Associations between Essential Amino Acids and Functional Health Outcomes in Older Adults: Analysis of the National Health and Nutrition Examination Survey, 2001–2018

Objectives

Little is known about the relationships between habitual essential amino acid (EAA) intake and functional health in older US adults. This cross-sectional study investigates associations between usual EAA intakes and body composition, muscle strength, and physical function in US adults ≥65 y.

Methods

The Food and Nutrient Database for Dietary Studies (FNDDS) 2001–2018 was linked to USDA FoodData Central to access existing EAA composition data for FNDDS ingredients. FNDDS ingredients without existing EAA data were matched to similar ingredient codes with available EAA data. Usual intakes of EAA, leucine, lysine, and sulfur-containing AAs (SAA; methionine + cysteine) from NHANES 2001–2018 were calculated as relative [mg/kg ideal body weight (IBW)/d] and absolute (g/d) intakes for individuals ≥65 y (n = 10,843). Dependent variables were muscle strength measured by isometric grip test, BMI, waist circumference (WC), DXA-measured appendicular lean mass and whole-body fat mass, and self-reported physical function. Regression analyses were used to determine covariate-adjusted relationships between EAA, leucine, lysine, and SAA intake and functional health outcomes. P < 0.0013 was considered significant.

Results

Absolute and relative EAA, leucine, lysine, and SAA intakes were not associated with muscle strength or self-reported physical function in males or females or with body composition in males. Absolute EAA intakes (per g) were associated with WC in females (β ± SEM, 2.1 ± 0.6 cm, P = 0.0007). Absolute lysine intakes (per g) were associated with BMI (3.0 ± 0.7 kg/m², P < 0.0001) and WC (7.0 ± 1.7 cm, P = 0.0001) in females. Relative EAA, leucine, and lysine intakes (per mg/kg IBW) were associated with BMI (0.07 ± 0.02, 0.26 ± 0.07, and 0.25 ± 0.04 kg/m², respectively; P ≤ 0.0004 for all) and WC (0.18 ± 0.03, 0.81 ± 0.17, and 0.64 ± 0.10 cm, respectively; P < 0.0001 for all) in females. Relative lysine intakes (per mg/kg IBW) were associated with whole body fat mass (0.24 ± 0.07 kg, P = 0.0006) in females.

Conclusions

EAA intakes, particularly lysine, were positively associated with measures of adiposity in women ≥65 y. Investigating sources of lysine intake may provide insight about which foods or food groups are driving this relationship.

Funding Sources

IAFNS Protein Committee, USAMRDC, DoD Center Alliance for Nutrition and Dietary Supplements Research.

Amino Acid Intake and Conformance with the Dietary Reference Intakes in the United States: Analysis of the National Health and Nutrition Examination Survey, 2001–2018

Objectives

The lack of complete amino acid composition data in food composition databases has made determining population-wide amino acid intake difficult. This cross-sectional study characterizes habitual intakes of each amino acid and adherence to dietary requirements for each essential amino acid (EAA) by age, gender, and race/ethnicity in the US population.

Methods

Food and Nutrient Database for Dietary Studies ingredient codes with missing amino acid composition data were matched to similar ingredients with available data, so that amino acid composition could be determined for virtually 100% of foods reported in What We Eat in America, the dietary intake assessment component of NHANES. Amino acid intakes during 2-y cycles of NHANES 2001–2018 (n = 84,629; ≥ 2 y) were calculated as relative [mg/kg of ideal body weight (IBW)/d] and absolute (g/d) intakes. Data from NHANES 2011–2018 were used to determine the percentage of the population consuming less than the Dietary Reference Intakes for each EAA by age, sex, and race/ethnicity.

Results

Relative intakes of EAAs were greatest in those 2–3 y (females: 1552 ± 9 and males: 1659 ± 9 mg/kg IBW/d) and lowest in those ≥80 y (females: 446 ± 2 and males: 461 ± 3 mg/kg IBW/d). Absolute intakes of EAAs were greatest in those 31–50 y (females: 31.4 ± 0.1 and males: 45.5 ± 0.1 g/d) and lowest in those 2–3 y (females: 22.4 ± 0.1 and males: 26.0 ± 0.1 g/d). In individuals 2–18 y and ≥19 y, relative intakes of EAAs were lowest in the NHB population (860 ± 16 and 505 ± 5 mg/kg IBW/d, respectively) and highest in the Asian population (994 ± 35 and 580 ± 7 mg/kg IBW/d, respectively). Less than 1% of individuals ≥19 y were not meeting the Estimated Average Requirements for each EAA.

