ADD FAT to the LIST of BASIC TASTES!

Chances are you haven't heard of this, even though the data have been accumulating since 2005...fat isn’t just texture, though of course texture is part of the experience of fat in the mouth. Data from both humans and experimental animals suggest that we are able to taste fat, or, to be more exact, we can taste long chain fatty acids.

In a series of elegant experiments, Fabienne Laugerette and her colleagues demonstrated that rats and mice sense fat through a receptor protein on the tongue called CD36.* As it turns out, humans taste fat in the same way.** 

In other parts of the body this same protein carries fatty acids into cells. On the tongue, however, CD36 appears to activate the same mechanisms as do the bitter, sweet and umami receptors, and it  sends messages to the same taste nerves in the tongue as do bitter, sweet, umami, and sour.

CD36 is associated with taste buds on the sides and back of the tongue, with a few on the tip of the tongue. It sits anchored to the surface of cells near the tip of taste buds. On the part of the protein outside the cell it has a cleft lined with amino acids that are hydrophobic. In other words, these amino acids don’t like to associate with water but do like to associate with lipid. This cleft can trap free long chain fatty acids, but not triglycerides. 

This image from the paper by Laugerette and her colleagues, shows a taste bud on the left, with a taste cell with CD36 attached. On the right is a model of the CD36 protein (the green ribbon) in the cell membrane, with fatty acids entering into the cleft. We don't know whether the fatty acid can trigger the cell to send a taste message by just sitting in the cleft or whether it needs to actually enter the cell. In any event we do know that in other locations CD36 is a fatty acid transporter that brings fatty acids into cells.

The fats we eat come in in the form of triglycerides—three fatty acids held together by a glycerol molecule. The fatty acids have to be detached from the glycerol for us to sense “fat.” The enzyme that does this breakdown is called lingual lipase—and (surprise!) where there is CD36 on a taste bud there is also lipase sitting on the surface of the tongue right next to it! 

It takes a little while for the lipase to break down the triglycerides, so fat has to be in the mouth for a longish time for you to taste it, while the sensation of sweet is sent to the nerves practically instantaneously. 

Think of eating something deliciously fatty such as hot fudge sauce. Do you savor it, moving it around your tongue to get maximum flavor? Now you know why you do this!

* Fabienne Laugerette et al. CD36 involvement in orosensory detection of dietary lipids, spontaneous fat preference, and digestive secretions. J Clin Invest. 2005;115(11):3177-3184. doi:10.1172/JCI25299.

** Pepino MY1, Love-Gregory L, Klein S, Abumrad NA. The fatty acid translocase gene CD36 and lingual lipase influence oral sensitivity to fat in obese subjects. J Lipid Res. 2012 Mar;53(3):561-6. doi: 10.1194/jlr.M021873. Epub 2011 Dec 31. Note that the authors of this paper looked at genetic variation in CD36. This variation leads to different thresholds for fat taste and intensity. In other words some people are much more sensitive to the taste of fat than others, on a genetic basis.