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New layout SEPTEMBER OCTOBER 2016 #32 THE MAGAZINE OF THE FRENCH NATIONAL INSTITUTE OF HEALTH AND MEDICAL RESEARCH Taste Friend or foe of nutritional balance? New layout Science&Santé new recipe: more reports, more portraits, for more flavor and always more rigorous scientific news. With an unchanged objective: to give you a "taste" of Inserm research! The Science&Santé editorial team EDITORIAL ©Loïc Briand Far more than a sensory experience! Loïc Briand am Leader rception Te Flavour Pe ciences du goût et s Centre des tion (Centre for the ta de l’alimen Taste & Diet), Inra, f Sciences o Université de CNRS, , Dijon Bourgogne #32 September - October 2016 Subscription free, write to: [email protected] Inserm, 101, rue de Tolbiac 75654 Paris Cedex 13 www.inserm.fr Taste is a chemical detection system that can evaluate the nutrient content of food and signal the presence of toxic compounds. This sense is very familiar to us and yet it is one of the most complex. Our understanding of the physiological mechanisms underlying gustatory function has progressed enormously in the last decade. Moreover, new flavors have been developed, such as that of "umami" or the taste of "fat", and the main receptors involved in tasting have been identified. The sequencing of genomes has revealed genetic differences that could affect taste perception and account for certain dietary preferences. Recent research has also revealed that receptors for sweetness can be found in many organs and tissues, including the gut, pancreas, adipose tissue, spermatozoa and the brain. Although the exact physiological role of these receptors remains unelucidated, in the gut they have been shown to be involved in regulating the absorption of glucose into the blood and in the release of hormones associated with satiety. These new roles are raising interest in the idea of modulating this receptor with inhibitory compounds to control diabetes or obesity. And taste has not finished surprising us. In laboratories, scientists and clinicians are continuing to advance our understanding of taste perception which has not yet unveiled all its secrets. Director of publication Yves Lévy Director of writing Arnaud Benedetti Editor-in-Chief Yann Cornillier Writing Assistants Coralie Baud, Marie-Charlotte Ferran Headlines Julie Coquart Editorial Assistant Coralie Baud Collaborators on this issue: Alice Bomboy, Françoise Dupuy Maury, Jean Fauquet, Caroline Guignot, François Maginiot, Stéphany Mocquery, Charles Muller, Agnès Noël, Julie Paysant, Hélène Perrin, Simon Pierrefixe, Vincent Richeux, Bruno Scala, Mehdi SixGraphic design Primo&Primo Art Direction Myriem Belkacem, Primo&Primo Symbols Cécile Depot Cover credits Illustration: Primo&Primo Printer Aubin Imprimeur N° ISSN: 2119-9051 Legal submission: September 2016 PEFC 10-31-1887 / Certified PEFC / This product is made with sustainably maintained drills and from controlled sources. / pefc-france.prg 4 #32 #32 Grand angle TASTE Friend or foe of nutritional balance? piled by Report com rrefixe ie P n Simo Sweet or salty, acidic or bitter: taste lets us appreciate the flavors in all the foods that we savor every day. For that reason, it plays an important role in regulating what we eat by helping us to determine exactly what we are eating. Above and beyond the nutritional aspect, taste is also a source of pleasure—a great deal of pleasure. Sometimes taste drives our behavior patterns to such an extent that we get sick. A paradox in the country of great cooking and good taste. It is nevertheless possible to combine gustatory pleasure and health. 5 6 #32 Tongue Salivary glands grand angle Retronasal olfaction Gustatory nerve A Anatomy of the caliciform papilla Thalamus Hypothalamus Olfactory bulb Hippocampus Olfactory epithelium Solitary nucleus Nasal cavity Orthonasal olfaction Tongue Gustatory nerves Retronasal olfaction Nerve circuits involved in taste The anatomy of taste: from the tongue (gustatory papillae, taste buds) to neurons in the brain via the thalamus k mong our five senses, it is taste that lets us appreciate dozens of different foodstuffs Taste bud may be, each day. As familiar as taste Sulcus it is far more complex than it appears at first glance. All the more so since eating does not just involve one sense but rather all of them. And taste, as we understand it in our everyday life, cannot be simply boiled down to physiology. Putting food in our mouth triggers a whole panoply of sensations: not only the foodstuff's savor but also its texture as well as the odors that are released by chewing it come into play. All this is referred to as "flavor". And Salivary surprise ... The sense of taste is not glands the most important; that distinction is reserved for the sense of smell.Gustatory "Threenerve quarters of sensory perception in the mouth isAnatomy down ofto olfaction " attests Loïc the Briand , Inra Research Director caliciform papilla at the Centre des sciences du goût et de l’alimentation – CSGA(Centre for the Sciences of Taste & Diet) in Dijon "which explains why we can't 'taste' anything when we have a cold." A cold impairs the sense of smell because the mucus blocks the passage of odor via the back of the nose to receptors on the olfactory epithelium, a mucous membrane at the top of the nasal cavity that lets us "smell" odors (see the figure). Another important component of taste is that which allows us to experience the tactile aspect of food and appreciate—or not—the bite of mustard, the fizz in carbonated drinks, the freshness of mint, the astringency of tannins in wine or the heat of chili pepper. These perceptions are called "trigeminal" because the signals are transmitted Nerve circuits involved in taste ©©Olivier AUDY te a olfaction via the trigeminal nerve that supplies the face, including the teeth and eyes. "That's why a strong dose of hot mustard or wasabi makes out eyes water" explains Loïc Briand. "Taste in the strictest sense of the word corresponds to the detection of savors by the gustatory papillae on our tongue. " Today, five "primary" tastes are recognized. We are all familiar with four of these, namely sweet, salty, bitter and acidic. But perhaps less so with the fifth, umami. Characterized in Japan Our other senses have taste Eating is an experience rich in sensations that begins long before the first mouthful. First of all, our appetites are whetted through our eyes: we salivate in advance when we see an appetizing meal. But simply seeing a foodstuff can likewise make you feel sick and entail rejection. Next, our sense of touch tells us about the texture of food before we put it into our mouth: hard or soft, elastic. Our hearing tells us if it is crunchy or crusty. So eating does not only stimulate our senses of taste and smell but all five senses. All contribute to our brain's image—pleasing or otherwise—which is generated in the course of this activity that is so important for our bodies. at the beginning of the 20 th century, umami—which translates as "pleasant savoury taste"—corresponds to the taste of glutamate, an amino acid that is one of the basic building blocks of protein. A common taste in Japanese cuisine, umami largely comes from soy sauce and certain types of seaweed, both of which are extensively used in Japan. But meat, tomatoes and parmesan cheese also have umami. Above and beyond pleasure, detecting these basic tastes is also an important physiological function of the body. "Sweet-tast- Loïc Briand: UMR6265 CNRS/UMR1324 Inra – Université de Bourgogne, Centre des sciences du goût et de l’alimentation (Centre for Sciences of Taste & Diet), Perception de la flaveur (Flavour Perception) Caliciform papilla Foliate papilla 7 #32 Salivary glands The tongue and its papillae Filiform papilla Gustatory nerve The tongue and its papillae Sulcus Anatomy of the caliciform papilla The tongue and its papillae Fungiform papilla ©©Olivier AUDY Caliciform papilla Filiform papilla Filiform papilla Taste bud Taste bud Sulcus Caliciform papilla Taste bud Sulcus Foliate papilla Foliate Caliciform papilla papilla Foliate papilla Salivary glands Salivary glands Retro S Gustatory Gustatory nerve g nerve Filiform papilla Fungiform papilla Fungiform papilla Fungiform papilla ing food signals an energy source that can be assimilated quickly", explains Loïc Briand "whereas a bitter taste could indicate toxicity." For example, alkaloids like caffeine, nicotine and cocaine—all of them toxic at high doses—taste bitter. "Detecting salt is also important for maintaining the body's electrolyte balance and replenishing salt lost through sweating and urination." Detecting acidity tells us if fruit is ripe and helps us avoid spoiled food. Many bacteria generate acid as they grow, e.g. dairy products acidify over time because bacteria found in them produce lactic acid. Finally, umami helps us detect the presence of protein, the only source we have for nitrogen and the essential amino acids we need because our bod- ies cannot produce enough of them. But how are these tastes recognized? Thanks to our precious taste buds or gustatory papillae. Our tongue carry hundreds of papillae of four different types: filiform, fungiform, foliate and circumvallate (see the figure). The first are the most numerous and give the tongue its sponge-like texture; these relay information about the texture of the food. "Only the last three are called gustatory papillae and are involved in taste sensation because they contain taste buds" says Philippe Besnard , Professor of Human Nutrition at AgroSup Dijon and director of the Inserm group at the Université de Bourgogne. It is our thousands of taste buds that let us detect the basic tastes. Their tips come into contact with the Anatomy of the caliciform papilla Anatomy of the caliciform papilla food and at their base, they feed into the gustatory nervous system. Anatomy of "Sapid compounds, i.e. those that carry taste, the caliciform papilla dissolve in saliva and stimulate membrane-bound receptors at the tips of the taste buds" explains the scientist. This stimulation triggers a cascade of biochemical reactions and ion fluxes which induce the release of neurotransmitters at the base of the receptors. In turn, the neurotransmitters activate gustatory nerves that transmit the information to the brain. Then, a number of different parts of the brain are involved in processing the Electrolyte balance. Equilibrium between the volume of water in our body and the minerals it requires to function, such as sodium, potassium and calcium. Neurotransmitter. Compound released into a synapse by a neuron or some other types of cell to transmit a signal to another neuron. Philippe Besnard: Inserm Unit 