Is fat the sixth taste?
Tucker-Falconer study explores possible taste/weight connection
High-fat foods are known for their textures—the smooth, creamy feel of ice cream or the crunch of a crispy French fry. The fatty acids in high-fat foods may also possess a taste. If so, is the ability to detect fatty acids in foods associated with weight problems? As obesity levels around the world continue to rise, researchers are looking for causes. Dr. Robin Tucker-Falconer is part of a team that explored whether people’s ability to taste fatty acids was related to their weight status.
Tucker-Falconer, a food and nutrition faculty member in the Department of Public and Allied Health, and her partners have conducted the largest study to date of subjects’ ability to taste the essential fatty acid linoleic acid.
“This study adds to the research that suggests ‘fat’ could eventually be added to the list of primary tastes we learned about in biology class: sweet, sour, bitter, salty and umami/savory,” she said.
In addition to measuring taste acuity, the researchers also looked at whether sensitivity to linoleic acid correlated with the tasters’ percentage of body fat (%BF). Partnering on the study were Tiffany Nuessle, research coordinator, and taste geneticist Dr. Nicole Garneau, both of the Denver Museum of Nature & Science; Dr. Gregory Smutzer of Temple University, who helped devise the tasting strips used in the study; and Dr. Richard Mattes, Distinguished Professor of Nutrition Science, director of Public Health and director of the Ingestive Behavior Research Center at Purdue University.
The results of the study, “No Difference in Perceived Intensity of Linoleic Acid in the Oral Cavity between Obese and Nonobese Individuals,” appear in the leading journal Chemical Senses, published by Oxford University Press.
The first purpose of the study was to determine whether people can, in fact, discern the presence of linoleic acid. In a survey of 735 subjects, ranging in age from 8 to 90, of white, black, Asian and Latino ethnicity, the answer was definitively yes, people can detect the taste — but to different degrees.
“This was far and away the largest sampling that has been conducted,” said Mattes, a longtime researcher into the biology of taste.
What was unusual about the study — and what enabled it to include such a large and diverse set of subjects — was that it was conducted with the help of “citizen scientist” volunteers that crowd sourced over 1,000 museum guests as research subjects at the Genetics of Taste Laboratory housed within the museum. Tucker-Falconer adapted the research methods she had used as a graduate student at Purdue, where she tested about 100 participants over four years, to the museum setting. She worked with Garneau, chair of the health sciences department and curator of human health at the museum, and her team to design the study and train the volunteers.
Unlike the majority of citizen scientists, who are observers and collectors of data in mostly ecological studies, museum volunteers are certified by the National Institutes of Health and are highly trained in all aspects of the work, including collecting and sequencing DNA samples.
“We’ve expanded what it means to be a citizen scientist,” Garneau said.
The cadre of volunteers administered taste tests to museum visitors that required participants to place a clear strip embedded with varying amounts of linoleic acid on their tongues, and then recorded their reactions.
“Instead of using liquid samples, the clear strips eliminated visual and textural cues about what the participants were tasting that might have influenced their responses,” Tucker-Falconer said. “The subjects also wore a nose clip to eliminate any odors the fat imparted.” The study was double-blinded, she added: neither the testers nor the tasters knew the fat concentration of any strip.
Tasters responded primarily to the intensity they sensed, and because there are no specific words in the English language to describe the taste of fatty acids, when they did try to describe it, subjects responded with things like “pungent,” “stale butter,” or “plastic-y,” Garneau said.
“It’s awful,” Mattes said of the taste. “The physical response is a gag reflex, at the higher concentrations, which would denote rancidity. But the subjects never received a concentration beyond what you could find in the food supply.”
Along with evaluating the tasting the strips, subjects were weighed and their %BF calculated. “Body fat percentage is a much more accurate measurement than the more common BMI, or Body Mass Index,” Tucker-Falconer said.
In addition, the researchers collected a DNA sample from each participant, which will yield valuable information for further study, she added.
The results proved some theories and virtually eliminated others, giving researchers a clearer path for their next steps.
In answer to their central question, the researchers found no link between %BF and ability to perceive the taste of the linoleic acid. “We didn’t find that %BF would predict someone’s sensitivity to fat,” Tucker-Falconer said. “Now we know we need to explore other areas, like genetics or dietary exposure, for those results.”
However, the results did reveal an interesting pattern in sensitivity. Women were much better than men at discerning the taste, and young people 17 and under, especially girls, were better than older people. “This was one of the first studies to look at how kids experience fat taste,” Tucker-Falconer said.
“There was enormous variation between people in their ability to taste the fatty acid,” Mattes said. “There could be a genetic basis for that variability.”
One difference was revealed between the population of people with obesity and those without: “What you ate beforehand had an impact,” Tucker-Falconer said. “If you had had a high-fat meal and were obese, it decreased your ability to detect the fatty acid. This lack of detection could possibly lead to the overconsumption of fatty foods.”
This finding was intriguing, she said, and tells researchers that future fat-taste test subjects should receive standardized meals beforehand.
Long-term goals of the research include further investigation into how the taste of food is detected in the oral cavity and the role of genetics in taste and perhaps in food preferences. In November, Tucker-Falconer will begin a new study with the museum into the oral microbiome and its role in taste sensitivity.
“Working with the citizen scientists is a wonderful scenario,” Mattes said. “With their interest and willingness to be trained and their commitment, it’s just a perfect situation. It enables us to study large populations in an efficient way.”
Eventually, applications of learning how fat is tasted could lead to improved consumer acceptance of low-fat foods, Tucker-Falconer said.
The study also provides more information about whether fatty acids actually qualify as a sixth primary taste, Mattes said. “Before calling it a primary taste, researchers have laid out a list of criteria it must meet: The stimulus has to have its own unique chemical structure; it must bind to its own receptor system that is different from those of the other primary tastes; its sensation must be carried by the specific three nerves that serve the sense of taste; the central nervous system must decode it into a unique sensation, and there must be a behavioral or physiological response to it. And there has to be a purpose. For instance, bitter tastes can warn us of harmful substances.”
Mattes said there is a substantive body of supportive science, but still more to be learned before fat is accepted as the next taste.
A story about the large-scale test was broadcast in March on Colorado public radio station KUNC. Also, up-to-date study results and access to the publication can be found at http://www.dmns.org/genetics.