BACKGROUND AND AIMS:Beta-hydroxy-beta-methylbutyrate (HMB), a natural breakdown product of the amino acid leucine, has been shown to increase protein synthesis in human skeletal muscle. After demonstrating in a randomised 10-day supplementation trial using isotopes, a significant reduction of net protein breakdown in critically ill patients, this post-hoc study aimed to investigate the global, extra-, and intracellular protein synthesis pathways impacted by HMB, and its influence on the inflammatory response. METHODS:This secondary post-hoc analysis used data from the previously published randomized trial, where critically ill patients were supplied with 3 g of HMB/day or placebo for at least 10 days. The study procedures were conducted in the postabsorptive state on days 4 and 15 after ICU admission. Blood analysis included cytokines (by Luminex), C-reactive protein (CRP), amino acids (AA), urea and creatinine. Amino acid whole body productions and plasma concentrations were measured after pulse administrations of an 8 mL solution containing 18 stable AA tracers. Data are presented as means [95%CI]. RESULTS:Altogether 37 patients were included (aged 65 [56, 74] years, SAPS2 48 [40, 52], and APACHEII 23 [19, 26]): baseline characteristics did not differ between the groups. Among the 37 measured cytokines, most declined by day 15, except for some specific growth factors. Twelve cytokines differed significantly between groups post-intervention, with levels being higher in HMB group (including 7 proinflammatory cytokines) (p < 0.05). Whole body production of AA and extracellular pool sizes did not differ significantly by day 15. In the HMB group (vs. placebo), the intracellular pool sizes of citrulline, glutamine, HMB, KMV (α-keto-β-methylvaleric acid), taurine, and tau-methyhistidine increased and were significantly higher post-intervention. Taurine production increased significantly and similarly in both groups (p < 0.05) but glutamine and HMB production increased significantly more in the HMB group. In parallel, the urea to creatinine ratio decreased significantly (125 vs 181, p = 0.002) by day 15 in the HMB group. CONCLUSION:The present study shows that HMB supplementation is associated with a different inflammatory pattern, suggesting a more efficient immune response. Furthermore, HMB has a significant impact on intracellular synthesis of selected AA, particularly glutamine. (NCT03628365: https://clinicaltrials.gov/ct2/show/NCT03628365).

BACKGROUND:Our recent Protein Recommendation to Increase Muscle (PRIMe) trial suggested that increasing daily protein intake via nutrition counseling in patients with colorectal cancer positively impacts muscle mass. OBJECTIVES:This post hoc analysis investigated whether baseline systemic inflammation, hormone, and/or amino acid disturbances influenced the effectiveness of nutrition support (focused on high protein) to increase lean soft tissue (LST). Outcomes were analyzed based on actual achieved protein intake, allowing exploration of dose-response effects. METHODS:In patients with stage II-IV colorectal cancer who received nutritional counseling to reach protein intake of 1.0 or 2.0 g/kg/d for 12 wk, LST was assessed by dual-energy X-ray absorptiometry, dietary protein intake by weighted 3-d food records, and cytokine, hormone (Luminex), and amino acid concentrations (liquid chromatography-tandem mass spectroscopy) at baseline and 6 and 12 wk. RESULTS:The mean protein intake of the entire group [50 patients, age 57 y (SD 11 y)] was 88.7 g/d, and baseline cytokines were elevated. Although protein intake (in grams) increased by 22% (9.34%) and 29% (16.42%) at 6 and 12 wk of supplementation, respectively, the LST response varied widely. At 6 wk, 77% of LST response variation was explained by baseline concentrations of interleukin (IL)-6, insulin, and specific amino acids (hydroxyproline, aspartate, taurine) and protein intake changes (P = 0.021). By 12 wk, IL-6 and methionine explained only 32% (P = 0.030). Tumor stage and concurrent chemotherapy type did not play a role. Positive LST change after 6 wk occurred at daily protein increase of 27 g. CONCLUSIONS:Elevated IL-6 blunts the anabolic capacity of protein support in colorectal cancer. At least 27 g/d of supplemental protein is needed to reach anabolism, although higher amounts may be needed in patients with higher IL-6 levels. These findings support the need to consider baseline inflammation to optimize the effectiveness of nutritional support in cancer. This trial was registered at clinicaltrials.gov as NCT02788955. https://clinicaltrials.gov/study/NCT02788955.

