Les acides gras : molécules informatives du contrôle nerveux de l’homéostasie énergétique

Free fatty acids (FFA) are not fuel for neurons and do not cross “easily” blood brain barrier. However, it is know well established that FFA could act as informative molecules and any change in plasma FFA concentration are detected at the level of central nervous system (CNS) structure such as hypothalamus and brainstem, where FFA sensitive neurons are located. These neurons control in turn energy homeostasis including food behaviour, hepatic glucose production or insulin secretion. Sub-populations of FFA sensitive neurons (either excited or inhibited) are now described in hypothalamus. Regarding, cell signaling, both acyl-CoA and malonyl-CoA could be major factor to mediate FFA effect. Indeed, increased intracellular concentration of malonyl-CoA in hypothalamus induce food intake inhibition. Such effects are partly related to decrease in NPY gene expression, as well as increase in alpha-MSH expression. Finally, dysregulation of FFA sensing in CNS could lead to development of metabolic diseases such as obesity or type 2 diabetes, in predisposed subject.     

Physiopathologie de l’insulinorésistance dans le muscle squelettique et implication des fonctions mitochondriales

In modern societies, decreased physical activity, nutritional transition and aging contribute to the increase in the prevalence of obesity and its associated pathologies (as cardiovascular diseases and type 2 diabetes). Obesity is tightly correlated with insulin resistance, which appears in the early stages of type 2 diabetes. As skeletal muscle is quantitatively the main tissue involved in glucose transport in response to insulin, muscle insulin resistance is a key step in the etiology of type 2 diabetes. Several alterations of skeletal muscle insulin signaling in various models of obesity or type 2 diabetes have been evidenced and numerous underlying mechanisms have been hypothesized. Among them, muscle lipotoxicity, obesity-induced adipose tissue inflammation and oxidative stress following excess of energetic substrates could be involved, independently or synergically, in the development of muscle insulin resistance. Moreover, mitochondrial alterations have been reported in the skeletal muscle of obese or diabetic patients and animals. This suggests that mitochondrion, through its capacity of regulating cellular fatty acids flux and redox state, may play a key role in obesity-induced skeletal muscle insulin resistance.     

Détection du glucose : le point sur les mécanismes cellulaires et moléculaires

The brain and particularly the hypothalamus, is involved in the regulation of metabolism by controlling either the secretory activity or the metabolic pathways of different tissues or organs. Numerous hypothalamic areas are informed in turn of the metabolic status of the individual. Various molecules (metabolites, hormones, neuropeptides) have been involved as signal, among which glucose. Thus, it has repeatedly been shown that the electrical activity of some neurones depends on glucose concentration. New insights into the cellular and molecular mechanism that support the fact that the electrical activity of some neurones depends on the glucose and/or insulin concentration, have been gained recently. Making the analogy with the beta cell of the islet of Langerhans, it has been proposed that proteins such as glucose transporter 2, glucokinase and the ATP–dependent potassium channel, could assure this sensing. Furthermore, it has been proposed that mitochondria, especially via production of reactive oxygen species during glucose oxidation, plays a role of metabolic sensor in various cells. Such glucose sensing systems have been also described outside the brain like in the portal vein. Alterations in glucodetection could participate in some extend to deregulations observed in metabolic pathologies such as obesity and diabetes.     

Le sel : vigilance dans la première année de vie*

For infants, sodium recommended dietary allowances are low. The influence of sodium intake on young children's blood pressure has been shown contradictory. Sodium intake increases as children get older from 2 months, 5 months, 9 months, 12 months. This is especially influenced by complementary foods. Moreover, sodium intake can also vary by a factor of 2 at any time period, depending on food choice, i.e. milk formula, baby's food and even usual family's food. In addition no benefit is expected from a high level sodium intake; an excessive sodium intake is often linked in toddler's food to an excess intake of protein and saturated fatty acids. That's why it seems safer to limit sodium level consumption. Therefore nutritional information has to be organised for mothers and caregivers in maternity wards and in day care centers to promote healthy food habits in early childhood.     