Conclusions

Individual amino acid intakes in the US population exceed recommended minimum population requirements. Future studies can use the method described here to quantify habitual amino acid intake and examine relationships with health and disease.

Funding Sources

Institute for the Advancement of Food and Nutrition Sciences (IAFNS) Protein Committee, US Army Medical Research and Development Command, and the Department of Defense Center Alliance for Nutrition and Dietary Supplements Research.

Effects of Energy Deficit on Secretory IgA During a Simulated Multi-Stressor Military Operation

Objectives

Secretory IgA (SIgA) is a critical component of mucosal immunity and a first line of defense against pathogens. Intense physical exercise, lack of sleep, and inadequate energy intake are frequently observed during military training and operations. These factors are associated with a decline in SIgA and may increase the risk of infection; however, to what degree each of these factors contributes to immune dysfunction is unclear. This study aimed to determine the effect of severe energy deficit on mucosal immunity (SIgA) during a multi-day period of intense training.

Methods

The parent study was a randomized, crossover trial in healthy males (n = 10, 22.4 ± 5.4 y, 87.3 ± 10.9 kg) to assess the effect of severe negative energy balance on inflammation, iron absorption, and other physiological and cognitive outcomes during a simulated sustained military operation (SUSOPS; high energy expenditure with repeated bouts of intense exercise). Participants completed two SUSOPS trials and were randomized to consume ± 10% of estimated total daily energy expenditure (TDEE, energy balance) or 45% of TDEE (energy deficit). At 0500 on each SUSOPS day (D1: baseline, D2:24 h, D3:48 h), participants placed polyester oral swabs under their tongue for 3-mins. A second swab was collected (i.e., placed under the tongue until saturation) to ensure adequate sample volume. SIgA secretion rate (μg/min) was calculated from SIgA concentration (μg/mL; enzyme-linked immunosorbent assay) and salivary flow rate (mL/min). Dependent variables were log10 transformed due to non-normal distribution and data were analyzed using linear mixed models.

Results

Independent of treatment, a main effect of time (P = 0.01) was observed where SIgA secretion rate declined by 20% from D2 [1.77 ± 0.34 μg/min] to D3 [1.41 ± 0.51 μg/min], P = 0.001, with no significant treatment by time interactions. A main effect of time (P = 0.01) was also found wherein SIgA concentration declined by 13% from D2 [2.67 ± 0.32 μg/mL] to D3 [2.33 ± 0.37 μg/mL], P = 0.001. There were no main or treatment effects with regard to SIgA flow rate.

Conclusions

Mucosal immune response, as measured by SIgA, declined in response to SUSOPS. Severe energy deficit did not exacerbate the decline in SIgA secretion rate observed in response to the high intensity, multi-stressor training scenario.

Funding Sources

US Army Medical Research and Development Command.

Declines in Dietary Iron Absorption Following Simulated Military Operations Are Exacerbated by Energy Deficit

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 &lt; 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, Pphase &lt; 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 &lt; 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

Dietary iron absorption is reduced following SUSOPS in healthy males with normal iron status and the reduction is exacerbated with energy deficit. Circulating concentrations of hepcidin following 72-h SUSOPS do not appear to mediate the reduction in dietary iron absorption.

Funding Sources

The views expressed are those of the authors and do not reflect official policy of the Army, DoD, or US Government. Supported by MRDC.

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

Objectives

Short-term energy deficit reduces acute measures of mixed muscle protein synthesis (MPS) and suppresses the hypothalamic-pituitary axis and endogenous testosterone synthesis. We hypothesized that testosterone supplementation could mitigate the effects of energy deficit on MPS. We conducted a randomized, double-blind, placebo-controlled trial to determine the effects of 28 days of tightly-controlled severe energy deficit (deficit 55% of total energy requirements) on measures of mixed-MPS and proteome-wide protein dynamics in non-obese men either given 200 mg testosterone enanthate (Testosterone, n = 24) or placebo (Placebo, n = 26) injections per week.

Methods

Participants received daily aliquots of deuterated water (2H2O) for 42 consecutive days (14-d weight maintenance period followed by 28-d energy deficit). Muscle biopsies were collected at rest in a fasted state at the end of the weight maintenance phase (PRE) and at the middle (MID) and end (POST) of the 28-d energy deficit. Mixed-MPS and proteome-wide protein fractional synthesis rates (FSR) were quantified. Changes over time and differences between Testosterone and Placebo were determined for mixed-MPS, and cross-sectional comparisons between Testosterone and Placebo were performed at MID and POST for proteome dynamics.

