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A bowl of unshelled pistachios on a wooden table

An estimated 38% of U.S. adults have prediabetes, and 74% of those people will develop Type II diabetes in their lifetime. Foods that reduce blood glucose levels may be able to help people maintain their health. A recent study by researchers in the Penn State Department of Nutritional Sciences examined whether pistachios could help regulate glucose when used as a nighttime snack. Though pistachios did not affect blood glucose levels, they did help people eat a healthier diet.

“A common dietary recommendation for individuals with prediabetes is to consume a nighttime snack consisting of 15-30 grams of carbohydrates to help regulate overnight and morning blood glucose levels,” said Terrence Riley, coauthor of this research and doctoral candidate in nutritional sciences at Penn State. “As an example, you could eat one or two slices of whole grain bread.”

To test whether pistachios were useful in this way, the researchers randomized 66 participants to receive two ounces of pistachios as an evening snack or to have 15-30 grams of carbohydrates as an evening snack for 12 weeks.

Kristina Petersen

For people who like pistachios, replacing their current evening snacks with pistachios may be a way to improve the overall quality of their diet.

Kristina Petersen

Results of the study, published in Journal of Nutrition, demonstrated that pistachio consumption did not regulate blood glucose levels better than education to have 15-30 grams of carbohydrate containing food. On the other hand, regular consumption of pistachios did improve diets overall because people consumed higher levels of plant-based proteins and unsaturated fatty acids, which are key components of healthy diets recommended by the United States Department of Agriculture’s Dietary Guidelines for Americans. 

“This study showed that eating two ounces of pistachios as an evening snack improved adherence to dietary recommendations,” said Kristina Petersen, associate professor of nutritional sciences and coauthor of the study. “For people who like pistachios, replacing their current evening snacks with pistachios may be a way to improve the overall quality of their diet, which in the long term is likely to have health benefits.” 

A parallel study by Petersen and her collaborators found that avocados had a similarly positive impact on people’s diet quality.   

Penny Kris-Etherton and Tricia Hart of the Penn State Department of Nutrition also contributed to this research. 

Petersen will be recruiting graduate students for Fall 2025. 

This study was conducted at the Clinical Research Center, a unit within the Penn State Clinical and Translational Science Institute. The study was funded by the American Pistachio Growers, but the sponsor was not involved in study design, data collection, analysis, interpretation, or writing of the research paper. 

Originally published in March 2024.