Beyond the role of dietary protein and amino acids in the prevention of diet-induced obesity

Low Muscle Mass Is Associated with Poorer Glycemic Control and Higher Oxidative Stress in Older Patients with Type 2 Diabetes

Body composition changes that occur during aging, such as loss of lean mass, are unfavorable at metabolic level and they can explain, in part, the appearance of certain age-associated diseases such as type 2 diabetes (T2D). Separately, T2D is associated with an increase in oxidative stress (OS) which negatively affects skeletal muscle. Our aim was to study the differences in clinical and nutritional parameters, disease control, and OS in a cohort of older patients with T2D classified according to the amount of lean mass they had. We included 100 adults older than 65 years with T2D. We found that women with low fat-free mass and muscle mass have worse T2D metabolic control. Moreover, the patients with a low percentile of muscle mass present a high value of OS. The study shows that the presence of low lean mass (LM) in the geriatric population diagnosed with T2D is associated with poorer glycemic control and greater OS.

Effects of Diets With Different Protein Levels on Lipid Metabolism and Gut Microbes in the Host of Different Genders

The purpose of this experiment was to investigate the effects of different protein levels on lipid metabolism and gut microbes in mice of different genders. A total of 60 mice (30 female and 30 male) were randomly assigned to six groups and fed female mice with low protein diet (FLP), basal protein diet (FBD), and high protein diet (FHP). Similarly, the male mice fed with low protein diet (MLP), basal protein diet (MBD), and high protein diet (MHP). The low protein diet contained 14% CP, the basal diet contained 20% CP, and the high protein diet contained 26% CP. The results of the study showed that both basal and high protein diets significantly reduced the perirenal adipose tissues (PEAT) index in male mice compared to low protein diet (p < 0.05). For the gut, the FHP significantly increased the relative gut weight compared to the FBD and FLP (p < 0.05). At the same time, the FHP also significantly increased the relative gut length compared with the FBD and FLP (p < 0.05). The MHP significantly increased TC concentration compared with the MLP (p < 0.05), and the MBD tended to increase TC concentration compared with the MLP in serum (p = 0.084). The histomorphology result of the jejunum and ileum showed that a low protein diet was beneficial to the digestion and absorption of nutrients in the small intestine of mice. While different protein levels had no effect on the total number of fecal microbial species in mice, different protein levels had a significant effect on certain fecal microbes in mice, the absolute abundance of Verrucomicrobia in the feces of male mice was significantly higher in both high and basal protein diets than in the low protein diet (p < 0.05). The high protein diet significantly reduced the absolute abundance of Patescibacteria in the feces of female mice compared to both the basal and low protein diets (p < 0.05). The absolute abundance of Patescibacteria in male feces was not affected by dietary protein levels (p > 0.05). Taken together, our results suggest that a low protein diet can alter fat deposition and lipid metabolism in mice, and that it benefited small intestinal epithelial structure and microbes.

Beneficial effects of fish and fish peptides on main metabolic syndrome associated risk factors: Diabetes, obesity and lipemia

The definition of metabolic syndrome (MetS) fairly varies from one to another guideline and health organization. Per description of world health organization, occurrence of hyperinsulinemia or hyperglycemia in addition to two or more factors of dyslipidemia, hypoalphalipoproteinemia, hypertension and or large waist circumference factors would be defined as MetS. Conventional therapies and drugs, commonly with adverse effects, are used to treat these conditions and diseases. Nonetheless, in the recent decades scientific community has focused on the discovery of natural compounds to diminish the side effects of these medications. Among many available bioactives, biologically active peptides have notable beneficial effects on the management of diabetes, obesity, hypercholesterolemia, and hypertension. Marine inclusive of fish peptides have exerted significant bioactivities in different experimental in-vitro, in-vivo and clinical settings. This review exclusively focuses on studies from the recent decade investigating hypoglycemic, hypolipidemic, hypercholesterolemic and anti-obesogenic fish and fish peptides. Related extraction, isolation, and purification methodologies of anti-MetS fish biopeptides are reviewed herein for comparison purposes only. Moreover, performance of biopeptides in simulated gastrointestinal environment and structure-activity relationship along with absorption, distribution, metabolism, and excretion properties of selected oligopeptides have been discussed, in brief, to broaden the knowledge of readers on the design and discovery trends of anti-MetS compounds.Supplemental data for this article is available online at https://doi.org/10.1080/10408398.2022.2052261 .