Results

In both Testosterone and Placebo, mixed-MPS were 40% and 33% lower (P &lt; 0.0005) at MID and POST energy deficit, respectively, compared to PRE, with no differences between groups or between MID and POST. Proteome-wide FSR of individual muscle proteins did not differ between Testosterone and Placebo at any time point. However, at POST, the number of individual proteins with higher FSR in Testosterone than Placebo was significant by 2-tailed binomial test (P &lt; 0.05), with values ranging from 20–32% higher FSR for myofibrillar, mitochondrial and cytosolic proteins.

Conclusions

Findings confirm the pronounced effect of short-term severe energy deficit on mixed-MPS and suggest the anabolic suppression occurs largely independent of testosterone. However, proteome-wide protein dynamics may reveal a novel time sensitive signal by which supplemental testosterone triggers a delayed increase in MPS, providing a synthetic mechanism for muscle mass preservation or accrual.

Funding Sources

Supported by DHP JPC-5/MOMRP; authors’ views not official U.S. Army or DoD policy.

How Successful Are U.S. Adults at Altering Nutrient Intakes and Meeting Dietary Guideline Recommendations?

Objectives

The Dietary Guidelines for Americans (DGAs) recommend dietary patterns that limit added sugar, sodium, and saturated fat and emphasize nutrient-dense foods. It is unknown whether individuals who self-report adhering to a diet that alters nutrient intake are, in fact, meeting DGA recommendations.

Objective: To compare dietary intakes and adherence to the DGAs in individuals who self-report following a special diet versus those who report following no diet.

Methods

NHANES 2003–2014 (≥19 y, n = 30,086) data were analyzed to determine % of the population answering yes or no to “Are you on any type of special diet?”. Individuals who answered yes, were further asked, “What kind of diet are you on?” and chose from a list of special diets (e.g., low salt or sodium; sugar free or low sugar). Mean nutrient intakes for each diet population were compared to the population following no diet. Individual usual intakes were estimated to determine the % of the population above or below nutrient-specific DGA recommendations. P &lt; 0.01 was considered significant.

Results

In U.S. adults, 15.6 ± 0.3% answered yes when asked if they adhere to a special diet. Individuals who reported following a low sugar diet (n = 208) consumed 8.8 ± 0.7% total daily energy from added sugars, which was less than those following no diet (13.8 ± 0.1%; P &lt; 0.01). Of individuals following a low sugar diet, 67 ± 4% met the recommendation to consume &lt;10% energy from added sugar, which was a greater percentage than those following no diet (32 ± 1%; P &lt; 0.01). Individuals who reported following a low salt/sodium diet (n = 580) consumed 3317 ± 110 mg/d sodium, which was less than those following no diet (3657 ± 17 mg/d; P &lt; 0.01). Only 17 ± 2% of individuals following a low salt/sodium diet met recommendations to consume &lt;2300 mg/d sodium, which was a greater percentage than those following no diet (10 ± 0%; P &lt; 0.01).

Conclusions

American adults who self-report adhering to a low sugar or low salt/sodium diet consume less added sugar and sodium, respectively, than individuals who report following no diet. However, a substantial proportion of individuals following low sugar or low salt/sodium diets are still not meeting DGA recommendations.

Funding Sources

DMRP/USAMRDC. Views expressed are those of the authors and do not reflect official policy of the Army, DoD, or US Government.

Muscle Regenerative Capacity May Be Reduced When Aerobic Exercise Is Initiated with Low Glycogen Content

Objectives

Maintaining low muscle glycogen content during recovery from aerobic exercise with low carbohydrate, high fat feeding has been shown to reduce insulin-mediated anabolic signaling compared to high carbohydrate feeding. The effects of low muscle glycogen content on intracellular regulators of muscle mass before and after aerobic exercise with carbohydrate ingestion is unclear. This study examined the effect of initiating aerobic exercise with low muscle glycogen content on postprandial insulin-dependent muscle anabolic signaling and myogenesis.

