The Study That Flipped the Diet Soda Narrative

A massive study of over 120,000 people found that diet soda may actually be harder on your liver than regular soda — and the one drink that cuts your risk is already in your tap.

Story Snapshot

A UK Biobank study found artificially sweetened drinks raised liver disease risk by 60%, while sugary drinks raised it by 50%.
Diet sodas were linked to higher liver-related death rates; regular sugary drinks were not.
Swapping diet soda for water cut liver disease risk by over 15%. Swapping regular soda for water cut it by nearly 13%.
Switching between sugary and diet drinks offered zero protection — both types appear to be the problem.

Silent Killer In The Can

Researchers tracked more than 120,000 adults in the United Kingdom over roughly ten years. They measured beverage habits and then watched who developed metabolic dysfunction-associated steatotic liver disease, or fatty liver disease — a condition where fat builds up in the liver and can lead to serious damage over time. The results, presented at the United European Gastroenterology Week 2025 in Berlin, were not what most people expected.

People who drank more than 250 grams per day of artificially sweetened drinks — that is about one standard can — had a 60% higher risk of developing fatty liver disease compared to non-drinkers. Those who drank sugary beverages at the same level had a 50% higher risk. Both numbers are alarming. But the diet soda number is higher. That detail matters because millions of people drink diet soda specifically because they think it is the safer choice.

Diet Soda and Liver Death Risk: A Finding That Demands Attention

The study went further than just tracking who got sick. It also looked at who died from liver-related causes. Artificially sweetened drinks were tied to a higher risk of liver-related death. Regular sugary drinks were not. That is a sharp and surprising distinction. It suggests the artificial sweeteners themselves — not just the sugar, not just the calories — may be doing something harmful to the liver specifically. Researchers have pointed to gut bacteria disruption and insulin response as possible reasons, though more study is needed.

A separate study published in the National Institutes of Health’s research library tracked postmenopausal women and found that drinking one or more sugary drinks per day raised liver cancer risk by 85% and chronic liver disease death risk by 68%. That study found no significant link between artificially sweetened drinks and liver cancer mortality — which actually conflicts with the newer UK findings. Science rarely moves in a straight line, and this is a case where two solid studies point in slightly different directions on the mortality question.

Water Is Not Just a Default — It Is the Actual Answer

The UK Biobank researchers did not just identify risks. They tested substitutions. Replacing sugary drinks with water cut fatty liver disease risk by 12.8%. Replacing artificially sweetened drinks with water cut it by 15.2%. Those are meaningful numbers for a disease that now affects roughly one in four adults worldwide. What did not help at all was swapping one type of sweetened drink for another. Switching from regular soda to diet soda — or the reverse — gave people no measurable benefit.

That finding alone should change how people think about the diet soda swap. For decades, the public health message was simple: cut calories, choose diet. This study says that logic does not apply to liver health. The liver does not care whether the sweetness came from sugar or a lab. Both drinks appear to stress it. Only water actually helped.

What the Research Cannot Yet Prove — and Why That Still Matters

This study has real limits. Participants self-reported what they drank, which means some people likely misremembered or underreported. The study also could not fully account for exercise habits, total diet quality, or other lifestyle factors. These are standard weaknesses in nutritional research, and they mean scientists cannot yet say diet soda causes fatty liver disease — only that a strong link exists. Randomized controlled trials, where researchers control exactly what people drink over years, are still needed to confirm cause and effect.

That said, waiting for perfect proof before acting is a luxury your liver may not afford. The association here is large, consistent across multiple studies, and biologically plausible. If two drinks both raise your disease risk and one drink lowers it, the choice is not complicated. Major health organizations have not yet updated their official guidelines to reflect this research — but the data is pointing clearly in one direction, and it has been for a while.