The additive and synergistic combinations of plant phytochemicals have been identified to provide health benefits associated with chronic disease risk reduction, including type 2 diabetes and cardiovascular disease. Attenuating insulin resistance, along with oxidative stress and inflammation, has been identified as a mechanism that underlies this protective effect. Studies have documented favorable postprandial (post-meal) effects of strawberries, a polyphenol-rich fruit, on glucose and lipid profiles as well as on mediating the inflammatory response and improving insulin action.
To build upon their previous research findings that whole berries optimize postprandial glucose and insulin responses to sucrose in healthy adults, researchers from the University of Eastern Finland conducted a series of three meal studies to identify the effects of berries on postprandial metabolic responses to starch. The three randomized, controlled crossover studies were conducted with 13 to 20 healthy female subjects who consumed reference meals that provided 50g of starch as white wheat bread (WB) or rye bread (RB), meals with WB and RB served with 6 different berries, or meals with WB or RB served with a mixture of four berries (strawberries, bilberries, cranberries and black currents).
Among berries rich in the ellagitannin polyphenols, only strawberries were found to have a significant effect on insulin response to WB, which suggests that total ellagitannin content is not a driving factor in lowering insulin response. The berry mixture was shown to have a similar insulin-lowering effect on both breads, despite the known differences in insulin responses between WB and RB. Finding no association of the insulin-lowering capacity and the polyphenol composition of the berries, the researchers suggest that the role of acidity and organic acid content of berries be addressed in future studies.
They concluded that consuming foods and food combinations that elicit a lower postprandial insulin response—such as the bread and berry pairings—may offer short- and long-term metabolic benefit for the prevention of type 2 diabetes, particularly for those high risk of developing the disease. Torronen R, Kolehmainen M, Sarkkinen E, Poutanen K, Mykkanen H, Niskanen L. Berries reduce postprandial insulin responses to wheat and rye breads in healthy women. J Nutr. 2013; 143: 430-436.