Brain glucose sensing: a subtle mechanism

PURPOSE OF REVIEW: Brain nutrient sensing allows a fine regulation of different physiological functions, such as food intake and blood glucose, related to energy homeostasis. Glucose sensing is the most studied function and a parallel has been made between the cellular mechanisms involved in pancreatic beta cells and neurons. RECENT FINDINGS: Two types of glucosensing neurons have been characterized--those for which the activity is proportional to changes in glucose concentration and those for which the activity is inversely proportional to these changes. A new level of complexity has recently been demonstrated, as the response and the mechanism appear to vary in function according to the level of the glucose change. For some of the responses, the detection is probably not at the level of the neuron itself, but astrocytes also appear to be involved, indicating a coupling between the two types of cells. Finally, numerous data have demonstrated the modulation of glucose sensing by other nutrients, in particular fatty acids, hormones (insulin, leptin and ghrelin) and peptides (neuropeptide Y). This implies a common pathway in which AMPkinase may play a crucial role. SUMMARY: Recent observations in brain nutrient sensing indicate subtle mechanisms, with different cellular and molecular mechanisms involved. This fact would explain the discrepancies reported in the expression of different proteins (glucose transporters, hexokinases, channels). Astrocytes may be involved in one type of response, thus adding a new level of complexity.     

Drinking saccharin increases food intake and preference--IV. Cephalic phase and metabolic factors

Rats that drink saccharin solution increase their short-term food intake and develop a preference for flavored food eaten when saccharin is ingested. In this paper, we examined whether these effects are mediated by cephalic-phase metabolic reflexes. The results show that the cephalic-phase insulin response could be dissociated from food intake in three ways. (1) Drinking saccharin increased the food intake and food preference of rats with sham surgery (SHM) or celiac vagotomy (CV), but not hepatic vagotomy (HV); it produced a short-lived increase in plasma insulin levels in all three groups, but the insulin response of both the CV and HV group was attenuated relative to the SHM group. (2) Rats increased food intake even when a 90 min interval was imposed between drinking saccharin and eating food, although insulin and glucose levels returned to normal within 30 min of drinking saccharin. (3) Streptozotocin-induced diabetes did not affect the increased feeding response to saccharin. The failure of rats given hepatic vagotomy to increase food intake and food preference when drinking saccharin suggests that a hepatic mechanism is involved. We propose that drinking saccharin increases food intake by temporarily altering the disposition of metabolic fuels towards storage and away from oxidation. Flavored food eaten after drinking saccharin becomes preferred because it provides fuel to counteract this reduction in oxidation.     

Consommation et habitudes alimentaires chez des femmes de l’ouest algérien atteintes de lithiase cholestérolique

Dietary consumption and food habits have been determined in normal or overweight west Algerian women with cholesterol gallstone disease compared to normal-weight control women. None of the lithiasic patients did any sporting activity, which represented a risk factor in gallstones formation. In patients, in particular overweight ones dietary intake was higher in energy, proteins and cholesterol (p<0.01), than that of controls, as a consequence of increased fish consumption, chicken and eggs and important simple sugar intakes. Low fresh vegetables but more important dried vegetables intakes were noted in all patients. These nutritional factors might play an important role in of cholesterol gallstones formation. The reduced intake of coffee (2 cups/day) noted in all patients could be suggest that coffee will have a protecting role. Moreover, a bad to day meal distribution could contribute to cholesterol lithogenesis.     

La néoglucogenèse intestinale: un nouvel acteur du contrôle de la prise alimentaire

Introduction: The interactions between glucose and energy homeostasis are well known, especially regarding the suppressing role on food intake of glucose into the portal vein.Material and Methods: The expression of genes of gluconeogenesis was characterized at the level of mRNA, protein, and enzymatic activity. Intestinal glucose production was quantified using a combination of (3-³H) glucose tracer dilution and arterio-venous glucose balance. The effect of portal glucose on food intake was studied using conscious rats with indwelling catheters into the portal vein. The effect of infusions at the hypothalamus level was studied by immunodetection of the protein c-Fos.Results: All regulatory genes of gluconeogenesis are expressed in the small intestine from rat and human. They are strongly induced in rat: during fasting; and by protein-enriched diet. In both cases, this promotes glucose release in the portal vein, lasting after the postprandial period for the protein-enriched regimen. The infusion of glucose at comparable rates into the portal vein decreases food intake in rat, and activates the hypothalamic regions involved in the control of food intake, just as does the protein enriched diet.Conclusion: These results provide a mechanistic explanation for the effect of satiety induced by diet protein, well known to occur in animals and humans, but unsolved up to now.     

