Ken Frondorf, 68, poses in front of a garage fridge full of Diet Coke in his Cincinnati, Ohio home in November 2025.

Ken Frondorf is known by friends and family as the “Diet Coke Guy.”

The 68-year-old from Cincinnati drinks about 10 plastic 16.9-ounce bottles of Diet Coke every day. It’s the only liquid he consumes besides a glass of water once or twice a week.

He takes his morning pills with Diet Coke and goes to sleep with a bottle on his nightstand. A fridge in his garage is dedicated to storing the cases he stocks up on every month, and he even built a shelving unit to contain the “overflow”; he'll scoop up more cases if there’s a deal at the grocery store.

Frondorf got hooked on Diet Coke about 20 years ago when he was diagnosed with diabetes, which forced him to replace his sugary drinks with other choices.

“The regular Coke was my soda of choice, but it wasn’t the only thing I drank,” he said. “Once I settled on the Diet Coke, it’s just gotten more over the years to the point where that’s all I drink now.”

Frondorf has tried cutting back and quitting several times. But it takes only a few days before he caves in, again.

He's not alone. More than 60% of American adults report drinking sugar-sweetened beverages one or more times a day, according to the Centers for Disease Control and Prevention. Recently, some USA TODAY journalists also learned firsthand how hard it can be to break soda habits when they tried to quit cold turkey.

Many people in America love soda, and some even believe they can't stop drinking it. And that's by design, medical experts say.

These drinks hijack the brain’s reward and motivation system and rewire the body’s metabolism, food and nutrition experts say, which can lead consumers to crave them more. Soda lovers are also trained to associate these products with certain events and moments after decades of intense product marketing by beverage companies, said Ashley Gearhardt, professor of psychology at the University of Michigan, where she runs the Food and Addiction Science and Treatment lab.

“They want to inundate every single domain of your life,” she said. “Just like a chain smoker is dosing themselves with nicotine all day, you’re dosing yourself with a naturally delivered sweet taste day after day because whenever it’s not there, a part of you feels slightly depressed and slightly dissatisfied.”

'It's just the taste'

Humans were born with a sweet tooth, Gearhardt said. The innate preference for sweetness was an evolutionary necessity for newborns to crave their mother’s milk and ultimately find nourishment.

“It’s one of the tastes that we don’t have to learn to like," she said.

Sweetness floods the brain with dopamine, a neurotransmitter that plays a role in reward, pleasure and motivation sensations. Sodas “hyperactivate” the dopamine systems and makes the brain crave it “in a way that makes them hard to resist,” Gearhardt said.

“This is something that served us, that was biologically beneficial for the vast majority of human and animal history,” she said. “It’s just now been used to sell us sugar water with a bunch of flavor additives that create brand loyalty.”

Frondorf can attest to this. He refuses to drink Pepsi products and immediately knows when he's accidentally served regular Coke instead of diet. When asked why he loves Diet Coke so much, his answer is simple: "It's just the taste."

Diet Coke doesn't contain sugar, but it does include an artificial sweetener called aspartame, which the Food and Drug Administration says is about 200 times sweeter than table sugar. This hyper-sweetness may help explain its appeal.

Soda also contains caffeine, a central nervous system stimulant that is known to be mildly addictive, said Vivica Kraak, associate professor for Virginia Tech’s department of human nutrition, foods and exercise. That probably contributes to withdrawal symptoms such as headaches, fatigue and irritability.

Decades of industry research and development have also led to a proprietary blend of enticing flavor enhancers that trigger other sensory reactions in our brain, forcing us to want more.

An 'insulin roller coaster ride'

It's not just about how these chemical components interact with our brain, Gearhardt said. It’s also about how they’re delivered into our bodies.

“The whole delivery vehicle is really what makes something addictive,” she said.

For example, a banana contains sugar, but most people don’t binge on bananas, she said. That’s because fruits are a plant matrix that also contains fiber, water and other components that require energy to break it down and nourish the body for longer periods of time. A can of soda is a straight shot of sugar.

But a sweet tooth is only secondary to what’s really going on here, said Dr. David Ludwig, endocrinologist and researcher at Boston Children’s Hospital.

Food rewards and cravings occur with any foods, not just sodas and those that are ultra-processed, he said.

“They’re there to get us to do behaviors that, if they’re done in a proper balance and in the right context, are actually helpful for us,” he said. “If we haven’t eaten for three days, we’re going to be cravings foods. That’s a natural thing.”

Sodas can be addictive but not because they’re hyper-palatable, said Ludwig, who is also a professor of nutrition at Harvard Public School and an adviser to the Coalition for Metabolic Health.

His research suggests the answer may lie in the body’s metabolism.

When consuming sodas, fast-digesting carbohydrates and sugars cause the blood sugar to spike, Ludwig said. This causes the pancreas to quickly release the hormone insulin to drive that blood sugar down, forcing sugar into the liver, muscles and fat tissue throughout the body.

Because these calories are being stored very quickly, they aren’t around long enough to nourish the body. Your metabolism begins to crash, which causes cravings to get the body’s blood sugar back up.

“It’s a double whammy because the calories are getting stored and you get hungry again too soon,” Ludwig said. “It’s not that these foods are so amazingly tasty, it’s that they alter our metabolism. ... [The] fundamental problem is that the processed carbs are sending us on a blood sugar and insulin roller coaster ride.”

Coca-Cola and PepsiCo did not respond to USA TODAY’s requests for comment. But William Dermody, a spokesperson for the American Beverage Association, said makers of popular soda brands support people's efforts to lead a healthy life. They offer alternatives such as sparkling waters, zero-sugar sports drinks and probiotic sodas "so families can make the choices that are right for them," he said.

"Today, 63% of the beverages consumers buy have zero sugar," he said. That figure includes Diet Coke

Sodas as the 'default beverage'

Many soda drinkers can pinpoint the time in their lives when they first fell in love with soda.

That’s by design, said Kraak from Virginia Tech. Soda manufacturers invest billions of marketing dollars each year.

They cross-market with certain foods and fast-food chains, university campuses, events, sports and alcoholic beverages. Their campaigns ensure that drinking soda is associated with every aspect of life.

“They’ve socially normalized sugary beverages as the default beverage,” Kraak said.

That's the case for Frondorf, who says he's not going to stop drinking soda anytime soon.

“I’ve got a lot of health problems, and I know drinking water would help, but it’s just not worth the effort," he said. "I just stick with my Diet Coke."

Adrianna Rodriguez can be reached at adrodriguez@usatoday.com.

This article originally appeared on USA TODAY: There's a reason you're so hooked on soda. It's not fully your fault

Reporting by Adrianna Rodriguez, USA TODAY / USA TODAY

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