Photograph by Joel Sartore, Nat Geo Image Collection
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This boy may or may not enjoy the taste of fat.
Photograph by Joel Sartore, Nat Geo Image Collection
The Plate

That Fatty Taste, Like Pluto, May Have a Hard Time Earning Respect

In the last few weeks, there’s been a slew of headlines announcing fat as the newest taste scientists have discovered in our palate. A new study in the journal Chemical Senses suggests that people can in fact distinguish the taste from the other five—sweet, salty, sour, bitter, and umami. But is that enough to make fat the next official taste? The answer is maybe.

One of the challenges in naming a new primary taste is that no one really agrees on what the criteria for one is. It’s a bit like the debate over Pluto’s status as a planet: Experts can, and do, disagree.

One thing that is not in dispute is the importance of taste in our evolution as an intelligent species (see From Campfire to Haute Cuisine: How Food and Flavor Drove Human Evolution.)

Despite the lack of a solid definition, scientists approach primary taste studies with two main questions: Is there a specific taste receptor for it and can people uniquely identify that taste? If a taste meets both of these measures, scientists generally agree that it’s a primary one.

The idea that fat is a unique taste has actually been around for hundreds of years. And scientists have known for the last 15 years that people have fatty-taste receptors. That means they’ve proven we have taste cells that exist only to recognize fat. But there hasn’t been enough evidence to prove that people can actually identify them as a separate taste until now.

To test if people could tell if fatty was different from the existing primary tastes, Dr. Richard Mattes of Purdue University and his colleagues fed people a series of solutions and had them sort the tastes into categories. When the subjects sampled all of the tastes, they grouped fatty with bitter, since fatty acids taste unpleasant, just like bitter and sour do for many people.

But when the subjects were given just bitter, umami, and fatty solutions to sample, they were able to uniquely identify fat as different from the other two. Dr. Mattes named this unique taste of fat oleogustus, which is just the Latin word for “oily” or “fatty.”

“Fatty taste itself is not pleasant,” explains Mattes. “When concentrations of fatty acids are high in a food it is typically rejected, as would be the case when a food is rancid.” The presence of a lot of fatty acids tells people that food is rotten, but a small amount could be appealing, just like how some people prefer slightly bitter coffee or chocolate.

And a little fat goes a long way. “Fatty acids are a very tiny amount of what’s in our food, but we can detect them, just like how a little sweetener is noticeable in drinks,” says Danielle Reed, a research scientist who studies taste at the Monell Chemical Senses Center in Philadelphia. She also mentions the taste of fat is not the same as the feel and texture of it, which further confuses people when they try to talk about it as a unique taste.

One of the main challenges is that the taste of fat is difficult to describe. We seem to lack the vocabulary to talk about it, which is a big factor in the debate over its status as a basic taste.

“When you eat sugar you have the words to talk about the experience,” explains Reed. “We quickly perceive and name salty and sweet, but it’s much more difficult with fatty acids—they just aren’t as salient.” Umami experienced similar issues when it first came on the scene in the early 2000s. In the beginning, people described it as salty, but now they have the words to explain the savory-like taste.

To be fair, designating some of the other primary tastes isn’t that straightforward either. Bitter, sweet, and umami are pretty well understood—they’re distinguishable and have well-studied receptors. Sour and salty are uniquely perceived by people, but not as much is known about their receptors on the molecular level. “They are generally agreed on because you can’t argue with the fact the tastes are easily identified when people eat them,” says Reed.

Most taste subtleties are more complex than our brains can handle. “There’s a lot we still don’t know, since our brain can only decode a small amount of taste information,” says Reed. “Most people have around 25 bitter receptors, all of which sense a different type of bitter, but our brain just understands it as one taste.”

Beyond fatty, taste scientists are exploring the potential for other primary tastes. What are some frontrunners for the next official taste? Minerals like calcium are a promising area of research, as is potassium chloride, which could be a healthier substitute for salt. Food companies are on the lookout for ways to make healthier snacks without compromising taste, because compromising taste means consumers won’t bite.

So, is fatty the newest primary taste? Evidence suggests yes, but it seems like it depends on who you ask. Some scientists just might not be convinced that people can identify fatty easily enough, making it more like a secondary taste. In any case, it doesn’t look like this will be the final word on fatty.

Kelsey Nowakowski is a spatially thinking reporter at National Geographic. Follow her on Twitter.