High-protein diet more effectively reduces hepatic fat than low-protein diet despite lower autophagy and FGF21 levels

BACKGROUND AND AIMS

Non-alcoholic fatty liver disease (NAFLD) is becoming increasingly prevalent and nutrition intervention remains the most important therapeutic approach for NAFLD. Our aim was to investigate whether low- (LP) or high-protein (HP) diets are more effective in reducing liver fat and reversing NAFLD and which mechanisms are involved.

METHODS

19 participants with morbid obesity undergoing bariatric surgery were randomized into two hypocaloric (1500-1600 kcal/day) diet groups, a low protein (10E% protein) and a high protein (30E% protein), for three weeks prior to surgery. Intrahepatic lipid levels (IHL) and serum fibroblast growth factor 21 (FGF21) were measured before and after the dietary intervention. Autophagy flux, histology, mitochondrial activity and gene expression analyses were performed in liver samples collected during surgery.

RESULTS

IHL levels decreased by 42.6% in the HP group, but were not significantly changed in the LP group despite similar weight loss. Hepatic autophagy flux and serum FGF21 increased by 66.7% and 42.2%, respectively, after 3 weeks in the LP group only. Expression levels of fat uptake and lipid biosynthesis genes were lower in the HP group compared with those in the LP group. RNA-seq analysis revealed lower activity of inflammatory pathways upon HP diet. Hepatic mitochondrial activity and expression of β-oxidation genes did not increase in the HP group.

CONCLUSIONS

HP diet more effectively reduces hepatic fat than LP diet despite of lower autophagy and FGF21. Our data suggest that liver fat reduction upon HP diets result primarily from suppression of fat uptake and lipid biosynthesis.

Licorice flavonoid oil supplementation promotes a reduction of visceral fat in exercised rats

BACKGROUND

The beneficial effect of exercise combined with licorice flavonoid oil supplementation on visceral fat was investigated.

METHODS

Male Sprague-Dawley rats were divided into 4 groups: control, exercise (Ex), control with licorice flavonoid oil supplementation (LFO), and exercise with licorice flavonoid oil supplementation (ExLFO) groups. The rats in the Ex and ExLFO groups ran on a treadmill (20-degree incline at 20 m/min for 30 min/day) 5 times a week for 7 weeks, and those in the LFO and ExLFO groups were orally administered with licorice flavonoid oil daily using a feeding needle.

RESULTS

Exercise or licorice flavonoid oil supplementation resulted in the reduction of the visceral fat mass and adipocyte size, respectively. In addition, exercise combined with licorice flavonoid oil supplementation more effectively decreased both measures. Exercise alone increased the β-hydroxyacyl-CoA dehydrogenase (β-HAD) and citrate synthase (CS) activities in the soleus and plantaris muscles, and licorice flavonoid oil supplementation alone increased the hepatic carnitine palmitoyl transferase-2 (CPT-2) activity. Furthermore, the combination of exercise and licorice flavonoid oil supplementation enhanced the both muscular β-HAD and CS activities, and hepatic CPT-2 activity.

CONCLUSIONS

These results suggest that exercise combined with licorice flavonoid oil supplementation may be effective to decrease visceral adipose tissue via enhancing skeletomuscular and hepatic fatty acids oxidative capacity.