Détection centrale des acides gras et contrôle du bilan d’énergie

Nutrient sensitive neurons (glucose and fatty acids (FA) are present in many sites throughout the brain, including the hypothalamus and brainstem, and play a key role in the neural control of energy and glucose homeostasis. Through neuronal output, FA may modulate feeding behaviour as well as both insulin secretion and action. For example, central administration of oleate inhibits food intake and glucose production in rats. This suggests that daily variations in plasma FA concentrations might be detected by the central nervous system as a signal, which contributes to the regulation of energy balance. At the cellular level, subpopulations of neurons in the ventromedial and arcuate hypothalamic nuclei are selectively either inhibited or activated by FA. Possible molecular effectors of these FA effects likely include chloride or potassium ion channels. While intracellular metabolism and activation of the ATP-sensitive K⁺ channel appear to be necessary for some of the signaling effects of FA, at least half of the FA responses in ventromedial hypothalamic neurons are mediated by interaction with FAT/CD36, a FA transporter/receptor that does not require intracellular metabolism to activate downstream signaling. Thus, FA or their metabolites can modulate neuronal activity as a means of directly monitoring ongoing fuel availability by brain nutrient-sensing neurons involved in the regulation of energy and glucose homeostasis. Besides these physiological effects, FA overload or metabolic dysfunction might impair neural control of energy homeostasis and contribute to obesity and/or type 2 diabetes in predisposed subjects.     

Nutrition et insuffisance rénale chronique de l'enfant

The nutritional management of the uremic child depends on the residual glomerular filtration rate. When it has dropped to 25% of the normal range, one can observe decreased growth velocity, anemia, hyperparathyroidism, poor tolerance to changes in water and sodium intake and anorexia. The assessment of the nutritional status is based on anthropometric measurements by using standard deviation scores — i.e. body weight, height, growth velocity, head circumference and skinfold thickness —, on some biochemical parameter — i.e. serum proteins, calcium, phosphorus, parathyroid hormone and urea: creatinine ratio — and sometimes on biophysical methods (dual energy X ray absorptiometry). The current nutritional practices of the uremic child are less restrictive than in adults due to energy and protein requirements for both cerebral maturation and statural growth. Such uremic children should therefore be fed according to recommended dietary allowances, that often require tube feeding in infants. In addition to diet, some other treatments have a nutritional impact, like recombinant human growth hormone and erythropoietin. Such strategies should be adapted to the type of treatment — i.e. conservative, transplantation, haemodialysis, peritoneal dialysis.     

Impact of inulin and oligofructose on gastrointestinal peptides

In the present paper, we summarise the data supporting the following hypothesis: dietary inulin-type fructans extracted from chicory root may modulate the production of peptides, such as incretins, by endocrine cells present in the intestinal mucosa, this phenomenon being involved in the regulation of food intake and/or systemic effects. To test this hypothesis, male Wistar rats received for 3 weeks either a standard diet or the same diet supplemented with 10 % inulin-type fructans with different degrees of polymerisation. All the effects were most pronounced with the diet containing oligofructose, and consisted of (i) a decrease in mean daily energy intake and in epididymal fat mass; (ii) a higher caecal pool of the anorexigenic glucagon-like peptide-1 (7-36) amide (GLP-1), and peptide YY (PYY), due to caecal tissue proliferation; (iii) an increase in GLP-1 and of its precursor - proglucagon mRNA - concentrations in the proximal colon; (iv) an increase in portal serum level of GLP-1 and PYY; (v) a decrease in serum orexigenic peptide ghrelin. Moreover, oligofructose supplementation improved glucose homeostasis (i.e. decreased glycaemia, increased pancreatic and serum insulin content) in diabetic rats previously treated with streptozotocin, a phenomenon that is partly linked to the reduction in food intake and that correlates with the increase in colic and portal GLP-1 content. Based on these results it appears justified to test, in human subjects, the hypothesis that dietary inulin-type fructans could play a role in the management of obesity and diabetes through their capacity to promote secretion of endogenous gastrointestinal peptides involved in appetite regulation.     