BACKGROUND:Establishing the metabolic fate of nutrients from food intake is crucial for interpreting the benefits of food interventions. Using stable isotopes labeled amino acids (AA) such as L-phenylalanine (Phe) during feeding allows for the determination of first-pass splanchnic extraction (SPE) on a whole-body level (WbSPE). The relationship between this measure and the total fraction of food-derived Phe retained by the splanchnic area has not been validated. OBJECTIVE:Therefore, we compared WbSPE with the enteral-derived Phe and actual PheSPE, measured by splanchnic-trans-organ fluxes in both healthy and early sepsis recovery states. METHODS:In 25 catheterized healthy control or Pseudomonas-induced-septic pigs (±25 kg), primed-continuous intravenous infusions of L-[ring-D5]-Phe and continuous enteral infusion of an AA mixture (per kg/h: 0.031 g N, 0.78 g maltodextrin), containing L-[1-13C]-Phe, were administered for 6 h. We collected arterial, portal, and hepatic venous blood and measured plasma enrichments and tracee concentrations by liquid chromatography-mass spectrometry (LC-MS/MS). Statistical analysis was performed using GraphPad Prism. Best-fit group means from the last 3 h were compared using an unpaired t-test. The data are presented as mean [95% confidence interval]. RESULTS:In the healthy control group, WbSPE was 38[16,61]% (P<0.0001) of the enteral-derived Phe SPE and tended to be 16[-1,34]% (P=0.0761) higher than the actual Phe tracee SPE. However, WbSPE was the same as first-pass SPE. In the septic group, WbSPE was increased 29[8,50]%, (P=0.001) whereas the actual Phe tracee SPE remained unchanged, whereas portal-drained viscera fluxes showed a diminished release of enteral-derived tracee Phe (P < 0.0001). CONCLUSIONS:WbSPE reflects first-pass SPE rather than enteral-derived tracee SPE or the actual SPE. Our observations suggest that whole-body level calculated SPE may be challenged in estimating food-derived amino acid SPE in response to steady meal intake. During early sepsis recovery, less AA are absorbed, and this changes the dynamics between first-pass and the actual SPE.

Nutritional support is a vital component of the rehabilitation process following sepsis. Essential amino acids (EAA) are recognized as a critical component for stimulating anabolism. However, it remains unclear whether EAA supplementation alone is more effective than providing a complete profile of total amino acids (TAA). We studied amino acid (AA) metabolism in 51 catheterized pigs (±27 kg) using the pulse tracer approach over a 7-day recovery period following sepsis. Animals were randomly and blindly assigned to receive post-sepsis nutrition containing either an EAA or a TAA mixture based on the composition of pig muscle. Statistical analyses were performed using a generalized linear mixed model. Plasma concentrations of EAA increased substantially in the EAA group post-sepsis (interaction effect, P<0.001), while those of non-essential AA increased in both groups (time effect, P<0.001). Whole-body intracellular production of most AA was reduced on day 3 and remained low on day 7 post-sepsis, with only small differences observed between the two groups. On day 7 post-sepsis, pigs receiving only EAA showed significantly (all P<0.001) lower intracellular production of hydroxyproline (-36%), ornithine (-11%), and tryptophan (-20%) and higher production of arginine (66%), citrulline (18%), glutamine (18%), taurine (22%), and some EAA. The EAA group showed a significantly higher net protein breakdown post-sepsis. In this sepsis-recovery pig model, dietary supplementation of both EAA and TAA failed to normalize the intracellular production of AA. More importantly, providing only EAA resulted in a significantly greater net protein breakdown compared with the TAA group.

