Abstract

TASTE PERCEPTION IN DIAGNOSIS AND TREATMENT- AN AYURVEDIC PERSPECTIVE

TASTE PERCEPTION IN DIAGNOSIS AND TREATMENT- AN AYURVEDIC PERSPECTIVE

According to Ayurveda, all forms of matter are derived from thecombination of five primordial elements such as pṛdhvi (“earth’), ap(“water”), tējas (“fire”), vāyu (“air”) and ākāśa (“sky”),collectively called pañcamahābhūta(the great primordial elements). The pañcamahābhūta do not exist inindividual states. They always stay in combinations, the ratios being dependenton the matter in question. All substances in this world are medicinal and theycan be put to good use if one knows their medicinal value. Ayurveda states thatthe medicinal qualities of matter are judged on the basis of five factors viz.,taste (rasa), qualities (guṇa), potency (vīrya),post-digestive taste (vipāka) and specific action (prabhāva).Unlike Western science, Ayurveda considers six taste modalities such as sweet (madhura),sour (amḷa), salty (lavaṇa),pungent (kaṭu), bitter (tikta) andastringent (kaṣāya). These six tastemodalities either increase or decrease tridōṣa consisting of vāta,pitta and kapha. Madhura, amḷa and lavaṇa pacifyvāta and aggravate kapha. Kaṭu, tikta and kaṣāyaaggravate vāta and pacify kapha. Madhura pacifies pitta.Amḷa, lavaṇa and kaṭu aggravate pitta. Tiktaand kaṣāya pacify pitta and kapha.

The concept of taste influencing pharmacological actions was deeplyembedded in traditional medicine of China, Greece and India. However, Ayurvedamade full use of this knowledge. Some modern research lends support to it.Fifty years ago, Roland Fischer and coworkers had demonstrated that thebitterness of certain compounds correlated with their pharmacological activity.They called attention to a general relationship prevailing between the tastethreshold of stereospecifc drugs and their biological activity (Nature1963, 200: 343–7. Arzneimittel Forschung1964, 14: 673–86). To cite anexample, with 1-quinine and d-quinine, as well as with d-amphetamine andl-amphetamine, the l- form of each drug pair is the biologically more potentcompound. Correspondingly, humans can taste the more active compound in a lowerconcentration (lower taste threshold). Based on these findings they came toregard a subject’s oral cavity as a pharmacological test preparation in situand the taste response as a sensory expression of pharmacological activity (Nature1965, 207, No. 5001: 1049–53, Recent advances in biological psychiatry,ed. J. Wortis, 183–95, Plenum Press).

In a subsequent publication they reported a statistically significantpositive correlation between quinine taste thresholds and the cumulativetrifuoperazine dose sufficient to induce extrapyramidal side-effects likeslowness of movement, tremor and jerky movements, for 48 acutely ill mentalpatients. Patients with high quinine taste thresholds, for instance, neededhigher trifuoperazine dosage for the induction of extrapyramidal side-effects (Arzneimittel-Forschung1965, 15: 1379–82.).

Ibuprofen is a non-steroidal potent modulator of inflammation andanalgesia. It is a non-selective inhibitor of the cyclooxygenase enzymes COX-1and COX-2, but not of lipoxygenase, which catalyses steps in the biochemical inflammationpathways derived from arachidonic acid. Newly pressed extra virgin olive oilcontains the aldehyde oleocanthal, whose pungency induces a strong stingingsensation in the throat, very similar to that caused by solutions of ibuprofen(Chemical Senses 2001, 26, no. 1: 55–65). Like ibuprofen, oleocanthalcaused dose-dependent inhibition of COX-1 and COX-2 activities. But it had noeffect on lipoxygenase in vitro (Nature 2005, 437, no. 7055: 45–6).This finding has striking similarity with the teachings of Ayurveda and is oneof the rare scientific reports noting common pharmacological activity forcompounds with similar taste. As such, it is consistent with the tenet ofAyurveda that the similarity of taste of substances indicates similarpharmacological activity.

It is often asked whether it is possible to identify the rasa, guṇa,vīrya, vipāka and prabhāva of herbal drugs outside theformulary of Ayurveda. In addition to vegetables like cabbage (Brassicaoleracea), carrot (Daucus carota), potato (Solanum tuberosum),Lady’s finger (Abelmoschus esculentus) and tomato (Lycopersiconlycopersicum), many fruits such as pineapple (Ananas sativa),mangosteen (Garcinia mangostana), papaya (Carica papaya),custard apple (Annona squamosa), guava (Psidium guayava),sapodilla (Manikara achras) and litchi (Niphelium litchi)were introduced into India by the Portuguese and English. Though they havemedicinal value, all of them are alien to Ayurveda. These herbs can besuccessfully incorporated into Ayurveda once the five ayurvedic features areknown. Taste sensitivity studies using juices of these herbs are essential inthis regard.

The concept of taste is important in diagnosis of diseases as well. Asdiseases spring from the derangement of tridōṣa, the patient experiencescravings for food and beverages that have tastes with the ability to restorethe steady state of tridōṣa. The tastepreferences of the patient also aid the physician in diagnosis. For example,interest in sour taste is a sign of diminution of blood. Interest in sour,salty and pungent tastes is a prodrome of fever. Similarly, aversion towardssweet taste is also a prodrome of fever. In addition to these, many forms ofpseudogeusia are also mentioned in Aṣṭāṅgahṛdaya. These are instances oftaste sensations felt by the patient in the absence of any external stimuli. Tocite some examples, sensation of sweet taste in mouth is a prodrome ofpolyureic diseases as well as consumption. Sensation of pungent taste is a signof morbid pallor and fever caused by derangement of pitta. 

Most of the conditions of pseudogeusia mentioned in Aṣṭāṅgahṛdayaare related to diseases like grahaṇi (diarrhea-like conditions), aruci(anorexia), chardi (emesis), tṛṣṇa (excessive thirst), kāsa(cough), pāṇḍu (morbid pallor), pratiśyāya (rhinitis) and rājayakṣma(consumption). It will be worthwhile to investigate whether these pseudogeusicconditions disappear following ayurvedic treatment of these diseases. Suchstudies are essential, as appropriate studies on the treatment of gustatorydysfunction are notably lacking (Archives of Neurology 2003, 60, no. 5:667–71).