Why Can’t We Quit Diet Coke? The Drink Hacks Our Brains In More Ways Than One

When Diet Coke first came out in 1983, its makers had one goal: Make it clear this is a diet soda.

After all, the drink was created, at least in part, in response to a failed attempt at a subtle, low-calorie soda. Twenty years earlier, Coca-Cola Company had debuted its first-ever diet soda, Tab (as in, keep a tab on your waistline.) But from the start, the new soda’s taste was somewhat off, its connection to dieting was far too subtle, and consumers didn’t associate “Tab” with Coca-Cola, among other things. So when Diet Coke was introduced, the soda conglomerate pulled out all the stops, with in-your-face commercials, a new tagline — “Just for the taste of it” — and, of course, a new name: Diet Coke. Definitely Coke, definitely diet, and definitely not subtle.

Sales for the beverage soared and Diet Coke soon solidified itself as the “It” drink if you wanted to lose weight and look cool doing it. Over the next few decades, Diet Coke has experienced its ups and downs in terms of sales and popularity, but today, the beverage is clearly experiencing another renaissance: It’s everywhere on our TikTok streams, posed sweatily in front of models in glossy ads, and once again the “It” drink at the club. Yes, Diet Coke is back — and selling like its 1999.

The decades-long appeal of this fizzy, caffeinated, sugar-free drink has always been boosted by glitzy marketing which has typically hinted at thinness. In the past, they were more explicit, stating right there in the ad that ​​it can “can help slimming or weight control … as part of a calorie controlled diet.” Today, you won’t find the statement, but you will see a Diet Coke in the hands of the famously thin Kate Moss, who was appointed the drink’s Creative Director two years ago or in the fridge of weight-conscious Kardashians on TikTok.

It's seemingly impossible to separate Diet Coke from diet culture (the word is right there on the can), even if the company no longer claims that it can help with weight loss. Numerous studies done in the years since Diet Coke was released have shown that despite its best, zero-calorie efforts the drink has never consistently helped people lose weight.

So it’s not exactly a beverage made for weight loss. But that even matter? Maybe not. Because it’s not just the idea of weight loss that continually lands Diet Coke in our glasses. Instead, Diet Coke’s intense sweetness, caloric emptiness, and caffeine content hacks our most innate neurological and psychological responses to keep us unconsciously reaching for another bottle. Some experts argue it’s this, perhaps even more than the marketing forces, that keep us coming back.

How Sweet It Is

The reward of sweetness is one of the more fundamental desires for humans. “We come out of the womb being hardwired for sweet taste,” Ashley Gearhardt, a psychology professor at the University of Michigan tells Inverse.

Research suggests that a penchant for sweetness is innate across species, and likely all for the same purpose. The ability to identify sweet molecules through taste lets us determine where we can readily find glucose (in other words, calories). When the sweet taste hits the tongue, it triggers the release of dopamine, which is a neurotransmitter involved in reward and pleasure. In fact, dopamine is an evolutionary mechanism that compels us to seek out and eat nutrients, says Gearhardt. When we fill our body with calories, our brains reward us by flooding our system with dopamine.

In a sense, Diet Coke hacks this system. The beverage is much sweeter than anything we can find in nature thanks to an organic molecule called a dipeptide, which is made out of a lab-grown combination of the amino acids aspartate and phenylalanine. This is what makes aspartame, a product that, according to the European Food Safety Authority, is about 200 times sweeter than sugar.

When we ingest this ultra-sweet compound, it actually increases the desire for sweetness, according to Kathleen Holton, a nutritional neuroscientist at American University. When sweetness hits the tongue, Holton says, the body anticipates incoming carbs. That anticipation causes preemptive insulin release, which makes cells absorb circulating glucose. As our cells gobble up all the available glucose, the amount of glucose actively circulating in the bloodstream goes down. This drop signals to the brain that more sugar is needed. Once your body registers an intake of calories, blood sugar goes back up, signaling to the brain that the body is satiated.

But Diet Coke is, of course, free of calories. This causes confusion. “Our brain might be telling us that we’re having a tasty drink with lots of energy, but then our hunger and satiety signals in our body may be saying something different,” says Kirrilly Pursey, a nutrition and dietetics lecturer at the University of Newcastle School of Health Sciences in Australia. Specifically, our satiety signals are still telling us that we need energy in the form of sweetness. Further, she says Diet Coke’s long-term effects on satiety signals are unclear.

Aspartame also changes how we perceive sweetness. It down-regulates our sweet taste receptors, which means that these receptors’ responses are suppressed. As a result, it takes higher amounts of sweetness for someone to taste that flavor. Holton contrasts this to someone on the ketogenic diet who has an upregulation of sweet taste, which makes them more sensitive to sweetness.

