Nighttime pistachio consumption affects gut bacteria in adults with prediabetes

Prediabetes affects a third of people in the United States and most of them will develop Type 2 diabetes, yet effective dietary intervention strategies remain limited. Pistachios have shown promise in improving markers of diet quality, yet little is known about how they influence the gut microbiome - a key player in glucose regulation and inflammation.

A new study led by Kristina Petersen, associate professor of nutritional sciences at Penn State, determined that nighttime pistachio consumption affects gut bacteria in adults with prediabetes. Though the potential therapeutic implications of the findings remain unclear, according to Petersen, they may prove significant for people who are working to improve their metabolic health.

The findings, published in the journal Current Developments in Nutrition, suggested that replacing a traditional carbohydrate-based bedtime snack with pistachios may reshape the gut microbiome. A previous study by these researchers demonstrated that pistachios have a similar effect on blood glucose as 15 to 30 grams of carbohydrates.

"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."

Researchers observed that consuming about two ounces of pistachios each night for 12 weeks resulted in significantly different stool microbial community profiles compared to those who consumed the recommended 15 to 30 grams of a carbohydrate snack. Specific bacterial groups, including Roseburia and members of the Lachnospiraceae family - known as "good" bacteria that produces beneficial short-chain fatty acids like butyrate - were more abundant following the pistachio condition.

According to Petersen, butyrate serves as a primary energy source for colon cells, helps maintain the gut barrier and supports anti-inflammatory processes. 

Pistachios seem to be able to meaningfully shift the gut microbial landscape in adults with prediabetes especially when consumed as a nighttime snack. 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."

Kristina Petersen, associate professor of nutritional sciences, Penn State

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."

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.

Jordan Bisanz, assistant professor of biochemistry and molecular biology at Penn State; Penny Kris-Etherton, retired professor of nutritional sciences at Penn State; Justin Wright of Wright Labs, LLC; and Regina Lamendella, Jeremy Chen See and Khushi Kanani of Juniata College all contributed to this research.

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).