Pepsi Zero Sugar isn’t acutely harmful, but drinking it regularly, especially two or more cans a day, is linked to meaningful health concerns. It contains zero calories and no sugar, which makes it a better option than regular soda for blood sugar and calorie intake. But its mix of artificial sweeteners, high caffeine, and acidic additives introduces trade-offs that are worth understanding before you make it a daily habit.
What’s Actually in Pepsi Zero Sugar
A 12-ounce can of Pepsi Zero Sugar contains carbonated water, caramel color, phosphoric acid, aspartame, acesulfame potassium (often called Ace-K), natural flavor, potassium benzoate as a preservative, caffeine, citric acid, and calcium disodium EDTA to protect flavor. There are zero calories, zero grams of sugar, and no fat or protein.
The two ingredients that get the most scrutiny are the sweeteners: aspartame and acesulfame potassium. These are blended together to mimic the taste of sugar more closely than either could alone. Pepsi Zero also packs 69 milligrams of caffeine per can, which is nearly double the 38 milligrams in regular Pepsi and roughly double Diet Pepsi’s 37 milligrams. That puts it closer to a cup of coffee than a typical soda.
What Regulators Say About the Sweeteners
The FDA considers aspartame safe at up to 50 milligrams per kilogram of body weight per day. For a 150-pound person, that works out to roughly 16 cans of Pepsi Zero daily, a threshold almost no one would hit. In 2023, the World Health Organization’s cancer research arm (IARC) classified aspartame as “possibly carcinogenic to humans,” its Group 2B category. That sounds alarming, but Group 2B is a low-confidence classification based on limited evidence. The WHO’s food safety committee reviewed the same data and reaffirmed the existing safe intake levels, concluding there was no sufficient reason to change them.
Acesulfame potassium has been approved by the FDA since 1988 and faces less public controversy than aspartame, though it appears in many of the same studies. Neither sweetener has been conclusively shown to cause cancer in humans at normal consumption levels.
Blood Sugar and Insulin Effects
One of the main reasons people reach for Pepsi Zero is to avoid blood sugar spikes. On that front, the evidence is reassuring. A systematic review of randomized clinical trials found that the aspartame and Ace-K blend used in drinks like Pepsi Zero did not significantly change blood glucose compared to either sugar or plain water. Incretin hormones, which help regulate insulin after meals, were also generally unaffected.
So if you’re choosing Pepsi Zero specifically to keep blood sugar stable, it does what you’d expect: it delivers sweetness without triggering the glucose response that regular soda causes.
The Gut Microbiome Question
Where things get more complicated is inside your gut. Because artificial sweeteners aren’t digested, they pass through your stomach and come into direct contact with the bacteria living in your intestines. Research from the National Human Genome Research Institute found that mice fed artificial sweeteners, including aspartame, developed elevated blood glucose levels and glucose intolerance compared to mice drinking plain water or sugar water. Even short-term consumption produced noticeable changes in the composition of gut bacteria.
When researchers gave the mice antibiotics to wipe out their gut microbes, the difference in blood glucose between the sweetener group and the sugar group disappeared. That strongly suggests the metabolic effects were driven by changes in gut bacteria, not by the sweeteners acting directly on blood sugar. The researchers also identified changes in microbial genes associated with pathways linked to obesity in both mice and humans.
This is animal research, and results don’t always translate directly to people. But it raises a legitimate concern: the calorie-free sweeteners in Pepsi Zero may not be metabolically “invisible” in the way the nutrition label implies.
Weight Loss and Appetite
The calorie math is simple. Swapping a 150-calorie regular Pepsi for a zero-calorie Pepsi Zero should theoretically help with weight management. But the real-world picture is murkier. Some human studies have found that people who drink artificially sweetened beverages tend to gain weight over time, while other studies show they can support modest weight loss. The contradiction likely comes down to a phenomenon called reverse causation: people who are already gaining weight are more likely to switch to diet drinks, making it look like the drinks caused the problem.
There’s also a biological wrinkle. A 2017 study found that carbonation itself, regardless of whether the drink contains sugar or artificial sweeteners, increases levels of ghrelin, the hormone that drives hunger. Rats drinking any carbonated beverage ate more food and gained weight faster than rats drinking water or flat versions of the same drinks. In the human portion of the study, college students who drank carbonated beverages (including carbonated water) had higher ghrelin levels than when they drank flat liquids. The study didn’t track whether those students actually ate more afterward, but elevated ghrelin typically makes people hungrier.
Separately, rodent research has found that aspartame can damage a brain area involved in signaling fullness, potentially undermining your ability to know when to stop eating. If Pepsi Zero makes you crave snacks or eat larger meals, the zero-calorie advantage could easily disappear.
Heart Disease and Stroke Risk
The most concerning long-term data comes from the Women’s Health Initiative, a large observational study published in the American Heart Association’s journal Stroke. Women who drank two or more artificially sweetened beverages per day had a 23% higher risk of stroke, a 31% higher risk of the most common type of stroke caused by a blood clot, and a 29% higher risk of coronary heart disease compared to women who rarely or never drank them.
The risks were even steeper in certain groups. Women with obesity who drank two or more daily had roughly double the risk of clot-based stroke. Women with no prior history of heart disease or diabetes who drank at that level had nearly 2.5 times the risk of a specific type of stroke affecting small blood vessels in the brain.
This is observational data, meaning it can’t prove the drinks directly caused these outcomes. Lifestyle factors, existing health conditions, and dietary patterns all play a role. But the size and consistency of the associations are hard to dismiss, particularly at the two-or-more-per-day level.
The Caffeine Factor
At 69 milligrams per 12-ounce can, Pepsi Zero delivers a noticeable caffeine hit. One can is fine for most adults, but if you’re drinking two or three throughout the day, you’re approaching 140 to 210 milligrams from soda alone. Add in a morning coffee and you could easily exceed 400 milligrams, the general upper limit for healthy adults. That level of caffeine can cause jitteriness, disrupted sleep, increased heart rate, and anxiety, especially if you’re sensitive to stimulants. If you chose Pepsi Zero partly because you thought it was lighter than coffee, check the label: it’s not far off.
How Much Is Too Much
The pattern across the research is consistent: occasional Pepsi Zero consumption appears to carry minimal risk, while daily heavy consumption (two or more cans) is where problems start showing up in studies. At one can a day or fewer, you’re well within the FDA’s safe intake limits for both sweeteners, your blood sugar likely won’t be affected, and the cardiovascular associations are much weaker.
The practical takeaway is that Pepsi Zero is a reasonable swap for regular soda if you’re trying to cut sugar or calories, but it works best as an occasional drink rather than a water replacement. The combination of artificial sweeteners, carbonation-driven hunger hormones, and high caffeine means that even a zero-calorie drink can quietly influence your appetite, your gut, and your cardiovascular risk profile when consumed in volume.