Protein Sparing Research Articles

Exploring the effects of dietary inulin in rainbow trout fed a high-starch, 100% plant-based diet

BackgroundHigh dietary carbohydrates can spare protein in rainbow trout (Oncorhynchus mykiss) but may affect growth and health. Inulin, a prebiotic, could have nutritional and metabolic effects, along with anti-inflammatory properties in teleosts, improving growth and welfare. We tested this hypothesis in rainbow trout by feeding them a 100% plant-based diet, which is a viable alternative to fishmeal and fish oil in aquaculture feeds. In a two-factor design, we examined the impact of inulin (2%) as well as the variation in the carbohydrates (CHO)/plant protein ratio on rainbow trout. We assessed the influence of these factors on zootechnical parameters, plasma metabolites, gut microbiota, production of short-chain fatty acids and lactic acid, as well as the expression of free-fatty acid receptor genes in the mid-intestine, intermediary liver metabolism, and immune markers in a 12-week feeding trial.ResultsThe use of 2% inulin did not significantly change the fish intestinal microbiota, but interestingly, the high CHO/protein ratio group showed a change in intestinal microbiota and in particular the beta diversity, with 21 bacterial genera affected, including Ralstonia, Bacillus, and 11 lactic-acid producing bacteria. There were higher levels of butyric, and valeric acid in groups fed with high CHO/protein diet but not with inulin. The high CHO/protein group showed a decrease in the expression of pro-inflammatory cytokines (il1b, il8, and tnfa) in liver and a lower expression of the genes coding for tight-junction proteins in mid-intestine (tjp1a and tjp3). However, the 2% inulin did not modify the expression of plasma immune markers. Finally, inulin induced a negative effect on rainbow trout growth performance irrespective of the dietary carbohydrates.ConclusionsWith a 100% plant-based diet, inclusion of high levels of carbohydrates could be a promising way for fish nutrition in aquaculture through a protein sparing effect whereas the supplementation of 2% inulin does not appear to improve the use of CHO when combined with a 100% plant-based diet.

Effect of starvation on physiological and survival traits of Mimachlamys varia (Linneaus, 1758)

In order to better understand Mimachlamys varia (Linneaus, 1758) response to nutritional stress, a controlled-condition experiment was conducted. Two scallop batches (i.e. juveniles and adults) were completely food-deprived for 3 months. Changes in mass and energy content of tissues (adductor muscle, digestive gland, rest of the soft tissues), as well as stable carbon and nitrogen isotope ratios of the adductor muscle were monitored weekly. Both batches exhibited a 3-phase response to starvation. For adults, phase 1, was characterized by a fast loss in mass, an δ15N-enrichment, a stable calorific power, and a low mortality, corresponding to a transitional stage associated with protein-storage consumption. Phase 2 (day 28–42) exhibited a stabilization of mass and δ15N values, coinciding with a digestive gland calorific power drop and an acceleration in mortality. This corresponds to a “protein sparing” stage where highly energetic fuel such as lipids, which are stored especially in the digestive gland in pectinids, are consumed in priority. Juveniles exhibited a distinct response characterized by a significant mass loss and an increase in calorific power during the first phase (day 0–28). This body weight decrease may involve the remobilization of low-caloric biochemical compounds (e.g. proteins) using the structure as internal fuel, thus limiting somatic maintenance costs. During the second month, body mass and calorific power stabilized, indicating a “protein sparing” stage. In a third phase for both age classes, mass decreased again together with a sharp increase in mortality: essential structure was ultimately remobilized. The survival rate of juveniles was higher than that of adults during the first two months of the experiment (97% and 64%, respectively). Although the time required for starvation to deplete of half the cohort is higher for juveniles than for mature individuals, increase in mortality rate after reaching the “Point of No Return”, (e.g. the beginning of the last phase) was higher in juveniles than in adults. These results highlight the potential impacts of starvation at the population level, beyond the direct impact on individual survival. For instance, individuals may not effectively contribute to reproduction during the spawning period if exposed to a prolonged winter starvation episode. In particular, since highly energetic compounds stored in the digestive gland are often used as fuel to initiate gametogenesis in pectinids. Similarly, decrease in somatic weight in juveniles may delay their sexual maturity and hence their ability to contribute to population reproductive potential.

