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Restaurant menus for Valentine’s Day can be described in one word: decadent. From molten chocolate cake to marbled steaks, fat makes these foods so palatable. For a long time, scientists thought that we find heavy foods more appealing because of their mouth feel and aroma. However, recent studies suggest that the tongue might be able to taste fat, along with the five basic tastes—sweet, sour, salty, bitter and umami. This could explain why we are extra perceptive to richness in foods.

As we chew and savor, chemicals released from the food stimulate proteins called taste receptors on the tongue’s taste buds. Each basic taste has dedicated taste receptors, and the basic tastes blend together to give food the flavor we perceive. Contrary to popular belief, the tongue does not have specific regions for each basic taste. Every taste bud has all the taste receptors. How do scientists judge if a flavor is really a basic taste? Many define a basic taste as having all of the following:

• a source,
• taste receptors that respond to it,
• a signaling pathway between the taste receptors and the brain so that we perceive the taste,
• sensitivity to it that’s controlled by the body, and
• subsequent effects on the body’s physiology.

So far, the prospect of fat becoming the sixth taste is looking good. Researchers identified the taste source: molecules in fat called fatty acids. They have a few ideas on which receptors fatty acids from fat stimulate, with the strongest evidence supporting a protein called CD36. Along with studies showing that stimulating CD36 sends signals to the brain, other studies have reported that people can tell fattiness without knowing appearance, smell and texture. Certain hormones also appear to control the craving for fat, at least in mice, and there’s evidence that fatty acids on the tongue have physiological effects—they signal to the intestines to get ready to digest fat.

Researchers are also exploring if obesity is related to fat as a taste. Obese mice seem less sensitive to fat and prefer the high-fat chow as a result. People who underwent gastric bypass surgery to treat obesity have said that fatty meals became less appealing after the procedure. More work needs to be done to say conclusively that fat is a basic taste, but imagine eating molten chocolate cake with a dash of “taste of fat” powder. Too decadent?

Maggie Kuo, PhD, is the former Communications and Social Media Coordinator for APS. Catch more of her writing in the Careers Section of Science Magazine.