Les compléments alimentaires à base de plantes : un nécessaire besoin de sécurité

The sell of herbal dietary supplements is booming. These products benefit by the strong confidence of consumers in their safety of use and their consumption rely to the notion of a health benefit. Their status of foodstuff allows them to be distributed without any official scientific evaluation before commercialisation. However, examples issued from scientific literature point out that some plants eventually used in dietary supplements are involved in adverse effects which can be serious. Considering the growing exposure of the population, it is necessary to control the security of use of these products in an optimal way. Measures as the realisation of an information campaign, the output of a sanitary vigilance, and the setting of a voluntary consensus for industrial good practices could provide better guarantees of security.     

Mécanismes de la dénutrition au cours de l'insuffisance respiratoire chronique

The study of the mechanisms of denutrition during chronic obstructive pulmonary disease is useful because this common evolutive complication has severe functional consequences and is associated with a poor prognosis, irrespective of respiratory functional status. Conversely, renutrition improves the prognosis in these patients. Adaptation to hypoxia, the basis of which is oxygen conformance, is described. Denutrition during chronic obstructive pulmonary disease is linked to the imbalance arising from increased energy expenditure and inadequate food intake. The origins of the imbalance are discussed. The clinical implications of knowing the mechanisms of denutrition are set out and perspectives for both experimental and applied research are proposed.     

Facteurs associés aux consommations alimentaires des bénéficiaires de l’aide alimentaire : étude abena

The majority of data available on the nutritional situation of low socioeconomic populations in industrialized countries describe a diet that is less favorable for health. The objective of this article is to describe the demographic and economic factors associated with low food intakes as defined by the National Nutrition and Health Program (Programme National Nutrition Santé, PNNS) dietary guidelines in a food aid dependent population.Subjects from the Abena (Food and nutritional status of food aid recipients) study were recruited in four urban zones (Marseille, Dijon, Paris, Seine-Saint-Denis). Questionnaires were principally about food intake frequencies, food supplies and food insecurity.Among the 1,164 included subjects, low consumption frequencies of fruits and vegetables (94.5% consuming <3.5/day), meat, fish and eggs group (42.6% <1/day), and dairy products (81.9% <3/day) were found. Men, young and aged people, and individuals with dependent children seem to be more often at risk for inadequate intakes with regard to the PNNS dietary guidelines. The food insecurity (49.2% declared not having enough to eat “sometimes” or “often”) was associated with an insufficient intake of fruits and vegetables, and meat, fish, and eggs.The described factors associated with lower food intakes observed in this precarious population confirms the notion that fruit and vegetable, and meat, fish and egg consumptions are markers of the socioeconomic status. This has been already observed in studies on more various socioeconomic statuses. The nutritional situation of food aid recipients described here underlines the need for food aid improvement, eventually focused on specific groups which have been identified.     

Rôles physiologiques des endocannabinoïdes dans le contrôle de l’homéostasie énergétique

Endocannabinoids are endogenous lipids which modulate the release of neurotransmitters and activate different signaling pathways, through the binding to cannabinoïd receptors, CB1 and CB2. Endocannabinoids are involved in the control of a variety of behavioural and neuroendocrine functions, including feeding behaviour. In the central nervous system, they essentially modulate the expression of orexigen or anorexigen neuropeptides thus resulting in the stimulation of food intake. Their peripheral targets are mainly the liver and the white adipose tissue where they stimulate lipogenesis, through the modulation of several enzymes and proteins expressions. Cannabinoïd receptor agonists are nowadays prescribed to improve appetite of people suffering from cancer or AIDS. In the same way, CB1 antagonist, such as Rimonabant, could provide efficient treatment of obesity.     

La réaction de Maillard dans les aliments : quels enjeux pour la santé humaine ?

The Maillard reaction is a complex mixture of temperature-dependent reactions between carbonyl compounds derived from sugars, lipids, and vitamins heat degradation products, and amino groups of amino acids, proteins or DNA. Among the numerous Maillard products (MP) formed, some are considered to raise safety problems because of their carcinogenicity, or pro-oxidant and inflammatory bioactivity. MP are produced in severely heat-treated food and partially absorbed, while reaching the endogeous pool of MP formed from glucose and lipid metabolites and biological proteins or DNA. If uncompletely degraded and/or excreted, they accumulate and promote the secretion of cytokines which are involved in the development of degenerative processes. The specific contribution of dietary MP in those physiopathological phenomena remains unknown. However, risk prevention supposes to control MP formation in food, while maintaining satisfactory sensorial quality.     