So if you’re drinking Diet Coke, you’re signaling to your body that it wants sugar. The body prepares itself for calorie intake and starts craving sweetness. Drinking Diet Coke brings no relief from that craving because no calories come in. Furthermore, your brain still yearns for sweetness, but aspartame has down-regulated your sweet taste receptors, so you might drink even more Diet Coke to hit that craving.

Caffeine: America’s Favorite Drug

Diet Coke has another combination that isn’t found in nature: sweetness plus caffeine.

“That combination of sweet taste plus caffeine is just something our brain has never really been equipped to handle,” Gearhardt says. “Through human ingenuity, we're now getting this taste profile, but not getting the secondary delivery in the gut…Even if you're not getting the calories your body expects, the uniqueness of getting that big burst of sweetness and the caffeine is stimulating in the gut.”

While Diet Coke has roughly half the amount of caffeine as the average cup of coffee, it does have more than regular Coke per serving. A can of regular Coke has 34 milligrams of caffeine, compared to a can of Diet Coke’s 46 mg. The more caffeine one drinks, the more of a dependency the body builds to it.

“That combination of sweet taste plus caffeine is just something our brain has never really been equipped to handle.”

“Caffeine is a mild stimulant and activates the same reward pathways in the brain as in other addictive substances,” Pursey says.

(Scroll a little deeper on the Diet Coke tag on TikTok and you’ll notice videos that are less about having a little treat and more about drinking caffeine to curb your appetite. Though it's been studied, there’s currently no evidence to suggest that caffeine has a significant influence on appetite.)

But what it does have, like any other addictive substance, is withdrawal symptoms if you don’t get enough of it. These withdrawal symptoms can range from headaches to drowsiness, depressed mood, and difficulty concentrating — all things that that 3 p.m. slump often brings. If you are used to drinking Diet Coke on the regular, now your body is hounding you for both sweetness and caffeine.

Who Needs Marketing When You Have “The Bliss Point?”

From a certain point of view, Diet Coke could be considered a perfect drink. As Pursey points out, there’s a “sweet spot for fat, sugar, and salt for optimal taste, texture, and smell of foods.”

The food industry has a term for this sweet spot, called the “bliss point,” which was coined by experimental psychology and food industry scientist Howard Moskowitz. The term was brought to the public’s attention by Michael Moss in his 2013 best seller Salt Sugar Fat: How the Food Giants Hooked Us.

Gearhardt says this meticulous attention to food appeal can really pay off. “Even the size of the bubble makes a really big difference in the crispness of the taste,” she says.

But is this blissful food “addictive” in the sense that it hijacks our ability to stop drinking it? The answer is complicated.

Our brains make all sorts of connections when it comes to cues, including the crack of the soda can tab, or the fizz of a bottle cap twisting open. The trigger for a dopamine hit starts as sweetness. But, after weeks and months of regular consumption, our brains take note of the other sensations that precede it. The cues we associate with consuming something, like ripping open a bag of chips, become a proxy for that reward chemical. A 2012 paper published in the journal Physiology & Behavior comprises a meta-analysis of various studies looking at brain responses to food and smoking cues, and found significant overlap in the regions engaged. This finding suggests that cues surrounding food can elicit similar responses to cues around, say, smoking cigarettes.

“The dopamine starts to move away from the ingestion and towards the cues,” Gearhardt says. The dopamine release, which is the motivational drive for ingesting something, starts to spike especially for people hooked on cues associated with consumption, not just consumption itself.

“We used to think that addiction is all about just liking,” Gearhardt says. She says this difference critically separates people who are addicted to things from those who are not. “It's more about that anticipatory cue, and we see that with addictive drugs as well,” she says. This is called the incentive sensitization theory of addiction. This theory of addiction helps illuminate why people engage in repetitive behaviors even when we know something might be bad for us: We begin to get the reward from the associated behaviors as well as from the substance itself.

As for sugar and sweet taste as addictive substances themselves, some research hints at their potential. A 2007 study published in PLoS One looked at whether rats would opt for intravenous cocaine or water sweetened with calorie-free saccharin. A whopping 94 percent of the 132 rats used in the study preferred the sweetened water to the drug.

Still, studies like this one don’t perfectly convert to human behavior. “They don’t take into account the social, environmental, and cultural influences on human eating behavior,” Pursey says. Which brings us back to the marketing.

Yes, Diet Coke presses all the biological buttons — a perfectly engineered carbonated liquid speaks to our neurons in a way that no other naturally occurring food or drink can. But when it’s everywhere — in the hands of celebrities and on display the front of the store, popping up in our social feeds and lining our friends’ fridges — it’s hard to say what really drove us to crack one open. Was it a biological draw or a psychological push? Or was it just a matter of convenience? No matter the answer, Diet Coke is likely here to stay in our lives for time to come.