BACKGROUND:Adding leucine (LEU) to protein meals enhances protein anabolism, but excess LEU reduces valine (VAL) and isoleucine (ILE) plasma concentrations. We examined in older adults whether additional LEU added to an essential amino acid (EAA) mixture reduces the intracellular catabolism of VAL and ILE, and their keto acids ɑ-ketoisovaleric acid (KIV)and 2-keto-3-methyl-pentanoate (KMV). METHODS:Using a randomized placebo-controlled crossover design, 11 older adults (60-80 years) consumed 20g EAA, 20g EAA+3g LEU (EAA + LEU), and water (baseline) on separate study days. A pulse of stable isotopes containing LEU, VAL, ILE, ɑ-ketoisocaproic acid (KIC), KMV, and KIV was administered IV to assess their whole-body and compartmental kinetics. Blood samples were taken, and enrichments analyzed using LC/GS-MS/MS. Data are expressed as percentage change after intake of EAA + LEU vs EAA [95%CI]. RESULTS:Plasma concentrations of LEU (55% [40%, 71%]; p < 0.001) and KIC (38% [26%, 51%]; p < 0.001) increased more after EAA + LEU than after EAA intake (both p < 0.0001) while ILE (-16% [-25%, -6%]; p = 0.001), KMV (-22% [-30%, -14%]; p < 0.001), and KIV (-21% [-29%, -13%]; p < 0.001) concentrations decreased. Intracellular disposal of LEU (43% [30%, 56%]; p < 0.001) and KIC (28% [4%, 52%]; p = 0.006) increased more after EAA + LEU mixture intake (LEU p < 0.0001, KIC p = 0.020), but those of ILE and VAL did not change. The intracellular pool sizes of KMV (19% [-35%, -4%],p = 0.019) and KIV (-25% [-43%, -7%]; p = 0.019) decreased. CONCLUSIONS:In older adults, adding LEU to an EAA mixture suppresses intracellular catabolism of the other BCAAs and their keto acids, possibly negatively affecting anaplerotic flux into the tricarboxylic acid cycle and thus muscle health. CLINICAL TRIAL REGISTRY:Trial registration ClinicalTrials.gov: NCT05400733.

Context Arginine (Arg) is an important amino acid in T2D as a potent insulin secretagogue and precursor for nitric oxide (NO). Citrulline (Cit), the substrate for de novo Arg synthesis, is mostly produced from glutamine (Gln).Objective We aimed to investigate their metabolism in T2D using a novel stable isotope tracer approach. Methods We studied 42 individuals (21 with T2D, 21 controls). After overnight fasting, blood samples were collected following pulse administration of stable amino acid tracers. Plasma concentrations and isotopic enrichments were measured by LC-MS/MS, and compartmental analyses were performed to calculate their whole-body production (WBP) rates and kinetics. Results The cohort was 59.5% female, with a mean age of 64.4 (7.5) years and a BMI of 33.0 (4.3) kg/m(2) (all P > .05). After adjusting for sex and age, the T2D group had lower plasma concentrations of Arg (P = .007), Cit (P = .002), and Gln (P = .002) than the control group. In T2D, WBP was lower for Cit (P = .004) but higher for Gln (P = .037) and glutamate (P = .017) after controlling for age, sex, and lean soft tissue mass. The T2D group also had lower Cit intracellular production, but higher Gln clearance and intracellular pool size, and a trend toward higher Arg clearance. Conclusion Significant dysregulation exists in Arg-Cit-Gln metabolism in T2D. Our findings suggest a working model in which increased Gln turnover stimulates gluconeogenesis, increases Gln consumption, and reduces Cit availability for Arg and NO synthesis, thereby contributing to metabolic dysregulation in T2D. Interventions targeting Gln-driven gluconeogenesis while increasing Cit availability may benefit T2D management.

