Consumption of Mixed Berries Containing Anthocyanins May Improve Post-prandial Insulin Response in Overweight and Pre-diabetic Adults

Diabetes mellitus has become a significant public health concern in the modern era. It is considered to be a lifestyle disease that can be moderated by dietary and lifestyle changes. Studies have shown long-term and acute consumption of berries, high in polyphenols and fiber, may have positive effects on glucose metabolism and glucose-regulation. The objective of this randomized cross-over study was to evaluate the glucoregulatory benefits of mixed berries containing an array of anthocyanins to determine whether flavonoids/anthocyanins and/or fiber proved beneficial.

The study was conducted at the U.S. Department of Agriculture’s Beltsville Human Nutrition Research Center in Beltsville, Maryland between January 2018 and March 2019. Participants were recruited through emails sent to the Beltsville Nutrition Center volunteer database, local federal agencies, and the University of Maryland in the Baltimore and Washington DC geographical area. Participants were included between the ages of 21 and 75 years with a body mass index (BMI) > 25 kg/m2. Exclusion criteria included smoking, pregnant or lactating, or participants with a history of bariatric surgery, diabetes, certain cancers, or use of blood thinners, other medications, or supplements that could interfere with the study. Individuals with gastrointestinal, malabsorption, or metabolic disorders were also excluded.

Seventy-six participants were recruited for the study; 74 provided written consent. Ten chose not to participate. Sixty-four were assessed for eligibility. Of those, six did not meet inclusion criteria, and 22 were not selected. Thirty-six participants were enrolled in the study. Thirty-three participants completed all four diets; three completed three of the four diets. The data from one participant completing all four diets were excluded due to blood sample collection issues. Data from 35 participants were included in the study. Baseline characteristics of the participants included mean age of 58.7 years, weight of 88.6 kg, BMI 30.8 kg/m2, fasting glucose 94.2 mg/dL, fasting insulin 80.0 pmol/L, fasting triglycerides 122.1 mg/dL, systolic blood pressure (SBP) 133.3 mm Hg, diastolic blood pressure (DBP) 79.7 mm Hg.

The primary treatment food was whole mixed berries consisting of equal parts blackberries (Rubus spp., Rosaceae), blueberries (Vaccinium corymbosum, Ericaceae), cranberries (Vaccinium macrocarpon, Ericaceae), raspberries (Rubus idaeus, Rosaceae), and strawberries (Fragaria × ananassa, Rosaceae). Participants were instructed to eat the berries with breakfast and dinner. The serving size was calculated based on energy needs resulting in 100 g of berries for every 450 kcal of overall energy requirements. Participants consumed between 80 g/day and 160 g/day of each berry type based on energy intake.

The randomized cross-over study included four treatment periods of eight days each with a two-week washout period. In the first seven days of each treatment period, participants consumed a fully controlled diet with the addition of one of the four treatment foods. These meals provided 45% of energy from fat, 42% of energy from carbohydrate and 13% of energy from protein. On the eighth day, participants were given a meal-based oral glucose tolerance test after a 12 hour fast. Blood samples were collected prior to the test meal. Blood samples were collected every 30 min after the test meal for three hours and analyzed for glucose, insulin, and non-esterified fatty acids.

The three remaining treatment foods included sugar-sweetened gelatin, sugar-sweetened fiber-enriched gelatin, and pressed berry juice. The sugar-sweetened gelatin included water, gelatin powder, fructose powder, glucose powder, and red and blue food coloring. This matched the primary treatment food for glucose, fructose, and mass-consumed but was devoid of anthocyanins and fiber. The sugar-sweetened fiber-enriched gelatin consisted of the same recipe as the sugar-sweetened gelatin with the addition of cellulose powder. This also matched the primary treatment food for glucose, fructose, mass, and fiber consumed but was devoid of anthocyanins. The juice was extracted using a manual fruit press from the same berry mixture as the primary treatment group. The juice matched the whole berries for sugar, containing phenolic compounds but no fiber. No further product description or manufacturer was provided.

The test meal consisted of a pancake, syrup, and berries or control treatment food. The pancake was made from flour (Triticum spp., Poaceae), egg, buttermilk, and glucose powder. Eighty grams of batter was pan-cooked and served with pancake syrup made from 60 g Karo brand light corn syrup (ACH Food Companies; Oakbrook Terrace, Illinois) and 1.2 g artificial maple flavoring, resulting in 68 g of glucose. The whole berries, sugar-sweetened gelatin, and sugar-sweetened fiber-enriched gelatin treatment foods serving size consisted of 300 g and 288 g for the berry juice. The total glucose provided from the meal-based glucose tolerance test was 79 g, consistent with the standard oral glucose test of 75 g.

Results showed that serum glucose and serum insulin were elevated while serum non-esterified fatty acids decreased following the meal-based oral glucose tolerance test. No significant differences were observed among the treatment groups for individual time points. Baseline glucose, insulin, and non-esterified fatty acids were not affected by treatment. No significant differences were observed for serum glucose area under the curve (AUC), serum insulin AUC, or non-esterified fatty acid AUC. When the berry treatments (whole berries and juice) data were combined, a significant reduction in serum insulin AUC was observed (P=0.023) compared to the combined non-berry treatments (sugar matched gelatin and sugar matched fiber-enriched gelatin). A lowering trend was observed for serum glucose AUC which was nearly statistically significant (P= 0.074). No effect was observed for non-esterified fatty acids AUC.

The authors explain the lack of significant findings by suggesting that the inclusion of mixed berries versus a single species may have diluted the effectiveness of the more potent berries. Previous studies have demonstrated greater benefits consuming berries with higher concentrations of anthocyanins (>361 mg/day) compared to this study where participants consumed 143 g/day. The strengths of this study included the tightly controlled diet prior to the meal-based glucose tolerance test and well-matched treatment food groups. Weaknesses of the study include berry consumption both before and during the food-based glucose tolerance test; thus, preventing the determination of whether long-term or acute feeding provided beneficial effects of berries.

The authors state that the “results suggest the potential for anthocyanin-rich mixed berry preparations to improve post-prandial insulin and possible glucose response.”

The authors declare no conflict of interest.


Solverson PM, Henderson TR, Debelo H, Ferruzzi MG, Baer DJ, Novotny JA. An anthocyanin-rich mixed-berry intervention may improve insulin sensitivity in a randomized trial of overweight and obese adults. Nutrients. November 2019; 11(12). PII: E2876 DOI: 10.3390/nu11122876.