Flavor: Keeping Pleasure In Its Place Interview with Monell Center Director Gary Beauchamp, Ph.D. Reprinted from Food Insight September/October 1991 Finding out more about how people enjoy themselves and the world around them may not sound like serious work to you, but don't tell the people at the Monell Chemical Senses Center. In this interview, Monell's director and president Gary K. Beauchamp, Ph.D., stresses that the chemical senses - taste and smell - are senses of pleasure, and that pleasure is no trifling matter. Pleasure seems to be nature's way of helping us find what is good and useful in the world around us. This is especially true in selecting the foods that we eat. The Monell Chemical Senses Center in Philadelphia is a nonprofit scientific institute, founded in 1968, where multidisciplinary research is exploring the mechanisms and functions of taste and smell, as well as pleasurable "irritation" - such as the burn of hot peppers. The expertise of scientists at Monell includes neuroscience, genetics, biochemistry, nutrition, synthetic chemistry, immunology, psychology - and spirited collaboration among them all. Monell's work has numerous practical applications and nearly boundless theoretical interest. That's because its research is unlocking more than a few of the simplest and most significant mysteries of human experience. What do you mean when you say the science of taste and smell is on "the cusp of a revolution?" The senses of smell and taste have been neglected - relative to vision and hearing - in fundamental research on how they work. Part of that is because the loss of vision or hearing obviously is quite serious, but it's unclear how serious it is to lose your senses of smell or taste. They're often called the secondary or minor senses. Scientific interest has grown in the past 20 years because tremendous technical advances in physiology and neurobiology have allowed researchers to look at the molecular events within a cell. Consider smell, which is a major portion of flavor. We are learning the structure of receptors that are responsive to particular odors, what genes are involved in making those receptors, how the receptors interact with the odorous molecule, and how that is translated into a neural signal. Much about this will be known within five to 10 years, so it will be possible to rationally design chemicals that will have particular flavors and odors. Do people understand how the Monell Chemical Senses Center relates to food? Perhaps not, but we couldn't be called the Monell Taste and Smell Center because we're broader than that. People are worried about "chemicals," but the fact is that all food is chemicals and there's no way around that. The job of our center is to understand how we and other species perceive and interact with our environment through our chemical sensors. The chemical senses are senses of pleasure. Pleasure has an anatomical basis and it has a function. Pleasure occurs for a reason, not by chance. It's a mistake to say that something is just hedonic, because hedonism is a fundamental and important aspect of life. Taste and smell are most closely tied to pleasure and displeasure because of their evolutionary history. These senses are involved in the most significant decisions that animals make about whether to accept or reject a chemical into the body. And smell and taste are among the oldest senses, the most primitive and the least analytic. We have difficulty with words describing those senses, yet no problem at all from a very early age expressing our likes and dislikes for these sensations. What are the practical outcomes of flavor research? If you look at taste reception, for example, there's a growing idea of how salt is perceived. It appears that the sodium ion goes through an ion channel into the cell itself, rather than into a typical receptor. What's interesting and important is that these channels for sodium are very specific to sodium. The idea that there could be a salt substitute is now thought to be unlikely. While there are many substances that are sweet, there is nothing besides sodium chloride that is pure salty except lithium chloride, which is poison. There might be ways to make a low level of salt taste saltier by doing something to these ion channels - opening them wider, keeping them open longer. Instead of finding an artificial salt, there's more interest in finding something that will magnify the perception of salt. We have also learned that if people go on lowered sodium diets for a period of time, they develop a new setpoint essentially. The desire for salt declines commensurate with declining intake, within a range. What seems to matter is not the amount of salt that's in the body, but rather the sensory experience of salt. The preference is for the level of saltiness, not the level of sodium. Why do most people love to eat fat? It's still not entirely clear how people even recognize fat. There are no specific receptors for fat as far as we know. The liking for fat seems to be mediated by things such as mouthfeel that are very difficult to get a handle on. And the liking for fat is presumably a learned phenomenon. Fat obtains its palatability because of the physiological properties it has in providing the richest of all energy sources to the body. Humans evolved like all animals facing the two biggest problems - reproducing and getting enough to eat. Because fat comes in so many different forms, we haven't evolved receptors for it. What we did evolve is a very sophisticated mechanism of learning to associate the high nutrient value of fat with its sensory characteristics. So that sensory quality takes on incredible importance. What other sensations affect human response to foods? Another very important response to food might be called irritation. Many foods contain some aspect that stimulates the fibers of our systems for detecting pain. Extreme temperatures of foods are an example. Also, many mints and menthols. Capsaicin, or the essence of hot peppers, is innately negative in that it stimulates pain fibers. Yet much of the world's population won't eat their food without it. It's interesting to think about why humans would find the sensory stimulation of pain systems desirable. One theory is that pain fibers stimulate the endogenous opioid system, and this may be true of sweet and salt tastes as well. Some of the pleasure involved in all of these senses might be due to a drug-like effect. Apparently when newborn babies are given a sweet taste, it will dampen pain during procedures such as circumcision or heel pricks for taking blood. The sweet taste becomes an analgesic by stimulating opioids that reduce pain. Do these chemical senses affect nutrition? The senses of taste and smell and irritation stimulate a cascade of physiological responses such as insulin release, uptake of nutrients in the gut and stimulation of pancreatic secretions. These events are reflexive and are mediated through neural pathways. An assumption is that the senses of taste and smell have nutritional consequences in preparing the body to utilize food. Monell studies of premature babies were designed to look at this. These babies are being tube fed because they have not developed reflexes to such and swallow. By not taking food orally from a bottle or by nursing, the oral sensory receptors are not stimulated. Studies show that just the oral stimulation of a pacifier while babies are being tube fed helps them utilize food. Our ongoing studies are looking to see whether a sweetened pacifier further improves their utilization of food, as measured in their growth. How are eating patterns influenced by taste and smell? The responses to sweet, sour, salt, bitter and possibly "umami" - the flavor of MSG - are part of a hard-wired taste system. But much of what we like and dislike about flavors and odors may be learned. A new project at Monell is looking at the idea that some of this learning may occur soon after birth, during nursing. We are finding that flavors that mothers consume do get transmitted into the milk and influence the baby's willingness to consume milk. An interesting finding is that babies will nurse for about 50 percent longer when their mother's milk is flavored with garlic. What makes the senses work for us nutritionally? In my view, the taste system is a hard-wired, evolution-driven system that differs among animal species. Years ago I did studies on cats to see if they like sweets, which you might guess they ought not - if they did they'd eat fruit instead of meat. And indeed they were indifferent to sweets, and they probably don't even have receptors for carbohydrate sweeteners. They like amino acids. Now, amino acids may taste sweet to them - that's almost a philosophical question! The sensory system is tailored to nutritional needs, so it makes sense for cats to have amino acid detectors - and for humans as well. That could explain the flavor enhancing role of monosodium glutamate (MSG), which is made up of one of the most common of all amino acids. That we have sensory receptors that home in on that particular aspect of human nutritional needs makes a lot of sense. Reprinted from the International Food Information Council Foundation, 1991

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