Sarcopenic obesity (SO; defined as obesity with low skeletal muscle function and mass) has been recently recognized as a relevant obesity phenotype, with substantial negative clinical impact. The prevalence of SO is likely increasing, due to the growing prevalence of major SO risk factors, including sedentary lifestyle, obesity-induced non-communicable diseases with muscle-catabolism, and a general global increase in the older adult population. Structured obesity management, including anti-obesity medications, also commonly leads to variable reductions in muscle mass with potential SO risk. Here, an international network of clinical nutrition Societies, including the European Society for Clinical Nutrition and Metabolism (ESPEN), the Latino American Federation of Nutritional Therapy, Clinical Nutrition and Metabolism (Federación Latinoamericana de Terapia Nutricional, Nutrición Clínica y Metabolismo - FELANPE), the Parenteral and Enteral Nutrition Society of Asia (PENSA), and the South African and Australasian Societies for Parenteral and Enteral Nutrition (SASPEN and AuSPEN) recognize SO as a research and clinical priority, with major implications for nutrition and nutritional care. They hereby promote a nutrition network focusing on SO nutritional implications, clinical nutrition research on SO, and implementation of SO diagnosis and treatment in routine clinical practice. The current paper includes statements on SO diagnosis, promoting simple tools based on the recent consensus-based Sarcopenic Obesity Global Leadership Initiative (SOGLI) diagnostic algorithm, and its relationship with malnutrition/undernutrition. Statements are also provided on nutritional prevention of SO through healthy diet and adequate protein and micronutrient provision, on the role of nutritional care in obesity with sarcopenia, and on nutrition-based strategies to minimize and monitor the risk of sarcopenia during obesity management. The relevance of multimodal treatment approaches including both optimal nutrition and exercise is also emphasized. This SOGLI Nutrition network hereby calls for coordinated action, including scientific, educational and advocacy initiatives, to raise awareness of SO and the key role of nutrition and nutritional care in its prevention and treatment, in order to reduce the burden of morbidity and mortality in the growing population of persons with obesity worldwide.

BACKGROUND:Biological sex plays a role in systemic features of patients with Chronic Obstructive Pulmonary Disease (COPD). We investigated whether male and female COPD patients show distinct trajectories in muscle and brain health decline during aging. METHODS:In total 228 patients (age >50 years) with stable COPD (GOLD: II-IV) were stratified into four groups based on their sex and age (50-70 years vs ≥70 years). Body composition (DXA), muscle strength (dynamometry), cognitive function and well-being (assessments and questionnaires), and risk factors of poor systemic health were analyzed in these groups. RESULTS:Body weight and lean mass remain unchanged with aging. The ≥70 years males showed higher visceral adipose tissue and lower muscle strength whereas females showed lower fat mass and fat-free mass index, and worse cognitive performance compared with their younger counterparts (P < 0.04). In males, lower physical activity was associated with higher visceral adipose tissue and lower muscle function, whereas poor cognition was associated with low O2 saturation. In females, lower muscle function was associated with higher age, dyspnea and lower caloric intake and physical activity, whereas mood disturbance and poor cognition were associated with smoking pack years (P < 0.05). CONCLUSION:Aging in male COPD patients is characterized by metabolic syndrome features and muscle weakness whereas aging in female COPD patients is associated with weight loss, sarcopenia, and cognitive decline. The observed systemic changes were influenced by different combinations of risk factors in male and female COPD patients. Our findings indicate that sex-specific therapies need to be considered when treating older patients with COPD.