Evaluation of an Amino Acid Mix on the Secretion of Gastrointestinal Peptides, Glucometabolic Homeostasis, and Appetite in Obese Adolescents Administered with a Fixed-Dose or ad Libitum Meal

Proteins have been demonstrated to reduce food intake in animals and humans via peripheral and central mechanisms. Supplementation of a dietetic regimen with single or mixed amino acids might represent an approach to improve the effectiveness of any body weight reduction program in obese subjects. The aim of the present study was to evaluate the effects of an amino acid mix (L-arginine + L-leucine + L-glutamine + L-tryptophan) on the secretion of some gastrointestinal peptides (i.e., ghrelin and glucagon-like peptide type 1, GLP-1), glucometabolic homeostasis (i.e., glucose, insulin, and glucagon), and appetite (hunger/satiety scored by visual analogue scale, VAS) in obese adolescents (n = 14; 10 females and 4 males; age: 16.6 ± 1.0 years; body mass index (BMI): 36.4 ± 4.6 kg/m²; fat-free mass (FFM): 54.9 ± 4.7%; fat mass (FM): 45.1 ± 4.4%) administered with a fixed-dose (lunch) or ad libitum (dinner) meal. Isocaloric maltodextrins were used as control treatment. During the lunch test, a significant increase in circulating levels of GLP-1, but not of ghrelin, was observed in the amino acid-treated group, which was congruent with significant changes in appetite, i.e., increase in satiety and decrease in hunger. A significant hyperglycemia was found in the maltodextrin-treated group during the prelunch period, without any significant changes in insulin and glucagon between the two groups. During the dinner test, there were no significant differences in appetite (hunger/satiety) and intake of calories. In conclusion, L-arginine, L-leucine, L-glutamine, and L-tryptophan, when administered to obese adolescents with a fixed-dose meal, are capable of evoking an anorexigenic response, which is, at least in part, mediated by an increase in GLP-1 released in circulation by L cells, which are capable of chemosensing specific amino acids present in the intestinal lumen. Further additional studies are requested to understand whether higher doses are necessary to inhibit ad libitum feeding.

Effect of short- and long-term protein consumption on appetite and appetite-regulating gastrointestinal hormones, a systematic review and meta-analysis of randomized controlled trials

AIM

High-protein diets are considered as useful diets for weight loss programs. We collected randomized controlled trials that evaluated the effect of protein on appetite and gastrointestinal hormones involved in appetite regulation.

METHODS

Trials were included if participants were healthy adults and isocaloric treatments were used in control and treatment arms. Random-effects model was used to calculate mean difference and 95% confidence intervals.

RESULTS

In total, 49 publications for acute and 19 articles for long-term effect of protein were included. In acute interventions, protein decreased hunger (-7 mm visual analogue scale (VAS), P<0.001), desire to eat (-5 mm, P = 0.045), and prospective food consumption (-5 mm, P = 0.001) and increased fullness (10 mm, P<0.001) and satiety (4 mm, P<0.001). There was also a decrease in ghrelin (-20 pg/ml, P<0.001) and increase in cholecystokinin (30 pg/ml, P<0.001) and glucagon-like peptide-1 (GLP-1) (21 ng/ml, P<0.001), but no change in gastric inhibitory polypeptide and peptide YY was observed. Appetite markers were affected by protein doses < 35 g but ghrelin, cholecystokinin, and GLP-1 changed significantly after doses ≥ 35 g. Long-term ingestion of protein did not affect these outcomes, except for GLP-1 which showed a significant decrease.

CONCLUSION

Results of this meta-analysis showed that acute ingestion of protein suppresses appetite, decreases ghrelin, and augments cholecystokinin and GLP-1. Results of long-term trials are inconclusive and further trials are required before a clear and sound conclusion on these trials could be made.

Metabolic effects of Tofogliflozin are efficiently enhanced with appropriate dietary carbohydrate ratio and are distinct from carbohydrate restriction

