The taste of food is significantly improved by fats and oils; for example, fatty tuna, marbled meat, and cakes. Additionally, fats and oils are the best source of calories among nutrients. They are an energy source the heart and muscles during endurance activities. The essential fatty acids and fat-soluble vitamins contained in fats and oils are also indispensable for animals. Although it is prone to being viewed as unusual in modern society, the act of actively ingesting foods high in fats and oils is a very beneficial behavior for animals. Animals select foods that are high in fats and oils based on the delicious flavor of fats and oils. However, unlike the other five basic tastes, humans are unable to strongly and clear sense the taste of fats and oils. Consequently, almost no scientific focus has been placed on the flavor of fats and oils.
○ Oils and fats excite taste cells
Do fats and oils have a taste?—The answer to this question is still controversial. In recent years, our research group reported that fatty acid receptors CD36 (FEBS Lett. 1997 Sep 8; 414 (2): 461-4) and GPR120 (Biomed Res. 2007 Feb; 28 (1):49-55) are expressed on taste cells in the tongues of mice. Taste cells are cells that receive taste substances on the tongue and transmit signals to the brain. This suggests that, similar to other taste qualities (sweetness, umami, acidity, saltiness, bitterness), fats and oils may stimulate taste cells via receptors like other taste qualities to produce the feeling of delicious flavor. In recent years, it has been reported that these fatty acid receptors are also expressed in human taste cells. Consequently, this suggests the possibility that the delicious flavor of foods containing a large number of oils is caused by the excitement of taste cells.
○ The delicious flavor of fats/oils and obesity
As soon as the mouse is provided with 100% oil and fat, it will come over and start licking the food. Fats and oils are a feast for mice. In addition to consuming a very large amount, mice show very strong obsessive behavior toward fats and oils. Furthermore, it has been clarified that fats and oils increase dopamine, endorphin, and other substances in the brain that cause pleasure. In other words, the delicious flavor of fats and oils causes pleasure. The relationship between overeating and dopamine has also been reported in humans. Indeed, the pursuit of pleasure causes humans to become addicted to fats and oils and become obese.
Furthermore, there is a report indicating differences in how the delicious flavor of fats and oils is perceived. Specifically, people who sufficiently feel the taste sufficiently even with a small amount of fats and oils are less likely to become obese, while people who feel that flavor is insufficient with a small amount of fats and oils are more likely to become obese (Reviewed in Prog Lipid Res. 2016 Jul; 63: 41-9). It is surmised that the delicious flavor of fats and oils is due to the expression level of fatty acid receptors in taste cells and the responsiveness of the brain through mechanisms such as dopamine neurons.
The taste of fats and oils sometimes leads to obesity, but not all people who prefer foods high in fats and oils are obese. Our body has an inherent function for suppressing excessive fat intake, and if we eat too many fats and oils, we will always lose our appetite the next day. This is a healthy physiological state, and it is surmised that obesity due to excessive consumption of fats and oils is caused by some sort of malfunction in this eating suppression function. In recent years, we have found that stress is one factor affecting this function for suppressing eating (Physiol Behav. 2019 May 15; 204: 112-120). When a mouse is subjected to mild stress, its daily intake of fats and oils increases, thus resulting in severe obesity. Even in humans, stress may affect the taste and metabolism of fats and oils.
Although the deliciousness of fats and oils is a common sensation for all people, there are still many unclear details of this phenomenon and it is still a developing research field. The deliciousness of fats and oils makes humans happy, but sometimes leads to obesity, which is a major problem in modern society. However, abstaining from oils and fats would cause worsen the taste of food and lead to decreased quality of life. In order to solve this problem, our future research theme is to determine a method for maintaining good health while enjoying the deliciousness of fats and oils.
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