Methods

Twelve men (mean ± SD, age: 21 ± 4 y; body mass: 83 ± 11 kg; VO2peak: 44 ± 3 mL/kg/min) completed 2 cycle ergometry glycogen depletion trials separated by 7 d, followed by a 24-h period of isocaloric high fat (1.5 g/kg carbohydrate, 3.0 g/kg fat) or high carbohydrate (6.0 g/kg carbohydrate, 1.0 g/kg fat) refeeding to elicit low (LOW; 217 ± 103 mmol/kg dry wt) or adequate (AD; 396 ± 70 mmol/kg dry wt) glycogen content in randomized order. Participants then performed 80 min of cycle ergometry (64 ± 3% VO2peak) while ingesting 146 g of carbohydrate. Protein signaling (Western blotting) and gene transcription (RT-qPCR) were determined from vastus lateralis biopsies obtained before glycogen depletion (baseline, BASE), and before (PRE) and after (POST) exercise. Data presented as fold change relative to BASE for LOW and AD.

Results

Independent of time, carbohydrate sensing p-AMPKThr172 was higher (P &lt; 0.05) in LOW compared to AD, while p-p38MAPKThr180/Tyr182 was higher (P &lt; 0.05) in LOW at POST, but not different PRE. Insulin sensitive p-AKTThr473 was higher (P &lt; 0.05) in AD compared to LOW, regardless of time. Anabolic regulators, p-mTORC1Ser2448, p-p70S6KSer424/421, and p-rpS6Ser235/236 were higher (P &lt; 0.05) POST compared to PRE and BASE, independent of group. Regulators of myogenesis, MYOD and MYOGENIN were lower (P &lt; 0.05) in LOW compared to AD, regardless of time, while PAX7 was lower (P &lt; 0.05) in LOW compared to AD at PRE, but not different POST.

Conclusions

Initiating aerobic exercise with low muscle glycogen content does not appear to affect downstream insulin-dependent anabolic signaling, yet reductions in myogenic regulator factors suggest muscle repair and remodeling in recovery from exercise may be impaired.

Funding Sources

Work supported by DHP JPC-5/MOMRP; authors’ views not official U.S. Army or DoD policy.

Energy Restriction Decreases Triglyceride Turnover in Subcutaneous and Visceral Adipose Tissue, but Has No Effect on Hepatic De Novo Lipogenesis in Obese Zucker Rats

Objectives

Obesity is associated with increased hepatic de novo lipogenesis (DNL) and altered triglyceride (TG) turnover. A previous trial in male Sprague Dawley rats demonstrated that both energy restriction and higher protein diets downregulate hepatic DNL. It is unknown whether energy restriction and higher protein diets alter kinetic measures of lipid metabolism in obese rodents. The present study examined the effects of energy restriction and dietary protein content on tissue-specific lipid kinetics in obese Zucker rats.

Methods

Six-week-old female obese Zucker rats (Leprfa+/fa+; n = 48) were randomized into one of four groups: ad libitum (AL) standard AIN-93 M diet (14% protein, 9% fat, 3 mg cholesterol/100 g feed), 60% energy-restricted (ER) diet, ad libitum high protein (AL + PRO) modified AIN-93 M diet (35% protein, 9% fat, 7.2 mg cholesterol/100 g feed), or a 60% energy-restricted high protein (ER + PRO) diet. Using 2H2O labeling and mass isotopomer distribution analysis, DNL, TG turnover, and de novo cholesterol synthesis were measured in hepatic, subcutaneous adipose tissue (SAT), and visceral adipose tissue (VAT) after 10 weeks of feeding. Two-way ANOVA and post-hoc Tukey pair-wise comparisons were performed.

Results

Energy restriction, independent of protein content, resulted in less body mass gain (main effect, P &lt; 0.05), although there were no differences in body fat % (ER: 50.8 ± 2.8%, ER + PRO: 50.5 ± 3.7%, AL: 47.3 ± 5.3%, AL + PRO: 50.0 ± 5.3%; P &gt; 0.05). Energy restriction decreased TG turnover in SAT and VAT (main effect, P &lt; 0.05), increased the contribution from DNL versus other sources to newly deposited TG in VAT (P &lt; 0.01), did not change total DNL in VAT or liver (P &gt; 0.05) but reduced DNL in SAT (P &lt; 0.01), and increased hepatic, SAT, and VAT de novo cholesterol synthesis (P &lt; 0.01). Dietary protein had no effect on lipid kinetics.

Conclusions

In obese Zucker rats, hepatic DNL was not altered by energy restriction or higher protein feeding. However, energy restriction did decrease TG turnover in SAT and VAT. In a leptin-deficient rodent model of obesity, energy restriction had differential effects on various measures of lipid metabolism.

