Postprandial whole-body protein metabolism after a meat meal is influenced by chewing efficiency in elderly subjects.

BACKGROUND: The rate of protein digestion affects protein utilization in elderly subjects. Although meat is a widely consumed protein source, little is known of its digestion rate and how it can be affected by the chewing capacity of elderly subjects. OBJECTIVES: We used a [1-(13)C]leucine balance with a single-meal protocol to assess the absorption rate of meat protein and to estimate the utilization of meat protein in elderly subjects with different chewing efficiency. DESIGN: Twenty elderly volunteers aged 60-75 y were involved in the study. Ten of them had healthy natural dentition, and the other 10 were edentulous and wore complete dentures. Whole-body fluxes of leucine, before and after the meal (120 g beef meat), were measured with the use of a [1-(13)C]leucine intravenous infusion. RESULTS: A rapid increase in plasma aminoacidemia and plasma leucine entry rate was observed after meat intake in dentate subjects. In complete denture wearers the increase in leucine entry rate was delayed (P<0.05), and the amount of leucine appearing in peripheral blood during the whole postprandial period was lower than in dentate subjects (P<0.01). Postprandial whole-body protein synthesis was lower in denture wearers than in dentate subjects (30% compared with 48% of leucine intake, respectively; P<0.05). CONCLUSION: Meat proteins could be classified as fast digested proteins. However, this property depends on the chewing capacity of elderly subjects. This study showed that meat protein utilization for protein synthesis can be impaired by a decrease in the chewing efficiency of elderly subjects.

Dietary pectin stimulates protein metabolism in the digestive tract.

OBJECTIVE: The aim of this study was to determine if protein metabolism was altered in small and large intestines by feeding pectin, a soluble fiber known to stimulate cecal production of short-chain fatty acids (SCFAs) and to have a trophic effect in these tissues. METHODS: Twenty-four weanling male Sprague-Dawley rats were fed ad libitum for 14 d with a balanced control diet or an isoproteic, isocaloric pectin (citrus) diet (80 g/kg). SCFA production, intestinal histomorphometry, and protein synthesis were determined in the proximal and distal parts of the small intestine, the cecum, and the colon. Protein synthesis rates were determined by measuring the (13)C valine incorporation rate in tissue proteins. RESULTS: Pectin feeding slightly decreased food intake and growth rate. It increased the acetate, propionate, and butyrate pools in the cecum. Pectin feeding resulted in heavier intestinal tissues corresponding to higher villus height in the small intestine and crypt depth in the small and large intestines compared with feeding of the control diet. Compared with the control group, the rats fed the pectin diet had significantly higher protein synthesis rates in all the parts of their intestines. CONCLUSION: Supplementation of pectin, as a soluble fiber, in the diets, stimulated SCFA production, had a trophic effect on the different parts of the intestines, and greatly stimulated protein synthesis in those tissues.

Differential variation of mitochondrial H2O2 release during aging in oxidative and glycolytic muscles in rats.

Mitochondrial free radical (ROS) production could be involved in sarcopenia. Our aim was to measure this production in various muscles during aging. Male Wistar rats aged 4.5 and 24 months were used. H(2)O(2) release and protein carbonyls were evaluated in isolated mitochondria from an oxidative (soleus) and a glycolytic (tibialis anterior) muscle. Total and Mn-superoxide dismutase (SOD), catalase, glutathione peroxidase (GPX) and glutathione reductase (GR) activities were measured in tibialis anterior. In soleus, glutamate/malate supported mitochondrial H(2)O(2) release was lower than in tibialis anterior in young rats, but increased significantly with age. In tibialis anterior, glutamate/malate or succinate supported H(2)O(2) release was unchanged with age. ROS generators were complexes I and III. Mitochondrial carbonyl content remained stable during aging in both muscles but tended to be higher in tibialis anterior than in soleus. Tibialis anterior total SOD (+17%), catalase (+84%), and GPX (-17%) activities varied significantly with age but Mn-SOD was unchanged, suggesting an increase in cytosolic ROS production. In conclusion, the higher life-long H(2)O(2) release observed in tibialis anterior is consistent with the known sensitivity of glycolytic muscles to sarcopenia. The fact that the rate of H(2)O(2) release increases with age in soleus seems to have little impact.