Sodium‐glucose cotransporter 2 inhibitors (SGLT2i) exert their antidiabetic effects by promoting urinary glucose excretion. Nutrition therapy is obviously important, but little is known about the interactions between SGLT2i agents and carbohydrate restriction. Therefore, we studied these interactions using an obese diabetic animal model. KK‐A^y mice were pair‐fed normal chow [NC; carbohydrate: fat: protein = 65:15:20], low carbohydrate [LC; 43:42:15] or severely carbohydrate restricted diets [SR; 12:45:43] for 12 weeks. Tofogliflozin (Tofo) was administered as the SGLT2i in the NC and LC diet groups. Blood glucose levels were significantly increased in the SR group. Tofo reduced blood glucose levels significantly in the NC group during the experiment and in the LC group at 2‐6 weeks. Plasma triglycerides were markedly elevated in the SR group without Tofo, but decreased in response to Tofo administration. Hepatic triglyceride contents were not changed by the LC or the SR diet alone. However, Tofo ameliorated hepatosteatosis in NC‐fed animals. Consistent with the downregulation of stearoyl‐CoA desaturase 1, the ratio of plasma monounsaturated to saturated fatty acids was significantly reduced in the LC with Tofo and in the SR alone groups, but was not altered in the NC with Tofo group. In summary, metabolism of glucose and lipids was improved by Tofo but not by the SR diet. Furthermore, Tofo improved these parameters more effectively in the NC than in the LC diet group. These data suggest that the effects of SGLT2i are distinct from those of carbohydrate restriction and that a nonrestricted dietary carbohydrate composition is essential for SGLT2i treatment to be effective.

Dietary Proteins, Brown Fat, and Adiposity

High protein diets have become popular for body weight maintenance and weight loss despite controversies regarding efficacy and safety. Although both weight gain and weight loss are determined by energy consumption and expenditure, data from rodent trials consistently demonstrate that the protein:carbohydrate ratio in high fat diets strongly influences body and fat mass gain per calorie eaten. Here, we review data from rodent trials examining how high protein diets may modulate energy metabolism and the mechanisms by which energy may be dissipated. We discuss the possible role of activating brown and so-called beige/BRITE adipocytes including non-canonical UCP1-independent thermogenesis and futile cycles, where two opposing metabolic pathways are operating simultaneously. We further review data on how the gut microbiota may affect energy expenditure. Results from human and rodent trials demonstrate that human trials are less consistent than rodent trials, where casein is used almost exclusively as the protein source. The lack of consistency in results from human trials may relate to the specific design of human trials, the possible distinct impact of different protein sources, and/or the differences in the efficiency of high protein diets to attenuate obesity development in lean subjects vs. promoting weight loss in obese subjects.

Dietary Sulfur-Containing Amino Acids Are Associated with Higher Prevalence of Overweight/Obesity in Northern Chinese Adults, an Internet-Based Cross-Sectional Study

BACKGROUND/AIMS

Elevation of plasma sulfur-containing amino acids (SAAs) is generally associated with higher body mass index (BMI) and unfavorable lipid profiles. It is not known how dietary SAAs relate to these associations in humans.

METHODS

A convenient tool named internet-based dietary questionnaire for Chinese (IDQC) was used to estimate dietary SAAs intake. A total of 936 participants were randomly recruited and asked to complete the IDQC. Furthermore, 90 subjects were randomly selected to perform a subgroup study. The associations between dietary SAAs and prevalence of obesity, lipid profiles, and status of insulin resistance (IR), inflammation and oxidative stress were assessed.

RESULTS

Dietary total SAAs and cysteine of overweight/obese participants were significantly higher. Dietary total SAAs and cysteine were positively associated with BMI and waist circumference. Higher dietary total SAAs were associated with higher prevalence of overweight/obesity. Higher dietary total SAAs and cysteine also associated with higher serum triglyceride (total cholesterol), low density lipoprotein, fasting blood glucose, 2 h-postprandial glucose, and homeostasis model assessment of IR. In the subgroup study, positive associations between dietary SAAs and inflammation biomarkers were also observed.

CONCLUSIONS

Dietary SAAs are associated with higher prevalence of overweight/obesity, unfavorable lipid profiles and status of IR, and inflammation.

