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Your sense of taste is being barraged by the loads of salt, fat, and sugar found in double cheeseburgers, waffle fries, and milkshakes.

Did you ever notice that all fast food joints have the same "smell"? Hot oil mixed with eau de onion? Some people have even half-jokingly suggested there may be a secret addictive chemical pumped in.

"[The sense of taste] is in a bad way," Steven A. Witherly, PhD, president and CEO of Technical Products Inc., a food consulting firm in Valencia, Calif., tells WebMD. "Fast food has ridiculously high levels of salt, fat, and sugar -- and the brain likes salt, fat, and sugar."

Everyone has about 10,000 taste buds on his or her tongue (although these may thin as people grow older). "Fast food does not so much dull the taste buds as affect how the brain processes that taste as pleasurable or unpleasant," Witherly says. Hormones such as insulin and leptin also affect the brain's impression of a given food. "Snack food is affecting how we process food."

Sense of Taste Deceptively Simple

Traditionally, scientists have said the sense of taste can detect salty, bitter, sour, and sweet. Now, Witherly says, a fifth taste found to be directly received by the tongue is umami (pronounced "ooo-mommy"), which is the monosodium glutamate (MSG) taste. Parmesan cheese is huge on this, 1% by weight; soy sauce is also 1%. Umami is tied to a protein found in breast milk that the brain is attracted to.

Witherly also says the human sense of taste can recognize the hot pepper taste and another he calls the fatty acid taste.

Marcia Levin Pelchat, PhD, a psychologist and research scientist with the Monell Chemical Senses Center in Philadelphia, tells WebMD the hot pepper taste is more of a skin irritation signal in the inner cheek rather than a taste. (Carbonation, she says, provides a similar irritation that can be studied by taste researchers.)

Whatever triggers them, your sense of taste picks up the signal and sends it to the brain for interpretation and combination with other tastes.

Certain sensations -- like salt, sugar, and to some extent, the sensation of fat -- become an expectation. People want to experience them. "I have seen people's brain scans light up in the pleasure centers when fat passes over their tongue," Witherly says.

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