Funding Sources

DMRP/USAMRDC. Views expressed are those of the authors and do not reflect the official policy of the Army, DoD, or U.S. Government.

Longitudinal Comparison of Lean Body Mass by Dual Energy X-Ray Absorptiometry and Muscle Mass by Creatine (methyl-d3) Dilution in Response to a 28-d Severe Energy Deficit

Objectives

We reported that healthy males supplemented with testosterone gained lean body mass (LBM) during 28-d of energy deficit and 14 d of ad libitium feeding when measured by dual energy x-ray absorptiometry (DXA), but with no increase in muscle strength. We were unable to determine whether LBM gains were due to muscle mass accrual since DXA does not deliniate muscle from visceral organs and body water. Objectives: To assess the effects of testosterone supplementation on muscle mass as measured by creatine (methyl-d3) dilution, and determine the relationship between muscle mass and DXA-measured LBM in response to short-term energy deficit.

Methods

Secondary analysis of a 3-phase, randomised, double-blind, placebocontrolled trial in healthy males: 14-d free-living, eucaloric phase (P1); 28-d live-in, 55% energy deficit phase with (200 mg testosterone enanthate/wk, TEST, n = 24) or without (PLA, n = 26) testosterone (P2); and 14-d free-living, ad libitum feeding phase (P3). Muscle mass was measured by creatine dilution and LBM by DXA at the end of each phase.

Results

We previously reported increased LBM in TEST (mean change from P1 ± SEM; 2.5 ± 0.4, P &lt; 0.01), but not PLA (−0.3 ± 0.3 kg, P &gt; 0.05), following P2. Both TEST (5.2 ± 0.4 kg) and PLA (2.2 ± 0.4 kg) gained LBM in P3 (P &lt; 0.01). There was a treatment-by-phase trend for change in muscle mass (P-interaction = 0.054), but muscle mass data were highly variable and no post-hoc comparisons met statistical significance (PLA, P2: −0.3 ± 1.6; TEST, P2: −0.7 ± 1.7; PLA, P3: −0.3 ± 1.6; TEST, P3: 3.8 ± 1.7 kg; P &gt; 0.05). Cross-sectional measures of muscle mass were correlated (P &lt; 0.001) with total and appendicular LBM at P1 (r = 0.63 and 0.67), P2 (r = 0.71 and 0.72), and P3 (r = 0.55 and 0.48), respectively. However, changes in muscle mass were not associated with changes in total or appendicular LBM at P2 or P3 (P &gt; 0.05).

Conclusions

Testosterone supplementation increased LBM in response to short-term energy deficit and recovery feeding, but had no significant effect on muscle mass or muscle function. The discordance between changes in LBM and muscle mass underscore the inherent limitations of LBM as a surrogate measure for skeletal muscle mass, particularly in response to short-term intervention studies.

Funding Sources

DHP JPC-5/MOMRP; authors’ views not official U.S. Army or DoD policy.

Effects of Prolonged Energy Restriction and Dietary Protein on Muscle Protein Synthesis and Proteome Dynamics in Obese Zucker Rats

Objectives

High protein (HP) diets during short-term energy restriction (ER) attenuate energy-mediated reductions in muscle protein synthesis (MPS). MPS-adaptive responses to HP diets during prolonged ER are not well described. This study examined the effects of prolonged ER and HP on MPS and the synthesis rates of numerous individual muscle proteins.

Methods

Female 6-wk-old obese Zucker (leprfa+/fa+, n = 48) rats were randomized to one of four diet groups for 10 weeks: ad libitum-standard protein (AL-SP; 14% protein), AL-HP (35% protein), ER-SP, and ER-HP (both fed 60% of intake of AL-SP). At the start of week 10, D2O was administered by intraperitoneal injection and isotopic equilibrium was maintained daily by providing D2O in drinking water. Rats were euthanized after 1 week of labeling, and mixed-MPS (gastrocnemius), absolute mixed-MPS (mixed-MPS x muscle protein content), proteome dynamics, and protein half-lives [rate/d (k) = –ln(1-f)/d, where f is mixed-MPS and t is time in days; t1/2 (days) = ln(2)/k] were quantified.

