Taste is in more than the mouth!

Did you know that we have taste and temperature receptors not only in our mouth and nose, but also all the way down the gut, from throat to end? 

We do, and their functions in digestion and metabolism are slowly coming to light. For example, bitter compounds can be toxic, so we start out life not liking bitter, and we refuse bitter foods—that’s the effect of the taste receptors in the mouth. 

Does the GI tract use the same bitter receptors to help reject food? Does the gut tell us “Stop eating!” when we consume something bitter?

Here is where green tea comes in. Green tea has bitter compounds, catechins, that make their way to bitter receptors lining the gut, the same receptors as in the mouth. In an elegant study, Won-Young Song and colleagues looked at the effects of catechins, and in particular (−)-epigallocatechin-3-gallate (EGCG) on hormone secretion in tissue-cultured gut cells and in mouse intestines.*

The result: EGCG induced the secretion of not one, not two, but three different hormones that are known to decrease appetite. Contrast this effect with, say, carbohydrates, which only induce the secretion of one or two of these hormones.

Does this mean that if you drink green tea you will lose your appetite?

(−)-Epigallocatechin-3-gallate, from Wikipedia 

Not necessarily — don’t go downing green tea by the gallon to get skinny. There’s a whole lot more to appetite than secretion of these hormones.

Furthermore, for many of you (as many as 50% of people apparently), EGCG isn’t all that bitter—whether this is due to this gene or different gene isn't known (there are at least two other bitter taste receptors that are activated by EGCG, and which may have a similar action in the gut. So if green tea doesn't seem very bitter to you it may mean that genetically you have receptors for EGCG that don’t work, either in the mouth or the gut. If so, you probably won’t have this hormonal response.  

And of course we must always give this caveat, namely humans may not have the same responses as mice or tissue culture cells... 

...as the saying goes, more research is needed!

* Won-Young Song et al. (−)-Epigallocatechin-3-gallate induces secretion of anorexigenic gut hormones.J Clin Biochem Nutr. 2015 Sep; 57(2): 164–169. Note: this article is freely available on the web.