Isomers of conjugated linoleic acid decrease plasma lipids and stimulate adipose tissue lipogenesis without changing adipose weight in post-prandial adult sedentary or trained Wistar rat.

The respective effects and interactions of supplementation with two conjugated linoleic acid (CLA) isomers and exercise on plasma metabolic profile, activity of lipogenic enzymes and cellularity in two adipose tissue sites, those of the liver and heart, were examined in adult Wistar rats. Rats that were either sedentary or exercise-trained by treadmill running were fed one of four diets: a diet without CLA; a diet with either 1% cis 9, trans 11 CLA or 1% trans 10, cis 12 CLA; or a mixture of both isomers (1% of each) for 6 weeks. We observed that the exercise decreased lipogenic enzyme activities in epididymal and perirenal adipose tissue. Plasma cholesterol, insulin, and leptin concentrations were lower in exercise-trained rats than in sedentary rats. The ingestion of either CLA mixture or the trans 10, cis 12 CLA increased lipogenic enzyme activities in epididymal tissue and more markedly in perirenal adipose tissue, especially in sedentary rats, and without affecting adipose tissue weight or cellularity. A similar effect of trans 10, cis 12 CLA was observed in regard to malic enzyme activity in the liver. In addition, this isomer decreased plasma lipid and urea concentrations and increased plasma 3-hydroxybutyrate levels. The ingestion of cis 9, trans 11 CLA increased fatty acid synthase activity in perirenal adipose tissue in sedentary rats and decreased plasma cholesterol and leptin concentrations. These results show that isomers of CLA decrease plasma lipids and stimulate adipose tissue lipogenesis without changing adipose weight in adult sedentary or exercise-trained rat, thus suggesting a stimulation of adipose tissue turnover.

Carnosine concentration of ingested meat affects carnosine net release into the portal vein of minipigs.

Because of its physiological effects, carnosine (beta-alanyl-L-histidine) can be considered as a bioactive food component. The objective of this study was to assess the quantitative significance of intact carnosine absorption after ingestion of different beef meats, using the minipig as animal model. In a preliminary experiment, we evaluated the level of dietary carnosine in intestinal digesta of pigs (n = 4) after a meat meal (0.94 g protein/kg body weight) of grilled top loin (TL) or stewed shoulder (S). In accordance with meat carnosine concentration (20.7 and 7.2 micromol/g for TL and S, respectively), intestinal carnosine concentration was greater for TL than S. For both meats, carnosine flow to mid-jejunum was almost completed in the first 3 h following intake, and about one-half of the ingested carnosine disappeared from the intestinal lumen before the mid-jejunum. In catheterized minipigs (n = 4), we assessed the portal net release of dietary carnosine after a meat meal (1.4 g protein/kg body weight) of TL, S, and a blend of grilled neck and brisket (NB; 12.2 micromol carnosine/g). Postprandial carnosine plasma concentration and portal net release were not affected after an S meal, but they increased, proportionally to meat carnosine content, with NB and TL. For these meats, carnosine net release throughout the whole postprandial period accounted for 22% of the ingested carnosine. These results indicated that meat carnosine can be absorbed across the intestinal wall and that carnosine bioavailability depends on carnosine content of cooked meat.

Dietary conjugated linoleic acid has limited effects on tissue protein anabolism in sedentary and exercising adult rats.