New drugs; exenatide and sitagliptin

Incretin hormones, secreted upon food intake, play an important role in the regulation of blood glucose levels. In type 2 diabetes mellitus, the incretin response is decreased. Substitution of incretin is a novel pharmacological target which restores postprandial glucose homeostasis. Exenatide is a mimetic of the incretin glucagon-like peptide-I (GLP-I). Sitagliptin is an inhibitor of the enzyme dipeptidyl peptidase 4 (DPP-4), which breaks down GLP-I. Both drugs increase the GLP-I concentration, thereby improving insulin secretion from pancreatic p cells, restoring glycaemic control, preventing beta cell destruction, delaying gastric emptying, and reducing food intake.     

Évaluation des apports alimentaires d’adolescents obèses et post-obèses : comparaison de la méthode iconographique SU.VI.MAX à la méthode de pesée des aliments

The objectives of this study were 1) to validate the SU.VI.MAX iconographic method against the weighed diet record method to assess food and nutrient intakes in obese and post-obese adolescents, and ; 2) to determine the effects of dietetic education on the precision of this method. Energy and nutrient intakes were determined by both methods in 26 institutionalised obese adolescents over 7-day-periods before the beginning and at the end of a weight-reduction programme, and 4 months later. The mean food, energy, carbohydrate, protein, and lipid intakes as assessed by the two methods were not significantly different, but the limits of agreement between the two methods were high. Obese and post-obese adolescents underestimated intake of their favourite meals (pasta, fried potatoes…) but often overvalued intake of vegetables, milk and hard cheese. The SU.VI.MAX iconographic method is, therefore, a reliable method to assess energy and nutrient intakes of obese and post-obese adolescents in epidemiologic studies, but it is unappropriate for assessment in individuals. In addition, dietetic education resulted in 50% decreases in the mean difference, and in the inter-individual differences in energy intake between the two methods.     

Apports alimentaires et dépenses énergétiques d’adolescents footballeurs de haut niveau: comparaison de deux méthodes d′évaluation des apports

Food intake was assessed over 7 consecutive days in 14 adolescent soccer players (14.1 y; 1.65 ± 0.07 m; 55.4 ± 7.6 kg) housed in a training Centre equipped with a self-service restaurant, using the weighed diet record method and the SU.VI.MAX iconographic method. Nutrient intake was estimated using the software Prodiet^®. Daily energy expenditure (DEE) was assessed using a factorial method after a seven day activity record. Mean food and nutrient intakes were nearly adequate. However, intakes of starchy foods, fruit and vegetables were too low, whereas intake of sugar rich foods was too high. Mean saturated fatty acid intake was in excess, whereas PUFA intake was lower than RDA. Calcium, magnesium and iron intakes were close to RDA. Mean daily energy intake agreed with the mean estimated DEE. However, the high inter-individual variability in food choice, food and nutrient intakes, as well as food inadequacy during the weekend, must be underlined. The SU.VI.MAX iconographic method was adequate to assess energy and nutrient intakes in a group of adolescent athletes, but unappropriate for assessment in individuals. In addition, the adolescents underestimated intake of their favourite meals (starchy foods) and overvalued intake of fruit and vegetables.     

L’Homme, victime de son cerveau ?

Is the obesity pandemia resulting from an inadequate human physiology faced to a changing alimentary environment or is it the consequence of his own peculiarities leading him to build himself an unadapted environment, thus differing from animals like apes (monkeys)?We propose an enlarged conceptual organization of the regulation of food intake and body mass. It would imply four partners. The level of energy intake, metabolic energy utilisation, the level of fat stores and functional digestive ability. Each of these four players would be a controlled variable in relation to the three others and at the same time working towards their control in a system in dynamic equilibrium. They would be under the permanent control of a central integrator able to limit the variation of the center of gravity of the system in acceptable bounds relatively to an individual set point.A number of physiologic knowledges support this concept and we may insist on the role of visceral sensitivity and central integration. The refinement of the regulation of our integrity offering important adaptative mechanisms lead us to consider that human physiology is able to cope with usual changes of our alimentary environment.By exploring what coud differenciate humans from animals, particularly apes, the idea arises that humans could be victimized by his cognitive capabilities and more particularly by his communicative capabilities. Able to construct and to infer from incomplete knowledge he is capable to build up an unadapted environment driving him to destruction.Again, whatever their illusions human beeings cannot infrige their physiologic limits.