By Elizabeth Grover
One of the most common non-motor symptom of Parkinson’s disease – affecting an estimated 90% of PWPs – is a reduction in (or complete absence of) a sense of smell. The reduction is called “hyposmia” and the absence is “anosmia.” Often this symptom predates many others. This loss has the potential to significantly affect our quality of life. The inability to accurately detect odors in one’s environment can be inconvenient (if you can’t tell whether your clothes or your body parts need cleaning and deodorizing) or even dangerous (if you cannot smell a fire or a gas leak.) But a related loss that may perhaps have even more of an impact on one’s quality of life is a reduction in the sense of taste.
The sense of taste and the sense of smell are very closely connected. In fact, our perception of food is comprised of three elements: the five basic tastes that we encounter directly on our tongues, the feel and texture of food encountered by the nerves in our mouth, and the aroma of the food as interpreted by our olfactory system. These together make up what we call flavor. As anosmia takes away the contribution of the olfactory system, those experiencing this reduced sense of smell primarily taste those flavors that are sensed by the tongue and miss the added complexity of foods that are enjoyed especially through aroma.
The human tongue has thousands of little bumps called papillae, each of which contains several hundred taste buds, which in turn each have 50 to 100 taste receptors that can detect flavors in one of five categories: sweetness, sourness, saltiness, bitterness, and savoriness (also called umami).
If you have lost much of your sense of taste, you may feel that you have also lost the ability to enjoy food. The reason it is good to enjoy the food we must eat to survive is not just pure pleasure; the absorption of nutrients from your food correlates with the degree to which you enjoy your food. One way to maximize your enjoyment of food is to focus on the ingredients and preparations that emphasize the five basic on-your-tongue flavors. You can prepare dishes that bring out these ingredients or you can add a sauce or spice to your portion at the table to enhance your meal.
Sweetness is one of the five basic tastes. The sweet flavor which can be tasted on the tongue is almost universally pleasant. It comes from one of several kinds of sugars. Naturally occurring sugars are found in foods such as fruit, sweet potatoes, and milk. Added sugars include any natural sugars or caloric sweeteners (such as white sugar, brown sugar, and honey), as well as other caloric sweeteners that are chemically manufactured (such as high fructose corn syrup), as well as artificial sweeteners. All of these are ways to stimulate the sweetness sensors on your tongue.
The benefit of sweetness in our diet is that it gives us energy without which we cannot function. But there are drawbacks as well. Too much sugar in our diet can lead to unhealthy weight gain (even obesity), heart disease, high blood pressure, and tooth decay and can put us at risk for diabetes, cancer, or depression. It can be difficult to balance the deliciousness of sweet foods and the health dangers of sugar in the diet. Added sugar can mean extra and nutritionally empty calories. Those foods with naturally occurring sugars tend to be more nutritious; fruits, for example, are often high in fiber and vitamins.
The next of the five basic tastes is saltiness. Salt is essential to our bodies, but we cannot store excess salt so we are programmed to crave salt. Even though salt is essential, too much salt can harm us. A high-salt diet can contribute to high blood pressure and maybe stomach cancer and heart disease. The foods commonly available in grocery stores and restaurants often have a large amount of salt, which serves as a flavor enhancer, so it is easy to get much more salt than we need in our diet..
However, one of the non-motor symptoms of Parkinson’s disease is low blood pressure. And several treatments for Parkinson’s (especially levodopa) can reduce blood pressure further. In fact, orthostatic hypotension is a condition common in PD, whereby one’s blood pressure drops steeply upon standing up. A primary treatment for this condition is an increased salt intake. If your doctor recommends a high salt intake, you could enjoy salty snacks or you can keep salt or seasoned salt on the dining table and use it liberally.
The pungency of a sour food may not be as pleasant as sweetness, but it certainly offers a tasteful experience. Historically humans developed the ability to taste sour foods to protect them from the potential dangers of rotting food. Pickles, barbecue sauce, and lemonade are examples of foods that have a sour element that can be detected by those with diminished sense of smell. Yogurt, kefir, and sourdough bread use fermentation to achieve a certain tartness or sourness. The use of condiments such as cranberry sauce, barbecue sauce, vinaigrette dressing or lemon juice can bring out the taste of foods that may otherwise be difficult to taste.
Like sourness, bitterness was developed in humans as a warning system. This flavor often marks toxicity in plant foods. And like sourness, we have developed an affinity for what was originally a bad taste. Bitter foods that can be considered not only palatable, but desirable include beverages such as coffee, tea, and beer; vegetables such as endive, broccoli and brussels sprouts; foods with citurs rind such as marmalade; and chocolate – darker chocolate is more bitter. For those of us with anosmia, the bitter category strips down the taste of a food or beverage to its bare elements. For example, a beer which has some bittnerness in it, such as an IPA, tastes only bitter to me.
The most recent addition to the list of five basic tastes is savoriness. This comes from a Japanese concept called umami. It is difficult to translate, but this element is the taste of glutamate. Umami is why monosodium glutamate is a flavor enhancer. This category has been described as beefy. Meats and mushrooms are abundant in umami.
Finally texture has an enormous impact on our food experiences. The variation in texture in a single meal – chewy steak, smooth mashed potatoes and crisp salad or crunchy cereal, soft eggs and cold orange juice – can offer a textural adventure to the diner who is paying attention. The sensations in our mouths provided by variations in the textures of what we eat are interpreted by the trigeminal nerve, the largest of the twelve cranial nerves. Its main function is to transmit sensory information to and from the skin, sinuses, and mucous membranes in the face, as well as stimulating movement in the jaw muscles. This territory includes all parts of the mouth; we experience food textures in the mucous membranes that are the lips, the tongue and the whole inside of the mouth, most of which is mucous membrane. These areas are so important to our survival that they are designed with exceptional healing power, so that if injured, they heal rapidly.
Because it is important to enjoy your food for nutritional purposes as well as for your quality of life, it is critical to pay attention to these elements of taste in order to maximize the quality of your eating experiences.