The effects of conjugated linoleic acid isomers (CLA) and endurance training on lean body mass are expected to result from their action on tissue protein metabolism. The aim of this study was to analyze their effects on protein metabolism in 2 muscles, the small intestine and liver of adult rats. Four-month-old male Wistar rats were fed diets containing either no CLA, cis-9, trans-11 CLA isomer (1 g.100 g(-1)), trans-10, cis-12 CLA isomer (1 g.100 g(-1)) or both isomers (1 g.100 g(-1) each) for 6 weeks. Half of the rats were subjected to endurance training by running on a treadmill. At the end of this period, the rats were injected with a flooding dose of (13)C-valine to determine protein synthesis rates in the post-absorptive (experiment 1) and in the post-prandial (experiment 2) states. No effect of CLA or endurance training were detected in the small intestine. Training reduced food intake and protein synthesis rates in the liver but no effect was found on the protein synthesis rates in muscles. In the post-absorptive state, protein synthesis rate was increased by feeding the trans-10, cis-12 CLA isomer alone in the liver (+9%) or in combination with the cis-9, trans-11 isomer in the gastrocnemius (+30%), mostly in sedentary rats. In the post-prandial state, the cis-9, trans-11 CLA isomer tended to reduce the protein synthesis rate in the gastrocnemius muscle. However, no effect of CLA was found on muscle protein amounts. In conclusion, CLA isomers would have limited but differential effects on tissue protein metabolism in adult rats.

Differential effects of cooked beans and cooked lentils on protein metabolism in intestine and muscle in growing rats.

AIMS: The effect of diets based on cooked beans or lentils on protein metabolism in intestines and muscles was studied in rats. METHOD: The cooked seeds were used as the unique protein source in balanced diets (containing 229 and 190 g of crude protein per kg dry matter) fed to young growing rats for 20 days. Their effects were compared with those of the control casein diet in pair-fed rats. Protein synthesis rates in small and large intestines and in gastrocnemius and soleus muscles were determined in vivo, in a fed state, by the flooding dose method, using 13C-valine. RESULTS: In the small and large intestine tissues of the legume fed groups, protein, RNA relative masses (mg.100 g BM(-1)) and protein synthesis rates (FSR and ASR) were higher than in the control rats (p < 0.05). In gastrocnemius and soleus muscles,protein and RNA contents (in mg) and protein synthesis rates were significantly (p < 0.05) lower in the legume-fed groups than in the control rats. CONCLUSION: The chronic intake of cooked legumes increased protein synthesis rates in intestinal tissues and decreased them in muscles. This effect was greater for beans than for lentils in the large intestine and in gastrocnemius muscle.

Daily protein intakes and eating patterns in young and elderly French.

An adequate level of protein intake is required to limit the gradual body protein loss observed during ageing. Different factors (cohort age, sex, life conditions) may modify protein intake and distribution. However the precise amounts, as well as their daily distribution which affects protein utilisation and N retention, are unknown in both young and elderly individuals. The hypothesis was tested that protein intake and its distribution over daily meals could be different between the young and elderly. The consumption of six different protein-rich food groups by 292 healthy individuals aged 20-30 and 65-75 years was determined throughout each day for 1 week. The data of the total protein intake and protein intakes at each meal were analysed by ANOVA for each sex separately, using age group as the independent factor. The average protein intake of men was lower in the older age group whilst the opposite trend was seen in women. The distribution of protein intake was different between the two age groups: 56.5 % of the daily protein was eaten at lunch by the elderly but only 47 % (P<0.0001) by the younger subjects. In the elderly subjects, those eating larger amounts consumed a greater proportion of protein-rich foods at dinner than those eating small amounts (30.4 v. 26.2 %, P=0.05). A high level of protein intake was related to a higher meat-product consumption in both the elderly and young individuals. In conclusion, the pattern of protein intake differs significantly between age groups and sexes.

Chronic inflammation alters protein metabolism in several organs of adult rats.