Productive Performance and Serum Biochemical Parameters of Nile Tilapia Fingerlings Fed on Different Dietary Carbohydrate: Protein Ratios with Biotin Supplementation

The current experiment evaluated the effects of different dietary carbohydrate: protein ratios (CHO: CP ratio) without or with biotin supplementation on the growth performance, body composition, serum biochemical parameters and intestinal morphology in Nile tilapia. Fingerlings were assigned to 6 treatments arranged as following; Group 1 (G1) fed the basal diet (BD) with a medium CHO: CP ratio (47:32); G2 with high CHO: CP ratio (57:21); G3 with low CHO: CP ratio (36:42); while G4, G5 and G6 had the same previous experimental design of the first 3 groups but with biotin supplementation (0.06 mg/kg diet). The growth performance was only assessed for the first 6 weeks, then the experiment continued to 4 months and ended by sampling for other parameters determined. Fish feeding on high CHO: CP ratio (57:21) significantly reduced the fish body weight, gain and feed intake (FI) (P ≤ 0.05), while improved the feed efficiency compared to the medium and low ratios. Biotin addition to the high or the medium ratios containing diets resulted in lower growth, increased FI and deteriorated the feed efficiency when compared to their control groups without biotin addition (P≤ 0.05). Different dietary CHO: CP ratios significantly altered tilapia body composition of nutrients (moisture, EE, and ash), serum parameters (glucose, triglyceride, LDL and VLDL) and the liver function enzymes (GPT and GOT) (P≤ 0.05). The relative mRNA expression of GHR and IGF was significantly upregulated in fish fed on the low and the high ratios containing diets respectively. In conclusion, feeding of the early fingerling of tilapia on the high CHO: CP ratio during the first 6 weeks of life resulted in lower growth, however, it showed a protein sparing effect. Supplementation of biotin (extra over the diet) was not recommended as it showed adverse effects on tilapia growth especially during the first periods of life, however it showed some beneficial effects on alleviating the high-dietary carbohydrate-induced effects. Feeding on medium CHO: CP ratio (47:32) or low ratio (36:42) would be recommended during the fry and early fingerling stage of tilapia while the high ratio (57:21) would be beneficial in the diet of late fingerlings or adult tilapia.

Chitosan-Based Sustained Expression of Sterol Regulatory Element-Binding Protein 1a Stimulates Hepatic Glucose Oxidation and Growth in Sparus aurata.

The administration of a single dose of chitosan nanoparticles driving the expression of sterol regulatory element-binding protein 1a (SREBP1a) was recently associated with the enhanced conversion of carbohydrates into lipids. To address the effects of the long-lasting expression of SREBP1a on the growth and liver intermediary metabolism of carnivorous fish, chitosan-tripolyphosphate (TPP) nanoparticles complexed with a plasmid expressing the N terminal active domain of hamster SREBP1a (pSG5-SREBP1a) were injected intraperitoneally every 4 weeks (three doses in total) to gilthead sea bream (Sparus aurata) fed high-protein-low-carbohydrate and low-protein-high-carbohydrate diets. Following 70 days of treatment, chitosan-TPP-pSG5-SREBP1a nanoparticles led to the sustained upregulation of SREBP1a in the liver of S. aurata. Independently of the diet, SREBP1a overexpression significantly increased their weight gain, specific growth rate, and protein efficiency ratio but decreased their feed conversion ratio. In agreement with an improved conversion of dietary carbohydrates into lipids, SREBP1a expression increased serum triglycerides and cholesterol as well as hepatic glucose oxidation via glycolysis and the pentose phosphate pathway, while not affecting gluconeogenesis and transamination. Our findings support that the periodical administration of chitosan-TPP-DNA nanoparticles to overexpress SREBP1a in the liver enhanced the growth performance of S. aurata through a mechanism that enabled protein sparing by enhancing dietary carbohydrate metabolisation.

High carbohydrate to protein ratio promotes changes in intestinal microbiota and host metabolism in rainbow trout (Oncorhynchus mykiss) fed plant-based diet

To ensure the sustainability of aquaculture, it is necessary to change the “menu” of carnivorous fish such as rainbow trout from a fish-based diet to one with plant-based ingredients. However, there is a major problem with the growth performance decrease of fish fed with a 100% plant-based diet due to the reduction in feed intake and feed efficiency. For the first time, we incorporated high levels of digestible carbohydrates (high-starch diet) in a 100% plant-based diet during a 12-week feeding trial in order to improve protein utilization for growth (protein sparing effect) and reduce nitrogen waste.We measured the changes in the intestinal microbiota, Short-Chain Fatty Acid (SCFA) levels and metabolic responses in liver. Dietary carbohydrates had a strong effect on alpha and beta diversity and abundance of 12 genera, including Ralstonia and Bacillus in digesta associated microbiota whereas mucosa associated microbiota was less affected. The change in microbial diversity might be linked to the change observed in SCFA production. High levels of Mycoplasma were observed in the intestinal mucosa. Overall, hepatic gene expression was significantly altered by the CHO/protein ratio. Up-regulation of genes involved in glucose metabolism (gcka, gckb, g6pcb2a), down-regulation of genes involved in lipid metabolism (hadh, acox3, srebp2a, and cyp51a) were associated with higher enzymatic activities (such as glucokinase or pyruvate kinase) and higher glycogen levels in the liver, suggesting adequate adaptation to diet. Interestingly, strong correlations were observed between abundances of certain bacterial OTUs and gene expression in the liver.The inclusion of digestible carbohydrates in combination with a 100% plant-based diet, could be a promising way to improve and reduce the use of plant proteins in rainbow trout. In addition, the relationship between intestinal microbiota and host metabolism needs further investigation to better understand fish nutrition.