Links between Dietary Protein Sources, the Gut Microbiota, and Obesity

The association between the gut microbiota and obesity is well documented in both humans and in animal models. It is also demonstrated that dietary factors can change the gut microbiota composition and obesity development. However, knowledge of how diet, metabolism and gut microbiota mutually interact and modulate energy metabolism and obesity development is still limited. Epidemiological studies indicate an association between intake of certain dietary protein sources and obesity. Animal studies confirm that different protein sources vary in their ability to either prevent or induce obesity. Different sources of protein such as beans, vegetables, dairy, seafood, and meat differ in amino acid composition. Further, the type and level of other factors, such as fatty acids and persistent organic pollutants (POPs) vary between dietary protein sources. All these factors can modulate the composition of the gut microbiota and may thereby influence their obesogenic properties. This review summarizes evidence of how different protein sources affect energy efficiency, obesity development, and the gut microbiota, linking protein-dependent changes in the gut microbiota with obesity.

Partial phenotype conversion and differential trait response to conditions of husbandry in mice

Functional genome analysis usually is performed on the level of genotype–phenotype interaction. However, phenotypes also depend on the relations between genomes and environment. In our experimental system, we observed differential response to environmental factors defined by different conditions of husbandry in a semi-barrier unit or in a SPF (specific pathogen free) barrier unit, which resulted in partial reversal of phenotypes previously observed under semi-barrier conditions. To provide an update of basic phenotypes in unselected and randomly mated controls (DUC) and long-term selected DUhTP (Dummerstorf high treadmill performance) mice in the SPF facility, we compared growth parameters, reproductive performance, the accretion of muscle and fat mass, physical activity, and running performance as well as food intake in all experimental groups. For selected parameters, the comparative analysis spans more than 30 generations. In DUC mice, under SPF conditions a more than threefold (P < 0.0001) higher subcutaneous fat mass, higher muscle mass by about 25% (P < 0.0001), but lower epididymal fat mass in DUhTP mice by about 20% (P < 0.0001) were observed. In SPF husbandry, body weight increased to a stronger extent in adult DUC mice (≈ 20%; P < 0.0001) than in DUhTP mice (≈ 8%; P = 0.001). The concentrations of IGF-1 and IGFBPs in the serum as well as the liver weights were similar in all experimental groups, indicating growth effects independent of the somatotropic axis. Under SPF conditions the litter size at birth increased in DUC mice (P < 0.001) but not in DUhTP mice. The differential effect of husbandry on body weights at day 21 and concentrations of triglycerides in the serum of our model were due to the different diets used in the semi-barrier and in the SPF facility. Our results demonstrate differential trait response to environmental factors resulting in partial phenotype conversion in our experimental system. The existence of conditional phenotypes as a result of genotype–environment interactions points to the importance of environmental factors in functional genome analysis.

Long-Term Intake of a High-Protein Diet Affects Body Phenotype, Metabolism, and Plasma Hormones in Mice

Background: High-protein diets (HPDs) recently have been used to obtain body weight and fat mass loss and expand muscle mass. Several studies have documented that HPDs reduce appetite and food intake.Objective: Our goal was to determine the long-term effects of an HPD on body weight, energy intake and expenditure, and metabolic hormones.Methods: Male C57BL/6 mice (8 wk old) were fed either an HPD (60% of energy as protein) or a control diet (CD; 20% of energy as protein) for 12 wk. Body composition and food intakes were determined, and plasma hormone concentrations were measured in mice after being fed and after overnight feed deprivation at several time points.Results: HPD mice had significantly lower body weight (in means ± SEMs; 25.73 ± 1.49 compared with 32.5 ± 1.31 g; P = 0.003) and fat mass (9.55% ± 1.24% compared with 15.78% ± 2.07%; P = 0.05) during the first 6 wk compared with CD mice, and higher lean mass throughout the study starting at week 2 (85.45% ± 2.25% compared with 75.29% ± 1.90%; P = 0.0001). Energy intake, total energy expenditure, and respiratory quotient were significantly lower in HPD compared with CD mice as shown by cumulative energy intake and eating rate. Water vapor was significantly higher in HPD mice during both dark and light phases. In HPD mice, concentrations of leptin [feed-deprived: 41.31 ± 11.60 compared with 3041 ± 683 pg/mL (P = 0.0004); postprandial: 112.5 ± 102.0 compared with 8273 ± 1415 pg/mL (P < 0.0001)] and glucagon-like peptide 1 (GLP-1) [feed-deprived: 5.664 ± 1.44 compared with 21.31 ± 1.26 pg/mL (P = <0.0001); postprandial: 6.54 ± 2.13 compared with 50.62 ± 11.93 pg/mL (P = 0.0037)] were significantly lower, whereas postprandial glucagon concentrations were higher than in CD-fed mice.Conclusions: In male mice, the 12-wk HPD resulted in short-term body weight and fat mass loss, but throughout the study preserved body lean mass and significantly reduced energy intake and expenditure as well as leptin and GLP-1 concentrations while elevating postprandial glucagon concentrations. This study suggests that long-term use of HPDs may be an effective strategy to decrease energy intake and expenditure and to maintain body lean mass.