Despite the prevalence of chronic inflammatory diseases in developed countries, few studies have considered the metabolic alterations observed in these disorders. To determine which perturbations in protein metabolism occur during chronic inflammation, and the consequences they have on nutritional requirements, a model of ulcerative colitis was adapted for use in adult rats. Adult Sprague-Dawley male rats (9 mo old) received dextran sulfate sodium (DSS) in their drinking water at 50 g/L for 9 d, then at 20 g/L for 18 d. A group of control rats, matched for age and weight, was pair-fed to the treated rats. DSS induced body weight loss and chronic inflammation characterized by an increase of spleen, liver, ileum and colon weights, of blood leukocytes and acute-phase protein levels. The main inflammatory site was the colon, which presented characteristic histological alterations and increased myeloperoxydase activity. Inflammation was accompanied by oxidative stress, characterized by increased plasma protein carbonyl content and increased liver glutathione concentration, but decreased glutathione concentration in muscle. This DSS-induced colitis led to a stimulation of protein synthesis in spleen (+223%), ileum (+40%) and colon (+63%). By contrast, protein synthesis in muscle slowed down (-23%). In conclusion, like acute inflammation, chronic inflammation induced a stimulation of protein metabolism in several splanchnic organs. In muscle, both protein synthesis and degradation were reduced. Taken together, these data are consistent with inadequate amino acid supply to meet the increased requirement resulting from chronic inflammation.

Differential effects of cooked common bean (Phaseolus vulgaris) and lentil (Lens esculenta puyensis) feeding on protein and nucleic acid contents in intestines, liver and muscles in rats.

AIM: Our aim was to investigate the influence of legume feeding on the protein and nucleic acid content of intestinal tissues and muscles. METHODS: Growing male Wistar rats were fed ad libitum on balanced diets containing cooked common bean or lentil as the unique protein source (180 g.kg(-1) dry matter) for 20 days. The control group was pair-fed with an iso-energetic, iso-nitrogenous balanced casein diet. RESULTS: Intestinal tissues were heavier in the legume-fed groups and higher relative mass (g per 100 g body mass) of protein, RNA and DNA were found in these tissues as compared to those of the control groups. In liver protein and RNA masses were significantly lower in the bean group than in the control group but the DNA content was not different in the legume and in the control groups. In gastrocnemius and soleus muscles, there was no significant effect of legume feeding on the fresh mass and on the protein and RNA contents, but the DNA content of the m. gastrocnemius was significantly lower in both legume groups than in their control group. The ribosomal capacity of intestines, liver and muscles was not significantly affected by legume feeding. CONCLUSION: Legume feeding had a trophic effect on both proximal and distal intestinal tissues; dietary fiber appears to be the main cause of this effect.

Pulse protein feeding pattern restores stimulation of muscle protein synthesis during the feeding period in old rats.

Muscle loss during aging could be related to a lower sensitivity of muscle protein synthesis to feeding. To overcome this decrease without increasing protein intake, we proposed to modulate the daily protein feeding pattern. We showed that consuming 80% of dietary proteins at noon (pulse pattern) improved nitrogen balance in elderly women. The present study was undertaken in rats to determine which tissues are the targets of the pulse pattern and what mechanisms are involved. Male Sprague-Dawley 11- and 23-mo-old rats (n = 32 per age) were fed 4 isoproteic (18% protein) meals/d for 10 d. Then half of the rats at each age were switched to a 11/66/11/11% repartition of daily proteins (pulse pattern) for 21 d. On d 21, rats were injected with a flooding dose of L-(13)C-valine (50 atom% excess, 150 micromol/100 g body) and protein synthesis rates were measured in liver, small intestine and gastrocnemius muscle in either the postabsorptive or the fed state. Epitrochlearis muscle degradation rates and plasma amino acid concentrations were measured at the same times. The pulse pattern had the following effects: 1) it significantly increased liver protein synthesis response to feeding and postprandial plasma amino acid concentrations at both ages; 2) it restored a significant response to feeding of gastrocnemius muscle protein synthesis in old rats; and 3) it had no effect in small intestine or on muscle breakdown. Thus, using a pulse pattern could be useful in preventing the age-related loss of muscle by increasing feeding-induced stimulation of muscle protein synthesis.