics during exercise. OBJECTIVES: This exploratory study primarily aimed to determine the effect of KE plus carbohydrate supplementation on glucose oxidation during steady-state exercise and physical performance compared with carbohydrate alone. METHODS: Using a randomly assigned, crossover design, 12 men consumed 573 mg KE/kg body mass plus 110 g glucose (KE+CHO) or 110 g glucose (CHO) before and during 90 min of steady-state treadmill exercise [54 ± 3% peak oxygen uptake (V˙O2peak)] wearing a weighted vest (30% body mass; 25 ± 3 kg). Glucose oxidation and turnover were determined using indirect calorimetry and stable isotopes. Participants performed an unweighted time to exhaustion (TTE; 85% V˙O2peak) after steady-state exercise and a weighted (25 ± 3 kg) 6.4 km time trial (TT) the next day after consuming a bolus of KE+CHO or CHO. Data were analyzed by paired t-tests and mixed model ANOVA. RESULTS: ßHB concentrations were higher (P < 0.05) after exercise [2.1 mM (95% CI: 1.6, .6)] and the TT [2.6 mM (2.1, 3.1)] in KE+CHO compared with CHO. TTE was lower [-104 s (-201, -8)], and TT performance was slower [141 s (19,262)] in KE+CHO than in CHO (P < 0.05). Exogenous [-0.01 g/min (-0.07, 0.04)] and plasma [-0.02 g/min (-0.08, 0.04)] glucose oxidation and metabolic clearance rate {MCR [0.38 mg·kg-1·min-1 (-0.79, 1.54)]} were not different, and glucose rate of appearance [-0.51 mg·kg-1·min-1 (-0.97, -0.04)], and disappearance [-0.50 mg·kg-1·min-1 (-0.96, -0.04)] were lower (P < 0.05) in KE+CHO compared with CHO during steady-state exercise. CONCLUSIONS: In the current study, rates of exogenous and plasma glucose oxidation and MCR were not different between treatments during steady-state exercise, suggesting blood glucose utilization is similar between KE+CHO and CHO. KE+CHO supplementation also results in lower physical performance compared with CHO alone. This trial was registered at www. CLINICALTRIALS: gov as NCT04737694.

Performance nutrition for cold-weather military operations.

.High daily energy expenditure without compensatory increases in energy intake results in severe energy deficits during cold-weather military operations. The severity of energy deficits has been proportionally linked to declines in body mass, negative protein balance, suppression of androgen hormones, increases in systemic inflammation and degraded physical performance. Food availability does not appear to be the predominant factor causing energy deficits; providing additional rations or supplement snack bars does not reduce the severity of the energy deficits. Nutrition interventions that allow greater energy intake could be effective for reducing energy deficits during cold-weather military operations. One potential intervention is to increase energy density (i.e. energy per unit mass of food) by increasing dietary fat. Our laboratory recently reported that self-selected higher energy intakes and reductions in energy deficits were primarily driven by fat intake (r = 0.891, r2 = 0.475), which, of the three macronutrients. Further, soldiers who ate more fat lost less body mass, had lower inflammation, and maintained net protein balance compared to those who ate less fat. These data suggest that consuming high-fat energy-dense foods may be a viable nutritional intervention that mitigates the negative physiological effects of energy deficit and sustains physical performance during cold-weather military operations.

Metabolic Adaptations and Substrate Oxidation are Unaffected by Exogenous Testosterone Administration during Energy Deficit in Men.