The Inhibitory Effects of Anthocyanin-Rich Sunrouge Tea on Pancreatic Lipase Activity

This study investigated the in vitro and in vivo effects of Sunrouge (SR), which is an anthocyaninrich green tea. Hot and cold water extracts (CWEX) of Yabukita (YK; regular green tea), SR second crop (SR2), and SR third crop (SR3) were prepared. The 50% inhibitory concentrations for YK, SR2, and SR3 CWEXs against pancreatic lipase in vitro were 12.3±2.8, 6.2±0.3, and 4.0±1.1 mg/mL, respectively. Epigallocatechin gallate (EGCG) accounted for 4.3%, 6.0%, and 6.3% of YK, SR2, and SR3 CWEXs, respectively. SR2 had the highest anthocyanin content of these three samples. In vivo, the increase in the plasma triacylglycerol (TG) concentration following oral administration of oil to mice was significantly suppressed at 60 and 120 min in animals treated with SR2. No significant differences were observed between the plasma TG concentration in the YK and control groups. These results suggested that concomitant administration of SR with oil may suppress lipid absorption and that EGCG may exert this effect.

High-protein diet improves sensitivity to cholecystokinin and shifts the cecal microbiome without altering brain inflammation in diet-induced obesity in rats

High-protein diet (HPD) curtails obesity and/or fat mass, but it is unknown whether it reverses neuroinflammation or alters glucose levels, CCK sensitivity, and gut microbiome in rats fed a Western diet (WD)-induced obesity (DIO). Male rats fed a WD (high fat and sugar) for 12 wk were switched to a HPD for 6 wk. Body composition, food intake, meal pattern, sensitivity to intraperitoneal CCK-8S, blood glucose, brain signaling, and cecal microbiota were assessed. When compared with a normal diet, WD increased body weight (9.3%) and fat mass (73.4%). CCK-8S (1.8 or 5.2 nmol/kg) did not alter food intake and meal pattern in DIO rats. Switching to a HPD for 6 wk reduced fat mass (15.7%) with a nonsignificantly reduced body weight gain, normalized blood glucose, and decreased feeding after CCK-8S. DIO rats on the WD or switched to a HPD showed comparable microbial diversity. However, in HPD versus WD rats, there was enrichment of 114 operational taxonomic units (OTUs) and depletion of 188 OTUs. Of those, Akkermansia muciniphila (enriched on a HPD), an unclassified Clostridiales, a member of the RF39 order, and a Phascolarctobacterium were significantly associated with fat mass. The WD increased cytokine expression in the hypothalamus and dorsal medulla that was unchanged by switching to HPD. These data indicate that HPD reduces body fat and restores glucose homeostasis and CCK sensitivity, while not modifying brain inflammation. In addition, expansion of cecal Akkermansia muciniphila correlated to fat mass loss may represent a potential peripheral mechanism of HPD beneficial effects.

