Taste the Rainbow

If you could eat a magic pill that could provide all the vitamins and nutrients that your body needed to survive, would you forgo eating altogether to take this pill every day for the rest of your life? Probably not, right? In fact, a magic encompassing vitamin and nutrient pill already exists in the form of meal replacements like Soylent, yet a vast majority of people still choose to eat food instead. Eating is one of the few daily rituals that most of us look forward to and outright enjoy several times a day! Eating great food is a synesthetic and intersensory experience, but the sense most associated with food is taste.

However, our sense of taste does not exist purely for hedonic purposes. It is a core means of our survival and enables us to ingest the right food that provides the energy to run body functions and the building blocks to grow and repair the body. One reason that taste is important is that it acts as a catalyst by readying our bodies to digest food, causing us to produce saliva and prepare our digestive system for intake. Without the ability to taste, our stomachs would not be ready for food, resulting in complications with digestion and limitations on the nutrients that we can extract. The evolutionary tool of taste grew over time to assist in determining the quality and content of sustenance, but have you ever wondered why we even have the ability to taste?

Flavor Town

Modern day cuisine is incredibly diverse and composed of a litany of ingredients sourced from all kinds of biomes, but in its evolutionary infancy, our eating tendencies developed from our ability to taste. Our prehistoric ancestors may not have had the luxury of having Michelin starred master chefs meticulously preparing their meals that we have today, but as hunter-gatherers engaging with their environment, their ability to taste was necessary for their survival.

Their taste buds not only indicated the flavor of the food they ate, but also their taste revealed practical properties. Tasting certain flavors uncovered the food’s composition without fully ingesting it. Based on flavor profile, they could remember which plants were and weren’t poisonous or taste if the meat from a prior hunt had expired.

Today, humanity has transformed a basic survival task into a culinary art that has brought cultural expression to the table. While we no longer spend our meal time gambling our lives away by foraging and eating random forest mushrooms, we still utilize our sense of taste as a key tool to ensure that we are eating a healthy and balanced diet of foods. The five major flavors (sweet, sour, salty, bitter, and umami) are found in different quantities and qualities in the variety of food we eat, each with its own purpose and index in the human body.

Sweet

Unsurprisingly, the sweetness in food is usually caused by sugar and its derivatives such as fructose or lactose. One of the major sources of energy for animals is carbohydrates, which includes sugars. Sweet flavors are indicators of calorie-rich foods, so in order to maximize our energy intake, our preference for food correlates with its sweetness. The enjoyment you feel from eating something sweet has been proven to be controlled by the same morphine-like biochemical systems in the brain, which motivates us to continue searching for sweets and associates eating sweet foods with euphoria and joy. In traditional Chinese medicine, sweet foods help “tone the body”, alleviate illness, and improve mood.

Sour

Sour flavors indicate the presence of organic acids. The ability to perceive sour can also help us determine if food has gone bad. From a beneficial standpoint, in geographies where the water is hard and highly alkaline like the Shangxi Province in China, eating sour foods helps dissolve mineral compounds such as calcium carbonate in the water and balance pH in the body. In a meal, the taste of sour food literally makes our mouth water and serves as a counter point to complement a dish (e.g. the brininess of a pickle cuts through the grease of a burger). When acidic ingredients are used in cooking, for instance, red wine and tomatoes in a bolognese, the acidity mellows over time yet retains its brightness. The smoothed sourness serves as a refreshing contrast to the salty, fatty, sweet, and starchy parts of the pasta dish.

Salty

Sodium and chloride come together to form salt crystals, resulting in the most ubiquitous and recognizable food seasoning in the world. Not only does salt deepen and amplify flavors, but also as an electrolyte, it is a crucial component of ensuring the proper function of the muscles and nervous system.

If electrolyte levels get too low — a condition known as hyponatremia — water shifts from the fluids outside the cell membranes to inside the cells, causing them to swell with too much water. During intense exercise, a person tends to sweat, losing not just water but also electrolytes in their sweat (think of why sweat is salty), and sports drinks such as Gatorade help replenish electrolytes to continue exercising without cramping. Without electrolytes, muscles contractions would not be possible, including the beating of the heart!

Fun fact: all salt originally comes from the sea (even cave salt or Himalayan salt), so eating food seasoned with salt brings a tiny part of the ocean to your meal.

Bitter

Bitter can be a confusing taste as it is an inherently unpleasant flavor, yet we find incorporations of bitter flavors in cuisines all over the world. From an evolutionary perspective, tasting a bitter plant could be an indicator that it is poisonous and recognizing the flavor without swallowing it could be a matter of life and death.

