Before you start a GLP-1, check this first

The bacteria that cause cavities just showed up in a new study on obesity.

Researchers looked inside the mouths of 628 adults. The people with obesity carried more of the same sugar-eating, acid-making bacteria I’ve spent nearly 40 years scraping off teeth.

Here’s what they found, and what I’d do before starting a GLP-1…

The bacteria linked to obesity are the same kind that cause cavities

People with obesity had more sugar-fermenting, acid-making bacteria (Streptococcus, Actinomyces, Lactobacillus) and more lactate, the acid those bacteria leave behind. (That’s the same crew that dissolves enamel.)

They also had fewer of the bacteria that make B vitamins, and fewer of the ones that turn the nitrate in leafy greens into nitric oxide. Your blood vessels depend on that nitric oxide to keep blood pressure down.

Which came first, the weight or the bacteria? The study can’t say, of course.

Sugar feeds these bacteria, and when blood sugar runs high, sugar shows up in saliva and feeds them too. I think it’s a loop, and your mouth is the one part of that loop you can see and actually treat.

Treating gum disease lowers blood sugar with no new prescription

In people with diabetes, treating gum disease lowered HbA1c by about 0.4 points within three to four months, according to a Cochrane review pooling dozens of randomized trials.

The treatment was mainly scaling and root planing, the professional deep cleaning. Infected gums keep the whole body inflamed, and inflammation makes blood sugar harder to control. Clear the infection, and the numbers move!

This is why both deep cleanings and proper diet are essential.

GLP-1 drugs can dry out your mouth, and saliva is your cavity defense

Dry mouth is one of the side effects reported with semaglutide (Ozempic, Wegovy).

Saliva neutralizes the acid those sugar-fermenting bacteria make, and it carries the calcium and phosphate that rebuild enamel.

Less saliva means the acid-makers win. Add the nausea and vomiting many people get on these drugs, and your teeth are being exposed to stomach acid too.

Four things to do before your first dose

1. Get your gums checked, and get the deep cleaning if you need it. An infection in your gums keeps working against your blood sugar the whole time you’re on the drug.
2. Throw out your antibacterial mouthwash. In a three-year study of 945 overweight adults, people who rinsed twice a day or more were about 50% more likely to develop prediabetes or diabetes than people who didn’t rinse. Those rinses wipe out the bacteria that make nitric oxide. If it says antibacterial, throw it out. Then brush with this, which is designed to feed the bacteria that make nitric oxide.
3. Eat leafy greens every day and cut the sugar. Greens are the nitrate your nitric-oxide bacteria run on. Sugar and refined carbs are what the acid-makers run on. And pour yourself a green tea. It suppresses S. mutans, one of the main acid-makers, and it’s the reason green tea is my daily drink.
4. Protect your saliva. Drink water all day, and add electrolytes (my favorite ones here) on the days you’re barely eating or feeling sick, because a dehydrated body can’t make much saliva. Electrolytes help prevent cavities, too. Tape your mouth at night so it doesn’t dry out while you sleep. 

What will you do next, now that you’ve read this?

The studies in this issue

1. The obesity and mouth bacteria study (628 adults): Shibl AA et al. “Integrative multi-omics analysis reveals oral microbiome-metabolome signatures of obesity.” Cell Reports, 2026. Read it
2. Treating gum disease lowers HbA1c: Simpson TC et al. “Treatment of periodontitis for glycaemic control in people with diabetes mellitus.” Cochrane Database of Systematic Reviews, 2022. Read it
3. Mouthwash and prediabetes (945 adults, 3 years): Joshipura KJ et al. “Over-the-counter mouthwash use and risk of pre-diabetes/diabetes.” Nitric Oxide, 2017. Read it
4. Mouthwash, nitric oxide and blood pressure: Kapil V et al. “Physiological role for nitrate-reducing oral bacteria in blood pressure control.” Free Radical Biology and Medicine, 2013. Read it
5. GLP-1 drugs and your mouth, including dry mouth: Bijoch J. “Oral Health Implications of GLP-1 Receptor Agonists and Other Incretin-Based Therapies.” Journal of Clinical Medicine, 2026. Read it

If you want to go deeper

• Nitric oxide bacteria and insulin resistance: Goh CE et al. “Association Between Nitrate-Reducing Oral Bacteria and Cardiometabolic Outcomes: Results From ORIGINS.” Journal of the American Heart Association, 2019. Read it
• Where the obesity and mouth bacteria question started: Goodson JM et al. “Is Obesity an Oral Bacterial Disease?” Journal of Dental Research, 2009. Read it
• Toddlers, weight gain and mouth bacteria: Craig SJC et al. “Child Weight Gain Trajectories Linked To Oral Microbiota Composition.” Scientific Reports, 2018. Read it