Can fluoride in tap water disrupt your gut bacteria?

What's actually in it

About 73% of Americans drink fluoridated water. Public water systems add fluoride to prevent tooth decay, typically at 0.7 milligrams per liter. You also get fluoride from toothpaste, mouthwash, tea, and processed foods made with fluoridated water. All of that fluoride passes through your gut, where it comes into contact with trillions of bacteria.

What the research says

A 2026 review in J Trace Elem Med Biol examined whether fluoride exposure at common levels affects the gut microbiome and metabolism. The review gathered evidence from both animal studies and human data.

The findings showed that fluoride can cause gut dysbiosis, a shift in the balance of bacteria that live in your intestines. Certain beneficial species declined while others increased. These changes were linked to metabolic problems including insulin resistance, disrupted fat metabolism, and inflammation.

The review traced the mechanism: fluoride appears to damage the gut lining and change the chemical environment inside the intestines. This forces bacteria to adapt, and the new bacterial mix doesn't do as good a job at protecting your metabolism.

Not everyone is equally affected. People who drink more water, cook with tap water, and consume lots of tea get higher doses. Children get a proportionally higher dose per body weight than adults. The review suggests that while fluoride benefits teeth, its effects on gut health deserve more attention from public health researchers.