Vertebrate animal models of Becker muscular dystrophy (BMD) have been developed. Here, we characterized the gait kinematics and muscle function of a naturally occurring BMD pig model of dystrophin insufficiency. BMD pigs tended to have alterations in hip range of motion (ROM): hip (67%, 95% CI -0.64 to 14.12 degrees). While parameters were unaltered in extensor muscles, the dystrophin levels in flexor tibiotarsal joint muscles correlated with fatigue index as well as reduced isometric force (48%, 95% CI -1.86 to -0.61 N-m), and a 33% increase in fatigue index (95% CI -36.25 to 96.71 percent); the extensor muscles had no observable reductions in muscle force, with a 48% increase in fatigue index (95% CI -232.6 to 472.6 percent). Histological analysis of muscle biopsies supported a BMD phenotype in the flexor muscles of BMD pigs, with a 75% (95% CI -55.14 to -15.66 percent) decrease in large and a 43% (95% CI 17.74 to 57.38 percent) increase in small muscle fiber cross-sectional area. Dystrophin protein abundance was 28% less in flexor muscles from BMD pigs (95% CI -49.63 to 11.41 arbitrary units). Together, our model may serve as a clinically relevant model of BMD to assess safety and efficacy of therapeutics.

Sarcopenia and hepatic encephalopathy (HE) are complications of chronic liver disease (CLD), which negatively impact clinical outcomes. Hyperammonemia is considered to be the central component in the pathogenesis of HE, however ammonia’s toxic effects have also been shown to impinge on extracerebral organs including the muscle. Our aim was to investigate the effect of attenuating hyperammonemia with ornithine phenylacetate (OP) on muscle mass loss and associated molecular mechanisms in rats with CLD. Six-week bile duct-ligated (BDL) rats and Sham-operated controls were treated with OP (1 g/kg, oral) for 5 weeks. Body composition, assessed by EchoMRI, and muscle protein fractional synthesis rate were evaluated. Signalling mechanisms regulating protein homeostasis, ATP content and metabolic intermediates in the tricarboxylic acid cycle (TCA) in skeletal muscle were quantified. OP treatment attenuated hyperammonemia, prevented brain edema and improved locomotor activity in BDL rats. Increased muscle ammonia, reduction in lean body mass, decreased muscle protein synthesis rate and ATP content were restored in OP-treated versus saline-treated BDL rats. TCA cycle intermediary metabolite, α-ketoglutarate, alterations of molecular markers regulating protein homeostasis including mTOR signalling and autophagy, were also preserved in muscle of OP-treated BDL rats. OP attenuated hyperammonemia, preserved muscle protein synthesis and prevented muscle mass loss in a preclinical model of CLD through restoration of perturbed signalling responses and altered TCA intermediary metabolites. Ammonia-lowering strategies have the potential for rapid clinical translation for simultaneous neuroprotection and sarcopenia prevention in patients with CLD.

Background and aims Critical illness is characterized by an intense inflammatory response that triggers major metabolic changes with protein catabolism resulting in major losses of muscle mass. The intensity of the inflammatory response appears as the principal driver of the changes involved in outcome, and especially those affecting protein metabolism and muscle catabolism, and resistance to nutrition. The present exploratory study aims to clarify the role of the different cytokines in amino acid metabolism. Methods In this post-hoc analysis of the previously published observational study, including 51 critically ill patients and 49 healthy controls aiming at identifying patient changes in amino acid metabolism, we assessed the association between a panel of cytokines and blood levels of amino acids (AA) and their turnover. The subjects were matched for age, sex, and BMI. The study was conducted in postabsorptive state. Blood analysis included cytokines (determined by Luminex), C-reactive protein (CRP or hsCRP), and AA. Protocol: 8 mL solution containing 18 stable AA tracers administered as a pulse to calculate amino acid whole body production (WBP). WBP was calculated from fitted decay curves. We measured amino acid enrichments and concentrations by LC-MS/MS and derived statistics using Generalized Linear Model (GLM) t and stepwise regression. Data as means [95%CI]. Results The study included 51 critically ill patients (age 63 yrs [58, 68], APACHEII 21.6 [20, 24]) and 49 matched healthy controls (age 57 yrs [52, 61]). While anthropometric characteristics were similar between critically ill patients and healthy adults, phase angle was lower (3.9 [3.5, 4.2] vs 6.0 [5.6, 6.3], p < 0.001), most AA blood levels were lower, while most cytokine levels were significantly higher. IL-6 and CRP were strongly associated (p < 0.001). IL-6 was the cytokine with the strongest association with the AA blood levels and WBP alterations in patients. Three patterns of changes in the plasma cytokine concentrations were observed. Of the 37 cytokines measured, 12 were higher in ICU patients, 5 were lower, and the rest were similar. Conclusions The present study shows a comprehensive picture of inflammation and simultaneous alterations of AA metabolism. The levels of IL-6 and CRP may become a good indicator of the metabolic capacity to respond positively to nutrition therapy. Clinical trial registry Data are from the baseline measurements of study NCT02770092 (URL: https://clinicaltrials.gov/ct2/show/NCT02770092) and NCT03628365 (URL: https://clinicaltrials.gov/ct2/show/NCT03628365).

