I Drank Diet Coke Daily For 25 years—Then Stopped: A Harvard Nutritionist Says I Did My Brain ‘A Favor'

A bobblehead of the author on a tower of Diet Coke. (Via NBC Los Angeles)


For decades, drinking a Diet Coke every day gave me a burst of caffeine and satisfaction.

I started popping cans of the stuff in the late 1990s, when I was a teenager. It made me feel like an adult. Once I was a proper adult, refusing to quit — no matter how many people told me I should — made me feel young.

I was a married, employed mom who practiced yoga, gave to charity, and voted in every election. Wasn't I allowed one relatively harmless vice?

Then I turned 40 and started thinking about my choices. That's common, I suppose, when you're caught in the tractor beam of Middle Age. I decided to make three changes at once: walk more, tweet less and, after 25 years, put down the Diet Coke.

A year later, I was three for three. I hadn't tweeted or scrolled since well before the bird app became X, though I "liked" various posts that crossed my path. My daily average step count was at 10,000 or more, up from 7,000. I got my buzz from coffee and tea.

And I didn't feel any different.

Nothing significant about my health, mind or appearance seemed to have changed. Had all this effort been a waste?

I decided to ask the pros — and was surprised to find them unanimous.
'You did your body a favor, and your brain'

"Your body is very happy," Michiko Tomioka, a certified nutritionist and longevity expert, told me in a firm and cheerful voice. "I am sure it is. Naturally, you are improving."

I got the sense that she wanted to supplement my lack of certainty with an excess of her own. But then, Dr. Uma Naidoo — a nutritional psychiatrist and faculty member at Harvard Medical School — agreed.

"You did your body a favor, and your brain," said Naidoo. "I think it's fantastic."

My sense of taste is no longer "tricked" by chemical surges of fake sugar, Naidoo said. Since diet soda is "hyper-sweetened," just a little bit of it can set off your taste buds and trigger a cascade of deleterious effects like cravings and crashes.

"This trickery that happens is just not good for the body," she said. Or the mind, for that matter: "Anxiety is also associated with sweeteners," which can disrupt the gut microbiome. (The Coca-Cola Company didn't immediately respond to CNBC Make It's request for comment.)

It was true, now that I thought about it, that I had fewer panic attacks over the past year. But why would a fizzy drink have that kind of an effect?

"The health of your gut is related to the health of your brain," Naidoo explained. "Once the gut is disrupted, the brain is affected as well."

Based on the research she's seen — which she laid out in her bestselling first book, "This is Your Brain on Food" — it's smart to avoid artificial sweeteners altogether. Instead, use small amounts of honey or dates, which at least have "some nutrition," said Naidoo. "It's food."
Health effects don't have to be visible to be serious

Other benefits of my new, more abstemious life may not be apparent — but they exist, the experts told me.

For one, I probably used to be dehydrated. "After you quit, you are drinking more coffee and more water," said Tomioka. That's a superior choice. "Water is the best beverage in the world."

Water helps with metabolism, for example, while Diet Coke can actively hurt it. People who regularly drink any kind of soda tend to gain weight, Tomioka said. Not just any weight, either: Long-term use of aspartame, the sweetener in Diet Coke, can lead you to collect "visceral fat," which is the "much more dangerous kind," Naidoo noted.

It can affect your insulin resistance, putting you at greater risk of diabetes, said Tomioka. Considering my father was pre-diabetic before he died, this one hits home.

Quitting bolsters my 10,000-step goal, too. The specific number of steps may be arbitrary, but walking more improves bone density while drinking diet soda can erode it, said Tomioka. That's due to the presence of phosphoric acid, which can also damage your tooth enamel.

The women in my family tend to stoop as they develop osteoporosis. I'm not exactly tall to start with. The last thing I need is a hunch.
My No. 1 takeaway isn't about bone density or diabetes

All in all, I was sobered by the long list of health effects both experts rattled off, which didn't even include a possible aspartame-cancer connection. I knew Diet Coke wasn't exactly barley tea or a turmeric latte. I hadn't thought it was like wine laced with iocane powder, either.

I'm happy to hear that my body is probably better off now. But honestly, I'm most proud of myself for another reason: I've shown that I can do something difficult and rewire my brain after 25 years.

Here I am, able to walk past a vending machine and not think about scrounging up quarters. It's good to know I can alter deeply ingrained habits. That alone helps foster a sense of relaxation and confidence, Tomioka pointed out.

Knowing that I can change, even or especially now that I'm in my 40s, brings satisfaction. As much as a crisp, cold Diet Coke at lunchtime? Maybe not — but satisfaction all the same.