“Room” for Dessert? The Psychology of Eating

When I was little I used to stubbornly insist to my mom that after eating a full dinner I could still eat dessert because I had a separate stomach where the dessert went. With the same adamant fury that I used to defend my decision to not eat another bite of green beans, I argued that because I had two separate stomachs for dinner and dessert, I could still have room for cookies even after eating an entire plate of chicken casserole. Now to give you a sense of my knowledge of food and biology at the time, I also thought that milk was skeleton blood, but it turns out that I did have something resembling a point. You see, due to what Psychologists call “Sensory specific satiety” humans actually do biologically have “room for dessert.”

According to the theory sensory specific  satiety, humans are evolutionarily conditioned to seek out as many different tastes as possible when eating. This is because by consuming as many flavors as possible, our savannah wandering ancestors would also ingest as many nutrients as possible. There are many key that people seek out when they eat. The ones that your tongue is adapted to pick out are salty, sweet, sour, bitter, and umami. Each of these tastes is communicative–it tells your brains something about what you are eating. Salty is obviously the presence of sodium, sour indicates acids, bitter indicates the presence of toxic substances (which is why we tend to avoid bitter foods), and umami signifies the amino acid glutamate–which is a marker of protein-dense foods. As you probably know, the reason cheap Chinese food tastes so good is because the cooks add monosodium glutamate to their recipes. While the jury is still out on the health effects of MSG, it is undeniable that it makes food taste better. You instinctively crave glutamate, so by hitting this evolutionary button, Chinese cooks can sell more Chinese food. It’s not just in Chinese food either. I have found MSG in everything from Tostito’s Hint of Lime Tortilla Chips to Triscuit’s Rosemary and Olive Oil crackers (you can find it naturally in ripe tomatoes, soy beans, and steak). Inserting glutamate into foods that wouldn’t normally have it makes people like them more. The food industry has carried this theory over to the other tastes as well, which is why you find high fructose corn syrup in bread now. If bread is sweet, people will buy more of it. Once companies figured out how to manipulate individual tastes in laboratories, they quickly moved on to engineering symphonies of tastes. For example, one of the reasons that ketchup is such a popular condiment is that it tastes sweet, sour, salty, bitter, and umami simultaneously. Heinz ketchup in particular achieves an ideal blend of these five fundamental tastes, which is, in part, the reason why the brand is so sucessful.

Beyond the big five tastes–which are dictated by the biology of the tongue–people seek out three tastes any time they eat: salt, sugar, and fat. We are so drawn to these tastes because salt, sugar, and fat are all inherently rare in nature. If our ancestors found something sweet, salty, or fatty, it made great sense to get excited, because this meant a reserve of calories that might not come along again for a while. Yet in modern life we can find these tastes everywhere, in ridiculously high concentrations between what occurs in nature. Indeed much of the business of food marketing is figuring out increasingly clever ways to rearrange salt, sugar, and fat in order to tug on the strings that make up the marionette of our evolutionary desires. Imagine some of the most appealing foods you can think of and I bet they have two of the big three tastes, and if they are really good, have all three. I can generate a pretty revealing list of my favorites right now: Kettle Corn (salt and sugar), Guacamole (salt and fat), Peanut Butter (salt, sugar, and fat), Nutella (sugar and fat), Chocolate (salt, sugar, and fat), Potato chips (salt and fat), and French Fries (salt and fat) Why does ketchup go so well with french fries? By adding ketchup to french fries you add sugar to the mix, completing the holy trinity of flavors. Once you see eating as the pseudo Freudian drive to consume these three sensual tastes, junk food makes a lot of sense, to the point where you almost have to tip your hat to it.

So when you finish your dinner, you have generally consumed some amount of salt and fat, but likely not very much sugar, which is why no matter how much you eat, you generally have “room” for something sweet afterwards. This is not to say that eating is by no means fully predetermined. You always excercise individual agency when you eat. Some people simply don’t eat desert, and even if you do, whether that something sweet you end up eating is a deep fried Twinkie or an apple remains up to you. However, increasingly the deck is stacked against you, as junk foods are cheaper and more readily available than ever before. The people that provide you with your food know what it is you want, and are pretty shameless about manipulating salt, sugar, and fat in order to get you to spend your money. So often you can find your attempt to have a healthy meal devolving into an unhealthy exercise in flavor surfing while the CEO of Kraft cackles maniacally in the distance.

Now before you dismiss me as an anti-dessert zealot I want to clarify two things. One is the fact that salt, sugar, and fat are not inherently evil. To the contrary they are essential nutrients for our survival. The problem is that now it is too easy to consume them in absurd excess, which is undeniably unhealthy. I also want to point out unavoidable fact that I too love dessert. Everyone is built to crave salt, sugar, and fat, and so I have no interest in nutritional elitism. What is valuable, I think, is understanding the psychological factors inherent in eating so that we might begin to navigate the landscape of food more effectively. As the perpetual human drive to desert illustrates, so much of what we eat and how we eat is due to things that we are largely unconscious of. For example while many people believe that they start eating when they are hungry and stop eating when they are full, scientific studies have repeatedly demonstrated that external context cues matter just as much if not more than hunger and fullness. In one experiment, people presented with a bowl of soup that continually refilled itself from the bottom ate a lot more soup than people who had just one bowl that they had to refill if they wanted more. Similarly, Movie theaters discovered long ago that while people would not go back for more popcorn, they would consume much more of it if a jumbo size was available, and thus the super sized portion was born. Just as the physical context of portion size matters when we eat, so too do social contexts.

During a long drive through Southern Arizona with my friend Julia last fall she pulled out a bag of Trader Joes Sesame sticks and began to snack. I reached my hand into the bag and joined in, savoring the crunchy texture, and the immediate hit of salt and oil present in each stick. After downing several handfulls Julia turned to me and said,

“I’m not even hungry, I don’t know why I’m even eating these. I think it’s just because I’m bored.”

Closing the bag and wiping the salt from my hands I responded,

“If it makes you feel any better I’m just eating because you are.”