Uridine alleviates high-carbohydrate diet-induced metabolic syndromes by activating sirt1/AMPK signaling pathway and promoting glycogen synthesis in Nile tilapia (Oreochromis niloticus).

Carbohydrates have a protein sparing effect, but long-term feeding of a high-carbohydrate diet (HCD) leads to metabolic disorders due to the limited utilization efficiency of carbohydrates in fish. How to mitigate the negative effects induced by HCD is crucial for the rapid development of aquaculture. Uridine is a pyrimidine nucleoside that plays a vital role in regulating lipid and glucose metabolism, but whether uridine can alleviate metabolic syndromes induced by HCD remains unknown. In this study, a total of 480 Nile tilapia (Oreochromis niloticus) (average initial weight 5.02±0.03g) were fed with 4 diets, including a control diet (CON), HCD, HCD+500mg/kg uridine (HCUL) and HCD+5,000mg/kg uridine (HCUH), for 8 weeks. The results showed that addition of uridine decreased hepatic lipid, serum glucose, triglyceride and cholesterol (P<0.05). Further analysis indicated that higher concentration of uridine activated the sirtuin1 (sirt1)/adenosine 5-monophosphate-activated protein kinase (AMPK) signaling pathway to increase lipid catabolism and glycolysis while decreasing lipogenesis (P<0.05). Besides, uridine increased the activity of glycogen synthesis-related enzymes (P<0.05). This study suggested that uridine could alleviate HCD-induced metabolic syndrome by activating the sirt1/AMPK signaling pathway and promoting glycogen synthesis. This finding reveals the function of uridine in fish metabolism and facilitates the development of new additives in aquatic feeds.

End-of-season supplementary feeding in European carp ponds with appropriate plant protein and carbohydrate combinations to ecologically boost productivity: Lupine, rapeseed and, triticale

The present study investigated end-of-season (July–September) supplementary feeding strategies for European fishponds (carp farming), which suffer from collapsed natural food base (protein availability). Treatment ponds receiving white lupine (Lupinus albus), resulted in higher polyunsaturated fatty acids (PUFA) content (276.1 mg n − 3 PUFA 100 g−1) in skinless fillet of Cyprinus carpio than control ponds receiving triticale (179.5 mg n − 3 PUFA 100 g−1). Despite lupine being richer in nitrogen (N) and phosphorus (P) than triticale, eutrophication was likely suppressed in treatment ponds. Treatment ponds (∼120 g acid detergent fiber, ADF kg−1 lupine) had higher water transparency and lower water column P than control ponds (∼31 g ADF kg−1 triticale). Surprisingly, triticale (8.5% digestible protein; low DIAASLYS 36%) resulted in similar yield (∼1 ton ha−1) as lupine (26.5% digestible protein; higher DIAASLYS 52%, but low DIAASMET 32%). Therefore, protein quality (methionine) deficiency in lupine was investigated. It was balanced iso‑nitrogenously (38% crude protein) with rapeseed expeller meal (Brassica napus): diets T1 (only lupine; Met 0.9% of protein) → T2 (75% lupine: 25% rapeseed; Met 1.2% of protein) → diet T3 (50% lupine: 50% rapeseed; Met 1.4% of protein). A gradual improvement in yield, N and P retention values was observed from T1 to T3 but it did not exceed a low protein (16% crude protein) ‘control’ diet (only triticale; Met 1.9% of protein). Nutrient conversion to fish biomass (protein efficiency ratio and P: N retention ratio) seemed highest in ‘control’ followed by ‘T3’. This could be attributed to starch-mediated protein sparing effect or high organic matter digestibility of triticale (ADCNFE 76%; ADCOM 72%). Which is lacking in either lupine or rapeseed (ADCNFE ≤ 1%; ADCOM ≤ 34%) due to predominance of fibrous carbohydrates (non-starch polysaccharides, NSP). However, in ponds, they may still enhance the food web. In absence of starch, higher ADF influx in pond carp gut may halve absorption of n-3 PUFA from zooplankton. The study concludes end-of-season supplementary feeding with high DIAASMET, LYS protein combinations (e.g., lupine-rapeseed) and inclusion of starch sources (e.g., triticale) could achieve higher yield and nutrient efficiency in ponds. Most proteinaceous plant feedstuff are rich in NSP or ADF and may contribute to improving pond water quality or food web. Balanced supplementary feeds (e.g., 50% triticale +25% lupine +25% rapeseed expeller), that feed both fish (starch, optimum DIAASprotein) and pond (NSP, ADF) are suggested.

