Is Fat the Sixth Basic Taste?

The ancient Indian system of medicine, Ayurveda deems sweet, salty, sour, pungent, bitter, and astringent as the basic tastes.

Don't you just love to chow down a slab of dark chocolate or just crave for a bite of the oh-so-enticing strawberry? Who doesn't?! But the next time you bite into a piece of chocolate, try pinching your nose so you don't get to smell it as much. We're sure that this time you might not enjoy the mouthful of your beloved dark chocolate very much.

That's the power of the sense of smell! Our perception of flavors comes from a combination of the taste and smell of the food that we eat.

Taste is basically the sensory perception of the chemical substances present in food.

It is the biological machinery that detects the chemicals present in our food and determines whether the food is fit for consumption or not. We usually classify taste into five categories―sweet, sour, salty, bitter, and umami.

When we taste something sweet, our body infers that the food is rich in carbohydrate, and thus, is fit for consumption.

Similarly, when we taste something umami, our body infers that the food is rich in amino acids, like glutamate, and is therefore required by the body. When we taste something bitter or sour, it is understood that the food is rich in minerals, like sodium, or has free hydrogen ions.

However, extremely sour or bitter taste is inherently avoided as the food may have gone bad or may contain toxins.

Fats are broken down by the lipase found in our mouth, but the source of this lipase is unclear. This so-called lingual lipase can either be of indigenous or microbial origin. These fats are broken down to fatty acids which are easily detected by their receptors. The threshold for the detection of these fatty acids is quite low as compared to that of carbohydrates or amino acids.

Recently, a taste receptor, CD36 receptor has been discovered. This receptor is found on the taste bud cells of humans and are seen to bind with the long fatty acid chains. It has been suggested that high levels of CD36 expression directly correlates with the sensitivity in detecting oleic acid, and may, therefore, play a role in detection of taste in humans.

This receptor works along with G protein-coupled receptors, GPCR120 and GPCR40, which help in signal transduction and the release of calcium. This released calcium activates the monovalent cation channel, TRPM5, that is involved in the processing of the taste.

When fatty acids bind to their receptors, there is a transduction of chemical energy into electrical impulses. These impulses are transferred through the afferent nerve fibers via neurotransmitters like noradrenaline and serotonin. Whether these neurotransmitters are released in response to the taste of fat is still not understood.

The body releases more amount of fats in the blood when the receptors on the taste bud cells were stimulated with fats. This increase was not seen when non-fat substitutes were used. This was suggested via an experiment where the participants were asked to put either butter or non-fat butter substitutes in their mouths and then spit them out. Participants who were given butter showed an increased level of plasma triacylglycerols.

It has also been suggested that individuals with a higher sensitivity to fatty acids (more number of receptors) have a lower body mass index (BMI), and vice versa. Some studies have also suggested a relation between the sensitivity to fatty acids, i.e., number of receptors for fatty acids, and dietary preference to fatty acids.

Although very little amounts of fatty acids can easily be detected, the perception of the flavor of fats only comes with the associated aroma and texture.

In an experiment, where the participants were given a solution of fatty acids in an increasing order to determine the threshold beyond which fatty acids could be detected by humans; the participants could only recognize the presence of something unusual.

They couldn't identify the taste as distinctly as other tastes. This might be one of the biggest drawbacks in proving fat to be a taste.

Whether to consider fat as taste or not is still open for debate, we hope that further research on this matter would help us to give a more conclusive answer in the near future.