866/EPHE – Université de Bourgogne, Lipides-Nutrition-Cancer, Physiologie de la nutrition et toxicologie (Lipids-Nutrition-Cancer, Physiology of Nutrition & Toxicology) G n gustatory signal. Stage 1: the information is processed in the thalamus and then relayed on to the cerebral cortex where the taste perception is generated. Gustatory information is then sent on to other parts of the brain, notably the hypothalamus and the hippocampus that are respectively important in regulating food intake and taste memory. It was believed for a long time that different tastes are detected on distinct parts of the tongue: sugar at the tip, bitter at the base, acidic and salty on the edges. However, this is wrong. In fact, every taste bud contains a set of gustatory detectors that respond to all five primary tastes. "These detectors were only discovered relatively recently" points out Loïc Briand. The first were not reported until the beginning of the 21st century. They are composed of G protein-coupled receptors (GPCRs), membrane-bound receptors that elicit an intracellular response (such as neurotransmitter release) when activated, in this case by a sapid molecule. "To date, twenty-five distinct receptors for bitterness have been identified in humans, as well as one for sweetness and another one for umami" specifies the grand angle k The five tastes that are currently recognized ©©Loïc Briand: #32 scientist. For salty and acidic tastes, different types of gustatory detectors are activated, namely ion channels. These channels through the cell membrane let pass sodium ions (Na+) from salty foods pass and hydrogen ions (H+) from acidic foods. k In red, fungiform papillae on the tongue seen in a scanning electron microscope (magnification x63, 6 x 7 cm) ©©Motta/SPL/Phanie 8 The taste of fat New receptors for the basic tastes may come to light soon. The scientific community suspects that there may be at least one more receptor for umami and probably another for salty. And even entirely new tastes may soon be recognized. A taste must fulfill a number of conditions: "The taste must be perceptible and unique" stipulates Loïc Briand "and the stimulus must induce physiological and behavioral responses." As described above, sapid molecules associated with said taste must activate a specific gustatory detector which in turn triggers the release of a signal that is transmitted via the gustatory nerves. Possible new tastes include that of "fat". Until recently, lipids were considered as tasteless or insipid, their appeal deriving simply from their texture and smell. However, recent work in rodents and humans suggest that "fat" is probably an entirely distinct taste. Everything started with the discovery of a receptor for lipid called CD36 (cluster of differentiation 36) in the gustatory papillae of the rat. "It is known to play a role in the gut, notably in the assimilation of lipid" says Philippe Besnard, whose research focuses on the metabolism of dietary fat. What does this receptor do in the papillae? This is one of the questions Besnard's group is seeking #32 Rosa at the Institute of Biology of the to answer. They first showed that this receptor is found on sensory cells in the taste buds of mice. "Then we showed that mice in which the CD36 gene had been knocked out no longer preferred the lipid when offered a choice between a lipid-rich solution and a control solution." They also showed that the presence of lipid in the mouth induces the release of neuromediators from taste buds towards gustatory nerves. The murine gustatory system is therefore fully equipped to detect lipid. Other experiments in Philippe Besnard's laboratory have shown that lipid induces a physiological response in mice, e.g. the presence of lipid in the mouth triggers the secretion of bile salts by the liver, and of digestive enzymes by the pancreas, even in the absence of any ingestion. It is now established that CD36 is also found on the gustatory cells of humans and many other mammals. The work of Richard Mattes and his team at Purdue University in the United States recently showed that humans can distinguish the taste of "fat", which they named oleogustus, from the other primary tastes. So can "fat" be considered as the sixth primary taste? "The groundwork has been accomplished in rodents and evidence is building in humans" judges Philippe Besnard. Being able to taste fat would make sense from a physiological point ©©Inserm/ Patrice Latron k The Inserm LipidsNutrition-Cancer group studies the metabolism of dietary lipid in mice. Paris École Normale Supérieure have shown that consuming bitter and acidic food induces the expression of a specific gene, Egr-1, in Zebrafish larvae. "The gustatory system works similarly in most living organisms" points out Brigitte Boyer. Being able to identify foodstuffs and evaluate their nutritional composition would represent a selective advantage that would have appeared very early in the course of evolution. It is therefore reasonable— to some extent—to extrapolate findings in other species like the Zebrafish to human beings. The Egr-1 gene encodes an early transcription factor that regulates the expression of other genes. Experiments in mice have shown that it is involved in memory. "We believe that Egr-1 is involved in the memorization of tastes and therefore in the gustatory learning process" explains