The experience of bitterness is one of the first things we remember as children. It haunts most people in the form of an oddly intense aversion to raw vegetables. When most people think of uncooked radishes, broccoli, or Brussel sprouts, the negative reactions are almost immediate and visceral. This is because, generally speaking, bitterness is perceived as unpleasant and off putting. It sets off bells and whistles in the brain that something is atypical about the thing that we are consuming at the moment. The primal reaction in young infants and and toddlers is to spit out the offending substance as quickly as possible. As human beings grow older many of us are better able to tolerate these bitter tastes and, as is the case with good number of people, actually enjoy the nuance of the flavor profiles they create. However there are some who still cannot bring themselves to tolerate the experience in the least. According to a 2006 study by Kendra Bell and colleagues, there is a phenotype, an observable characteristic, that is present in approximately 70 percent of the Caucasian population in the United States alone that causes them to notice the flavors of phenylthiocarbamide (PTC) and 6-n-propylthiouracil (PROP), the two most commonly studied bitter constituent classes found in cruciferous vegetables. It lingers in their mouths and overwhelms most of the other flavors when it is present. Most people deem to rather cook their vegetables in ways that mitigate the intensity of the chemicals that cause this. Many recipes try to mask the flavor with sours, such as vinegar, or umami flavors, such as pork and turkey. Even while there are a great many of us that see bitterness as a delightful way to break up the monotony of other tastes, he seeming consensus among the majority of people is that bitterness is simply not a flavor to relish in and of itself.
Perhaps it is related to an ancestral self-preservation mechanism by which our early mammalian predecessors identified which plants were potentially harmful (Drewnowski, 2000). This might well be valid, as several of the constituents found in plants that cause bitterness can be quite toxic in certain doses. One prime example being processed Aconite (Aconitum carmichaelii) a primary ingredient in many Kampo and Traditional Chinese remedies. The bitter alkaloidal constituents that make it medicinal also serve as potent poisons in any dose greater than used in these medical systems (Anjiki, 2011). With so many poisonous herbs and fungi in the world, self-preservation is a perfectly reasonable conclusion. However it should be more realistic to say that the development of the concept of bitterness is a consensual matter between plants, their environment, and the animals that consume them.
In order to paint a clearer picture of that idea, we have to remember that bitter constituents are intrinsically unpleasant in their own right as a chemical class. Flavor aside, many are antimicrobial or fungicidal, meaning that they prove toxic to many species of bacteria and fungus that have no means of taste. The chemical make-up of these constituents can interfere with certain processes in the life cycle of these creatures, often resulting in death. It is stating the obvious to point out that it is rare that something poisonous has an enticing flavor. Fruits that are well propagated through fecal fertilization are often sweet or even have a smell that resembles some savory rot, as is the case with durian fruit (Durio zibethinus). Most bitter plants are either toxic, pretending to be toxic, medicinal, or some combination thereof. The plants that began producing these phytochemicals did so to send distress signals between different parts of its body and as a defensive measure against being eaten or infected.