INTRODUCTION/PURPOSE: The effects of testosterone on energy and substrate metabolism during energy deficit are unknown. The objective of this study was to determine the effects of weekly testosterone enanthate (TEST; 200 mg·wk -1 ) injections on energy expenditure, energy substrate oxidation, and related gene expression during 28 d of energy deficit compared with placebo (PLA). METHODS: After a 14-d energy balance phase, healthy men were randomly assigned to TEST ( n = 24) or PLA ( n = 26) for a 28-d controlled diet- and exercise-induced energy deficit (55% below total energy needs by reducing energy intake and increasing physical activity). Whole-room indirect calorimetry and 24-h urine collections were used to measure energy expenditure and energy substrate oxidation during balance and deficit. Transcriptional regulation of energy and substrate metabolism was assessed using quantitative reverse transcription-polymerase chain reaction from rested/fasted muscle biopsy samples collected during balance and deficit. RESULTS: Per protocol design, 24-h energy expenditure increased ( P < 0.05) and energy intake decreased ( P < 0.05) in TEST and PLA during deficit compared with balance. Carbohydrate oxidation decreased ( P < 0.05), whereas protein and fat oxidation increased ( P < 0.05) in TEST and PLA during deficit compared with balance. Change (∆; deficit minus balance) in 24-h energy expenditure was associated with ∆activity factor ( r = 0.595), but not ∆fat-free mass ( r = 0.147). Energy sensing (PRKAB1 and TP53), mitochondria (TFAM and COXIV), fatty acid metabolism (CD36/FAT, FABP, CPT1b, and ACOX1) and storage (FASN), and amino acid metabolism (BCAT2 and BCKHDA) genes were increased ( P < 0.05) during deficit compared with balance, independent of treatment. CONCLUSIONS: These data demonstrate that increased physical activity and not exogenous testosterone administration is the primary determinate of whole-body and skeletal muscle metabolic adaptations during diet- and exercise-induced energy deficit.

Changes in Immune Function during Initial Military Training.

PURPOSE: Initial military training (IMT) is a transitionary period wherein immune function may be suppressed and infection risk heightened due to physical and psychological stress, communal living, and sleep deprivation. This study characterized changes in biomarkers of innate and adaptive immune function, and potential modulators of those changes, in military recruits during IMT. METHODS: Peripheral leukocyte distribution and mitogen-stimulated cytokine profiles were measured in fasted blood samples, Epstein-Barr (EBV), varicella zoster (VZV), and herpes simplex 1 (HSV1) DNA was measured in saliva by quantitative polymerase chain reaction as an indicator of latent herpesvirus reactivation, and diet quality was determined using the healthy eating index measured by food frequency questionnaire in 61 US Army recruits (97% male) at the beginning (PRE) and end (POST) of 22-wk IMT. RESULTS: Lymphocytes and terminally differentiated cluster of differentiation (CD)4+ and CD8+ T cells increased PRE to POST, whereas granulocytes, monocytes, effector memory CD4+ and CD8+ T cells, and central memory CD8+ T cells decreased ( P ≤ 0.02). Cytokine responses to anti-CD3/CD28 stimulation were higher POST compared with PRE, whereas cytokine responses to lipopolysaccharide stimulation were generally blunted ( P < 0.05). Prevalence of EBV reactivation was higher at POST ( P = 0.04), but neither VZV nor HSV1 reactivation was observed. Diet quality improvements were correlated with CD8+ cell maturation and blunted proinflammatory cytokine responses to anti-CD3/CD28 stimulation. CONCLUSIONS: Lymphocytosis, maturation of T-cell subsets, and increased T-cell reactivity were evident POST compared with PRE IMT. Although EBV reactivation was more prevalent at POST, no evidence of VZV or HSV1 reactivation, which are more common during severe stress, was observed. Findings suggest increases in the incidence of EBV reactivation were likely appropriately controlled by recruits and immune-competence was not compromised at the end of IMT.

Effects of energy balance on cognitive performance, risk-taking, ambulatory vigilance and mood during simulated military sustained operations (SUSOPS).

