Eating Pistachios at Night Could Transform Your Gut Health, Study Reveals
Eating pistachios every night for 12 weeks changed the composition of gut bacteria, according to a new study.
Roughly one-third of individuals in the United States are affected by prediabetes, and the majority are likely to progress to Type 2 diabetes. Despite this, there are few proven dietary strategies that effectively prevent or delay the condition. Pistachios have been linked to improved markers of diet quality, but their specific effects on the gut microbiome—a key factor in regulating blood sugar and inflammation—are not well understood.
In a recent study led by Kristina Petersen, associate professor of nutritional sciences at Penn State, researchers examined how eating pistachios as a nighttime snack influenced gut bacteria in adults with prediabetes. While the full therapeutic impact is not yet known, Petersen noted that these findings could be meaningful for individuals aiming to support their metabolic health.
Published in Current Developments in Nutrition, the study found that substituting pistachios for a typical carbohydrate-based snack before bed may alter the gut microbiome. Prior research by the same team showed that pistachios can affect blood glucose in a manner comparable to consuming 15 to 30 grams of carbohydrates.
Pistachios vs. traditional carb snacks
“A common dietary recommendation for individuals with prediabetes is to consume a nighttime snack consisting of 15 to 30 grams of carbohydrates to help regulate overnight and morning blood glucose levels,” said Terrence Riley, lead author of this research who earned his doctorate in nutritional sciences at Penn State and currently works as a postdoctoral research fellow at Louisiana State University. “As an example, you could eat one or two slices of whole grain bread.”
Over a 12-week period, researchers found that individuals who ate approximately two ounces of pistachios each night developed noticeably different gut microbial profiles compared to those who followed the standard recommendation of consuming 15 to 30 grams of carbohydrates as a bedtime snack. Among the changes observed, certain beneficial bacteria—such as Roseburia and members of the Lachnospiraceae family, which are known for producing health-supporting short-chain fatty acids like butyrate—were present in greater numbers after pistachio consumption.
Microbial byproducts and anti-inflammatory potential
Petersen explained that butyrate acts as a key energy source for cells in the colon, plays a role in preserving the integrity of the gut lining, and contributes to reducing inflammation.
“Pistachios seem to be able to meaningfully shift the gut microbial landscape in adults with prediabetes especially when consumed as a nighttime snack,” Petersen said. “These microbiome changes may offer other long-term health benefits — potentially helping to slow the development of Type 2 diabetes or to reduce systemic inflammation — which we hope to explore in future research.”
Clinical trial design and participants
The study involved 51 adults with prediabetes and was conducted over two 12-week periods separated by a break, so the effects of the first part of the trial would not affect the second part. By the end of the study, all participants received both treatments. Stool samples were collected and analyzed using 16S rRNA gene sequencing, a technique that can help classify bacteria based on their genetic makeup.
Petersen noted that participants who ate pistachios also experienced reductions in several bacterial groups that have been linked to less favorable metabolic outcomes.
“Levels of Blautia hydrogenotrophica — a bacterium that helps produce compounds that can build up in the blood and harm kidney and heart health — were lower after pistachio consumption,” Petersen said. “Levels of Eubacterium flavonifractor, which breaks down beneficial antioxidant compounds from foods like pistachios, also decreased.”
Study design helps isolate pistachio effects
Petersen added that the strength of this study is the design used — a randomized crossover clinical trial, in which all participants receive both treatments in a randomized order. By including all participants in the pistachio group and the standard care group, the study helped the researchers better understand how specific foods like pistachios can influence the gut microbiome.
While the study demonstrated shifts in gut bacteria, it remains unclear whether these changes directly translate to improvements in health — a question that requires further research, Petersen said.
Reference: “Nighttime Pistachio Consumption Alters Stool Microbiota Diversity and Taxa Abundance Compared with Education to Consume 1–2 Carbohydrate Exchanges (15–30 grams) over 12 Weeks in Adults with Prediabetes: A Secondary Analysis from a Randomized Crossover Trial” by Terrence M Riley, Justin Wright, Regina Lamendella, Jordan E Bisanz, Jeremy Chen See, Khushi Kanani, Penny M Kris-Etherton and Kristina S Petersen, 27 May 2025, Current Developments in Nutrition.
DOI: 10.1016/j.cdnut.2025.107481
The study was funded by the American Pistachio Growers, Penn State’s Clinical and Translational Science Institute through the National Center for Advancing Translational Sciences of the National Institutes of Health, and additional support from Juniata College and the U.S. National Science Foundation. It is registered at ClinicalTrials.gov (NCT04056208).
