Evening pistachio snacking may improve prediabetic adults’ gut microbiome

Eating pistachios at night could improve gut bacteria in adults with prediabetes, with the added benefit of supporting metabolic health, new research suggests. While potential therapeutic implications of the finding remain unclear, the benefits come with replacing a traditional carbohydrate-based bedtime snack with the nut. 

Specific bacterial groups, including Roseburia and members of the Lachnospiraceae family — known as “good” bacteria that produce beneficial short-chain fatty acids like butyrate — were more abundant following the pistachio condition.

Butyrate serves as a primary energy source for colon cells, which 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,” says Kristina Petersen, study author and associate professor of nutritional sciences at Penn State University, US.

A previous study by these researchers demonstrated that pistachios have a similar effect on blood glucose as 15 to 30 g of carbohydrates, similar to one or two slices of whole grain bread.

“A common dietary recommendation for individuals with prediabetes is to consume a nighttime snack consisting of 15 to 30 g of carbohydrates to help regulate overnight and morning blood glucose levels,” says Terrence Riley, lead author of this research and postdoctoral research fellow at Louisiana State University, US. 

Two ounces of pistachios

The gut microbiome plays a critical role in regulating glucose and tackling inflammation.

Studyparticipants who ate pistachios experienced reductions in several “bad” bacteria groups.The study involving 51 adults with prediabetes collected and analyzed stool samples using 16S rRNA gene sequencing, a technique that can help classify bacteria based on their genetic makeup.

The 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 15–30 g of a carbohydrate snack. 

Reducing “bad” gut bacteria

Petersen adds that participants who ate pistachios 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,” she highlights. 

“Levels of Eubacterium flavonifractor, which breaks down beneficial antioxidant compounds from foods like pistachios, also decreased.”

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 notes.

“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.”

Prediabetes affects a third of people in the US. Although most of them will develop type 2 diabetes, the researchers stress that effective dietary intervention strategies remain limited.

The study findings are published in the journal Current Developments in Nutrition. 

Previous clinical research supports that daily pistachio consumption may significantly improve eye health. In particular, scientists conclude that eating 57 g of pistachios daily for 12 weeks increases macular pigment optical density due to the plant pigment lutein found in the nuts.