Do we taste fat?

The flavors that make good food taste delicious are dissolved in fat. Scientists used to think that when we ate fat, we tasted these dissolved flavors and that fat itself was tasteless. We now know that’s not quite true. But the efforts involved in isolating the “taste” of fat are considerable.

What do you “sense” when you eat fat?

To answer the question “Do we taste fat?” we first need to isolate taste from the other senses. Fats have a very distinctive texture. They have a thickness, called viscosity, and a slipperiness, called lubricity. If Jack Sprat would eat no fat, it could be because he disliked the slimy texture.

When a taste researcher asks a subject if a certain food “tastes” like fat, the subject could be detecting the texture. “Fat molecules literally press against the taste buds, producing a tactile sensation that’s interpreted by the brain as viscous, slippery or greasy.”

Fats also have an odor. Even monkeys can smell cream. As with most complex flavors, when you pinch your nose, it’s more difficult to detect fats.

When fats are exposed to the air, they combine with oxygen: They oxidize. Manufacturers add antioxidants, such as BHA and BHT, to prevent oxidation and its offensive, rancid odor. Oxidation speeds up when fats are exposed to heat or light, which is why we keep food in cold, dark refrigerators.

In addition to texture and odor, there’s another clue that tells us we’re eating fat: Immediate activity in our digestive system. Fats need to be broken down before they can be absorbed. As soon as you eat fat, the pancreas releases a substance that breaks down complex fatty acids into simpler ones. The gall bladder is also involved. Normally oil (fats) and water don’t mix. The gall bladder secretes bile, which disperses fatty acids in liquid, like mixing cream into milk. These emulsified fats are more easily absorbed by the digestive tract.

Since these digestive processes begin as soon as we taste fat, they could signal the body that we’re eating fat. Just putting fat in your mouth will change the level of fat in your blood. So when scientists want to determine if people (or rats) can detect the taste of fat, they need to eliminate not only texture and aroma, but also the automatic digestive response.

When a rat is as good as a human

We’ll never know for sure what it’s like for a rat to taste food. We do know that they need to be very discriminating. Unlike most species, rats lack the muscles that would allow them to vomit. Rats eat a wide variety of foods, just as humans do, and what they eat is very similar to what people eat. (They love chocolate.) The reason rats have flourished for centuries in close association with humans is probably due to our similar food preferences. This makes them an ideal subject for experiments on taste.

Normally rats detect fats easily and prefer foods with fat. But do they really “taste” fat? Experimenters can minimize the texture component of fat by diluting it. They can measure the reaction to food so quickly that they eliminate feedback cues from the digestive system. When they do these things, rats still prefer fat. But, when experimenters eliminate the sense of smell, rats are less able to detect fat.

What about humans? Would they respond to fat if they couldn’t smell it? To test this hypothesis, scientists offered subjects cream cheese on crackers in three different ways. The first group was only allowed to smell the cream cheese. The second group was allowed to smell it and taste it. The third group wore nose plugs while tasting. Experimenters measured the rise in blood fat levels in these three groups. Smell alone did not increase blood fat levels. Taste alone, without smell, increased blood fat levels just as much as both tasting and smelling. The conclusion: The body responds to the taste of fat.

But is this really taste, the way we taste sweet, sour, and bitter?

A gene that controls the taste of fat

With rats, experimenters can knock out the olfactory bulb to eliminate smell. They can prevent food from going down the throat, stimulating digestion, by esophageal ligation. (I hope that’s reversible.)

Isolating the taste for fat in humans is much more complex and requires that experimenters go to great lengths. They use refrigeration to prevent oxidation. Subjects use a mouth rinse of capsaicin (the main ingredient in chili peppers) in deionized water just before each taste test. The nostrils are blocked with plugs to eliminate smell. Exclusively red lighting eliminates visual cues. Subjects are carefully screened: Nonsmokers, not pregnant, supertasters. Researchers prepare a range of concentrations of fats mixed with mineral oil, so all concentrations will have the same texture. When all that is done, they test for sensitivity to fats.

What do they find? We can detect fat in the mouth. In fact, we have a taste receptor for fats in our taste cells.

In a previous post I explained that taste buds contain taste cells that contain taste receptors: Proteins that change shape in response to specific chemicals in food. Researchers already knew we had taste receptors for bitter, sweet, and savory. They also knew that the bitter taste receptor had a genetic component: Nontasters can’t detect certain test chemicals because they’re genetically programmed never to produce a taste receptor for them.

It turns out there’s a receptor protein that can detect fats (fatty acids). It’s called the CD36 receptor protein, and it’s located on the surface of cells in a variety of tissues, including the digestive tract, heart tissue, skeletal muscles, and fat cells. The CD36 receptor appears to help fats pass from the outside of a cell to the inside.

Here’s the interesting part: There are CD36 receptors on the tongue. They happen to be located primarily in the taste buds at the sides and back of the tongue, not in the ones on the front of the tongue that are so numerous in supertasters.

Oversimplifying things a bit, it turns out there’s a gene for CD36 receptors. If you “knock out” this gene in rats, they don’t have any CD36 receptors. Without CD36 receptors, rats no longer prefer fatty foods.

Humans have different levels of CD36 “expression.” It’s possible that these differences account for an individual’s preference for fatty foods. People with low levels may not “taste” fat, and so they may not prefer fatty foods, whereas people with high levels of CD36 may have a strong preference. As far as I know, this is still at the level of scientific conjecture.

Not the next diet pill

Lowering your CD36 level is definitely not the next diet pill. Theoretically you could genetically “knock out” CD36 receptors in humans, but that would be a bad idea. The CD36 protein performs a number of vital functions throughout the body, not just on the tongue. If we could selectively lower the number of CD36 receptors on the tongue while increasing them in the muscles, then the muscles would take in and burn more fat. Not only would this mean we’d store less fat, but our muscles could work harder and longer. Perhaps sports scientists are working on this as the next secret weapon for an upcoming Olympics. The processed food industry certainly has an interest in understanding CD36. If they knew how it worked, they might be able to create artificial fats that “taste” like real fats without the calories.

So, in the end, do we “taste” fat? As I said, it’s a bit complicated. Every so often you see headlines like “‘Taste bud’ for fatty foods found” or “Tongue sensors seem to taste fat.” But I’m not yet convinced we “taste” fat in the same way we experience the taste of sugar, salt, sour, and bitter. It’s still an interesting and open question.

Related posts:
A matter of taste
How do you taste?
Orange juice and toothpaste
What is a supertaster?
The genetics of supertasting
Are you a supertaster: Do you really want to know?
Are you a supertaster: Look at your tongue
Are you a supertaster: How does PROP Taste to you?
Are you a supertaster: DNA testing
Why do we love high-fat foods?
The taste advantage
“Killer” grapefruit?
Grapefruit and the Pill
This is your brain on sugar — and sugar substitutes
The Pepsi challenge: How beliefs affect what you taste