Why fat is delicious and the mystery of fat perception

Whether it’s sizzling bacon or a generously iced donut, fatty foods are delicious. There’s no getting around it.

As the authors of a review note dryly, “Mammals, including humans, like foods abundant in oil and fats very much.” 

But why do we love fatty foods, and how can you tell when food contains fat?

This feature aims to answer these questions. And it turns out that the science of fat perception is more complex than you might expect.

Why do we like fat?

In short, fat is energy-dense, and your body is excellent at storing excesses of it. 

In today’s world of infinite fast food and brightly lit cake shops, we often consider the body’s ability to hold on to fat a bad thing.

But during our evolutionary history, it was a different story. Living in the wild, you don’t know when your next meal will come. 

In the past, scientists thought that humans and other animals identified fatty food based on its texture and aroma alone. And that’s certainly part of the story. 

But it’s more complicated than it might seem, so let’s start with the confusing bit.

Can we taste fat at all?

The classic tastes humans can detect are bitterness, saltiness, sourness, sweetness, and umami (savoriness). 

Some experts believe that detecting each of these flavors has played an important role in our survival:

• Sweetness helps us detect high-energy foods rich in carbs.

• Bitterness helps us avoid toxic chemicals.

• Salt contains sodium ions, which are essential for maintaining our water balance and other aspects of health.

• Umami helps us detect amino acids — the building blocks of protein.

• Sourness helps our bodies determine how acidic a food is.

Not all experts agree on this way of explaining the evolution of these tastes. Either way, you’ll have noticed the absence of anything specific to fat.

And we don’t really have a word to describe a fatty taste. Why is that?

Fat: The 6th taste?

Taste, or “basic taste,” as scientists call it, is a specific series of events. They go like this:

1. A compound from food, like glucose, activates a taste receptor on your tongue.

2. This fires a signal from your tongue to your brain, and you perceive a taste.

3. Your gut-brain axis is activated, which helps your body prepare for the food you’re eating. 

Although it comes close, fat doesn’t quite fulfill these criteria. 

A small percentage of the fat you eat is broken down into fatty acids by enzymes in your saliva. These fatty acids do work at receptors in your mouth, and they do send signals to your brain. 

However, these receptors aren't taste receptors, so you don't get a fatty taste.

According to a review, short-chain fatty acids taste sour, and long-chain fatty acids “evoke an unpleasant sensation.”

Now, you might be thinking, “I can definitely taste fat!” But that might be down to terminology. Although it’s not a basic taste, you can detect fat’s flavor. 

The importance of smell

Taste is all about your tongue. But flavor takes into account both the taste and smell of food. 

As we all know, food loses much of its flavor when you've got a stuffy nose. Smell, also called olfaction, is important for enjoying your food.

A fascinating study demonstrates that even without your tongue getting involved, you can tell how much fat is in something.

The scientists used sealed cups with straws. They filled the cups with milk containing different amounts of fat. 

To test retronasal olfaction, participants wore nose clips, so aromas couldn’t use that entry point. The scientists asked the participants to suck in air from the cup of milk (not the milk itself), then breathe the air out.

To investigate orthonasal olfaction, the participants put a straw up each nostril, breathed in the air from the cup, removed the straws, and breathed out through their noses.

Another study also found that people could correctly identify the fat content of milk using smell alone. 

Concerning our evolutionary past, the authors of the study write, “It would be clearly advantageous to detect the fat content of food from a distance in order to maximize the chances of finding a source of calories.”

Now, let’s look at how the texture of fatty foods plays a part in how delicious these foods are.

The joy of mouthfeel

Foods with a high fat content, like peanut butter, chocolate, and cheese, have a mouthfeel we enjoy.

The inevitable next question is, how does fatty food’s mouthfeel drive us to go back for second helpings?

Scientists have identified nerve cells (neurons) in your brain that respond specifically to the texture of fat. 

Some of these neurons respond to fatty food’s viscosity, or thickness. And others respond to its “coefficient of sliding friction.”

And because your brain knows that fat is full of energy, detecting these attributes makes sure you perceive fatty food as delicious, encouraging you to eat more.

Interestingly, studies have shown that if you thicken low-fat milk with thickening agents, people perceive it as being more fatty. So, the texture of fat-containing foods and drinks is clearly important. 

But texture, aroma, and flavor aren’t the only reasons that we enjoy fat in our food.

Other factors

Fat itself might not have a distinct taste, but it can help enhance other flavors in food. 

For instance, fat can absorb some flavor compounds, changing how they taste. And as you chew the food, the fat releases these compounds slowly. 

When you cook fat, it also releases the flavor compounds that it has trapped.

This is one reason why an uncooked steak doesn’t smell of much, but the heady aroma of a steak sizzling in a pan can fill a room.

The take-home

In a nutshell, we’re attracted to fatty foods because, in our evolutionary past, this urge probably helped keep us alive.

And today, although fat perhaps isn’t a basic taste, we can still tell when it’s there because of its flavor and texture.

Although fat has been demonized in recent decades, there’s no reason to cut out all foods that contain it. Fat is an essential nutrient, after all.

If you’d like to learn more about fats and oils and their role in health, try our podcast on the topic.