Raspberries improve postprandial glucose and acute and chronic inflammation in adults with type 2 diabetes

Background: Postprandial metabolic impairments in diabetes have been shown to play an important role in vascular complications. Dietary polyphenols and other bioactive compounds in berries have been shown to improve postprandial hyperglycemia and related metabolic impairments, but few clinical studies have been reported in diabetes. Objective: To examine the effects of daily dietary raspberries on postprandial and 4-week fasting glucose, lipids and biomarkers of inflammation in obese adults with type 2 diabetes. Design: This was a randomized crossover study with 2 different phases: a "postprandial phase" of acute raspberry supplementation (2 separate days at least 1 week apart), followed by a 1-week washout phase and then a 10-week "diet supplement phase", with and without raspberry supplementation periods of 4 weeks each, separated by 2-week washout phase. Results: The postprandial phase revealed significantly lower levels of serum glucose at 2 and 4 h postprandial after raspberry versus control phase. In addition, among the serum biomarkers of inflammation, interleukin (IL)-6 and high-sensitivity tumor necrosis factor alpha (hsTNF-α) were also lower at 4 h postprandial following raspberry versus control meal (all p < 0.05). Finally, postprandial serum triglycerides showed a decreasing trend at 4 h in the raspberry versus control phase. Four-week daily raspberry supplementation continued to show a significant lowering effects on IL-6 and hsTNF-α versus control phase (all p < 0.05); systolic blood pressure revealed a decreasing trend after 4-week of raspberry supplementation. No effects were noted on fasting glucose and lipids, C-reactive protein and arterial elasticity. Conclusions: Thus, dietary raspberries, which are low in calories and high in polyphenols and other nutrients may lower postprandial hyperglycemia and inflammation, and in general exert selected anti-inflammatory effects in adults with diabetes. These findings deserve further investigation.