Eating pistachios in the evening could subtly change the makeup of gut bacteria in people with prediabetes, according to new research. The study found that replacing typical carbohydrate-based evening snacks with pistachios led to notable shifts in the gut microbiota, which may play a role in supporting better metabolic health. The findings were published in the journal Current Developments in Nutrition.
Researchers looked at 51 adults diagnosed with prediabetes who participated in a 12-week dietary intervention. Instead of the usual advice to eat one or two carbohydrate exchanges before bed, participants were given a daily portion of unsalted dry-roasted pistachios, equivalent to 57 grams. Stool samples were collected before and after the trial to assess how the gut microbiome responded.
While there were no significant changes in markers such as blood sugar or cholesterol between the two dietary approaches, analysis of stool samples revealed that pistachio consumption resulted in meaningful differences in the diversity and composition of gut bacteria. Although overall richness and evenness of microbes remained similar, several specific bacterial groups shifted in abundance.
Among the bacteria that increased following pistachio consumption were strains within the Lachnospiraceae family, including the Roseburia metagenome. These bacteria are known to produce butyrate, a short-chain fatty acid that fuels cells in the colon and may help reduce inflammation. In contrast, the usual carbohydrate-rich snack group showed higher levels of other microbes, such as Flavonifractor and Eubacterium coprostanoligenes, which have been linked to less favourable gut outcomes.
The study also found that participants who consumed pistachios had higher diet quality scores. This improvement in dietary quality, however, was not directly linked to the changes in gut bacteria, suggesting the pistachios themselves may have unique properties that influence microbial composition.
One of the factors thought to contribute to these changes is pistachios’ fibre content, especially insoluble fibre. Although not easily digested by bacteria, this type of fibre may still affect the gut environment by speeding up food transit and altering nutrient availability. The nuts are also rich in other compounds like phytosterols and polyphenols, which may also influence the microbial ecosystem.
Previous studies have shown similar effects from other tree nuts, such as almonds and peanuts, indicating that nuts in general might be beneficial for maintaining a healthy gut. However, this new study specifically demonstrates that pistachios can create distinct microbial shifts even without dramatic changes in metabolic markers.
The researchers caution that while these findings are promising, the effects were modest and the study did not control participants’ entire diets. Future studies are needed to understand whether changes in gut bacteria caused by pistachios lead to long-term improvements in health.