This may all sound rather negative and dreadful at first, but it is the primer for the greatness of evolutionary ingenuity in hominids. Our early ancestors regularly ingested a multitude of phytochemicals on a daily basis and used them as the first medicines that we as a species had available to us. Our bodies, through evolution and adaptation, had come to be able to metabolize a number of these chemicals to our benefit. Interestingly enough, though 70 percent of the modern U.S. Caucasian population has the phenotype to taste PTC and PROP, the remaining percentage perceives of the taste as mild or non-existent. Perhaps through these non-tasters, humans learned to tolerate the shock of the more bitter herbs and through continual consumption learn to integrate them into our daily lives. Not only could we eat many bitter plant greens, like dandelion (Taraxacum officinale), as food, but we could use them as medicine when we fell ill. Still, eating aromatic and bitter plants regularly as foodstuffs was not the most pleasant of things, so selective breeding alongside various cooking methods became our tools for getting the most nutritional benefit out of plants that might be too difficult to eat regularly. The brassicas were bred into our most common vegetables today, including broccoli, cauliflower, kale, and cabbage. Celery and other apiaceae became part and parcel of our diet through cultivation. While this process removed some of the most pungent flavors, it did not alleviate the actual bitterness of many of these crops. In fact many of the most nutritious of these are indeed the bitterest. Many people will cook these crops with sweets, acids, or simply roast them to bring out other qualities and ameliorate the acrid flavor that may be perceived. This is not always to the detriment of the herb. Thanks to the multitudinous constituents that cause these flavors, not every combination of sweet and bitter will turn out the same (Breslin, 1996). The combinations that we have come up with through out the years have in some instances served synergistically with each other to improve bio-availability of certain micronurients or to simply create a unique flavor that intrigues our taste buds. Coating bitter vegetables in oils, some rich in omegas, can pacify the shudder inducing flavor in them. Broccoli rabe (Brassica rapa) combined with butter and garlic is a common way to enjoy one of the more bitter brassicas out there. In the end, it is impossible to deny that, no matter what flavorings or pairings we come up with, a diet rich in green vegetables is the healthiest choice. Though our ancestors might not have had a scientific explanation for this, they certainly could associate the correlative effect of feeling good health and the consumption of dark bitter greens.
Some modern studies can shed a better light on this relationship. The most common chemicals in regularly consumed produce that cause bitterness to occur are phenols, polyphenols, flavonoids, isoflavones, terpenes, and glucosinolates (Drewnowski, 2000). It just so happens that these are the very compounds that appear to have a effect in reducing incidence of cancer and heart disease in people who consume higher amounts of these nutrients. These secondary plant metabolites are proving to be more and more critical in the matter of good heart health as many of them have proven to inhibit platelet aggregation. Isoflavones in soy have been shown to serve as antioxidants particularly against LDL cholesterol. The phenolics in more bitter varieties of olive oil provide anti-inflammatory and antioxidant properties (Visioli, 2000). In study after study we have found that these various micronutrients are vital to a healthy diet.
It has also been noted in recent years, that T2R bitter taste receptors are located throughout the GI tract, as opposed to only in the mouth and upper GI tract (Rozengurt, 2006). Some theorize that this is perhaps to mitigate any possible irritating or toxic stimuli, usually having a bitter taste associated with it, that might have made its way into the system. In rats, the introduction of bitters into the gastric chamber delayed gastric emptying, perhaps to give the lower gut time to prepare. The T2R receptors have been shown to have a direct relationship with the enteroendocrine response system, causing the release of hormones that might serve as protective agents in this matter (Egan, 2008). While the system may have originally evolved to provide a protective function, it has the secondary purpose of toning and strengthening our immune and digestive responses accordingly to the nature of the world around us. Not only are we safer thanks to this system but more robust overall.
When examining the influence of spices on digestion in 2004, Platel and colleagues noted that fenugreek, ginger, capsicum, and turmeric all had an effect on stimulating bile secretion in the lower GI tract, while black pepper did not however. This seems to lend credence to the idea that the bitter elements of these herbs, not the pungency, is what seems to have a direct influence on the endocrine secretory system.
Interestingly, one of the most bitter plants known to humans, Gentian (Gentiana spp.), is generally considered one of the best digestifs according to traditional practice. Its primary bitter constituent is known as Amarogentin and is said to be the most bitter substance verified. It also has shown DNA-protective properties, cancer preventative properties, and anti-microbial properties, specifically against a parasitic protozoans (Singh, 2008). Several other constituents have stomach protective, soothing, and anti-spasmolytic properties. In herbal medicine, practitioners use this remedy to aid with dyspepsia, improve digestion, and ameliorate diarrhea. Traditional medicine systems took note of the effects, perhaps without seeing all the mechanisms involved, but made good use of the properties regardless. This plant is a prime example of how humans, upon tasting the most bitter of herbs imaginable, waited and observed what it could do for them. This taste and see method, however crude, proved which plants could be used in large nutritional amounts, which plants should be taken sparingly as medicine, and which plants should be avoided entirely or needed further processing to manage.
