For years, when patients asked me about weight gain, I’d deflect. “That’s not really my area. Talk to your doctor.”
I was wrong.
A study just came out that connects dots I’ve been trying to connect for decades: the bacteria in your mouth might be influencing your weight.
Scientists at NYU Abu Dhabi collected saliva from 628 adults. They compared people with obesity to people at a healthy weight—matching them carefully by age, sex, lifestyle, and how well they brushed their teeth.
Then they looked at the bacteria living in everyone’s mouths.
Your mouth contains over 750 different types of bacteria. And what the researchers found was striking: people with obesity had different bacteria doing different things.
Think of it this way: bacteria are like tiny factories. They take in nutrients and produce compounds as byproducts.
The researchers found 94 different ways these bacterial “factories” were operating differently in people with obesity.
Some factories were in overdrive:
- Breaking down carbs and producing lactate (which your body can store as fat)
- Breaking down an amino acid called histidine in ways that create inflammation
Some factories were barely running:
- Producing B vitamins (which you need for energy)
- Producing compounds for oxygen transport (which affects how efficiently your body burns calories)
And some were producing more of certain byproducts:
- Like a compound called uridine, which animal studies suggest makes you eat more
These bacterial byproducts don’t just stay in your mouth.
They get swallowed, enter your bloodstream, and travel to other parts of your body—including your gut and your brain, where they may influence how hungry you feel.
In other words, certain mouth bacteria might be making you crave more food.
The researchers don’t know yet whether bacteria cause obesity or whether obesity changes your bacteria. They need more studies to prove cause and effect.
But they’ve identified something important: a feedback loop.
Here’s how it might work:
You eat sugar and processed carbs → bacteria that love those foods multiply in your mouth → they produce compounds that make you hungrier → you eat more sugar and carbs → those bacteria multiply even more.
It’s a cycle that reinforces itself.
And this is why willpower alone often isn’t enough. You’re not just fighting cravings—you’re fighting bacteria that may be influencing those cravings.
The study also found that these bacterial differences were connected to health markers doctors already track for heart disease and metabolic problems—things like triglycerides (fats in your blood) and liver enzymes.
Scientists are starting to see your mouth and gut bacteria as one connected system—what they call the “oral-gut axis.”
This makes your mouth like an early warning system for metabolic health. We’re just beginning to understand how to read those warning signs
What You Can Do Starting Today…
1. Stop using antiseptic mouthwashes. They kill beneficial bacteria indiscriminately. Let your saliva maintain balance naturally.
2. Switch to microbiome-friendly toothpaste. Most contain essential oils that disrupt beneficial bacteria. I created Fygg to avoid this—nano-hydroxyapatite with zero microbiome-disrupting ingredients. (Code ATD15)
3. Add an oral probiotic at bedtime. Look for one with Streptococcus salivarius, like this one. Let it dissolve slowly after brushing.
4. Chew xylitol gum after meals. It feeds beneficial bacteria while starving harmful ones, helping break the feedback loop.
5. Support healthy saliva flow. Beneficial bacteria need moisture. Magnesium helps salivary glands function properly. Look for one that isn’t just one or two types of mangesium, like this one, which contains seven forms.
6. And this recommendation is key! Test your oral microbiome. If you’ve been struggling with weight despite doing everything right, a saliva test can show exactly which bacteria are out of balance. I’m a scientific advisor for Bristle, which offers home testing that maps your oral microbiome and identifies bacteria linked to inflammation and metabolic issues. (I cant emphasize this rec enough. No test, no data, no hands on the steering wheel.)
7. Cut or reduce ultra-processed foods and refined carbs. These feed bacteria that produce appetite-increasing metabolites.
8. Address mouth breathing. If you snore or wake up with a dry mouth, mouth breathing could be killing beneficial bacteria for 56 hours a week. Mouth taping can help. Find help at AADSM.org or in my Functional Dentist Directory. (More in my book on this topic.)
Medicine has treated the mouth as separate from the body. But your oral health IS your metabolic health. The metabolites oral bacteria produce can affect your appetite, inflammation, and cardiovascular markers.
If you’ve been struggling with weight despite doing everything right, your oral microbiome might be the missing piece.
And unlike genetics, you can change it.
Which changes will you make today?
Mark
Further Reading & Citations
1. Article on New Scientist: Our oral microbiome could hold the key to preventing obesity (January 22, 2026)
2. Study: Integrative multi-omics analysis reveals oral microbiome-metabolome signatures of obesity (January 22, 2026)
3. Previous newsletter: Is your mouthwash blocking weight loss? (July 1, 2025)