Sustained operations (SUSOPS) require military personnel to conduct combat and training operations while experiencing physical and cognitive stress and limited sleep. These operations are often conducted in a state of negative energy balance and are associated with degraded cognitive performance and mood. Whether maintaining energy balance can mitigate these declines is unclear. This randomized crossover study assessed the effects of energy balance on cognitive performance, risk-taking propensity, ambulatory vigilance, and mood during a simulated 72-h SUSOPS. METHODS: Ten male Soldiers (mean ± SE; 22.4 ± 1.7 y; body weight 87.3 ± 1.1 kg) completed two, 72-h simulated SUSOPS in random order, separated by 7 days of recovery. Each SUSOPS elicited ∼4500 kcal/d total energy expenditure and restricted sleep to 4 h/night. During SUSOPS, participants consumed either an energy-balanced or restricted diet that induced a 43 ± 3% energy deficit. A cognitive test battery was administered each morning and evening to assess: vigilance, working memory, grammatical reasoning, risk-taking propensity, and mood. Real-time ambulatory vigilance was assessed each morning, evening, and night via a wrist-worn monitoring device. RESULTS: Participants exhibited heightened risk-taking propensity (p = 0.047) with lower self-reported self-control (p = 0.021) and fatigue (p = 0.013) during energy deficit compared to during energy balance. Vigilance accuracy (p < 0.001) and working memory (p = 0.040) performance decreased, and vigilance lapses increased (p < 0.001) during SUSOPS, but did not differ by diet. Percentage of correct responses to ambulatory vigilance stimuli varied during SUSOPS (p = 0.019) independent of diet, with generally poorer performance during the morning and night. Total mood disturbance (p = 0.001), fatigue (p < 0.001), tension (p = 0.003), and confusion (p = 0.036) increased whereas vigor decreased (p < 0.001) during SUSOPS, independent of diet. CONCLUSION: Prolonged physical activity combined with sleep restriction is associated with impaired vigilance, memory, and mood state. Under such conditions, maintaining energy balance prevents increased risk-taking and improves self-control, but does not improve other aspects of cognitive function or mood. Given the small sample in the present study, replication in a larger cohort is warranted.

Carbohydrate intake in recovery from aerobic exercise differentiates skeletal muscle microRNA expression.

Posttranscriptional regulation by microRNA (miRNA) facilitates exercise and diet-induced skeletal muscle adaptations. However, the impact of diet on miRNA expression during postexercise recovery remains unclear. The objective of this study was to examine the effects of consuming carbohydrate or a nutrient-free control on skeletal muscle miRNA expression during 3 h of recovery from aerobic exercise. Using a randomized, crossover design, seven men (means ± SD, age: 21 ± 3 yr; body mass: 83 ± 13 kg; V̇o2peak: 43 ± 2 mL/kg/min) completed two-cycle ergometry glycogen depletion trials followed by 3 h of recovery while consuming either carbohydrate (CHO: 1 g/kg/h) or control (CON: nutrient free). Muscle biopsy samples were obtained under resting fasted conditions at baseline and at the end of the 3-h recovery (REC) period. miRNA expression was determined using unbiased RT-qPCR microarray analysis. Trials were separated by 7 days. Twenty-five miRNAs were different (P < 0.05) between CHO and CON at REC, with Let7i-5p and miR-195-5p being the most predictive of treatment. In vitro overexpression of Let7i-5p and miR-195-p5 in C2C12 skeletal muscle cells decreased (P < 0.05) the expression of protein breakdown (Foxo1, Trim63, Casp3, and Atf4) genes, ubiquitylation, and protease enzyme activity compared with control. Energy sensing (Prkaa1 and Prkab1) and glycolysis (Gsy1 and Gsk3b) genes were lower (P < 0.05) with Let7i-5p overexpression compared with miR-195-5p and control. Fat metabolism (Cpt1a, Scd1, and Hadha) genes were lower (P < 0.05) in miR-195-5p than in control. These data indicate that consuming CHO after aerobic exercise alters miRNA profiles compared with CON, and these differences may govern mechanisms facilitating muscle recovery.NEW & NOTEWORTHY Results provide novel insight into effects of carbohydrate intake on the expression of skeletal muscle microRNA during early recovery from aerobic exercise and reveal that Let7i-5p and miR-195-5p are important regulators of skeletal muscle protein breakdown to aid in facilitating muscle recovery.

Mild to Moderate Food Deprivation Increases Hepcidin and Results in Hypoferremia and Tissue Iron Sequestration in Mice.