PROTEIN SPARING USING SAGO STARCH ON THE PERFORMANCE OF TIGER GROUPER, EPINEPHELUS FUSCOGUTTATUS ♀ × GIANT GROUPER, E. LANCEOLATUS ♂ HYBRID

Starch is an important non-protein energy source in the practical diets for fish and its optimal inclusion can maximise the use of dietary protein for growth. In the present study, a feeding trial was conducted to investigate the effects of protein sparing with carbohydrates on growth and diet digestibility in hybrid grouper (Epinephelus fuscoguttatus × E. lanceolatus). Diets were formulated with lowered levels of protein (50% to 45% and 40%) and increased levels of starch (20% to 25% and 30%). At the end of the feeding trial, growth performance and body indices (except for viscerosomatic index) were not significantly influenced (P &gt; 0.05) by the dietary treatments. In contrast, the whole-body proximate fish and liver compositions depended on the test diets. The dietary starch influences the haematological parameters, even though no clear trend was observed. Meanwhile, the apparent digestibility coefficient of protein and lipid was considered high in all experimental diets. Overall, the diet with protein level lowered to 45% and starch level increased to 30% performed as well as the control diet, indicating some ability of hybrid grouper to utilise sago starch as an energy source to spare protein.

Growth Performance, Digestive Enzyme Activities, and Oxidative Stress Markers in the Proximal Intestine of European Sea Bass (Dicentrarchus labrax) Fed High Starch or Lipid Diets

The effect of different main dietary compositions on growth, anticipatory digestive enzyme activities, and oxidative status was studied in the proximal intestine of juvenile European sea bass. A control diet (C, 44% protein, 17.6% lipid, and 20% starch), three diets with increasing starch levels to test protein sparing (P36S36, P40S29, and P43S24), and two diets with high lipid content (L20S13 and L22S7) were tested. After 20 weeks, growth, digestive enzyme activities, lipid peroxidation, antioxidant enzyme activities, and G6PDH activity were measured after a 24-h fast. Sea bass fed P43S24 and L20S13 maintained an oxidative status like C fish, up-regulated CAT activity, and adjusted anticipatory protease activity. Instead, the lipid peroxidation increased in the L22S7 group, although CAT activity increased, whereas anticipatory total protease activity was downregulated. P40S29 also triggered LPO and CAT activity, but G6PDH levels diminished significantly. Moreover, an up-regulation in digestive enzyme activities was found. Finally, P36S36 fish showed less antioxidant enzyme activity and G6PDH, although their LPO tended to increase and their lipase and α-amylase activities were upregulated. In conclusion, the inclusion of carbohydrates up to 24% or lipids up to 20% is possible for this species if protein requirements are met without negative effects on growth.

Food Deprivation Modifies Fatty Acid Partitioning and β-Oxidation Capacity in Rat Liver

The involvement of lipids under starvation conditions in the shift from the phase of protein sparing (phase II) to the phase of increased protein breakdown (phase III) has been investigated. Plasma and liver were sampled from fed and unfed rats at two distinct stages which were characterized according to the changes in specific loss in daily body mass and nitrogen excretion. In the two groups of food-deprived rats corresponding to phases II and III, the liver concentration of triglycerides (µmol/g) was significantly lower, that of cholesterol significantly higher and that of the other lipid classes was moderately affected compared with concentrations in fed rats. Hepatic phospholipids had significantly higher concentrations (mol/100 mol) of 22:6(n-3) in food-deprived rats than in fed rats. Triglycerides had significantly higher concentrations of stearic and arachidonic acids in livers of both groups of food-deprived rats compared with fed rats. The total activity of carnitine palmitoyl transferase [mmol/(min·liver)] was 48% higher in rats studied at the end of phase II than in fed rats but was similar in fed rats and in rats studied at the beginning of phase III. The total activity of fatty acyl-CoA oxidase was 73% lower only in rats studied at the beginning of phase III when compared with fed rats. Our results indicate that during food deprivation the change in the rate of protein utilization is associated with important qualitative and quantitative alterations of hepatic lipids and oxidative capacity of fatty acids. These modifications appear to be related to the change from a preferential use of lipids to a preferential utilization of proteins.