Background & aims Disturbances in arginine (ARG) and protein metabolism, as well as in gut function have been observed in response to an endurance exercise session in patients with Chronic Obstructive Pulmonary Disease (COPD). We studied whether resistance exercise also affects the acute response in arginine (role in nitric oxide synthesis), citrulline (CIT, marker of gut health), and (muscle) protein metabolism differently in COPD as compared to healthy older adults. Methods Patients with stable moderate to severe COPD (n = 24) and healthy controls (n = 25) completed a high-intensity resistance exercise session in the postabsorptive state. We administered a pulse of multiple stable isotopes of amino acids before, and 1 h and 24 h post-resistance exercise to assess the whole body production (WBP) and intracellular productions by compartmental analysis of ARG and CIT, and of tau-methylhistidine (TauMETHIS), phenylalanine (PHE), tyrosine (TYR), and PHE > TYR conversion as markers of muscle (myofibrillar) protein breakdown and whole body (net) protein breakdown, respectively. Muscle fatigue was determined by assessing the decay in peak leg extension torque post-resistance exercise. Results COPD patients overall exhibited lower WBP ARG (p < 0.0001), CIT (p < 0.0001), PHE (p = 0.0001), TYR (p < 0.0001), and tau-METHIS (p = 0.0004) compared to controls. Resistance exercise did not change WBP of PHE, tau-METHIS, or PHE > TYR conversion, despite prolonged muscle fatigue in COPD. WBP CIT was increased at 1- and 24-h post-exercise in both groups (p < 0.003). Plasma CIT concentrations were reduced in both groups (p < 0.006) and remained lower at 24 h post-exercise in COPD only (p < 0.05) despite a third less work performed. Conclusions Both COPD and healthy participants exhibited upregulated whole-body citrulline production following resistance exercise. However, in COPD, this increase was insufficient to counteract the sustained reduction in plasma citrulline concentration, despite performing significantly less work during the exercise session. This prolonged disturbance in citrulline metabolism in COPD points to a potential exercise-induced enterocyte dysfunction, highlighting a novel area for understanding the impact of resistance exercise on gut health in this population. Clinical trial registry Trial registration ClinicalTrials.gov: NCT02780219.

Sepsis leads to an acute breakdown of muscle to support increased caloric and amino acid requirements. Little is known about the role of adipose and muscle tissue breakdown and intestinal metabolism in glucose substrate supply during the acute phase of sepsis. In a translational porcine model of sepsis, we explored the across organ net fluxes of gluconeogenic substrates. In 13 pigs, acute sepsis was induced by IV infusion of Pseudomonas aeruginosa, while in 9 pigs saline (control) was given for 18 h. Blood samples were collected between 12 and 18 h and analyzed with HPLC and LCMS. In sepsis, glucose plasma concentration was reduced (p = 0.0028). A concordant increase in splanchnic area net release of glucose (p = 0.0049), due to reduced uptake in the portal drained viscera (PDV) (p = 0.0032) with an unchanged liver production (p = 0.7861). The hindquarter showed a higher release of alanine (p = 0.0002), glutamine (p = 0.003), and lactate (p = 0.0007), but not for glycerol (p = 0.5718). Diminished PDV uptake of gluconeogenic amino acids, increased liver uptake of these substrates (p < 0.05), while no change in liver glycerol uptake (p = 0.3170), did not lead to an increased net liver glucose release. In the acute phase of sepsis, we hypothesize an important role of altered intestinal amino acid metabolism and breakdown of muscle proteins, but not of glycolysis to support gluconeogenesis.