Results

Mixed-MPS was not altered by energy status and protein intake. Gastrocnemius mass was lower (P &lt; 0.001) in ER-fed rats than AL-fed rats and higher (P = 0.034) for AL-HP than AL-SP. As a result, absolute mixed-MPS was lower (P &lt; 0.005) in ER than AL, regardless of dietary protein. Absolute synthesis in 24 of 26 myofibrillar, 32 of 61 mitochondrial, and 55 of 60 cytoplasmic measured proteins were lower in ER than AL (P &lt; 0.05), regardless of dietary protein. The difference in absolute synthesis of myofibrillar, mitochondrial, and cytoplasmic proteins due to ER compared to AL was 28%, 16%, and 27%, respectively. Comparison of HP and SP within each energy state revealed lower turnover rates and prolonged half-lives for a majority of measured muscle proteins in HP than in SP in both ER and AL conditions (P &lt; 0.001).

Conclusions

Prolonged ER in obese Zucker rats exerted a strong suppressive effect on myofibrillar, mitochondrial, and cytoplasmic MPS, suggesting reduced protein accretion contributed to lower gastrocnemius mass in ER-fed rats. Lower turnover rates of most muscle proteins in HP-fed rats without reductions in protein pool size (i.e., tissue mass) suggests prolonged HP intake, independent of energy, may prolong muscle protein lifespan of in obese Zucker rats.

Funding Sources

Supported by USAMRDC; authors’ views not official U.S. Army or DoD policy.

Greater Protein Intake at Breakfast or with Snacks and Less at Dinner Is Associated with Improved Metabolic Health in US Adults (P18-003-19)

Objectives

Greater protein intakes have been associated with decreased weight, BMI, waist circumference (WC) and increased HDL-cholesterol (HDL-C) concentrations. However, the relationship between protein intake during specific eating occasions and metabolic health is not well described. This study measured protein intake at meals (breakfast, lunch, dinner) and snacks and evaluated associations between protein intake at meals or snacks and markers of metabolic health in US adults.

Methods

Using the National Cancer Institute method, deciles of individual usual intake (IUI) for protein at meals and combined snacking occasions were calculated using NHANES 2013–2016 data (n = 10,112; ≥19 y). Relationships between protein intake at meals and snacks and markers of metabolic health were determined using regression analysis. Covariates included age, age2, sex, ethnicity, physical activity level, poverty income ratio, IUI of carbohydrate at specific meal/snack, IUI of total fat at specific meal/snack, BMI (non-weight-related variables), and IUI of protein at other meals/snacks. P < 0.01 was considered significant.

Results

Deciles of protein intake ranged (10th and 90th percentiles, mean ± SE) from 5.9 ± 0.1 to 22.6 ± 0.3 g/d at breakfast, 14.0 ± 0.1 to 34.6 ± 0.4 g/d at lunch, 24.3 ± 0.3 to 46.8 ± 0.2 g/d at dinner, and 4.9 ± 0.1 to 16.5 ± 0.2 g/d at snacking occasions. Greater protein intake at breakfast was positively related to HDL-C (0.51 ± 0.17 mg/dL per decile, P = 0.004). Protein intake at dinner was positively associated with the homeostatic model assessment of insulin resistance (0.23 ± 0.08 per decile, P = 0.008). Protein intake from snacks was inversely associated with diastolic blood pressure (−0.27 ± 0.09 mm Hg per decile, P = 0.004) and positively associated with HDL-C (0.68 ± 0.20 mg/dL per decile, P = 0.002). Protein intakes at meals and snacks were not associated with BMI, WC, systolic blood pressure, insulin, glucose, total cholesterol, LDL-cholesterol, triglycerides, or CVD risk.

Conclusions

In US adults, consuming greater protein at breakfast or with snacks and less protein at dinner may be related to improved metabolic health.

Funding Sources

The views expressed herein are those of the authors and do not reflect official policy of the Army, DoD, or U.S. Government. Supported by DMRP/USAMRMC.

Higher-protein Intakes Are Associated with an Improved Dietary Micronutrient Profile (FS03-06-19)

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 shortfall and performance-related micronutrients in young healthy adults entering the military.

Funding Sources

Supported by US Army Medical Research and Materiel Command; authors’ views not official US Army or DoD policy.

