Do you enjoy raspberries?
If so, it might be a good idea to add more of them to your diet. Initial research shows that raspberries can help improve blood sugar control, increase satiety, and improve gut health.
Several new studies on the potential health benefits of red raspberries were presented at the 2017 Experimental Biology conference in Chicago.
Participants in human trials experienced an improvement in glucose control and increased satiety. Meanwhile, longer-term animal trials also revealed promising effects on the gut microbiota after red raspberry intake.
The observations from animal and in vitro studies provided insights that support future hypotheses for red raspberry research exploring potential beneficial effects on pathways related to reducing inflammation, obesity, and type 2 diabetes risk.
Preliminary evidence from these studies suggests that the actions of essential nutrients, fiber, and polyphenolic phytochemicals found in red raspberries may play a role in supporting key metabolic functions, including anti-inflammatory, anti-oxidative and metabolic stabilizing activity.
Blood Sugar Control
In this human trial, investigators from the Center for Nutrition Research at the Illinois Institute of Technology looked at two study groups: obese individuals with impaired fasting glucose and hyperinsulinemia (PreDM) and healthy weight individuals with normo-glycemia and insulinemia. Participants experienced a significant reduction in postprandial glucose when 2 cups (250g) of red raspberries were consumed with meals compared to no raspberries. The glucose lowering was accompanied with less insulin suggesting improved insulin sensitivity in individuals with pre-diabetes and insulin resistance.
In a secondary objective of the blood sugar control study, researchers found that subjects in the PreDM group who reported the highest level of hunger at baseline experienced greater satiety after the control meal compared to raspberry containing meals (p<0.05). In contrast, the healthy weight participants experienced significantly greater hunger suppression and wanted to eat less after a breakfast containing 2 cups (250g) of red raspberries compared to a calorie-matched control meal without raspberries. Because this study was limited to three meals, further research is needed to determine the factors that influenced outcomes.
In an eight-week pilot study, researchers from the Institute for Food Safety and Health from the Illinois Institute of Technology examined the impact of consumption of red raspberry purée or fructo-oligosaccharide on the gut microbiota and the subsequent bioavailability of red raspberry polyphenols in healthy volunteers. Consumption of the red raspberry puree and the fructo-oligiosaccharide for 4 weeks resulted in decreased Firmicutes and increased Bacteroidetes, which was more pronounced after red raspberry intake.
Additionally, a type of bacteria called Akkermansia that has been associated with metabolic health was increased during red raspberry intake only. These preliminary results are promising. Further research is needed to support the hypothesis that the consumption of raspberry puree may change the composition of the gut microbiota.
Dr. Giuliana Noratto and colleagues of the Department of Food and Nutrition Science at Texas A&M University studied if dietary supplementation with red raspberries could modulate the fecal microbiota of obese mice with diabetes and dyslipidemia.
In this study, raspberry supplementation was associated with higher levels of Lachnospiraceae – a family of bacteria that can be depleted during diseases of the intestinal tract, such as inflammatory bowel disease. These findings provide a basis for formulating hypotheses for conducting additional studies, particularly in human trials.
Type 2 Diabetes
In an animal study, mice fed 5% freeze dried raspberry for 12 weeks, showed signs of improved insulin resistance and reduced inflammation in skeletal muscle while consuming a high-fat diet. These data corroborate a short-term study in humans reported by Xiao and colleagues at the same meeting supporting further work in humans to provide additional insight into these findings.
A research team from the University of Michigan studied the potential biologically active properties of red raspberries with in vitro assays including antioxidant and anti-inflammatory capacities. Follow-up research explored the potential relationship between feeding freeze-dried whole raspberry powder and cardiometabolic risk in obesity prone rats.
Red raspberries were found to upregulate the expression of specific cardiac-protective molecular proteins (myocardial adiponectin, its receptor 2, and apolipoprotein E). Rats fed the red raspberries also experienced altered nicotinamide phosphoribosyltransferase mRNA, a protein associated with multiple functions in conditions related to obesity and type 2 diabetes. More research is needed to determine if compounds in red raspberries play a role in human cardiometabolic pathways.
In a mouse model, red raspberry supplementation of 5% dry feed weight was found to suppress inflammation and facilitate epithelium repair compared to mice with induced colitis (inflammation of the colon) and fed a standard chow diet. These observations are not conclusive, and further research is needed to determine if red raspberry supplementation supports epithelial function in humans.