The tongue-map-myth and bitter foods

Updated: Mar 18, 2019

Think about your digestion. Are you thinking about your stomach or did you picture your mouth? Because that's where it starts...


There is literal digestion of carbohydrates that occurs in the mouth through the enzyme "salivary amylase".


But then there are also the neurological triggers caused by different tastes. Although researchers in Columbia have recently found that the “taste map” we were taught at school is wrong (Barretto R., et al. 2015), we still have the ability to detect 6 main flavours. Namely; salty, bitter, sour, sweet, water and umami (protein). The taste receptors (TRs) for these flavours lie throughout the tongue and are not localised to one area. The TRs dedicated to sweet flavours are comprised of one type of protein that is coded for by 3 genes and detects sugar. The TRs for umami (protein) are similarly simple and they detect amino acids (Buchanan et al., 1993). Sour tastes are slightly more complex. They have two receptor subtypes that detect hydrogen ions (responsible for acidity). There is also a receptor for fats and a receptor for salts. All of which are made from 1 to 5 genes with 1 to 3 subtypes. But then we turn to the bitter taste-receptor family. This is known as the T2R receptor family and it has 20 different subtypes and is coded for by 34 genes (McCraty et al., 1998). This gives these TRs the ability to detect over 100 unrelated, bitter compounds.


Why do the bitter tastes receptors need to be so complex?

The bitter flavour is used as a signal for potential poisoning from the vegetable kingdom. A low concentration of bitterness is tolerable; however, a high concentration can lead to vomiting. (...handy if you’ve just consumed poison!) Not only are these TRs used to detect poisoning, but they also serve as a trigger, via the vagus nerve, for bile and enzyme secretion from the liver. In turn, this increases the efficacy of digestion and the ‘detoxification’ pathway of the liver, while decreasing the rate of digestion and leaving you feeling fuller for longer. The bitter flavour also supports the function of the liver. For the creative-minded out there, I could say that bitter foods ‘tickle the liver into being awake, alive and challenged’. The other benefit of eating bitter food is that it is an appetite-regulating pathway. If our primal selves sense that we might be eating poison, then it makes sense that we would eat lower quantities of that food. This is also an important dietary aspect for diabetic patients (type 2) to utilise because bitter tastes lower blood glucose (sugar) levels. (Guido Mase, 2013)



So… bitter flavours help to reduce caloric intake, increase effective digestion and detoxification of the liver and decrease blood glucose. Yet this flavour is an outcast within the Western Diet.

Traditionally, people would forage to supplement their meals. They might add stinging nettle, dandelion, wild rocket or a number of green leaves to a stew or soup. Sweet gums or honey were rare to come across, but when you did they evoked a deeply satisfying sensation. We have discussed bitter foods and how the neurological trigger in the mouth leads to changes in digestion. However, the neurological triggers of sugars largely remain within the mind and do little to activate digestion. This taste makes us feel loved, safe and rewarded and we naturally begin to seek it out. In small doses, this is a beneficial response because it provides energy-dense meals. However, as we have moved away from a foraging lifestyle and stepped into a world of supermarkets our ‘small, sweet dose’ has become the main component of our daily diet. In the small intestine, sweet carbohydrates are met with a sluggish enzymatic response. In turn, this leads to pieces of carbohydrates fermenting in the stomach and that leads to gas, bloating and halitosis (bad breath). A sluggish gut also becomes inflamed and the inflammation irritates nerve endings along the gut and ultimately reaches the central nervous system via the vagus nerve. And this is partially how the vicious cycle between food and mental behaviours begins. But that is an incredibly simplified version of the gut-brain axis.


I realise that bitter foods are so lost in our supermarkets that many of you might not know how to incorporate them into your diet. How about a cup of green tea (without sugar or honey) before a meal? Or try roasting minced dandelion roots in a pan until they are dry and slightly nutty. Store this in an air tight container and use in a coffee plunger whenever you need a cup of “coffee”!

Alternatively, here is my ‘Forager’s soup’ recipe:


1. Forage for a handful of dandelion leaves (best foraged during spring) and a large handful of nettles.

I usually put a shopping bag over my hand and pick them straight. I like to cut the leaves straight into the rinsing bowl to avoid being stung. Then I pour boiling water with a tiny bit of apple cider vinegar (to remove anything unwelcome on our plants…it’s not always possible to avoid pollution and occasional dog wee when foraging) over the foraged matter.

2. Chop up a carrot, a potato, a tomato, a clove of garlic and half an onion.

3. Add to a pot with 1 tablespoon of olive oil and lightly simmer until things start to smell good.

4. Add the washed, nettle and dandelion leaves to the pot and pour in the water to adequately cover the vegetables.

5. Add some salt and let it boil until cooked. I normally use a hand blender to make it smooth as I do not particularly like chunky soup.


Enjoy! Keep your liver, your gut and your mind happy.


References

Barretto R., Gillis-Smith S., Chandrashekar J., Yarmolinsky D., Schnitzer M., Ryba N., Zuker C. (2015) “The neural representation of taste quality at the periphery”. Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.

Buchanan LM., Cowan M., Burr R., Waldron C., Kogan H. (1993) “Measurement of Recovery from myocardial Infarction”. Nursing Research.

Guido Mase. (2013) “The Wild Medicine Solution”. Lake Book Manufacturing Inc, United States of America.

McCraty R., Barrios-Choplin B., Rozman D., Atkinson M., Watkins AD. (1998) “The Impact of a New Emotional Self-Management Program on Stress”. Integrative Physiological Behavioural Science.

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