[ YOUR BODY ]

A matter of taste

I love to generously sprinkle my pizza with chili peppers; my 6-year-old son can't stand them. "Too hot," he says. I told him that when I was his age, I didn't like spicy stuff, either. Age, as it turns out, has a lot to do with our perception of smell and taste, and can partially explain why over time we abandon our "old favorite" foods for new ones. It is not because we have become bored, but rather that the food just doesn't "taste the same" as it used to.

So how exactly does our smell and taste work? Both are the result of complex chemical reactions on nerve cells in our nasal passage and mouth. When these cells are stimulated, they send a message to our brain, which in turn draws upon our own memory and a pre-wired defense system to recognize familiar odors or tastes, as well as identify new ones.

In the nose, olfactory cells process the odor molecules we inhale and exhale. These molecules collide with the cells attached to the olfactory bulb, a small organ connected directly to our brain. The direct connection is no coincidence -- the more direct the connection, the faster the processing. For our ancestors, smell was much more important than taste. In order to survive, they needed to rapidly detect dangerous scents, such as that of a wild beast. In modern times this rapid processing helps us identify such things as smoke or spoiled food.

The gustatory cells located throughout the mouth, including the throat, register taste. But the most sensitive cells are on our tongue, the ones we refer to as "taste buds." Taste buds alone are not enough for a satisfying taste experience. It also requires a chemical reaction with our saliva, a resistance (or lack thereof) to the particular food being chewed, the food's temperature and even its auditory response. If cold, soggy french fries were popular, there would be more of them sold.

It is commonly believed there are four taste sensations -- sweet, sour, salty and bitter -- but the Japanese recognize a fifth called "umami," a unique flavor that comes from glutamic acid, better known as MSG. The Chinese also have a fifth sensation -- "pungent" -- which might explain why you never see "four spice" powder in a Chinese market.

Finally, sometimes these two senses are dependent upon each other. Some tastes, like coffee, are only possible to detect by using both senses. You can prove this yourself by holding your nose next time you have a sip. That's the same reason a head cold often results in a loss of appetite. We just aren't as hungry because we can't taste anything.

Science hasn't yet determined exactly why our sense of smell and taste diminish, but we do know that as we age our olfactory bulb shrinks, and the number of taste buds can decline by 40 percent or more. In addition, saliva production decreases so that the "strength" of the chemical signal may decrease.

However, because these changes are subtle, occurring over many years or decades, we often don't realize that during this same time we are gradually compensating for the loss. In the case of smell, it might be favoring stronger fragrances, or with taste, spicier or sweeter foods.

And age is not the only factor. Smoking, toxins in food, water and air, head trauma and even some medications can inhibit our ability to smell and taste. Then there are age-related diseases involved. For example, a very pronounced loss of taste has been noted in patients with Alzheimer's, Parkinson's and ALS (Lou Gehrig's disease).

A compromised sense of smell and taste not only interfere with one's ability to enjoy many of the fragrances or foods so loved in the past; it can be dangerous as well. Some of the more obvious problems include food poisoning from the inability to detect spoiled food or being unaware of leaking gas or smoke from a fire.

But there are other, less obvious problems, too. When certain foods are no longer enjoyable, they are often omitted from the diet. Things like vegetables, especially those with subtle flavors, might no longer be appetizing, or to make them palatable, generous amounts of butter, sour cream or other unhealthy flavor enhancers might be added. Omitting vegetables and other foods that contain essential vitamins can also result in bone density loss or compromise the immune system.

In addition, studies have found that the elderly might require 15 times more salt or sugar to achieve the same taste sensation of a younger person. As a result, seniors might pass over healthy foods and opt for the pastries and sweets, or add too much salt and sugar, a particular problem for those with high blood pressure or diabetes.

Fortunately, at least as far is taste is concerned, some help is on the way. Aware of this growing problem, dietitians are now identifying safer flavor enhancers and experimenting with textures and color additives to make food more appealing. And at the University of Tsukuba in Japan, a scientific team has built a taste simulator that is programmed to mimic the mouth characteristics of seniors. Through the use of artificial flavors and textures, they are determining what combinations are the most satisfying. The ultimate goal is to create new foods or learn to prepare foods differently, thus making eating for seniors more healthy and enjoyable.