the biologist, "because progressive habituation of view: lipid-rich food is not only a of the young fish to bitter and acidic very good source of energy, but it is tastes as a result of repeated exposure also likely to contain essential fatty is accompanied by lowering of the exacids like the omega-3 series as well pression of Egr-1." Dietary preferences as important vitamins (A, D, E and K). are therefore to And the purpose some extent writof taste is to identen in our genes. tify foodstuffs that "The gustatory system But preferences are provide the best works similarly in most dynamic and evolve nourishment. It also according to our helps us link first living organisms" experiences. contacts with our To investigate chilenvironment. dren's dietary preferences and how they change, a number of groups from How does taste change? a variety of disciplines (biology, medicine, psychology, sociology, ethology, The gustatory system develops very statistics, etc.) came together in 2005 early on in utero. Gustatory papillae to assemble a cohort called Opaline appear before the end of the first trimester of pregnancy and it is believed (Observatoire des préférences alimenthat the fetus can sense tastes present in the amniotic fluid by the third trimester. Work by Benoist Schaal, CNRS Benoist Schaal: UMR6265 CNRS/UMR1324 Inra – Université Research Director at the Dijon Centre de Bourgogne, Centre des sciences du goût et de l’alimentation (Centre for Sciences of Taste & Diet), Perception de la flaveur (Flavour Perception) for the Sciences of Taste & Diet, has shown that new-born babies are atBrigitte Boyer, Frédéric Rosa: Inserm Unit 1024/ CNRS – École normale supérieure Paris, IBENS, Early Development tracted by the smell of aniseed if their mother regularly ate this kind of sweet F. Laugerette et al. Journal of Clinical Investigation, 1 November 2005; in the last two weeks of pregnancy. So 115 (11): 3177-84 the first experiences of tasting occur D. Gaillard et al. The FASEB Journal, May 2008; 22 (5): 1458-68 in the mother's womb. At birth, babies C. A. Running et al. Chemical Senses, September 2015; 40 (7): 507-16 have an innate preference for sugar and B. Schaal et al. Chemical Senses, December 2000; 25 (6): 729-37 instinctively reject bitter and acidic foods. This could have a genetic basis. B. Boyer et al. Frontiers in behavioral neuroscience, 22 May 2013; 7: 51 Work by Brigitte Boyer and Frédéric 9 grand angle #32 Sophie Nicklaus: UMR6265 CNRS/UMR1324 Inra – Université de Bourgogne, Centre des sciences du goût et de l’alimentation, Développement et dynamique des préférences et des comportements alimentaires (Centre for Sciences of Taste & Diet, Development & Dynamics of Eating Preferences & Habits) C. Schwartz et al. British Journal of Nutrition, November 2009; 102 (9): 1375-85 C. Schwartz et al. British Journal of Nutrition, March 2013; 109 (6): 1154-61 C. Schwartz et al. Physiology & Behavior, 26 September 2011; 104 (4): 646-52 Breast feeding encourages a liking for umami. k k Dietary diversification is a key phase of learning about taste. "Children who like vegetables when they first taste them still like them at two" children readily accept new foodstuffs. Thus, between five and seven months, the reactions of 88% of children to new foods were judged positive. Familiarity breeds liking Vegetables are usually what children like least—and what they eat least. Even though they are healthy by virtue of the vitamins, minerals and fiber that they contain. To determine what influences children's eating habits and thereby help parents with practical guidelines, the work on the Opaline cohort addressed how taste for unloved vegetables changes. Based on data collected from volunteers, the statisticians detected significant links between preferences at the beginning of weaning and the situation at two years of age. "Children who like vegetables when they first taste them still like them at ©©Africa studio/Fotolia taires du nourrisson et de l’enfant, Observatory of the Dietary Preferences of Babies & Children). This longitudinal study being sponsored by Inra, CNRS and Inserm followed 319 mother-andchild pairs from the Dijon area from the end of pregnancy until the child reached the age of two. "We set out to determine their dietary experience and sensory exposure in depth" states Sophie Nicklaus, Inra Research Director at the Dijon Centre for the Sciences of Taste & Diet and Head of the Opaline Steering Committee. Comprehensive data were collected on the foods consumed by the mother during pregnancy, the duration of breast feeding, the variety of foods and preparations introduced at weaning and the dates when salt, fat and sugar were added. Laboratory tests were also carried out to investigate the babies' preferences vis-a-vis the five primary tastes. By comparing water consumption with that of a sapid solution (sweet, salty, acidic, bitter or umami), these tests confirmed that the first taste that babies like is sweet. Milk—be it breast milk of formula—is slightly sweetened. The taste for salt develops between four and six months, around the time of weaning, and grows over the first year. On the other hand, reactions to umami are usually neutral. "But we observed that prolonged, exclusive breast feeding is associated with a liking for the umami taste by six months" adds Sophie Nicklaus. This is