BACKGROUND: Short-term starvation and severe food deprivation (FD) reduce dietary iron absorption and restricts iron to tissues, thereby limiting the amount of iron available for erythropoiesis. These effects may be mediated by increases in the iron regulatory hormone hepcidin; however, whether mild to moderate FD has similar effects on hepcidin and iron homeostasis is not known. OBJECTIVES: To determine the effects of varying magnitudes and durations of FD on hepcidin and indicators of iron status in male and female mice. METHODS: Male and female C57BL/6J mice (14 wk old; n = 170) were randomly assigned to consume AIN-93M diets ad libitum (AL) or varying magnitudes of FD (10%, 20%, 40%, 60%, 80%, or 100%). FD was based on the average amount of food consumed by the AL males or females, and food was split into morning and evening meals. Mice were euthanized at 48 h and 1, 2, and 3 wk, and hepcidin and indicators of iron status were measured. Data were analyzed by Pearson correlation and one-way ANOVA. RESULTS: Liver hepcidin mRNA was positively correlated with the magnitude of FD at all time points (P < 0.05). At 3 wk, liver hepcidin mRNA increased 3-fold with 10% and 20% FD compared with AL and was positively associated with serum hepcidin (R = 0.627, P < 0.0001). Serum iron was reduced by ∼65% (P ≤ 0.01), and liver nonheme iron concentrations were ∼75% greater (P ≤ 0.01) with 10% and 20% FD for 3 wk compared with AL. Liver hepcidin mRNA at 3 wk was positively correlated with liver Bmp6 (R = 0.765, P < 0.0001) and liver gluconeogenic enzymes (R = >0.667, P < 0.05) but not markers of inflammation (P > 0.05). CONCLUSIONS: FD increases hepcidin in male and female mice and results in hypoferremia and tissue iron sequestration. These findings suggest that increased hepcidin with FD may contribute to the disturbances in iron homeostasis with undernutrition.

Testosterone undecanoate administration prevents declines in fat-free mass but not physical performance during simulated multi-stressor military operations.

Male military personnel conducting strenuous operations experience reduced testosterone concentrations, muscle mass, and physical performance. Pharmacological restoration of normal testosterone concentrations may attenuate performance decrements by mitigating muscle mass loss. Previously, administering testosterone enanthate (200 mg/wk) during 28 days of energy deficit prompted supraphysiological testosterone concentrations and lean mass gain without preventing isokinetic/isometric deterioration. Whether administering a practical dose of testosterone protects muscle and performance during strenuous operations is undetermined. The objective of this study was to test the effects of a single dose of testosterone undecanoate on body composition and military-relevant physical performance during a simulated operation. After a 7-day baseline phase (P1), 32 males (means ± SD; 77.1 ± 12.3 kg, 26.5 ± 4.4 yr) received a single dose of either testosterone undecanoate (750 mg; TEST) or placebo (PLA) before a 20-day simulated military operation (P2), followed by a 23-day recovery (P3). Assessments included body composition and physical performance at the end of each phase and circulating endocrine biomarkers throughout the study. Total and free testosterone concentrations in TEST were greater than PLA throughout most of P2 (P < 0.05), but returned to P1 values during P3. Fat-free mass (FFM) was maintained from P1 to P2 in TEST (means ± SE; 0.41 ± 0.65 kg, P = 0.53), but decreased in PLA (-1.85 ± 0.69 kg, P = 0.01) and recovered in P3. Regardless of treatment, total body mass and fat mass decreased from P1 to P2 (P < 0.05), but did not fully recover by P3. Physical performance decreased during P2 (P < 0.05) and recovered by P3, regardless of treatment. In conclusion, administering testosterone undecanoate before a simulated military operation protected FFM but did not prevent decrements in physical performance.NEW & NOTEWORTHY This study demonstrated that a single intramuscular dose of testosterone undecanoate (750 mg) administered to physically active males before a 20-day simulated, multi-stressor military operation increased circulating total and free testosterone concentrations within normal physiological ranges and spared FFM. However, testosterone administration did not attenuate decrements in physical performance across multiple measures of power, strength, anaerobic or aerobic capacity.