Inadequate sleep has been associated with an increased risk of mortality and various health issues. We previously conducted a placebo-controlled vaccination trial of healthy adults who were monitored by blood samples, questionnaires, and wearable devices. C-reactive protein (CRP), a systemic marker of inflammation, has been linked to numerous health outcomes, and was found to significantly increase post-vaccination in the trial. In this retrospective study, we investigated that if sleep was associated with an inflammation response triggered by perturbations from vaccine and placebo injections. Plasma hs-CRP levels were measured on the same day as the intervention, prior to the vaccine/placebo administration and two days after the intervention. Associations of sleep duration and CRP levels after vaccine/placebo administration in 188 trial participants were investigated by regression models adjusting for age, sex, body mass index (BMI), comorbidities, vaccination status (vaccination or placebo), and averaged daily steps. We found that shorter wearable-derived Total Sleep Time (TST) and Total Time in Bed (TIB), as well as subjectively assessed sleep duration from the Pittsburgh Sleep Quality Index (PSQI), were independently associated with higher incidence of CRP elevation after vaccine/placebo administration. Our study suggests that sleep deprivation could be a predictor for an increased inflammatory response and highlights a potential application of wearable-derived sleep metrics in public health.

There is an increased need to establish the protein requirements for body weight maintenance and optimal health in humans. Different methods were developed in the past to assess protein requirements in which known amounts of protein/amino acids were provided. The purpose of this paper is to propose a new concept of establishing protein requirements in healthy and diseased conditions using a novel stable isotope approach.In the past years, we consistently found that when using a novel stable isotope pulse approach the intracellular production of amino acids (i.e., phenylalanine and tyrosine) is more than double the plasma rate of appearance, as measured by the commonly used primed constant infusion approach, leading to a net protein breakdown that is more than twice than estimated in the past. Net protein breakdown in the fasted state may provide a good estimation of the actual net protein loss that would take place during the day and thus can be used to estimate daily protein requirements. Our recent study found that a net protein breakdown ∼1 g protein/kg body weight/day was equal to the habitual protein intake, suggesting that there is a relation between habitual protein intake and protein requirements. As net protein breakdown is lower with advanced aging and in patient populations with comorbidities, a lower protein requirement for body weight maintenance is suggested.We propose a new concept to establish actual protein requirements of healthy and disease conditions, using a pulse tracer administration and to consider individual habitual protein intake and health conditions.

BACKGROUND:Beneficial short-chain fatty acids (SCFAs) are produced through intestinal microbial fiber fermentation. Using stable tracer methodology and compartmental modeling, we observed lower SCFA production in older (OAs) than in young adults (YAs) in both an accessible [that is, systemic circulation; whole-body production] and inaccessible [potentially representing intestine absorbing microbially produced SCFAs (U2)] pool. OBJECTIVES:We now investigated whether fiber supplementation increases SCFA production in OAs and whether concentrations reflect production rate changes. METHODS:In this randomized, placebo-controlled, double-blind crossover study, 21 YAs (20-29 y) and 40 OAs (59-87 y) adults were supplemented with inulin or placebo (maltodextrin) for 7 d (final intake: 30 g/d). Before and after interventions, participants collected stool and received an intravenous pulse containing [U-13C]-labeled SCFAs followed by blood draws. We measured plasma tracer enrichments, plasma and fecal concentrations by gas chromatography-mass spectrometry and performed compartmental analysis. Data are mean (95% confidence interval). RESULTS:Inulin evoked a 44% increase in butyrate production (μmol/min) in the inaccessible pool {YA: 28-44 [+16.2 (4.3, 28.1); P = 0.038], OA: 14-20 [+6.1 (2.2, 9.9); P = 0.011]} and were not different between YAs and OAs. In addition, a 34% increase in propionate production in YA only. We found a 50%-60% increase in fecal acetate, propionate, and butyrate and a 34% increase in plasma butyrate in OA, whereas in YA only 34% increase in fecal acetate. Plasma but not fecal concentrations correlated positively with SCFA production in the inaccessible pool (R2 = 0.20-0.45; P < 0.001). CONCLUSIONS:OAs have a lower SCFA production. Inulin intake increases SCFA production. Tracer pulse approach detects SCFA metabolism changes more sensitively than plasma or fecal concentration measurements (NCT04459156).