probably due to the fact that breast milk is very rich in glutamate, the amino acid that underlies this taste. As for acidic and bitter, these are the least popular tastes, although they are not completely rejected by children of the ages studied. Preferences for certain tastes affect young children's eating habits but only to a certain extent: at weaning, most ©©Muro/Fotolia 10 two" she says. However, no association was observed between the vegetables consumed by the pregnant mothers and their child's preferences. Nor does the duration of breast feeding seem to have any effect, in contrast to the conclusions of some previous studies. Conversely, "Variety of vegetables and recipes has a strong effect on a child's preferences at the time of weaning" continues Sophie Nicklaus. In the same way as the Zebrafish gets used to bitterness, repeated exposure to vegetables promotes acceptance: an effective, reproducible way of guiding the learning process. "A baby may be offered a foodstuff eight, ten or even fifteen times before it is accepted but, in the end, it usually is. " Getting to like a new foodstuff is a learning process. The influence of education on liking for vegetables was also studied. Two parental practices #32 were associated with the consumption of less vegetables by the age of two. "Offering something else when a child refuses a new foodstuff will limit his or her exposure to varying tastes" explains Sophie Nicklaus. "The child will never learn to like the new foodstuff." Similarly, forcing a child to clear the plate creates a prejudicial atmosphere when it comes to liking food, vegetables in particular. "It is important to favor exposure and introduce variety by changing recipes, but without forcing the child to eat" concludes the scientist. "The pleasure of tasting is fundamental during this key period when it comes to dietary preferences." This is the period of life when neophobia—rejection of any new foodstuff—can become installed in a child. And previous work by Sophie Nicklaus for her doctorate had demonstrated significant links between dietary habits acquired in young childhood and those at the beginning of adulthood. 11 ogy seems to play an important role. "They tend to eat under the influence of their emotions and prefer sweet and fatty-sweet products" adds Caroline Méjean. Socio-economic status is also important, with those on low incomes generally having a stronger liking for fat than the better-off. Cheaper food tends to be less healthy, largely because specific types of fat are often added to processed products to enhance their taste. And "the more fat you eat, the more you are attracted to collected and analyzed by Aurélie Lampuré, a doctoral student working with Caroline Méjean, identified a series of specific profiles, especially concerning likings for fatty-salty and fatty-sweet food. First determinant observed: gender. Men tend to prefer fatty-salty food whereas women seem to prefer fattysweet. "Men seem to let themselves be guided by their sensory likings that generally drive them towards consuming more fatty-salty products" explains the epidemiologist. In women, psychol- Gender is the most important determinant of liking for fatty-salty and fatty-sweet foods k NutriNet-Santé study. Cohort study started in 2009, focusing on the dietary habits of a large population of Internetusing adults (in June 2016, there were 274,011 on-line subjects) followed for at least five years to investigate relationships between nutrition and health. www.etude-nutrinet-sante.fr Caroline Méjean: Inserm Unit 1153/Inra/Université Paris 13- Paris Nord/Université Paris 7-Denis Diderot – Université Paris-Descartes, CRESS, EREN S. Bouhlal et al. Appetite, 1 December 2014; 83: 209-17 S. Nicklaus, Étude longitudinale des préférences et de la variété alimentaire de la petite enfance jusqu’à l’âge adulte : choix des enfants de 2 à 3 ans et lien avec leur comportement de 4 à 22 ans. (Longitudinal study of preferences and dietary variety from young childhood through adulthood: choices of 2-3 year-old children and their behavior from 4 to 22 years of age) Dissertation for a doctorate in Food Science defended at the Université de Bourgogne in 2004 ©©NutriNet-Santé In the young, dietary preferences therefore have their roots in young childhood and family history. But in adults? "Most of the data available are experimental and confined to some specific, relatively homogenous population" says Caroline Méjean, Inra scientist at the Sorbonne Paris Cité Centre for Research in Epidemiology & Statistics (CRESS). However, taste is the most important parameter when it comes to making dietary choices. Sensory determinants are a major factor in our behavioral patterns vis-a-vis eating. To mitigate the lack of <data, Investigators from the NutriNet-Santé study are working with a cohort of volunteer Internet users helping to shed light on the eating habits of the French and Belgian populations. The aim is to identify population characteristics associated with sensory attraction. A total of 37,181 surfers filled out a scientifically validated questionnaire about their dietary preferences for fatty, salty and sweet foods. These volunteers also gave details on what they ate and drank over three days, as well as how much. Data ©©Michael Donne/SPL/Phanie Fatty-salty or fattysweet? S. Nicklaus et al. Appetite, June 