Revised Protein Sparing Diet in Obesity and Type 2 Diabetes Mellitus.

Effective nutrition therapy is a pressing issue in obesity and type 2 diabetes mellitus (T2DM) management. As such, this research aimed to determine the performance of a revised dietary strategy built on the protein-sparing diet in obesity and type 2 diabetes mellitus with regard to obtaining a rapid and stable improvement in glucometabolic control, body weight, body composition, and energy metabolism when applying the strategy in just twenty-one days. The revised protein-sparing diet differs from the traditional protein-sparing modified fast (PSMF) because it does not include foods. The daily calorie intake of this diet is exclusively derived from Isolate whey protein in addition to a formulation of Isolate whey protein enriched with essential amino acids in free form, with the addition of lipids such as extra virgin olive oil and coconut oil as a source of medium chain fatty acids, where the latter is taken for only the first four days of the diet, together with the use, for the same duration, of extended-release metformin, as the only antihyperglycemic allowed. Anthropometric measurements, bioimpedance analysis, indirect calorimetry, and blood chemistry assessments were conducted at the beginning of the study, time 0 (T0), and at the end, time 1 (T1), i.e., on the 21st day. The main outcomes of the revised protein-sparing diet after only twenty-one days were a reduction in body weight with the predominant loss of visceral atherogenic abdominal fat and, therefore, a possible contextual reduction in ectopic fat deposits together with a simultaneous reduction in insulin resistance and normalization of insulin levels, maintenance of free fat mass and basal metabolism, restoration of metabolic flexibility, and improvement of the glucometabolic and lipidic parameters. These results demonstrate the promising potential of the revised protein-sparing diet as an "etiologic tool" in the integrated nutritional treatment of metabolic diseases such as obesity and type 2 diabetes mellitus.

Impact of Preoperative Protein Sparing Modified Fast Diet on Bariatric Surgery.

Bariatric surgery can become technically challenging in the setting of liver steatosis and hepatomegaly. The protein sparing modified fast (PSMF) diet helps in achieving rapid weight loss. The aim of this study is to explore the results of a preoperative PSMF diet on liver volume and steatosis as well as on intraoperative and postoperative complications in patients with hepatomegaly undergoing Roux-en-Y gastric bypass (RYGB). Between January 2010 and January 2021, 713 patients undergoing RYGB as a primary bariatric surgery were divided in two groups. Those with a measured liver length above 16cm and or evidence of liver steatosis on ultrasound (group 1) were offered a preoperative PSMF diet while the remaining (group 2) proceeded directly to surgery. Between January 2010 and April 2012, patients included in group 1 had liver volume measurements on magnetic resonance imaging the day before the diet was started and the day before the surgery. For the length of the study, intraoperative and postoperative data were recorded for both groups. Five days of preoperative PSMF diet resulted in a significant reduction of total and left liver volume (15.8% and 21% respectively, p < 0.001). There was no difference in intraoperative bleeding and conversion rate or postoperative complication rate between both groups. The PSMF diet helps in achieving a rapid decrease in liver volume. Patients with hepatomegaly initially thought to be at a higher risk of intraoperative complications reached comparable rates to patients without hepatomegaly after the diet regimen without any impact on the postoperative course.

Dietary Succinate Impacts the Nutritional Metabolism, Protein Succinylation and Gut Microbiota of Zebrafish

Succinate is widely used in the food and feed industry as an acidulant, flavoring additive, and antimicrobial agent. This study investigated the effects of dietary succinate on growth, energy budget, nutritional metabolism, protein succinylation, and gut microbiota composition of zebrafish. Zebrafish were fed a control-check (0% succinate) or four succinate-supplemented diets (0.05, 0.10, 0.15, and 0.2%) for 4 weeks. The results showed that dietary succinate at the 0.15% additive amount (S0.15) can optimally promote weight gain and feed intake. Whole body protein, fat, and energy deposition increased in the S0.15 group. Fasting plasma glucose level decreased in fish fed the S0.15 diet, along with improved glucose tolerance. Lipid synthesis in the intestine, liver, and muscle increased with S0.15 feeding. Diet with 0.15% succinate inhibited intestinal gluconeogenesis but promoted hepatic gluconeogenesis. Glycogen synthesis increased in the liver and muscle of S0.15-fed fish. Glycolysis was increased in the muscle of S0.15-fed fish. In addition, 0.15% succinate-supplemented diet inhibited protein degradation in the intestine, liver, and muscle. Interestingly, different protein succinylation patterns in the intestine and liver were observed in fish fed the S0.15 diet. Intestinal proteins with increased succinylation levels were enriched in the tricarboxylic acid cycle while proteins with decreased succinylation levels were enriched in pathways related to fatty acid and amino acid degradation. Hepatic proteins with increased succinylation levels were enriched in oxidative phosphorylation while proteins with decreased succinylation levels were enriched in the processes of protein processing and transport in the endoplasmic reticulum. Finally, fish fed the S0.15 diet had a higher abundance of Proteobacteria but a lower abundance of Fusobacteria and Cetobacterium. In conclusion, dietary succinate could promote growth and feed intake, promote lipid anabolism, improve glucose homeostasis, and spare protein. The effects of succinate on nutritional metabolism are associated with alterations in the levels of metabolic intermediates, transcriptional regulation, and protein succinylation levels. However, hepatic fat accumulation and gut microbiota dysbiosis induced by dietary succinate suggest potential risks of succinate application as a feed additive for fish. This study would be beneficial in understanding the application of succinate as an aquatic feed additive.

