Why Losing Weight Feels Harder — What You Can Do Now

For years, when patients asked me about weight gain, I would often redirect them: “That’s not really my area. Talk to your doctor.”

I was wrong.

A recent study has connected pieces I’ve long suspected: the bacteria in your mouth may influence your weight.

Researchers at NYU Abu Dhabi collected saliva from 628 adults, carefully matching people with obesity to those at a healthy weight by age, sex, lifestyle, and oral hygiene habits. Then they analyzed the bacteria living in each person’s mouth.

The human mouth hosts more than 750 types of bacteria. The study found clear differences in how those bacteria function in people with obesity versus those at a healthy weight.

Think of oral bacteria as tiny biochemical factories: they consume nutrients and release metabolic byproducts. The researchers identified 94 distinct functional differences in bacterial activity associated with obesity.

Some bacterial pathways were overactive:

Breaking down carbohydrates and producing lactate, a compound the body can convert to fat
Degrading the amino acid histidine in ways that promote inflammation

Other pathways were underactive:

Producing B vitamins that support energy metabolism
Generating compounds involved in oxygen transport, which can affect how efficiently the body burns calories

Certain byproducts were produced in greater amounts:

For example, uridine, which in animal studies is linked to increased food intake

These bacterial byproducts do not stay confined to the mouth.

They are swallowed, enter the bloodstream, and travel to other organs—including the gut and the brain—where they can influence appetite and metabolism.

In other words, some oral bacteria may promote cravings and overeating.

The study does not prove whether the bacteria cause obesity or whether obesity alters the oral microbiome. More research is needed to establish causation.

Still, the researchers describe a plausible feedback loop:

You consume sugar and refined carbohydrates → oral bacteria that thrive on these foods multiply → those bacteria produce metabolites that increase hunger → you eat more sugar and refined carbs → the bacteria flourish further.

This self-reinforcing cycle helps explain why willpower alone often fails: cravings may be driven in part by microbial activity, not just personal choice.

The study also linked these oral bacterial patterns to medical markers that predict cardiovascular and metabolic risk, including triglyceride levels and liver enzyme activity.

Researchers are increasingly viewing oral and gut microbes as a connected system—the “oral-gut axis.” That perspective positions the mouth as an early indicator of metabolic health, with oral microbial metabolites signaling risks before they appear elsewhere.

Practical steps you can take now

1. Avoid antiseptic mouthwashes. They can kill beneficial bacteria along with harmful ones and disrupt the oral ecosystem.

2. Consider microbiome-friendly toothpaste that avoids ingredients known to disrupt beneficial bacteria.

3. Try an oral probiotic at bedtime containing Streptococcus salivarius. Let it dissolve slowly after brushing to help repopulate beneficial strains.

4. Chew xylitol gum after meals. Xylitol can support beneficial bacteria while inhibiting harmful species, potentially helping to break the appetite-promoting feedback loop.

5. Support healthy saliva flow. Saliva maintains microbial balance; nutrients like magnesium support salivary gland function.

6. If weight is difficult despite diet and exercise, test your oral microbiome. A saliva test can identify imbalances linked to inflammation and metabolic problems, giving you actionable data to guide changes.

7. Reduce ultra-processed foods and refined carbohydrates. These feed bacteria that produce metabolites associated with increased appetite.

8. Address mouth breathing. Snoring or waking with a dry mouth can reduce protective oral moisture and harm beneficial bacteria. Addressing nasal breathing and sleep-disordered breathing can help preserve oral microbial health.

Medicine has long treated the mouth as separate from the rest of the body, but oral health is tightly connected to metabolic health. Metabolites produced by oral bacteria can affect appetite, inflammation, and cardiovascular risk factors.

If you’ve struggled with weight despite healthy habits, your oral microbiome could be a missing piece—and unlike genetics, it is something you can change.

Which change will you make today?

Mark

Further Reading & Citations