The Bedtime Snack That May Help Gut Bacteria and Prevent Diabetes

A handful of pistachios before bed might do more than satisfy a late-night craving. A new study from Penn State suggests that replacing a typical nighttime carbohydrate snack with pistachios can meaningfully shift gut bacteria in adults with prediabetes—potentially supporting metabolic health and slowing the progression to Type 2 diabetes.

The 12-week randomized clinical trial found that eating about two ounces of pistachios every night increased levels of beneficial gut microbes, including Roseburia and members of the Lachnospiraceae family, while reducing harmful bacteria linked to poorer metabolic outcomes.

Gut Changes That Could Protect Against Diabetes

Prediabetes affects roughly one-third of U.S. adults, most of whom will develop Type 2 diabetes without intervention. A person with Type 2 diabetes doesn't have as good of an insulin response, so the way the body processes sugars is hindered, and blood sugar is tougher to manage.

The pistachio group saw a boost in Roseburia, a bacteria that produces butyrate—a short-chain fatty acid that supports colon health, strengthens the gut barrier, and helps regulate inflammation. Participants also showed a drop in Blautia hydrogenotrophica, a bacterium associated with kidney and heart complications, and Eubacterium flavonifractor, which breaks down beneficial antioxidants from plant foods.

A positive gut environment can help reduce inflammation and promote overall health, thereby slowing the progression of prediabetes into full Type 2 diabetes.

How to Help Gut Bacteria and Prevent Diabetes? Try a Simple Snack Swap

For decades, standard advice for people with prediabetes has been to eat a bedtime snack with 15 to 30 grams of carbohydrates to help regulate blood sugar overnight—often something like whole-grain bread. In this study, that standard snack was replaced with pistachios for half the trial period in a randomized crossover design, meaning all 51 participants experienced both treatments.

Pistachios are not a magic food, and they have a similar impact on blood sugar levels as a 15 to 30-gram carbohydrate snack. However, they are much more beneficial to the microbiome than a typical carb snack, and this means benefits for the gut and overall health.

More Research Ahead

While the study provides compelling evidence that pistachios can reshape the gut microbiome in beneficial ways, the researchers caution that more work is needed to confirm whether these changes directly reduce diabetes risk or if the impact is only indirect.

“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,” said the study's leader.