We know five basic tastes. They are sweet, salty, sour, bitter and umami. Could fat be the sixth?

In 2015, scientists in the US asked people to taste many liquids and put similar tastes into groups. Fatty acids, which come from fat, made their own group. The scientists named this taste "oleogustus."

But it was not a nice taste. Alone, it was unpleasant. Scientists are still not sure it is a basic taste.

Scientists widely accept five basic tastes. These are sweet, salty, sour, bitter and umami. Some researchers believe fat could be the sixth.

Fat itself is a large molecule, but when it is broken down, it produces fatty acids, which may be detected by the tongue. In 2005, a French team found that mice without a protein called CD36 lost their preference for fatty food.

Then, in 2015, researchers at Purdue University asked people to sort different taste solutions into groups. Fatty acids formed a separate group from sweet, sour, salty and bitter, so the team named this taste "oleogustus." Surprisingly, it tasted unpleasant on its own. Fried food is delicious partly because of its smell and texture.

Sweet, salty, sour, bitter and umami are widely recognized as basic tastes, but researchers have long asked whether fat deserves a place on the list. To qualify, a taste generally needs a specific chemical stimulus, receptors that detect it, a nerve pathway to the brain, and a perceptual quality distinct from other tastes. Because whole fat molecules are large, attention has focused on fatty acids released when fat is broken down.

In 2005, a French team reported that mice lacking the protein CD36 lost their preference for fat and showed reduced digestive responses to it. In 2015, a Purdue University group asked participants to sort taste solutions by similarity while minimizing other cues such as smell. Medium- and long-chain fatty acids formed a cluster separate from the other tastes, and the team coined the term "oleogustus."

Paradoxically, this taste is unpleasant on its own; the appeal of fatty food seems to come largely from aroma, creamy texture and satiety. The study also had few participants, smell and touch cues are hard to remove completely, and researchers still debate whether fat taste is truly independent. So scientists disagree about whether fat counts as a sixth basic taste.