The beauty of bitterness is in its expression. It can be harsh and provocative or it can be mild and intriguing. It is our guidebook to the natural world. Not only does it keep us safe by stimulating our natural aversion response, but in moderate doses, it helps to medicate and protect our internal systems from more insidious dangers like heart disease, atherosclerosis, and neoplasms. When we take this flavor in, it lets our body know that something that will powerfully alter the body is on the way. It serves as a kind of temperance factor we might not even think about. In helping us to avoid dangerous foods as children, unaware of what is poisonous and what is not. As we age, our tastes change as well, allowing for more nuance and enjoyment of bitter flavors. Coincidentally, diseases such as the aforementioned arise around this time in life. It is as if our cravings begin to reflect our needs. For herbal clinicians, bitters are a powerful and inexhaustible resource when it comes to providing tools for clients. They are variable and applicable in almost every situation. The primary mode of administration for many herbs is orally and therefore it is beneficial to include herbs that promote efficient digestion in any edible formula. Clinicians can use bitters of both hot and cold energetics to send the tonics to the systems in which they can prove most effective. Bitter foods and drinks are the primary line of defense that people can employ in improving their overall life experience. The benefits of improved health are clearly evident in populations that embrace the intense and subtle flavor variety that bitter combinations can provide. Bitterness can be versatile and applicable in a number of aspects of daily life. Tinctures, tonics, tablets, salads, or smoothies, bitter-taste constituents can be manipulated to be taken in myriad ways. This versatility means that even those who disdain this flavor can find ways to get the chemical properties into their body. So while bitterness is not a flavor most people flock to, it is an important and vital flavor that has shaped our lives and can help us in more ways than most of us know.
References
Anjiki, N., Hosoe, J., Fuchino, H., Kiuchi, F., Sekita, S., Ikezaki, H., … & Goda, Y. (2011). Evaluation of the taste of crude drug and Kampo formula by a taste-sensing system (4): taste of Processed Aconite Root. Journal of natural medicines, 65(2), 293.
Bell, K. I., & Tepper, B. J. (2006). Short-term vegetable intake by young children classified by 6-n-propylthoiuracil bitter-taste phenotype. The American journal of clinical nutrition, 84(1), 245-251.
Breslin, P. A. (1996). Interactions among salty, sour and bitter compounds. Trends in Food Science & Technology, 7(12), 390-399.
Drewnowski, A., & Gomez-Carneros, C. (2000). Bitter taste, phytonutrients, and the consumer: a review. The American journal of clinical nutrition, 72(6), 1424-1435.
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Mancuso, G., Borgonovo, G., Scaglioni, L., & Bassoli, A. (2015). Phytochemicals from Ruta graveolens activate TAS2R bitter taste receptors and TRP channels involved in gustation and nociception. Molecules, 20(10), 18907-18922.
Platel, K., & Srinivasan, K. (2004). Digestive stimulant action of spices: a myth or reality?. Indian Journal of Medical Research, 119(5), 167.
Rozengurt, E. (2006). Taste receptors in the gastrointestinal tract. I. Bitter taste receptors and α-gustducin in the mammalian gut. American Journal of Physiology-Gastrointestinal and Liver Physiology, 291(2), G171-G177.
Singh, A. (2008). Phytochemicals of Gentianaceae: a review of pharmacological properties. International Journal of Pharmaceutical Sciences and Nanotechnology, 1(1), 33-36.
Visioli, F., Borsani, L., & Galli, C. (2000). Diet and prevention of coronary heart disease: the potential role of phytochemicals. Cardiovascular Research, 47(3), 419-425.