2005; 44 (3): 289-97 S. Nicklaus et al. Food Quality and Preference, October 2004; 15 (7-8): 805-18 A. Lampuré et al. British Journal of Nutrition, October 2014; 112 (8): 1353-63 A. Lampuré et al. The Journal of Nutrition, 1 March 2015; 145 (3): 587-94 12 #32 grand angle However, these broad findings cover substantial variation between different individuals. "Some inter-individual variability is due to genetic polymorphism" explains Loïc Briand. For example, some 2% of people do not sense the umami taste of glutamate. In this form of impaired taste function (or partial ageusia), a number of polymorphisms—different variants of a given gene—influencing how the umami receptor works have been shown to play a role in work which Loïc Briand contributed to. Similarly, some 30% of the population is insensitive to phenylthiocarbamide, a bitter-tasting compound found in many green vegetables, including broccoli and Brussels sprouts. These "non-tasters" are more likely to like these vegetables because they do not find them so bitter. Conversely, there are "super-tasters" who are particularly sensitive to bitterness. And the same goes for sugar: "Sensitivity to sweetness can vary by a factor of ten from one person to another" confirms Loïc Briand. k Tastes vary! A given ©©Olly/Fotolia dish will not taste the same to everyone. fatty foods" she says. Lifestyle is important too: smokers and heavy drinkers tend to prefer fatty-salty food. "Smoking and drinking impair taste sensation" specifies Caroline Méjean. "So these people tend to consume larger quantities of fatty-salty products to get the same sensation as non-smokers or light drinkers." Finally, data collected for this study also indicate that taste for both fat and sugar wanes with age. "It is possible that, as one gets older, one becomes more aware of the impact of nutrition on health" proposes Caroline Méjean. "And this "The more fat you eat, the more you are attracted to fatty foods" Taste governs our diet We do not all perceive all tastes in the same way. Some prefer sweet, others savory... and this will be reflected in what they eat. And what we eat has direct impact on our health. Poor diet (see Box on page 33) is associated with an increased risk of cancer, cardiovascular disease, obesity and diabetes. Could our taste make us sick? At least in part, according to some findings. For instance, Caroline Méjean and her team have shown that the dietary profile of volunteers in the NutriNetSanté study who are most attracted by fatty foods is less healthy from a nutritional point of view. "They ingest more calories from meat, fat and sugar" stipulates Caroline Méjean "and in parallel, they do not eat much fruit, vegetables or fish. "With all the longterm health consequences that go with that. In a recent longitudinal study, her team looked at how fondness for fat is related to the prevalence of obesity. would tend to lead to a more balanced diet." Eventually, eating less fat and sugar leads to a reduced desire for such foods. It is also possible that this agerelated effect could be due to reduced physiological sensitivity to tastes and smells. k ©©Loïc Briand Japanese display of foodstuffs rich in the taste of umami (shrimp, dried seafood, etc.) O. Lugaz et al. Chemical Senses, February 2002; 27 (2): 105-15 M. Raliou et al. Chemical Senses, July 2011; 36 (6): 527-37 13 #32 A genuinely "gentle" drug Other experiments are also showing that obese mice are less sensitive to sweet things, and that the same phenomenon can be observed in humans. However here too, scientists do not all agree. Although sugar never comes out whiter than white. It is believed to be Nutritional balance in a logo What is a balanced diet? It means eating enough healthy, varied foodstuffs to meet our energy needs and keep us in good health. To encourage people to eat a balanced diet, French public agencies established the Programme national nutrition santé (PNNS, National Nutrition & Health Program) in 2001*. Its recommendations include eating at least five fruits and vegetables a day as well as cutting down intake of salt, sugar and fat. To encourage choice of more "nutritionally" desirable foods, a labeling system for commercially available products is being set up. This will make it possible to compare the nutritional quality of similar products by means of a simple logo. However, this will not take into account what the product tastes like. "Such a labeling system will push companies to improve their products' nutritional quality by cutting down their fat, salt and sugar content" notes Serge Hercberg, President of PNNS, Professor of Nutrition at Paris 13 Medical School and Inserm Research Director in Nutritional Epidemiology, which should eventually reduce intake of these nutrients and help wean consumers off from these tastes. " www.mangerbouger.fr * See S&S # 26, In the headlines, "PNNS begins to yield fruit", p. 4-5 addictive and playing a central role in the explosion of metabolic diseases like diabetes and obesity in our societies of dietary abundance**. "Addiction is a behavioral problem that undermines control of how much of something is consumed" explains Serge Ahmed, Director of a CNRS team at the Institut des maladies neurodégénératives (IMN) (Institute of Neurodegenerative Disease in Bordeaux) and specialist in pathological addiction. It is usually associated with