Scientists have identified more than 3,000 species of bacteria living in the human gut. We know they play a role in digestion and immune function. But can they also influence the kinds of food we crave?
In a 2014 study in the journal BioEssays, researchers proposed that gut microbes might manipulate the eating behavior of their hosts by generating cravings for foods the bacteria thrive on, or even causing discomfort until the host eats what benefits them.
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Salmonella Typhimurium is one example. It hijacks the chemical signals between the gut and brain to keep its host eating through infection.
“Typically, when you have a GI [gastrointestinal] infection, you stop eating,” Alcock said. “And Salmonella [Typhimurium] seems to actually impair that … so that animals continue to eat and continue to produce infectious particles in their poop that go on to infect other animals.”
However, this was a theoretical paper — it proposed mechanisms by which microbes could manipulate cravings, but hadn’t demonstrated that they do. The pathways it proposed — including things like altering taste receptors and hijacking the vagus nerve — were plausible, but unconfirmed, especially in the context of everyday food cravings.
How the microbiome may influence food choices
In 2022, researchers tested this hypothesis. In their study, Kevin Kohl, an associate professor of biology who focuses on how interactions with microbes impact the physiology, ecology and evolution of animal hosts at the University of Pittsburgh, and Brian Trevelline, a microbiologist and postdoctoral fellow at Cornell University, transplanted microbiomes from wild rodents with different diets — carnivore, herbivore and omnivore — into germ-free mice, and then measured what they ate.
“I perhaps naively thought that the carnivore-inoculated mice were going to eat the high-protein diet,” Kohl told Live Science. “That’s not what we saw.”
Instead, the mice with herbivore microbiomes preferred protein, while the mice with carnivore microbiomes preferred carbs. But a key finding held: Different microbiomes led to significantly different food choices.
But how? Gut bacteria can produce many of the same neurotransmitters the brain uses to regulate appetite, including serotonin, which signals to the brain when you’ve had enough to eat. In fact, roughly 90% of the body’s serotonin is produced in the gut, not in the brain, and research has shown that gut bacteria play a direct role in that production.
I could totally see some feedback cycles where shifts in the microbiome either perpetuate behaviors or bring about different cravings
Kevin Kohl, associate professor of biology at the University of Pittsburgh
In the mouse study, the team found that the mice that received the herbivore microbiome had significantly more tryptophan — a building block of serotonin — in their blood. Previous research has shown that higher serotonin levels suppress carbohydrate cravings in particular, which may explain why those mice shifted toward a high-protein diet.
“That might be at least one potential avenue in which the microbiome is affecting diet, appetite and dietary preferences,” Trevelline said.
The findings also raise the possibility that the relationship runs both ways. If your microbiome shapes your cravings, and your diet shapes your microbiome, small changes in what you eat could shift the cycle over time.
“I could totally see some feedback cycles where shifts in the microbiome either perpetuate behaviors or bring about different cravings,” Kohl said.
However, Kohl and Trevelline’s study was in mice. “Food choice is really tricky and totally different in humans,” Kohl said. “It’s influenced by culture, society, economics, learned behaviors, associations.” In other words, a lot of other factors affect our dietary choices.
Still, one recent research paper has started to connect these findings to human health. In a 2025 study published in the journal Nature Microbiology, researchers found that a gut bacterium called Bacteroides vulgatus can suppress sugar cravings in mice by producing a metabolite that triggers the production of glucagon-like peptide-1 (GLP-1), the same hormone targeted by drugs like Ozempic. People with type 2 diabetes also had lower levels of this bacterium, the researchers found.
But Kohl cautioned against giving your microbes too much credit for your choices. “Free will still exists,” he said. “The microbes are not driving our choices. But these cravings, low-grade feelings about food — those come from our internal nutritional state” — things like amino acids and other compounds circulating in the body — “which we know is influenced by the microbiome.”