Acute Hypoxia Suppresses Exogenous Glucose Oxidation, Lowers Fat Oxidation, and Increases Muscle Glycogenolysis During Steady-state Aerobic Exercise (P08-084-19)

Objectives

Lowlanders performing steady-state aerobic exercise during high-altitude (HA) sojourns, hypoxia mediates increased endogenous carbohydrate oxidation compared to sea level (SL). At SL, ingesting carbohydrate during exercise spares endogenous carbohydrate stores and improves endurance. However, it is unclear whether that strategy is effective at HA, as data from a recent study suggests exogenous glucose oxidation is suppressed during aerobic exercise performed 5 hr after arriving at HA. This observation has not been replicated. The objective of this study was to determine substrate oxidative responses to exogenous carbohydrate ingestion during steady-state aerobic exercise at SL and HA.

Methods

Using a randomized, crossover design, native lowlanders (n = 8 males, mean ± SD, age: 23 ± 2 yr, body mass: 87 ± 10 kg, and VO2peak: SL 4.3 ± 0.2 L/min and HA 2.9 ± 0.2 L/min) consumed 145 g (1.8 g/min) of glucose while performing 80 min of metabolically-matched (SL: 1.66 ± 0.14 L/min 347 ± 29 kcal, HA: 1.59 ± 0.10 L/min, 369 ± 39 kcal) treadmill exercise at SL (757 mmHg) and HA (460 mmHg) conditions after a 5 hr exposure. Total carbohydrate and fat oxidation rates (g/min) during exercise were determined by indirect calorimetry, and exogenous, muscle- and hepatic-derived glucose oxidation by tracer technique using breath and blood measurements of 13C-glucose.

Results

Total carbohydrate oxidation was higher (P < 0.05) at HA (2.15 ± 0.32) compared to SL (1.39 ± 0.14). Exogenous glucose oxidation was lower (P < 0.05) at HA (0.35 ± 0.07) than SL (0.44 ± 0.05). Muscle glycogen oxidation was higher at HA (1.67 ± 0.26) compared to SL (0.83 ± 0.13). There was no difference in hepatic glycogen oxidation between SL (0.13 ± 0.03) and HA (0.13 ± 0.04). Fat oxidation was lower at HA (0.05 ± 0.07) than SL (0.31 ± 0.08).

Conclusions

These data confirm that acute hypoxic exposure suppresses exogenous carbohydrate oxidation during steady-state exercise. Coupled with observations that fat oxidation was reduced and muscle glycogenolysis accelerated in hypoxia, these findings suggest that ingesting carbohydrate during exercise upon acute hypoxia exposure is not an effective strategy for attenuating oxidation of endogenous carbohydrate stores.

Funding Sources

Views expressed are the authors and do not reflect the official policy of the Army, DoD, or the U.S. Government. Supported by USAMRMC.

Higher Usual Energy Intake, Body Mass, Body Mass Index, and Fat Free Mass Index Are Associated with Lower Attrition from an Arduous Military Selection Course (P23-005-19)

Objectives

To determine whether usual energy intake and body composition are associated with attrition from an arduous military selection course characterized by energy deficit and strenuous physical events, including fitness tests, loaded road marches, runs, land navigation, and an obstacle course.

Methods

Energy intake and body composition were assessed in U.S. Army Soldiers (n = 776) at the start of a military assessment and selection course. Usual energy intake (kcal) over the previous year was estimated from a 127-item Block food frequency questionnaire. Body composition measures, including body mass (kg), body mass index (BMI, body mass in kg/height in m2), fat free mass index (FFMI, fat free mass in kg/height in m2), and fat mass index (FMI, fat mass in kg/height in m2) were assessed by calibrated scale and 3-site skinfold caliper measures. Associations between energy intake, body composition, and demographics were determined with analysis of variance. Logistic regression was used to determine likelihood of attrition [odds ratio (OR), 95% confidence interval (CI)] based on quartiles of energy intake and body composition. Models were adjusted for age, education, duration of aerobic exercise, duration of strength training, smoking status, and smokeless tobacco use.

Results

Soldiers that were younger (18–24 y), engaged in longer duration of aerobic exercise (≥200 min/wk) and strength training (≥400 min/wk), had more education (≥some college), and were smokeless tobacco users had higher energy intakes (P < 0.05). Higher energy intake was associated with higher body mass and FFMI (P < 0.05). After adjustment, Soldiers with higher energy intake, body mass, BMI, and FFMI were less likely to fail the strenuous course (Q1 vs. Q2, Q3, and Q4: OR range = 0.25–0.54; 95% CI lower bound range = 0.15–0.33; 95% CI upper bound range = 0.46–0.87). FMI was not associated with attrition.