Healthwise, bitter foods are typically packed with both soluble and insoluble fiber, stimulates the growth of healthy gut bacteria and improves the efficiency of the digestive system. Culturally, Jewish people eat bitter herbs like horseradish at Passover seders to remind them of the suffering endured by their ancestor. God commands them : “They shall eat the lamb that same night; they shall eat it roasted over the fire with unleavened bread and bitter herbs” (Exodus 12:8). Bitter flavors are a reminder that food doesn’t have to be pleasant to be attractive (e.g. a 90% extra dark chocolate or a dark roasted coffee).

Savory

Umami is a taste most associated with protein and is usually caused by glutamic acid or aspartic acid. Think of a rich golden chicken soup or a roasted portobello mushroom. Umami corresponds with savory and meaty flavors. The foods packing the greatest umami punch are the ones that have already broken down their proteins into free amino acids like glutamates and nucleotides. These “free” amino acids can be released through any chemical process (aging, toasting, roasting, braising, or stewing) that can break down complex proteins into their constituent parts. Our digestive system can burn a lot of energy breaking whole proteins down into amino acids, but the amino acids in umami foods are already in a free state, so they are more quickly and easily digested than complete proteins.

Tongue in Cheek

For animals that don’t have the luxury of spending their time dreaming up well balanced, crafted dishes like humans do, their existence comprises of spending their waking moments figuring out how to procure food for themselves and their progeny. Whether or not the carrot they’re eating has enough salt in it to bring out its natural earthy sweetness is not an urgent priority, it just needs to be able to sustain them.

Thus, certain animals have evolutionarily developed taste for only certain flavors. Carnivores such as cats, for example, do not need sugar or carbohydrates in their diet and therefore have no need to taste sweet things. Cats have only a few hundred taste buds that they use as taste receptors for meat and fats, which drive their appetite and diet. For the rest of the animal kingdom, they have evolved to only be able to taste that which it can use to survive.

Following this paradigm, some animals decide to search with the food’s destination in mind and use their taste buds as a primary investigator. While the other senses may assist in the hunt for food, the sense of taste is ultimately how the animal experiences and remembers what it has eaten and what to look for again in the future. Without a sense of taste, the animal would have no choice but to consume the food and hope that it wasn’t deadly. Additionally, not being able to taste for flavor would prevent the animal from determining whether the food was providing the proper nutrition.

Swimming Tongues

Humans have around 10,000 taste buds, all of which are located on the tongue. In contrast, some species of catfish don as many as 175,000 taste buds not just in its mouth, but over the skin of its entire body. Because most catfish have no scales, instead opting for a mucus covered skin, the catfish “tastes” everything it touches. The whole body serves as a swimming tongue: the head, the whisker-like barbels, the back, the belly, the sides, and even the tail. If you were a catfish, you might be able to taste a piece of chocolate cake by sitting on it (would not recommend attempting this as a human).

It’s not exactly groundbreaking to say that the use of taste influences an animal’s search for food, but the extent to which their sense of taste enables the fish’s survival is nothing short of impressive. For a catfish, its taste allows it to find prey, avoid predators, locate fish of the same species, coordinate spawning time and home in on spawn sites.

Typically, a sense of smell would allow the fish to detect the substance from a distance while taste would determine the palatability of the substance by eating it. Catfish, however, can taste substances dissolved in water without having to bite into them, even at a distance of up to 25 body lengths. This would be the equivalent of an Olympic swimmer sitting at one end of a pool and tasting a burger dropped into the water at the other end.

Taste Test

John Bardach, a Professor of Fisheries at the University of Michigan, investigated whether bullhead catfish could use the taste buds on their body to locate and distinguish stimuli by taste alone.

In the experiment, blinded catfish sought direct contact with either an amino acid, cysteine hydrochloride, or pork liver juice dropped into the tank. Without sight or smell, the catfish demonstrated a pattern of movement that showed it was comparing taste concentrations and orienting its body to move in the direction of the release point of the stimulus (i.e., pork juice). Even without the use of their barbels, the catfish could locate the source within 24 seconds.

It’s clear that having a highly discerning sense of taste would be necessary for survival for an animal that scours the bottom of muddy and murky waters, but the catfish’s ability to taste from afar allows the fish to taste test without ever having to put the substance in its mouth. The catfish diet consists of algae, small fish, and scavenged debris. By using their amazing sense of taste, catfish can lackadaisically swim through the waters, tasting the entire menu as they go.

Imagine being able to perceive your surrounding world through a hypersensitive sense of taste. Sitting in a restaurant and passively trying dishes as waiters zoom by with plates seems like a fun way to decide what to order. Walking into a grocery store, you could always pick the best produce without getting banned from the shop for taking a bite out of every piece. We would add another dimension to our experience of flavor and increase the depth by which we understand the world through our taste buds.