28 Aug 2017 --- Findings from several studies presented earlier this year at the 2017 Experimental Biology conference in Chicago have emphasized the wide range of potential health benefits of red raspberries. Participants in short-term human trials funded and supported by the US National Processed Raspberry Council (NPRC) experienced an improvement in glucose control and increased satiety, the NPRC reports in a press release, while longer-term animal trials showed promising effects on the gut microbiota after red raspberry intake.

Red raspberries have previously been found to support age-sensitive measures of learning, memory and motor performance in older rats, while their close relatives black raspberries have been linked to improved cardiovascular disease risk in metabolic syndrome. Now the observations from animal and in vitro studies have provided insights that could lead to more red raspberry research exploring potential beneficial effects on reducing inflammation, obesity and type 2 diabetes risk.

“We are excited about this new flurry of studies, which builds on previously published research aimed to better understand the potential health benefits of red raspberries,” says Tom Krugman, Executive Director of the National Processed Raspberry Council (NPRC). “Our council is committed to delivering the highest quality nutrition and health science that consumers can use to make informed choices when aiming for a healthy diet.”

Preliminary evidence from the 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.

Keeping blood sugar in check
In a 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 normoglycemia and insulinemia. They reported that participants experienced a significant reduction in glucose after a meal when two cups (250g) of red raspberries were consumed with meals compared to no raspberries. The glucose lowering came with less insulin, suggesting improved insulin sensitivity in individuals with pre-diabetes and insulin resistance.

Type 2 diabetes’ effects could decrease
Possible benefits for those with diabetes were also observed. In an animal study, mice fed 5 percent freeze dried raspberry for 12 weeks showed signs of improved insulin resistance and reduced inflammation in skeletal muscle while consuming a high-fat diet.

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. It is noted that more research is needed to determine if compounds in red raspberries play a role in human cardiometabolic pathways.

Feeling full
In a secondary objective of the blood sugar control study, researchers for “The Effect of Red Raspberry on Satiety” study 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 two cups (250g) of red raspberries compared to a calorie-matched control meal without raspberries. However, the researchers note that because this study was limited to three meals, further research is needed to determine the factors that influenced the study’s outcomes.

Good for the gut
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 four 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 noted to be promising, although further research is needed to support the hypothesis that the consumption of raspberry puree may change the composition of the gut microbiota.

Meanwhile, Dr. Giuliana Noratto and colleagues of the Department of Food and Nutrition Science at Texas A&M University tried to determine if supplementing a diet with red raspberries could modulate the fecal microbiota of obese mice with diabetes and dyslipidemia. In this animal study, it was discovered that 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 could be the basis for formulating hypotheses for conducting additional studies, particularly in human trials.

Fighting inflammation
In a mouse model, red raspberry supplementation of 5 percent 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. However, these observations in mice are not conclusive, and further research is needed to determine if red raspberry supplementation supports epithelial function in humans.

Anthocyanin profiles of processed raspberries
Researchers looked at anthocyanin profiles among common processed forms of raspberries (frozen, juice concentrate, seeded puree, and seedless puree) on the US market. They reviewed 34 samples, both domestic and imported. Seven individual anthocyanins were identified in the samples. While anthocyanin profiles varied slightly, contents varied considerably. This may reflect differences in varieties, origins and processing methods, among other influential factors.

Despite the variety of findings, the NPRC notes that conclusions cannot be drawn at this time. It says additional research, particularly in humans, is warranted.