July 18, 2025, 11:00 am | Read time: 5 minutes
Diabetics are often advised to have a small carbohydrate-rich snack before bedtime, ideally in the form of whole grains or legumes, to maintain stable blood sugar levels overnight. Additionally, previous studies have shown that consuming pistachios can positively affect glucose levels. A recent study has now combined both approaches–and according to the study authors, achieved promising results. FITBOOK author Laura Pomer explains what the researchers discovered.
Overview
Study on the Effect of Pistachios as an Evening Snack
The study focused on individuals with prediabetes, a condition with elevated blood sugar levels that are still below the threshold for type 2 diabetes. Prediabetes is considered a serious precursor to the chronic disease–without targeted interventions, it can develop into full-blown diabetes. However, this also means that those affected have a last chance to prevent this progression. FITBOOK recently reported that a certain weekly exercise regimen can reverse prediabetes.1
Of course, diet is also a crucial factor when it comes to metabolism. In the context of diabetes and prediabetes, previous studies have already shown an effect of pistachios. They suggest that regular consumption of the nuts can positively impact certain health markers.2,3 However, little is known about the effects of pistachios on the gut microbiome–which plays a key role in glucose regulation and inflammation. Study leader Kristina Petersen aimed to change that.4,5
Study Procedure
Fifty-one adults with prediabetes participated in the study. It was conducted in two test phases of twelve weeks each, with a time gap between them. This was to exclude overlapping effects, meaning the effects of each intervention could be evaluated independently. In the first test phase, participants were instructed to consume 57 grams of pistachios every evening before bedtime. In the second phase, they had a snack of whole-grain crackers and low-fat cheese with a similar calorie content to the pistachios. The snack contained 15 to 30 grams of carbohydrates, which is generally associated with a favorable effect on blood sugar levels. Throughout the study, all participants experienced both dietary forms.
The researchers collected various health parameters from the participants. These included fasting blood sugar, insulin levels, and certain indicators of the participants’ overall diet. At the beginning and end of the two twelve-week study phases, the researchers also collected stool samples from the participants. These were analyzed using a special molecular biological method to examine the gut microbiome, focusing on microbial diversity. The researchers looked at both the overall diversity within a single microbiome and the differences between individual samples.
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Results: Pistachios in the Evening Improve Gut Bacteria Profile
The evaluations showed that the composition of the gut flora changed significantly during the pistachio phase compared to the carbohydrate phase. In particular, “good” bacteria like Roseburia and Lachnospiraceae increased. These are considered particularly beneficial to health because they produce short-chain fatty acids, which serve as an energy source for intestinal cells. An example is butyrate, also known as butyric acid, which has been proven to contribute to gut health. Additionally, the researchers found that stool samples after the pistachio phase “showed fewer bacterial groups associated with less favorable metabolic outcomes,” according to Peterson.
In summary, the study suggests that regular consumption of pistachios in the evening positively affects the gut microbiome. As an evening snack, the nuts could thus improve metabolic health. This is not far-fetched–the high-quality “inner values” of pistachios have long been known. In addition to high amounts of valuable unsaturated fatty acids, they contain a remarkable protein content for nuts. More information can be found here.
Important Limitations
The study was funded by the American Pistachio Growers (APG), an interest group of the U.S. pistachio industry. The authors emphasize that this did not influence the study design, data collection, or analysis. However, a potential conflict of interest should be considered when evaluating the results.
Additionally, the small size of the study is a limitation. Only 51 people participated, the majority of whom were male. Therefore, the results need to be supported by more extensive studies. And since only prediabetics were examined, doubts remain about the applicability to healthy individuals. Finally, the evaluation did not consider other factors that could influence the gut microbiome besides the impact of pistachios or carbohydrate-rich snacks in the evening. It is possible that participants engaged in other habits or measures during the test phases that positively or negatively affected the bacterial colonization in the gut. Lastly, it is not even guaranteed how strictly the participants adhered to the study guidelines, as the researchers did not monitor their evening routine. It is conceivable that they did not stick to the defined amount of cheese crackers, or perhaps they occasionally skipped the pistachio servings–various scenarios are possible.
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Conclusion
At present, it cannot be stated that snacking on pistachios in the evening can reverse prediabetes. However, the researchers view the observed effect on the gut microbiome as a promising finding. It is clear, though, that while the gut microbiome may play an important supportive role, it is not solely decisive in whether prediabetes can be alleviated or completely halted.