drugs such as heroin and cocaine or nicotine and alcohol. The consumption of such drugs activates neurons in the reward circuit that release dopamine in the brain. "Release of this neurotransmitter rewards the behavior that induced its release, in this case taking the drug" the scientist goes on. "This reinforcement then drives some people to take it again and again in a pathological pattern." Could ©©Monkey Business/ Fotolia Data from questionnaires filled out by 24,776 adults from the NutriNetSanté cohort show that a taste for fat is associated with a higher risk of becoming obese within five years: people who like fat eat a less healthy diet than those who do not like it as much. According to this epidemiological survey, a taste for "fat" is associated with a poorly balanced diet which ultimately raises the risk of obesity. But once it is installed, does obesity in turn affect taste, notably that for fat? The answer is apparently yes according to experiments in mice carried out by Philippe Besnard. "Obese mice detect ingested lipid less effectively than mice of normal weight" he states. This lack of sensitivity leads to more frequent eating in these animals. "These rodents probably have to eat more lipids to get the same gustatory gratification—referred to as the hedonistic threshold" explains the scientist. This work has also shown that the CD36 lipid receptor does not work properly in these obese mice, similar to what is seen in mice in which this receptor has been knocked out (see page 29). "This finding confirms how important this receptor is in lipid detection." However, this loss of sensitivity can be reversed by feeding the mice a low-calorie diet: as the obese mice lose weight, their perception of lipid intake steadily improves. Obesity would seem therefore to be the cause of the dysregulation in mice. But what about humans? "Work on lipid detection in obese subjects has given contradictory results, sometimes causing controversy" regrets Philippe Besnard. Still, gustatory tests carried out by his team and that of Sophie Nicklaus have shown that the detection of certain lipids is perturbed in these subjects compared with this function in slim people. Serge Hercberg: Inserm Unit 1153/Inra/Université Paris 13-Paris Nord/Université Paris 7 – Denis Diderot – Université Paris-Descartes, CRESS, EREN certain foodstuffs sometimes act like a recreational drug? "Extrapolating the criteria that define addiction to foodstuffs, 5 to 10% of people of normal weight display addictive behavioral patterns to food " proposes Serge Ahmed "and this proportion rises with body mass index, reaching 40% in obese people." And many foods that Serge Ahmed: UMRS293 CNRS, Université de Bordeaux, IMN, Prise de décision pathologique de l’addiction (Decision-making in pathological addiction) ** See S&S # 25, Opinions, "Sugar addiction: reality or myth?", p. 40-41 C. Méjean et al. Appetite, 1 July 2014; 78: 147-55 A. Lampuré et al. International Journal of Nutritional Behavior and Physical Activity, 4 July 2016; 13: 74 M. Chevrot et al. Journal of Lipid Research, September 2013; 54 (9): 2485-94 M. Chevrot et al. The American Journal of Clinical Nutrition, 1 May 2014; 99 (5): 975-83 #32 Dopamine. Neurotransmitter secreted by dopaminergic neurons (which are mainly involved in controlling motility and in the reward system). Body Mass Index (BMI). Parameter that estimates an adult's corpulence, calculated by dividing weight in kilograms by the square of height in meters. A BMI of between 18 and 25 corresponds to normal corpulence. Someone with a BMI of over 30 is considered as obese. E3N cohort. Prospective cohort study launched in 1990 covering about 100,000 French women born between 1925 and 1950 affiliated with the National Education Mutual Insurance System. www.e3n.fr Guy Fagherazzi: Inserm Unit 1018/Université Versailles-Saint- Quentin-en-Yvelines – Université Paris-Sud 11, Centre de recherche en épidémiologie et santé des populations (Center of Research into Population Epidemiology & Health) M. Lenoir, F. Serre et al. PLoS One, 1 August 2007; 2 (8): e698 G. Fagherazzi et al. The American Journal of Clinical Nutrition, March 2013; 97 (3): 517-23 Experiment to assess sugar's addictive potential. The rat can press on a lever to get a sweet drink. It is also connected to a system that administers an injection of cocaine. The animal can choose between these two substances. k some people claim to be addicted to— fizzy drinks, ice cream, chocolate— contain sugar—a great deal of it. However, not everyone who likes these products is a junkie. "The same is true of recreational drugs" explains Serge Ahmed. "It is estimated that one in three smokers are dependent; and with alcohol, the proportion is one in ten." Addictive potential thus depends on the substance. To compare the addictive potential of sugar with that of cocaine, Serge Ahmed subjected rats to a dual choice test: the animals could choose between a sweet drink and an injection of cocaine. Results: 85% of the rats preferred the sweet drink. So in rats, sugar seems to be more addictive than cocaine. Such findings can obviously not be directly extrapolated to human beings but they do show that the addictive potential of sugar is real. More than other foodstuffs? "We think that the addictive potential of sugar is largely due to what it does in the brain" proposes