Initial military training modulates serum fatty acid and amino acid metabolites.

Initial military training (IMT) results in increased fat-free mass (FFM) and decreased fat mass (FM). The underlying metabolic adaptations facilitating changes in body composition during IMT are unknown. The objective of this study was to assess changes in body composition and the serum metabolome during 22-week US Army IMT. Fifty-four volunteers (mean ± SD; 22 ± 3 year; 24.6 ± 3.7 kg/m2 ) completed this longitudinal study. Body composition measurements (InBody 770) and blood samples were collected under fasting, rested conditions PRE and POST IMT. Global metabolite profiling was performed to identify metabolites involved in energy, carbohydrate, lipid, and protein metabolism (Metabolon, Inc.). There was no change in body mass (POST-PRE; 0.4 ± 5.1 kg, p = 0.59), while FM decreased (-1.7 ± 3.5 kg, p < 0.01), and FFM increased (2.1 ± 2.8 kg, p < 0.01) POST compared to PRE IMT. Of 677 identified metabolites, 340 differed at POST compared to PRE (p < 0.05, Q < 0.10). The majority of these metabolites were related to fatty acid (73%) and amino acid (26%) metabolism. Increases were detected in 41% of branched-chain amino acid metabolites, 53% of histidine metabolites, and 35% of urea cycle metabolites. Decreases were detected in 93% of long-chain fatty acid metabolites, while 58% of primary bile acid metabolites increased. Increases in amino acid metabolites suggest higher rates of protein turnover, while changes in fatty acid metabolites indicate increased fat oxidation, which likely contribute changes in body composition during IMT. Overall, changes in metabolomics profiles provide insight into metabolic adaptions underlying changes in body composition during IMT.

Circulating and skeletal muscle microRNA profiles are more sensitive to sustained aerobic exercise than energy balance in males.

MicroRNAs (miRNAs) regulate molecular processes governing muscle metabolism. Physical activity and energy balance influence both muscle anabolism and substrate metabolism, but whether circulating and skeletal muscle miRNAs mediate those effects remains unknown. This study assessed the impact of sustained physical activity with participants in energy balance (BAL) or deficit (DEF) on circulating and skeletal muscle miRNAs. Using a randomized cross-over design, 10 recreational active healthy males (mean ± SD, 22 ± 5 years, 87 ± 11 kg) completed 72 h of high aerobic exercise-induced energy expenditures in BAL (689 ± 852 kcal/day) or DEF (-2047 ± 920 kcal/day). Blood and muscle samples were collected under rested/fasted conditions before (PRE) and immediately after 120 min load carriage exercise bout at the end (POST) of the 72 h. Trials were separated by 7 days. Circulating and skeletal muscle miRNAs were measured using microarray RT-qPCR. Independent of energy status, 36 circulating miRNAs decreased (P < 0.05), while 10 miRNAs increased and three miRNAs decreased in skeletal muscle (P < 0.05) at POST compared to PRE. Of these, miR-122-5p, miR-221-3p, miR-222-3p and miR-24-3p decreased in circulation and increased in skeletal muscle. Two circulating (miR-145-5p and miR-193a-5p) and four skeletal muscle (miR-21-5p, miR-372-3p, miR-34a-5p and miR-9-5p) miRNAs had time-by-treatment effects (P < 0.05). These data suggest that changes in miRNA profiles are more sensitive to increased physical activity compared to energy status, and that changes in circulating miRNAs in response to high levels of daily aerobic exercise are not reflective of changes in skeletal muscle miRNAs. KEY POINTS: Circulating and skeletal muscle miRNA profiles are more sensitive to high levels of aerobic exercise-induced energy expenditure compared to energy status. Changes in circulating miRNA in response to high levels of daily sustained aerobic exercise are not reflective of changes in skeletal muscle miRNA.

Effects of Testosterone on Mixed-Muscle Protein Synthesis and Proteome Dynamics During Energy Deficit.