A High-Protein Diet Reduces Weight Gain, Decreases Food Intake, Decreases Liver Fat Deposition, and Improves Markers of Muscle Metabolism in Obese Zucker Rats

A primary factor in controlling and preventing obesity is through dietary manipulation. Diets higher in protein have been shown to improve body composition and metabolic health during weight loss. The objective of this study was to examine the effects of a high-protein diet versus a moderate-protein diet on muscle, liver and fat metabolism and glucose regulation using the obese Zucker rat. Twelve-week old, male, Zucker (fa/fa) and lean control (Fa/fa) rats were randomly assigned to either a high-protein (40% energy) or moderate-protein (20% energy) diet for 12 weeks, with a total of four groups: lean 20% protein (L20; n = 8), lean 40% protein (L40; n = 10), obese 20% protein (O20; n = 8), and obese 40% protein (O40; n = 10). At the end of 12 weeks, animals were fasted and euthanized. There was no difference in food intake between L20 and L40. O40 rats gained less weight and had lower food intake (p < 0.05) compared to O20. O40 rats had lower liver weight (p < 0.05) compared to O20. However, O40 rats had higher orexin (p < 0.05) levels compared to L20, L40 and O20. Rats in the L40 and O40 groups had less liver and muscle lipid deposition compared to L20 and L40 diet rats, respectively. O40 had decreased skeletal muscle mechanistic target of rapamycin complex 1 (mTORC1) phosphorylation and peroxisome proliferator-activated receptor gamma (PPARγ) mRNA expression compared to O20 (p < 0.05), with no difference in 5' AMP-activated protein kinase (AMPK), eukaryotic translation initiation factor 4E binding protein 1 (4EBP1), protein kinase B (Akt) or p70 ribosomal S6 kinase (p70S6K) phosphorylation. The data suggest that high-protein diets have the potential to reduce weight gain and alter metabolism, possibly through regulation of an mTORC1-dependent pathway in skeletal muscle.

Human splanchnic amino-acid metabolism

Plasma levels of several amino acids are correlated with metabolic dysregulation in obesity and type 2 diabetes. To increase our understanding of human amino-acid metabolism, we aimed to determine splanchnic interorgan amino-acid handling. Twenty patients planned to undergo a pylorus preserving pancreatico-duodenectomy were included in this study. Blood was sampled from the portal vein, hepatic vein, superior mesenteric vein, inferior mesenteric vein, splenic vein, renal vein, and the radial artery during surgery. The difference between arterial and venous concentrations of 21 amino acids was determined using liquid chromatography as a measure of amino-acid metabolism across a given organ. Whereas glutamine was significantly taken up by the small intestine (121.0 ± 23.8 µmol/L; P < 0.0001), citrulline was released (−36.1 ± 4.6 µmol/L; P < 0.0001). This, however, was not seen for the colon. Interestingly, the liver showed a small, but a significant uptake of citrulline from the circulation (4.8 ± 1.6 µmol/L; P = 0.0138) next to many other amino acids. The kidneys showed a marked release of serine and alanine into the circulation (−58.0 ± 4.4 µmol/L and −61.8 ± 5.2 µmol/L, P < 0.0001), and a smaller, but statistically significant release of tyrosine (−12.0 ± 1.3 µmol/L, P < 0.0001). The spleen only released taurine (−9.6 ± 3.3 µmol/L; P = 0.0078). Simultaneous blood sampling in different veins provides unique qualitative and quantitative information on integrative amino-acid physiology, and reveals that the well-known intestinal glutamine–citrulline pathway appears to be functional in the small intestine but not in the colon.

Hepatic steatosis: a role for citrulline

PURPOSE OF REVIEW

The high worldwide prevalence of nonalcoholic fatty liver disease (NAFLD) makes it a major public health issue. Amino acids offer a promising approach for its prevention, and several experimental studies highlight the nutritional importance of citrulline in this setting. The purpose of this review is to discuss the potential interest of citrulline in the prevention and treatment of NAFLD.

RECENT FINDINGS

Current findings shed light on the role of the gut-liver, adipose tissue-liver, and muscle-liver axes in NAFLD progression. Recent experimental studies have produced evidence for a role of citrulline in controlling the pathophysiological mechanisms involved in NAFLD through its action on these three axes. Data are needed to distinguish between direct and indirect effects of citrulline on the liver and between a specific effect and a nitrogen supply-related effect.

SUMMARY

Good level of experimental evidence suggests that citrulline supply may be associated with an attenuation of NAFLD development, but further human studies are now needed to support these findings. This review may help define novel strategies to control fatty liver diseases.