Conclusions

Optimization of body composition by adequate consumption of calories prior to a physically demanding military selection course may be associated with reduced attrition.

Funding Sources

Supported by U.S. Army Medical Research and Materiel Command. The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or reflecting the views of the Army or the Department of Defense.

Supporting Tables, Images and/or Graphs

Testosterone Administration During Energy Deficit Suppresses Hepcidin Concentrations and Increases Iron Utilization in Healthy Males (OR15-08-19)

Objectives

Military personnel are exposed to periods of energy deficit and stress, which is typically accompanied by reductions in testosterone concentrations and declines in iron status. Exogenous testosterone administration may increase erythropoiesis and iron availability.

The objective of this study was to determine the effects of exogenous testosterone on iron homeostasis in healthy young males during energy deficit.

Methods

Fifty males (24.8 ± 5.0 y, 78.6 ± 12.2 kg) completed this randomized, double-blind, placebo-controlled trial. Participants were provided a eucaloric diet during a 2-week free-living phase (day 1–14). Following the free-living phase, participants completed a 4-week live-in phase (day 15–42). During the live-in phase participants were randomized to 200 mg testosterone enanthate/week (n = 24) or 1 mL sesame oil/week (placebo, n = 26) and were in an energy- and exercise-induced energy deficit equal to 53 ± 4%. Blood was collected on days 14 and 42 to determine concentrations of testosterone, hemoglobin, hematocrit, ferritin, hepcidin, and erythroferrone. Data are reported as change scores (mean ± SD).

Results

Total testosterone concentrations increased with testosterone and declined with placebo (569 ± 271 nmol/L and −83 ± 142 nmol/L, P < 0.0001). Testosterone attenuated the decline in hemoglobin (−0.04 ± 0.7 g/L and −0.6 ± 0.8 g/dL, P < 0.01) and hematocrit (0.6 ± 2.2% and −1.3 ± 2.1%, P < 0.01) that occurred with placebo. Hepcidin (−3.7 ± 5.0 ng/mL and 2.1 ± 5.0 ng/mL, P < 0.001) and ferritin (−32.5 ± 38.6 ng/mL and 15.4 ± 41.2 ng/mL, P < 0.0001 ) were reduced with testosterone as compared to placebo. Erythroferrone (−0.5 ± 2.1 ng/mL and 0.5 ± 2.0 ng/mL, P = 0.11) did not differ when comparing testosterone to placebo.

Conclusions

Testosterone administration during energy deficit suppressed hepcidin concentrations and increased iron utilization in healthy young males. The reduction in hepcidin with testosterone administration appears to occur through an erythroferrone-independent mechanism.

Funding Sources

The views expressed are those of the authors and do not reflect the official policy of the Army, DoD, or the U.S. Government. Supported by the Collaborative Research to Optimize Warfighter Nutrition II and III projects and the Defense Health Program Joint Program Committee-5.

The role of exercising muscle length in the protective adaptation to a single bout of eccentric exercise

The purpose of this study was to determine if the protective adaptation to a single bout of eccentric exercise (repeated bout effect) is dependent on the muscle length at which the eccentric contractions are performed. Ten subjects (six men, four women) performed two bouts of 120 isokinetic eccentric contractions separated by 2 weeks (target intensity was 90% of maximum isometric strength at 70 degrees). In the initial bout one limb exercised from 30 degrees to 70 degrees of knee flexion (short initial bout; SIB) and the contralateral limb exercised from 70 degrees to 110 degrees (long initial bout; LIB). For the repeated bout 2 weeks later, the limb that initially exercised at a short length now exercised at a long length (long repeated bout; LRB) and the limb that initially exercised at a long length now exercised at a short length (short repeated bout; SRB). Isometric strength and pain (scale 0-10) were assessed immediately post exercise and on the next 3 days. Strength loss and pain were greater following LIB versus SIB (strength loss P < 0.01; pain P < 0.001) and following LRB versus SRB (strength loss P < 0.01; pain P < 0.001). Strength loss and pain were not different between LIB and LRB. Pain was significantly greater following SIB compared with SRB (P < 0.05). Strength loss was not different between SIB and SRB. These results confirm that the symptoms of muscle damage are highly dependent on exercising muscle length and also demonstrate that the repeated bout effect is dependent on muscle length. Performing an initial bout of eccentric exercise at a shortened muscle length did not protect against strength loss and pain following a repeated bout at a longer muscle length. Data are given as mean (SE) unless otherwise stated.