Changes in apolipoprotein abundance dominate proteome responses to prolonged fasting in elephant seals.

Unlike many animals that reduce activity during fasting, northern elephant seals (NES) undergo prolonged fasting during energy-intensive life-history stages such as reproduction and molting, fueling fasting energy needs by mobilizing fat stores accrued during foraging. NES display several unique metabolic features such as high fasting metabolic rates, elevated blood lipid and high-density lipoprotein (HDL) cholesterol levels, efficient protein sparing and resistance to oxidative stress during fasting. However, the cellular mechanisms that regulate these adaptations are still not fully understood. To examine how metabolic coordination is achieved during prolonged fasting, we profiled changes in blubber, skeletal muscle and plasma proteomes of adult female NES over a 5week fast associated with molting. We found that while blubber and muscle proteomes were remarkably stable over fasting, over 50 proteins changed in abundance in plasma, including those associated with lipid storage, mobilization, oxidation and transport. Apolipoproteins dominated the blubber, plasma and muscle proteome responses to fasting. APOA4, APOE and APOC3, which are associated with lipogenesis and triglyceride accumulation, decreased, while APOA1, APOA2 and APOM, which are associated with lipid mobilization and HDL function, increased over fasting. Our findings suggest that changes in apolipoprotein composition may underlie the maintenance of high HDL levels and, together with adipokines and hepatokines that facilitate lipid catabolism, may mediate the metabolic transitions between feeding and fasting in NES. Many of these proteins have not been previously studied in this species and provide intriguing hypotheses about metabolic regulation during prolonged fasting in mammals.

Supplementing cultured human myotubes with hibernating bear serum results in increased protein content by modulating Akt/FOXO3a signaling.

Hibernating bears remain in their dens for 5–7 months during winter and survive without eating or drinking while staying inactive. However, they maintain their physical functions with minimal skeletal muscle atrophy and metabolic dysfunction. In bears, resistance to skeletal muscle atrophy during hibernation is likely mediated by seasonally altered systemic factors that are independent of neuromuscular activity. To determine whether there are components in bear serum that regulate protein and energy metabolism, differentiated human skeletal muscle cells were treated with bear serum (5% in DMEM/Ham’s F-12, 24 h) collected during active summer (July) and hibernating winter (February) periods. The serum samples were collected from the same individual bears (Ursus thibetanus japonicus, n = 7 in each season). Total protein content in cultured skeletal muscle cells was significantly increased following a 24 h treatment with hibernating bear serum. Although the protein synthesis rate was not altered, the expression of MuRF1 protein, a muscle-specific E3 ubiquitin ligase was significantly decreased along with a concomitant activation of Akt/FOXO3a signaling. Increased levels of insulin-like growth factor-1 (IGF-1) were also observed in hibernating bear serum. These observations suggest that protein metabolism in cultured human myotubes may be altered when incubated with hibernating bear serum, with a significant increase in serum IGF-1 and diminished MuRF1 expression, a potential target of Akt/FOXO3a signaling. A protein sparing phenotype in cultured muscle cells by treatment with hibernating bear serum holds potential for the development of methods to prevent human muscle atrophy and related disorders.

