Salty, sweet, sour, bitter, and umami are the five main tastes we are familiar with. Japanese for delicious , is a relatively new term for a taste that can be described as savoury or meaty. The taste is created by the combination of glutamate, which is one of the amino acids that make up proteins, and nucleotides. So, foods like pork, chicken, tomatoes, sea weeds, mushrooms, black olives, soy sauce, cheese, fresh corn, red bell peppers, and tree nuts such as almonds and walnuts give you the taste of umami.
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The taste system
The sense of taste is mediated by taste receptor cells that occur in clusters called taste buds. Each taste bud may comprise 50 to 100 taste receptors. Taste buds are located on the front and back of the tongue, the palate, and the epiglottis. They contain 3 types of taste receptors:
Type I receptors detect salt taste
Type II receptors detect sweet, bitter and umami tastes
Type III receptors detect sour taste
These taste buds report a sensation of taste to the brain via nerves. Many nerves, including cranial nerves VII, IX and X, are responsible for transmitting taste information from the mouth and pharynx to the brain. Taste buds are also continually bathed in secretions from the salivary glands, and excessive dryness can distort taste perception. There are many other causes of alteration in taste too. Actually, taste disturbances are classified into 4 main categories -
- Hypogeusia or decreased sensitivity to taste;
- Dysgeusia or taste confusion , such as foul, rancid or metallic taste sensation;
- Phantogeusia or phantom taste, which is a lingering unpleasant taste in the mouth even when nothing is in there;
- Ageusia or loss of taste, which is actually a rare condition since multiple nerve pathways are involved in taste sensation.
- Causes of alteration in taste
Taste disturbances are not a disease in itself but are signs or side effects of medical conditions or procedures. Some common causes of taste disorders are
- Chemotherapy
- Infection or inflammation
- Autoimmune disorders such as diabetes, hypertension, liver disease, kidney disease and thyroid disease
- Psychiatric causes such as anorexia, depression, etc.
- Denture or dental surgeries
- Natural aging
Sometimes, the cause of taste alteration can be due to zinc deficiency, medications, smoking, alcohol, or suboptimal oral hygiene.
#1 Chemotherapy
Taste alteration is a common but neglected side effect of chemotherapy. Almost 70 percent of cancer patients suffer from taste alterations. Rita is one of them. A breast cancer patient undergoing chemotherapy, she loved cheesy pasta with marinara sauce. But during treatment, she found the food repulsive. The pasta tasted like cardboard and the sauce was sharp and stinging!
Taste alterations can negatively affect the quality of life in cancer patients. Food aversion may
- Impede ability of to maintain social eating habits
- Cause mood disturbances and decreased social functioning
- May cause malnutrition
- Changes in taste perception are first perceived at the beginning of treatment and become more severe over time and may persist well after the chemo has ended.
Why does taste alter during chemotherapy?
Taste cells have a quick turnover. That means these cells grow fast and die and new cells are produced. The purpose of chemotherapy is to destroy fast-growing cancer cells. Because taste cells also grow fast, the drugs end up targeting taste cells along with the cancer cells. In many patients, taste alterations disappear shortly after the end of chemo because by then cell turnover is restored. Researchers believe that the chemo agents not only distort the receptor activity but affect the mucus and saliva production also. Again, these chemicals can pass into the saliva or diffuse into the oral cavity from plasma. [1]
A study on self-care strategies to cope with taste changes in cancer patients revealed that these varied somewhat according to chemotherapy regimen. In general, avoiding strong-smelling or -tasting foods, eating blander foods, drinking more water with foods, oral care before eating, and eating smaller, more frequent meals were reported to help.
The following tips might also help.
- Eating cold foods for metallic taste
- Avoiding beef
- Eating smaller, more frequent meals, which may be better tolerated and have less taste and aroma for bitter taste
Eating room temperature or cold foods and more flavourful protein food for patients who develop ageusia or a salty taste.
- Use acids such as lemon, lime and oranges if you develop a metallic taste.
- Use sea salt or add more salt to food that tastes like cardboard.
- Trick your taste buds by using different spices such as cumin, coriander, and cinnamon.
- Fat is a natural flavour carrier. Use healthy fats like olive oil, coconut oil, and nuts and seeds.
#2 Infections and inflammation
Patients with infectious diseases such as upper respiratory viral infection, oral cavity infection, or viral hepatitis, frequently develop taste abnormalities.
Toll-like receptors (TLRs), protein cells called interferon (IFN) receptors and other signalling components are present in taste tissue. These are released whenever the body senses the presence of virus, bacteria, and other pathogens. Researchers found that IFNs produced during infection/inflammation activate signalling pathways that may cause taste bud death and abnormal cell turnover, and skew the representation of different taste bud cell types, leading to the development of taste disorders.
#3 Autoimmune disorders
In autoimmune disorders such as diabetes there is an alteration in the neuro-autonomic regulation of the salivary gland that decreases the salivary flow. The decrease in the salivary flow causes many changes in the oral cavity including bad taste, taste bud cell alterations, infection in the mouth, and low production of protein gustin resulting in zinc deficiency.
#4Dentures and dental surgery
Taste alteration after a dental surgery or using dentures is pretty common say scientists. Many researchers reported that a removable prosthesis (for example, upper dentures) covering the palate may cause alteration in sense of taste and smell. The contact between the tongue and the palate helps in dispersing the food and bringing it into a closer contact with the taste buds. Now because of the upper denture this contact is disturbed as it interferes with the normal mobility of the tongue and cheeks, thus affecting the release of the food flavours.
Sometimes a dental surgery can also cause taste disorders as the possibility exists for injury to the peripheral nerves catering to the taste buds because of their anatomic proximity. Nerve damage may also be a result of local anaesthetic injection due to direct needle trauma.
#5 Zinc deficiency
Zinc helps in repair and maintenance of taste buds by aiding in synthesis of the protein gustin, which is linked to the building of taste buds. When there is a decrease in the gustin levels in the saliva, taste and smell disorders occur. Thus treating with zinc can help deal with taste disturbances.
For example, a study reported that zinc gluconate (50 mg, thrice daily) had a positive effect on taste disorders in a zinc-deficient population and also in patients with idiopathic taste loss, regardless of the serum zinc level. Zinc supplementation treats taste disorders by promoting the increasing the number of taste bud cells. Here are health benefits and source of zinc you need to know.
#6 Natural aging
Taste and smell alterations cause loss of appetite leading to malnutrition in older people. The problem is further exacerbated by disease and drugs. A study found that an elderly person with one or more medical conditions, and who takes an average of three medications, needs 11 times as much salt and almost three times as much sugar to detect these tastes in foods compared with younger people.
Scientists believe that reduction in the number of taste buds, or a decrease in the functioning of taste bud receptors may be the cause of taste disturbances in the elderly. Choosing alternative medicines, suggesting alternatives to coping with bland or bitter taste (see tips in chemotherapy), may help. Artificial saliva or sugar-free candy can help in cases of dry mouth.
#7 Drugs causing taste disturbances
Many medications affect taste, smell, or salivation though the mechanism by which these drugs affect taste or smell remains unknown. These include drugs in the following groups
- Lipid lowering drugs
- Antihistamines
- Antibiotics
- Anti inflammatories
- Bronchodilators and other asthma drugs
- Blood pressure medicines
- Parkinson's disease treatments and antidepressants
- In most cases, the taste alteration reverses by stopping the offending medication or treatment.
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