The protein source determines the potential of high protein diets to attenuate obesity development in C57BL/6J mice

The notion that the obesogenic potential of high fat diets in rodents is attenuated when the protein:carbohydrate ratio is increased is largely based on studies using casein or whey as the protein source. We fed C57BL/6J mice high fat-high protein diets using casein, soy, cod, beef, chicken or pork as protein sources. Casein stood out as the most efficient in preventing weight gain and accretion of adipose mass. By contrast, mice fed diets based on pork or chicken, and to a lesser extent mice fed cod or beef protein, had increased adipose tissue mass gain relative to casein fed mice. Decreasing the protein:carbohydrate ratio in diets with casein or pork as protein sources led to accentuated fat mass accumulation. Pork fed mice were more obese than casein fed mice, and relative to casein, the pork-based feed induced substantial accumulation of fat in classic interscapular brown adipose tissue accompanied by decreased UCP1 expression. Furthermore, intake of a low fat diet with casein, but not pork, as a protein source reversed diet-induced obesity. Compared to pork, casein seems unique in maintaining the classical brown morphology in interscapular brown adipose tissue with high UCP1 expression. This was accompanied by increased expression of genes involved in a futile cycling of fatty acids. Our results demonstrate that intake of high protein diets based on other protein sources may not have similar effects, and hence, the obesity protective effect of high protein diets is clearly modulated by protein source.

Stable isotope analysis of dietary arginine accrual and disposal efficiency in male rats fed diets with different protein content

The administration of diets with different protein/energy ratios induce variable but distinctive responses in rats; an excessive protein content tends to decrease fat accumulation, but reversion of this ratio tends to increase adipose tissue mass.

Influence of plasma macronutrient levels on hepatic metabolism: role of regulatory networks in homeostasis and disease states

Multilevel regulations by metabolic, signaling and transcription pathways form a complex network that works to provide robust metabolic regulation in the liver. This analysis indicates that dietary perturbations in these networks can lead to insulin resistance.

Consumption of Branched-Chain Amino Acids Is Inversely Associated with Central Obesity and Cardiometabolic Features in a Population of Brazilian Middle-Aged Men: Potential Role of Leucine Intake

OBJECTIVE

To assess the potential associations of branched-chain amino acids (BCAA) consumption with central obesity (CObesity) and cardiometabolic risk factors in a population of Brazilian middle-aged men. Special attention was given to leucine intake.

DESIGN

Cross-sectional study.

SETTING

Universidade Federal de Viçosa, Viçosa, Brazil.

PARTICIPANTS

Two-hundred ninety-six middle-aged men (Age: 50.5 ± 5.0 years; Body mass index: 25.8 ± 3.5 kg/m2).

MEASUREMENTS

Anthropometry, lifestyle features, blood biochemical parameters were assessed and dietary intake was estimated by a food frequency questionnaire. Participants were classified by the occurrence of CObesity, hypertriglyceridemia (HTG), hypertriglyceridemic waist phenotype (HWP) and metabolic syndrome (MetS).

RESULTS

Subjects in the BCAA highest tertile (≥0.17 g/kg/d) presented lower occurrence of CObesity (36.0% vs 72.4%, P<0.01, z=-5.10), HTG (17.0% vs 30.6% P<0.032, z=-2.32), HWP (23.0% vs 46.9%, P<0.01, z=-3.57) and MetS (19.0% vs 34.7%, P<0.01, z=-2.57). They also exhibited lower values for Castelli index (total cholesterol:HDL-c) and triglycerides: HDL-c ratio than those in the first tertile, regardless of interfering factors (i.e. habitual physical activity, work position, smoking habit, and energy intake). Interestingly, leucine consumption showed similar associations with cardiometabolic risk factors, as compared to BCAA consumption (P<0.05).

CONCLUSION

BCAA consumption was cross-sectionally and negatively associated with relevant cardiometabolic risk factors in a population of Brazilian middle-aged men. The content of leucine in BCAA consumption may have contributed to such relationship.