Effect of protein and glucogenic precursor supplementation on forage digestibility, serum metabolites, energy utilization, and rumen parameters in sheep

Supplementation of glucogenic precursors in roughage diets may increase production responses due to improved efficiencies of nutrient utilization. Therefore, the objective of this study was to determine the effect of source of supplemental glucogenic potential (GP) on forage digestibility, serum metabolites, energy utilization, and rumen parameters of growing wethers consuming a roughage diet (8.8% crude protein, 71.4% ash-free neutral detergent fiber). Crossbred wethers (49.1 ± 4.7 kg initial BW; n = 16) were utilized in a 4 × 4 replicated Latin Square design with four periods of 21 d. Supplements were designed to supplement increasing amount of GP: 1) no supplementation (CON; 0 g), 2) 40 g of calcium propionate (CAP; 30 g of GP), 3) 70 g of blood meal + 100 g of feather meal (BF; 40 g of GP), or 4) combination of CAP and BF (COMBO; 70 g of GP). Total fecal and urine collection was conducted from days 13–17 to calculate digestibility estimates and urinary losses. An acetate tolerance test was administered on day 17 to determine the effect of GP on acetate clearance. Blood samples were collected on day 19 and were analyzed for serum concentrations of glucose, urea N (SUN), non-esterified fatty acids, and amino acids. Rumen fluid was collected on day 21 to determine supplementation effects on ruminal volatile fatty acid (VFA) and ammonia concentrations. Wethers receiving BF and COMBO supplementation had greatest (P ≤ 0.01) DM and OM total tract digestibility. Supplementation did not affect (P ≥ 0.37) NDF digestibility or digestible energy. Urinary nitrogen excretion was greatest (P = 0.02) for BF and COMBO. Circulating serum essential amino acid concentration was increased (P < 0.01) in BF and COMBO compared to CAP and CON. In addition, BF and COMBO had increased (P < 0.01) SUN concentrations compared to CAP and CON. Acetate half-life was not affected (P = 0.39) by supplementation strategy. However, area under the curve (AUC) for acetate was decreased (P = 0.04) with supplementation of BF and COMBO compared to CON-fed wethers. Ruminal propionate concentration was increased (P ≤ 0.01) for wethers fed CAP and COMBO supplementation, which resulted in decreased (P ≤ 0.01) A:P ratio. Overall, these results indicate that the increased propionate supply by providing propionate salts did not result in a protein sparing impact or increased N retention.

Recombinant Bovine Growth Hormone-Induced Metabolic Remodelling Enhances Growth of Gilthead Sea-Bream (Sparus aurata): Insights from Stable Isotopes Composition and Proteomics.

Growth hormone and insulin-like growth factors (GH/IGF axis) regulate somatic growth in mammals and fish, although their action on metabolism is not fully understood in the latter. An intraperitoneal injection of extended-release recombinant bovine growth hormone (rbGH, Posilac®) was used in gilthead sea bream fingerlings and juveniles to analyse the metabolic response of liver and red and white muscles by enzymatic, isotopic and proteomic analyses. GH-induced lipolysis and glycogenolysis were reflected in liver composition, and metabolic and redox enzymes reported higher lipid use and lower protein oxidation. In white and red muscle reserves, rBGH increased glycogen while reducing lipid. The isotopic analysis of muscles showed a decrease in the recycling of proteins and a greater recycling of lipids and glycogen in the rBGH groups, which favoured a protein sparing effect. The protein synthesis capacity (RNA/protein) of white muscle increased, while cytochrome-c-oxidase (COX) protein expression decreased in rBGH group. Proteomic analysis of white muscle revealed only downregulation of 8 proteins, related to carbohydrate metabolic processes. The global results corroborated that GH acted by saving dietary proteins for muscle growth mainly by promoting the use of lipids as energy in the muscles of the gilthead sea bream. There was a fuel switch from carbohydrates to lipids with compensatory changes in antioxidant pathways that overall resulted in enhanced somatic growth.

Is muscle and protein loss relevant in long‐term fasting in healthy men? A prospective trial on physiological adaptations

BackgroundFasting is attracting an increasing interest as a potential strategy for managing diseases, including metabolic disorders and complementary cancer therapy. Despite concerns of clinicians regarding protein catabolism and muscle loss, evidence‐based clinical data in response to long‐term fasting in healthy humans are scarce. The objective of this study was to measure clinical constants, metabolic, and muscular response in healthy men during and after a 10 day fast combined with a physical activity programme.MethodsSixteen men (44 ± 14 years; 26.2 ± 0.9 kg/m2) fasted with a supplement of 200–250 kcal/day and up to 3 h daily low‐intensity physical activity according to the peer‐reviewed Buchinger Wilhelmi protocol. Changes in body weight (BW) and composition, basal metabolic rate (BMR), physical activity, muscle strength and function, protein utilization, inflammatory, and metabolic status were assessed during the 10 day fast, the 4 days of food reintroduction, and at 3 month follow‐up.ResultsThe 10 day fast decreased BW by 7% (−5.9 ± 0.2 kg, P < 0.001) and BMR by 12% (P < 0.01). Fat mass and lean soft tissues (LST) accounted for about 40% and 60% of weight loss, respectively, −2.3 ± 0.18 kg and −3.53 ± 0.13 kg, P < 0.001. LST loss was explained by the reduction in extracellular water (44%), muscle and liver glycogen and associated water (14%), and metabolic active lean tissue (42%). Plasma 3‐methyl‐histidine increased until Day 5 of fasting and then decreased, suggesting that protein sparing might follow early proteolysis. Daily steps count increased by 60% (P < 0.001) during the fasting period. Strength was maintained in non‐weight‐bearing muscles and increased in weight‐bearing muscles (+33%, P < 0.001). Glycaemia, insulinemia, blood lipids, and blood pressure dropped during the fast (P < 0.05 for all), while non‐esterified fatty acids and urinary beta‐hydroxybutyrate increased (P < 0.01 for both). After a transient reduction, inflammatory cytokines returned to baseline at Day 10 of fasting, and LST were still lower than baseline values (−2.3% and −3.2%, respectively; P < 0.05 for both).ConclusionsA 10 day fast appears safe in healthy humans. Protein loss occurs in early fast but decreases as ketogenesis increases. Fasting combined with physical activity does not negatively impact muscle function. Future studies will need to confirm these first findings.