the scientist. "Unlike other nutrients, the glucose in sugar directly interacts with the brain's reward circuit." But sugar's addictive potential remains a controversial subject. Of course, industrial lobby groups raise doubts but the same is true of some voices in the scientific community who point to the lack of evidence that there is such a thing as sugar tolerance. And tolerance—the need to consume more and more of something to obtain the grand angle ©Eric Augier 14 same degree of gratification—is usually considered as a necessary characteristic of addiction to a substance. No more sugar substitutes natural sugar. They could even be worse. A recent epidemiological Artificial sweeteners like aspartame survey of a sample of 66,118 women make food sweet without all the caloin the E3N cohort conducted by ries of sugar; could these be part of the Guy Fagherazzi, an Inserm researcher solution to the possibility of sugar adat Gustave-Roussy in Villejuif, showed diction? "In theory, that artificially yes" answers Serge sweetened lite Ahmed. But drinkdrinks are associ"Artificial sweeteners ing artificially ated with a higher activate sugar receptors risk of diabetes sweetened drinks is often associated than drinks conin the gut" taining regular with the consumption of sugar in sugar. To cut down other forms which ultimately mainglucose absorption in the gut, comtains a craving for sugar." Moreover, pounds that inhibit these receptors receptors that mediate the taste of could be developed for therapy. "Plants sweetness are not only found on the used in ayurvedic medicine like tongue but also in many other tissues Gymnema sylvestre contain such inhibitory substances, in this case gymnelike the small intestine, colon, pancreas mic acid" notes Loïc Briand. "They and brain. And "synthetic sweeteners have long been used in this ancient Inactivate these receptors in the gut to dian medical practice to lower glucose promote the absorption of glucose into levels in the blood of diabetics." Howthe blood" points out Loïc Briand. So ever, scientific evidence of their theraartificial sweeteners affect glycaemia peutic benefits remains restricted to just (the concentration of glucose in the a few clinical trials. blood) and could be as guilty in the Just like likings for fat and sugar, a taste development of diabetes mellitus as #32 for salt may also have health consequences. Salt tends to raise blood pressure. Hypertension is associated with a risk of cardiovascular disease, especially stroke and, to a lesser extent, myocardial infarction . And according to the results of the NutriNet-Santé study, the French are eating too much salt: 8.4 grams a day on average while the World Health Organization recommends a maximum of 5 grams; 2% of volunteers systematically put salt on their food before tasting it and 8% declare doing so on a regular basis. Hypertension due to excess salt can nevertheless be reversed by consuming a low-salt diet which gradually reduces cravings for salty food. Salty food can even become unpleasant-tasting, leading to a permanent feeling of thirst. The attraction of different foods—salty or not—is therefore not static; it can change with a change in diet. Taste rehab Our senses can help us learn or relearn how to taste. Sensory education gain. A recent study of 52,163 volunteers from the NutriNet-Santé cohort just detected a significant link between intuitive eating and weight: people who only eat when they feel hungry (rather than in response to emotion) and stop eating once they feel full are less likely to be overweight or obese. Taste could therefore be made an ally in the fight against many dietary problems, making it possible to find or restore the pleasure of healthy eating. n k Patient consulting a dietitian at a hospital specializing in the treatment of obesity in children and teenagers is a therapeutic tool used to treat certain metabolic problems like obesity, against which it can be more effective than serially repeated dieting. "Intuitive eating" is one of the methods based on sensory education. "The principle is not to ban any foodstuff but to restrict the amount consumed and, at the same time, enhance the pleasure associated with eating it, notably by eating it slowly" specifies Dr DominiqueAdèle Cassuto, endocrinologist and nutritionist, who uses it on groups of obese teenagers at La Pitié-Salpêtrière Hospital in Paris. A preliminary phase consists of helping patients put words on their relationship with food and then helping them to get used to feelings of hunger and satiety by listening to their bodies. Then they attend tasting workshops to restore the sensory aspects of eating; not only taste but also the other senses. And the results can be surprising. "The teenagers' attitudes to food change." celebrates the nutritionist. "They come to realize that 'little' and 'good'' can be enough to satisfy." Which checks their weight Find the Saveurs & Santé (Tastes and Health) Train from 5-23 October 2016 at any of its 15 stops. ©©AJ PHOTO/HPR BULLION/SPL/Phanie www.inserm.fr Stroke. Obstruction or bursting of a blood vessel in the brain that causes the death of nerve cells. Myocardial infarction/ A "heart attack" is characterized by the death of heart muscle cells in an area of variable size. G. M. Camilleri et al. Obesity, May 2016; 24 (5): 1154-61 15 FREE MAGAZINE NOT FOR SALE