BACKGROUND:Exercise training is essential for pulmonary rehabilitation in chronic obstructive pulmonary disease (COPD), yet patient responsiveness varies widely. We previously observed metabolic disturbances in amino acids critical for muscle health-such as glutamate, glutamine, branched-chain amino acids (BCAAs), and taurine-in COPD patients after an endurance exercise session, possibly related to increased energy demands and oxidative stress. However, the impact of resistance exercise on these metabolic pathways remains unclear. METHODS:We measured plasma concentration, whole-body production (WBP), and intracellular production of glutamate, glutamine, BCAAs, and taurine using stable isotope pulse techniques in 24 COPD and 25 healthy older participants. Measurements were obtained before, and at 1 and 24 h after, a resistance exercise session. RESULTS:At baseline, COPD participants exhibited lower WBP of glutamine, taurine, and BCAAs compared to healthy participants (p < 0.05). Resistance exercise increased WBP of glutamate by 37-42 %, glutamine by 9-10 %, and intracellular glutamate production by 37-40 %, while decreasing WBP of taurine by 7 % (all p < 0.0001). These effects persisted at 24 h post-exercise (p < 0.05). Although WBP of BCAAs remained unchanged, plasma leucine and isoleucine levels decreased by 16 % and 13 %, respectively, in COPD participants post-exercise (p < 0.05). CONCLUSIONS:A single resistance exercise session alters glutamate-related metabolism for at least 24 h in healthy and COPD participants. A high BCAA clearance is likely required to rapidly upregulate glutamate production in COPD to meet increased energy demands, but this occurs at the cost of lowering plasma levels of BCAA necessary for muscle anabolism. CLINICAL TRIAL REGISTRY:Trial registration ClinicalTrials.gov: NCT02780219.

Background Skeletal muscle weakness and mild cognitive impairment (MCI) commonly occur with aging. Objective We examined whether presence of chronic morbidities in MCI is associated with specific alterations in muscle health, functional capacity, and whole body amino acid kinetics. Methods A group of 247 older adults were stratified into MCI/non-MCI (Montreal Cognitive Assessment) and presence/absence of chronic diseases. We measured lean mass by dual-energy x-ray absorptiometry, strength by dynamometry, and functional capacity by 6-min walk test. Postabsorptive whole body production (WBP) of amino acids were assessed by pulse administration of a mixture of 18 amino acid stable isotopes. Results MCI was associated with lower lean mass, functional capacity (p < 0.003), and WBP of arginine, glycine, leucine, and phenylalanine to tyrosine conversion (reflecting net protein breakdown (net PB)) but higher WBP of taurine (all p < 0.05). Presence of chronic morbidities was associated with lower muscle strength, WBP of glycine, and net PB (p < 0.0001), but higher WBP of phenylalanine, glutamate, taurine, tryptophan, and leucine (all p < 0.05). MCI*chronic morbidity interactions were found for muscle strength and net PB (p < 0.0001), with the lowest values in MCI with chronic morbidities. Conclusions Presence of MCI and chronic morbidities in the older population affect different markers of muscle health and functional decline. Individuals with both MCI and chronic morbidities are at increased risk for severe muscle weakness likely related to a severe downregulation of glycine production and net protein breakdown. Therefore, it is important to consider the presence of chronic morbidities when investigating muscle health and functional capacity in MCI.