CONTEXT: Effects of testosterone on integrated muscle protein metabolism and muscle mass during energy deficit are undetermined. OBJECTIVE: The objective was to determine the effects of testosterone on mixed-muscle protein synthesis (MPS), proteome-wide fractional synthesis rates (FSR), and skeletal muscle mass during energy deficit. DESIGN: This was a randomized, double-blind, placebo-controlled trial. SETTING: The study was conducted at Pennington Biomedical Research Center. PARTICIPANTS: Fifty healthy men. INTERVENTION: The study consisted of 14 days of weight maintenance, followed by a 28-day 55% energy deficit with 200 mg testosterone enanthate (TEST, n = 24) or placebo (PLA, n = 26) weekly, and up to 42 days of ad libitum recovery feeding. MAIN OUTCOME MEASURES: Mixed-MPS and proteome-wide FSR before (Pre), during (Mid), and after (Post) the energy deficit were determined using heavy water (days 1-42) and muscle biopsies. Muscle mass was determined using the D3-creatine dilution method. RESULTS: Mixed-MPS was lower than Pre at Mid and Post (P < 0.0005), with no difference between TEST and PLA. The proportion of individual proteins with numerically higher FSR in TEST than PLA was significant by 2-tailed binomial test at Post (52/67; P < 0.05), but not Mid (32/67; P > 0.05). Muscle mass was unchanged during energy deficit but was greater in TEST than PLA during recovery (P < 0.05). CONCLUSIONS: The high proportion of individual proteins with greater FSR in TEST than PLA at Post suggests exogenous testosterone exerted a delayed but broad stimulatory effect on synthesis rates across the muscle proteome during energy deficit, resulting in muscle mass accretion during subsequent recovery.

Effect of High-Protein Diets on Integrated Myofibrillar Protein Synthesis before Anterior Cruciate Ligament Reconstruction: A Randomized Controlled Pilot Study.

Increasing dietary protein intake during periods of muscle disuse may mitigate the resulting decline in muscle protein synthesis (MPS). The purpose of this randomized pilot study was to determine the effect of increased protein intake during periods of disuse before anterior cruciate ligament (ACL) reconstruction on myofibrillar protein synthesis (MyoPS), and proteolytic and myogenic gene expression. Six healthy, young males (30 ± 9 y) were randomized to consume a high-quality, optimal protein diet (OP; 1.9 g·kg−1·d−1) or adequate protein diet (AP; 1.2 g·kg−1·d−1) for two weeks before ACL reconstruction. Muscle biopsies collected during surgery were used to measure integrated MyoPS during the intervention (via daily deuterium oxide ingestion) and gene expression at the time of surgery. MyoPS tended to be higher, with a large effect size in OP compared to AP (0.71 ± 0.1 and 0.54 ± 0.1%·d−1; p = 0.076; g = 1.56). Markers of proteolysis and myogenesis were not different between groups (p > 0.05); however, participants with greater MyoPS exhibited lower levels of MuRF1 gene expression compared to those with lower MyoPS (r = −0.82, p = 0.047). The data from this pilot study reveal a potential stimulatory effect of increased daily protein intake on MyoPS during injury-mediated disuse conditions that warrants further investigation.

Military nutrition research: Contemporary issues, state of the science and future directions.

The importance of diet and nutrition to military readiness and performance has been recognized for centuries as dietary nutrients sustain health, protect against illness, and promote resilience, performance and recovery. Contemporary military nutrition research is increasingly inter-disciplinary with emphasis often placed on the broad topics of (1) determining operational nutrition requirements in all environments, (2) characterizing nutritional practices of military personnel relative to the required (role/environment) standards, and (3) developing strategies for improving nutrient delivery and individual choices. This review discusses contemporary issues shared internationally by military nutrition research programmes, and highlights emerging topics likely to influence future military nutrition research and policy. Contemporary issues include improving the diet quality of military personnel, optimizing operational rations, and increasing understanding of biological factors influencing nutrient requirements. Emerging areas include the burgeoning field of precision nutrition and its technological enablers.