Replacing a bedtime carb snack with pistachios significantly altered gut bacteria in adults with prediabetes.
Beneficial microbes linked to anti-inflammatory effects and gut health increased after pistachio snacking.
Harmful bacteria tied to heart and kidney risks were reduced during the pistachio phase of the study.
If you’ve ever reached for toast or a few cookies before bed, you’re not alone.
However, researchers at Penn State recently asked a fun question: what if you replaced that carb-heavy snack with pistachios instead?
For adults with prediabetes, they wondered whether a nighttime pistachio habit could nudge the gut microbiome in a healthier direction.
“Pistachios seem to be able to meaningfully shift the gut microbial landscape in adults with prediabetes especially when consumed as a nighttime snack,” researcher Kristina Petersen said in a news release.
“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.”
The study
The study involved 51 adults diagnosed with prediabetes. For 12 weeks, the participants were assigned to one of two different test groups: one group was instructed to eat two ounces (57 grams) of unsalted pistachios each night, and the other group was instructed to eat 15-30 grams of carbs.
“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,” researcher Terrence Riley said in the news release.
“As an example, you could eat one or two slices of whole grain bread.”
At the beginning and end of the 12‑week period, stool samples were collected and analyzed using 16S rRNA gene sequencing. That’s a lab method that lets scientists identify and compare which bacterial species are present in the gut .
The results
At the end of the pistachio phase, participants showed clear differences in their stool bacterial communities compared to when they followed the carbohydrate snack routine. Statistical tests confirmed that the overall bacterial diversity was significantly different between the two conditions.
Specifically, levels of bacteria like Roseburia and members of the Lachnospiraceae family increased. These are known to produce butyrate, a short‑chain fatty acid that fuels colon cells, helps maintain the gut lining, and supports anti‑inflammatory pathways.
At the same time, the pistachios led to decreases in some bacterial taxa linked to less favorable outcomes. For example, Blautia hydrogenotrophica — which produces compounds associated with adverse effects on heart and kidney health — and Eubacterium flavonifractor — which can break down antioxidant compounds — were both lower after pistachios.
Bottom Line
While this doesn’t mean pistachios are a miracle cure for prediabetes, the findings suggest that switching from a simple-carb bedtime snack to pistachios could meaningfully reshape the gut microbiome in a way that may support metabolic and gut health.