Body Protein Sparing in Hibernators: A Source for Biomedical Innovation.

Proteins are not only the major structural components of living cells but also ensure essential physiological functions within the organism. Any change in protein abundance and/or structure is at risk for the proper body functioning and/or survival of organisms. Death following starvation is attributed to a loss of about half of total body proteins, and body protein loss induced by muscle disuse is responsible for major metabolic disorders in immobilized patients, and sedentary or elderly people. Basic knowledge of the molecular and cellular mechanisms that control proteostasis is continuously growing. Yet, finding and developing efficient treatments to limit body/muscle protein loss in humans remain a medical challenge, physical exercise and nutritional programs managing to only partially compensate for it. This is notably a major challenge for the treatment of obesity, where therapies should promote fat loss while preserving body proteins. In this context, hibernating species preserve their lean body mass, including muscles, despite total physical inactivity and low energy consumption during torpor, a state of drastic reduction in metabolic rate associated with a more or less pronounced hypothermia. The present review introduces metabolic, physiological, and behavioral adaptations, e.g., energetics, body temperature, and nutrition, of the torpor or hibernation phenotype from small to large mammals. Hibernating strategies could be linked to allometry aspects, the need for periodic rewarming from torpor, and/or the ability of animals to fast for more or less time, thus determining the capacity of individuals to save proteins. Both fat- and food-storing hibernators rely mostly on their body fat reserves during the torpid state, while minimizing body protein utilization. A number of them may also replenish lost proteins during arousals by consuming food. The review takes stock of the physiological, molecular, and cellular mechanisms that promote body protein and muscle sparing during the inactive state of hibernation. Finally, the review outlines how the detailed understanding of these mechanisms at play in various hibernators is expected to provide innovative solutions to fight human muscle atrophy, to better help the management of obese patients, or to improve the ex vivo preservation of organs.

Is Water-Only Fasting Safe?

BackgroundWater-only fasting (WF) is a practice used to improve and maintain health.ObjectiveThe aim of the study was to show whether WF performed for 8 days may be a threat to the health and/or life of people undergoing this practice.MethodsTwelve middle-aged men participated in the study. During the 8-day WF, the subjects ate no food except for drinking mineral water. Before and after WF, all subjects had a series of tests performed, beginning with the level of perceived stress and somatic measurements. The concentrations of creatinine, sodium (Na+), potassium (K+), total calcium (Ca), magnesium (Mg++), urea (U), uric acid (UA) and total protein were determined in this urine and in the serum. For these substances, the values ​​of clearance, renal filtration and fractional excretion were calculated. The osmotic clearance and free water clearance as well as the amount of daily urinary excretion of creatinine, Na+, K+, Ca, Mg++, U and UA were also calculated. Moreover, the concentration of glucose in the serum and the concentration of β-hydroxybutyrate in the plasma were determined. In urine, specific gravity, pH and osmolality were also measured.ResultsAfter 8 days of WF, the study showed a significant reduction in the level of perceived stress, weight loss, changes in body composition, dehydration, increased ketogenesis, hyperuricemia, decreased serum glucose concentration, and hyponatremia. These changes were accompanied by Na+, K+ and protein sparing, decreased serum Ca and Mg++ concentrations, and reduced daily volume of more acidic urine with elevated specific gravity.ConclusionsAfter 8 days of WF, all subjects were found to remain safe and feel the sense of well-being. However, the appearance of the above-mentioned adverse metabolic effects, despite partially effective renal compensations, suggests that the further continuation of fasting intervention by the subjects would be detrimental to their body.