When it comes to questions about health and longevity, many researchers have been turning to the gut microbiome — the community of microorganisms like bacteria, viruses, and fungi that live in the human gut — for answers. Scientists are only beginning to understand the many ways the microbiome affects our health, but early evidence suggests it can play a role in disease outcomes like some kinds of cancer, long Covid, and Parkinson’s Disease.
Determining what foods are beneficial to the microbiome and, ultimately, different aspects of one’s health is an area of particular interest; it could provide a plethora of preventative and treatment options that currently don’t exist.
One particular area of interest is determining how spices affect our gut health. Herbs and spices have been used for centuries therapeutically, and the anti-inflammatory and antioxidant benefits of some common spices like garlic, ginger, and chili pepper are well documented. But these benefits are not necessarily mediated through the microbiome. So what do we know about spicy food and the microbiome?
Are spices beneficial to the gut microbiome?
A study published at the end of last year in the Journal of Nutrition sought to understand the effect of daily consumption of spices on the microbiome of people at a high risk of developing cardiovascular disease. These spices included cinnamon, ginger, cumin, and turmeric. All 48 study participants had obesity and at least one other cardiovascular risk factor, such as elevated glucose.
All participants were given the same diet for four weeks but given three different doses of herbs and spices: one group received 0.5 grams per day, one received 3.3 grams per day, and the last group received 6.6 grams per day.
Kristina Peterson, an assistant professor in the Department of Nutritional Sciences at Texas Tech University and one of the study researchers, tells Inverse that she and her colleagues wanted to build on previous research looking at spices and the microbiome. A 2019 study published in the journal Nutrients found that a 5-gram capsule containing spices, including ginger, black pepper, and cayenne pepper, changed the composition of gut bacteria after two weeks.
In contrast to previous studies, like the 2019 study in Nutrients, “Our study is the first to look at spices consumed as part of meals and snacks [as opposed to a supplement],” Peterson says.
In particular, the researchers wanted to see how the composition of the Ruminococcaceae family of bacteria might change after adding spices to meals and snacks. The researchers focused on this family of bacteria because previous research suggested people with more Ruminococcaceae had lower long-term weight gain.
A different study found that changes in gut bacterial composition in mice, including enrichment of Clostridia from the Mogibacteriaceae and Ruminococcaceae families, contributed to the suppression of diet-induced obesity with exposure to cold temperatures. “This suggests that gut bacteria contribute to metabolic pathways that increase energy expenditure to protect against diet-induced obesity,” she says.
Ultimately, the researchers found that all groups saw an enrichment of the Ruminococcaceae bacteria; the results were dose-dependent: the group with the biggest increase in spice intake saw the biggest changes from baseline following the four weeks.
While we often hear about “good” bacteria compared to “bad” bacteria — Peterson cautions against assuming we know exactly how a certain kind of bacteria will affect the microbiome, much less clinical health outcomes.
“I would hesitate [to] describe bacteria as “good” or “bad,” we don’t know enough yet. Also, we need to think about the entire structure of the microbiome. Whether or not bacteria are suppressing or enhancing the enrichment of other bacteria and what the functions of these are,” she says.
Joe Schwarcz, the director of McGill University’s Office for Science and Society, agrees. His work s work focuses on helping the public accurately interpret science and health information. Schwarcz tells Inverse, “We have to be careful not to put the cart before the horse here. It’s so easy to say, ‘we have to nourish our microbiome and make sure that the good bacteria multiply at the expense of the bad bacteria,’” he says. “But nobody's really sure what those good bacteria are; over 500 bacterial species have been isolated from the gut. So the real question is, which of these are beneficial in a way that has clinical significance?”
Peterson is very aware of the distinction and wants to be clear about what the study she and her colleagues published says.
“In this study, we only looked at the composition of the gut microbiome; basically, we took a roll of who was present. We need more research investigating what these organisms are doing, their functionality, and how this contributes to health or disease.”
Indeed, other studies evaluating how spices may affect the microbiome are decidedly mixed. For example, a 2016 study published in The Journal of Endocrinology and Metabolism found that capsaicin — the compound that makes chili peppers hot — may be more beneficial for people with certain microbiome profiles. On the other hand, a 2022 study published in the journal Foods found that when researchers gave mice 40 mg of capsaicin, the mice experienced no ill effects, but at higher doses, the mice experienced inflammation of the GI tract and GI injury.
Further investigation led the researchers to conclude that the “underlying mechanisms might be related to the regulation of gut microbiota.” While people aren’t mice, these studies illustrate some of the challenges with definitively determining which spices are beneficial for the microbiome, if those benefits translate to clinical health outcomes, and if the same spices are necessarily beneficial for everyone.
“Now we have established that intake of herbs and spices as part of a diet that reflects what Americans eat does affect the composition of the gut microbiota, we can do further work to understand this more,” Peterson says. “At this point, it is premature to suggest herbs and spices should be consumed for gut health.”
However, Peterson says other benefits of consuming herbs and spices have nothing to do with the gut microbiome.
“Most importantly, adding herbs and spices is a great way to flavor healthy foods like vegetables to increase the taste and enjoyment of the food. We know veggies are good for health. So this is another way herbs and spices can indirectly help to improve diet, and in turn, health.”
Schwarcz puts it this way: “There's no reason not to add spice to your food. It may add some spice to your life. Just don’t expect it to make you live longer.”
