The nauseating taste of bitter

Swallow the good, spit out the bad. A new study from the Monell Center highlights the vital role taste plays as the body's gatekeeper. The research shows that strong bitter taste in and of itself can cause people to both report the sensation of nausea and display a pattern of stomach activity characteristic of actual nausea.

“Nausea is a huge negative modulator of quality of life for many people, including pregnant women, patients undergoing chemotherapy, and virtually all types of GI patients,” said senior author Paul A.S. Breslin, Ph.D., a sensory scientist at Monell. “Our findings may help clinicians ease suffering in these patients by advising them to avoid strongly bitter foods.”

The findings demonstrate that our bodies anticipate the consequences of food we eat. It was already known that the taste of nutrients such as sugars and fats causes the body to release hormones in preparation for digestion and metabolism. The current study reveals that the body also responds to the taste of possible toxins.

Bitter taste is thought to have evolved to signal the potential presence of toxins, which are abundantly present in plants. Breslin believes that strong bitter taste causes the bad feeling of nausea “to punish us so that we won't eat that toxin again.” Thus nausea serves to distinguish the everyday bitterness of foods like coffee, chocolate, and beer from the very strong bitterness of potentially poisonous substances.

In the study, published in Current Biology, 63 subjects sampled an intensely bitter but non-toxic solution known as sucrose octa-acetate (SOA). After holding the solution in their mouths for three minutes, they were asked to rate the degree of perceived nausea. Sixty-five percent were at least mildly to moderately nauseated and 20 percent indicated that they were strongly nauseated. A different bitter solution produced the same results. The findings were specifically related to bitter taste, as sweet, salty or umami taste did not cause nausea.

To illustrate how bitter taste affected gastric motility – the rhythm of stomach muscular activity – the researchers first simulated motion-related nausea. Stomach motor activity was recorded from subjects sitting in a drum with vertical black stripes painted inside while the drum rotated around their heads. All but one were strongly nauseated.

The scientists then measured stomach activity from 23 subjects who were holding SOA in their mouths. Individuals who described feeling nauseous also had a pattern of stomach activity that was very similar to that recorded from those in the drum.

“This is a wonderful example of what is called 'the wisdom of the body,'” said Breslin. “The findings show that taste detects toxins before they enter our bodies. Further, their ingestion is punished by the feeling of nausea and our gastric function is disturbed to minimize their entry into our blood.”

Future studies will explore the effectiveness of bitter blockers in reducing nausea in clinical populations.

Also contributing to the study were first author Catherine Peyrot des Gachons and Gary K. Beauchamp, both of Monell; Robert M. Stern from The Pennsylvania State University; and Kenneth L. Koch from Wake Forest University School of Medicine. Dr. Breslin is also faculty at Rutgers University School of Environmental and Biological Sciences. The research was funded by the National Institute on Deafness and Other Communication Disorders.

The Monell Chemical Senses Center is an independent nonprofit basic research institute based in Philadelphia, Pennsylvania. Monell advances scientific understanding of the mechanisms and functions of taste and smell to benefit human health and well-being. Using an interdisciplinary approach, scientists collaborate in the programmatic areas of sensation and perception; neuroscience and molecular biology; environmental and occupational health; nutrition and appetite; health and well-being; development, aging and regeneration; and chemical ecology and communication. For more information about Monell, visit www.monell.org.