Genetics and Taste

 

You probably learned about the five different flavors we sense in foods: sweet, salty, sour, bitter, and umami (a savory, meaty flavor) in school.

It’s believed that the ability to sense each of these flavors evolved to improve our survival as a species. The sweet taste of fruit is due to the carbohydrates, often sugars, in the fruit that are an important source of energy. Meanwhile, our bodies need some salt to maintain fluid balance. Sour tastes are often found in spoiled foods and plants produce some toxic compounds that have a bitter taste to help us avoid eating potentially harmful foods. Umami signals protein in foods.

How we sense flavors is a complicated process that involves smell, taste buds and genetics.

Olfactory cells in our mouth and nose sense smells. Taste cells are clustered together in taste buds that are located throughout our mouth, on our tongue, and on the back of the throat. Since flavor is the number one reason why we choose to eat certain foods, understanding flavor plays an important role in our health. While there are only five different flavors, we are able to sense over 10,000 different odors. We have two pathways for sensing the smell of foods. The first pathway is through our nose (think about the wonderful aroma of freshly baked chocolate chip cookies as you walk into the house) and the second is when the aroma of food is released through the backs of our mouths into our noses as we chew food. You might be surprised to learn that this second pathway accounts for 80-85% of the flavor of foods.

Taste combines both smell and flavor. That’s why when we have a cold and our nose is stuffed, nothing tastes good to us. If we lose our sense of smell, we also lose the ability to distinguish most flavors.

Cells that contain the receptors for taste and smell are replaced every 10-30 days.

As we get older, the total number of these taste and smell receptor cells decreases, especially after age 70. That decrease in taste and smell receptor cells can contribute to decreased appetite due to less enjoyment of food. Many people add more sugar or salt to foods to improve the taste as they get older and are less sensitive to tastes, but increasing the amount of added sugar and salt we consume can lead to numerous health problems including heart disease, high blood pressure, and type 2 diabetes.

New discoveries of taste receptors in our gastrointestinal tract

Recent research has shown the presence of taste receptors for in our gastrointestinal tract that initiate glucose absorption, insulin secretion, gastrointestinal motility, and the release of hormones that generate feelings of fullness or satiety signals to the brain that help us decide when to stop eating.

One study published in Diabetes in 2013 suggests that sweet taste receptors in the gut may enhance the rate of glucose absorption and contribute to increased blood glucose levels after meals in people with type 2 diabetes. It is still too early to definitively understand what role these receptors might play in weight gain, obesity, and diabetes.

The role of genetics in taste

Our sense of taste is built into our genes and can be observed before 6 months of age. Babies inherently prefer the sweeter taste of breast milk and dislike the sour taste of lemons. Although genetics are important for smells, recognizing smells is actually a learned experience. Genetic differences in taste and smell receptor cells play an important role in why some people have a sweet tooth and others prefer salty flavors. Genetic differences are also the reason why one of my neighbors detects a soapy smell and taste when he eats cilantro, another smells a fragrant odor in her urine after eating asparagus, and many people dislike cruciferous vegetables like broccoli, Brussels sprouts, cauliflower, and kohlrabi because they taste very bitter.

People who taste soap when they eat cilantro possess both the gene that detects the soapy flavor as well as a variant of an olfactory gene that makes them more sensitive to bitter tastes.

To smell the fragrant odor in urine after eating asparagus, people must be genetically wired to produce the right amount of these smelly compounds plus they must also have the olfactory gene that transmits the signal about the asparagus fragrance to the brain.

Cruciferous vegetables contain naturally-occurring sulfur-based compounds that bind to a bitter taste receptor, which then sends a message to our brain to process the taste as bitter. Our genetics determine how much of a bitter flavor we detect. The good news is that oven roasting or grilling cruciferous vegetables destroys some of the sulfur compounds so that the once bitter-tasting broccoli now tastes more sweet.

Super-tasters

You might have heard some people described as "super-tasters," which is a term first developed by Linda Bartoshuk, PhD, a pioneer in studying the role genes play in taste.

Dr. Bartoshuk found that about 25% of the United States population is extremely sensitive to tastes while about 25-35% of the population is far less sensitive. That leaves the majority of us in the middle. Super-tasters actually have a larger number of taste receptors, which makes some flavors, especially bitter or spicy flavors, taste awful. Super-tasters often have a reduced preference for sweets, dislike alcohol, and often are non-smokers; however they also tend to consume more sodium because salt tends to mask the bitterness in many foods, especially cruciferous vegetables.

Non-tasters, the group of people who are less sensitive to tastes, tend to prefer foods that are higher in fat, sodium and sugar which are implicated in heart disease, high blood pressure, obesity, and type 2 diabetes. Dr. Bartoshuk’s research shows that there is a strong relationship between our sense of taste and smell and overall health status.

Understanding our own personal taste preferences can help us learn to make healthier food choices. For example...

  1. Gradually reduce the amount of salt added to foods, and over time your taste buds will adjust and you’ll enjoy foods with less salt.
  2. If you enjoy the flavor of fat, choose healthier types of fats such as olive oil and canola oil, or spread mashed avocado or hummus on sandwiches instead of butter or mayonnaise.
  3. Replace cookies, cakes and sweets high in added sugars with fruit. Fresh fruit in season is at its sweetest flavor and dried fruit tastes sweeter because it contains less water. Dates are fresh fruit with the lowest water content which makes them taste sweeter.
  4. Use a variety of herbs and spices instead of salt, sugar or fat to flavor foods.
  5. Cinnamon and vanilla increase the sweet flavor of foods without sugar: stir cinnamon into coffee, sprinkle sliced apples or bananas with cinnamon, or add vanilla to your morning oatmeal.

By Lynn Grieger, RDN, CDE, CPT, CHWC

References:

  1. Harvard T. H. Chan School of Public Health. The Nutrition Source. Super-Tasters and Non-Tasters: Is It Better to be Average? Guy Crosby, PhD, CFS. https://www.hsph.harvard.edu/nutritionsource/2016/05/31/super-tasters-non-tasters-is-it-better-to-be-average/ published 5-31-16. Accessed 9-20-19
  2. U.S. Department of Health and Human Services. National Institute on Aging. How Smell and Taste Change as You Age. https://www.nia.nih.gov/health/smell-and-taste content reviewed 4-1-15. Accessed 9-21-19
  3. AgingCare. Why Seniors’ Tastes Change With Age. Marlo Sollitto. https://www.agingcare.com/articles/loss-of-taste-in-the-elderly-135240.htm Accessed 9-21-19
  4. The Academy of Nutrition and Dietetics. The Role of Genetics in Food Tastes and Smells. Barbara Gordon, RDN, LD. https://www.eatright.org/food/nutrition/healthy-eating/the-role-of-genetics-in-food-taste-and-smells published 9-22-19. Accessed 9-20-19
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