Berries Improve Glycemic Response to Bread or Sugar

Törrönen R, Kolehmainen M, Sarkkinen E, Poutanen K, Mykkänen H, Niskanen L. Berries reduce postprandial insulin responses to wheat and rye breads in healthy women. J Nutr. 2013;143(4):430-436.

 

Subjects participated in 3 randomized, controlled, crossover, 2-hour meal studies.

 

Healthy females (n=13–20)

 

Participants consumed white bread (WB) or rye bread (RB), both equal to 50 g of available starch, with 150 g whole-berry purée or the same amount of bread without berries as reference. In study 1, WB was served with strawberries, bilberries, or lingonberries, and in study 2 with raspberries, cloudberries, or chokeberries. In study 3, WB or RB was served with a mixture of berries consisting of equal amounts of strawberries, bilberries, cranberries, and blackcurrants.

 

Postprandial insulin and blood glucose levels

 

Eating strawberries, bilberries, lingonberries, or chokeberries with white bread significantly reduced the postprandial insulin response. So did eating the mixed berry puree with either white bread or rye bread. Both strawberries and the mixed berry puree significantly improved the glycemic profile of both breads (about 40% for the white bread and about 20% for the rye). When white bread is consumed with berries, less insulin is needed for maintenance of a normal or even slightly improved postprandial glucose metabolism. Even the insulin profile to rye bread, which is initially better than white bread’s, is improved.

 

This bread and berry study is the third in a series conducted by Riitta Törrönen and colleagues at the University of Eastern Finland, a country apparently blessed with all sorts of juicy berries. Few of us would have predicted the results reported in any of these studies.

 

The 2 earlier studies were published in May and September of 2012. The May study measured the impact of a combination of berries and sucrose on postprandial insulin, serum glucose, and glucagon-like peptide 1. Twelve subjects were randomized into a single-blind, placebo-controlled crossover study in which 2 test meals were consumed on separate days. One meal was a berry purée (150 g) made of bilberries, blackcurrants, cranberries, and strawberries with 35 grams of added sucrose. The ‘control meal’ was 35 grams of sucrose dissolved in water. The berries significantly improved the glycemic profile over the sugar water; plasma glucose and serum insulin concentrations were all lower at 15 min and higher at 90 min. The berry mixture also reduced the maximum increases in glucose and insulin concentrations and improved the glycemic profile. Glycemic control was improved by adding berries to sucrose.¹

 

The second study in Törrönen’s series was published in September 2012. Twenty healthy women participated in this randomized, controlled, crossover meal study. They consumed either blackcurrants or lingonberries (150 g served as purées) or blackcurrant or lingonberry nectars (300 mL) with 35 grams of added sucrose. Sucrose alone (35 g in 300 mL water) was used as a reference.

 

 

Again, compared with sucrose alone, adding berries to sucrose resulted in lower glucose and insulin concentrations during the first 30 min and a slower decline during the second hour and a significantly improved glycemic profile. Berries prevented the sucrose-induced late postprandial hypoglycemic response and the compensatory free fatty acid rebound. Nearly similar effects were observed with the sugar and berry nectars. The improved responses were evident despite the higher content of available carbohydrate in the berry and nectar meals.²

 

These 3 studies tell us that the addition of berries to high-sugar or starch-containing foods improves the glycemic profile.

 

Readers should be wondering what exactly these researchers mean by the term glycemic profile? The glycemic profile (GP) system was developed by Liza Rosén, doctor in applied nutrition at Lund University in Sweden. It is a specific measuring system used to describe the blood glucose response. It goes beyond the low glycemic index concept we are familiar with. GP is “defined as the duration for the incremental postprandial blood glucose response divided with the blood glucose incremental peak (min/mM).”³

 

In simpler words, the GP is based on the graph of the rise and fall of postprandial blood glucose. Glycemic profile scores reflect the appearance of this graph’s curve. The flatter the curve, the better the glucose profile and the higher it is scored. The best scores are for blood sugar curves that are even and reasonably low. High scores describe when blood sugar rises slowly and evenly after a meal and then drops down slowly. Low scores describe sudden spikes and rebound drops into hypoglycemia. Taking these variations into account provides a more accurate prediction of a person’s response to a particular meal, how long their energy is sustained after eating—or conversely how soon they will crash.

 

“A food with a high GP indicates that the energy lasts longer. The absolute best situation is if the product has a low GI and high GP. This means it’s a really good product! One example is boiled rye kernels, which have a GI of 73 (where 100 is the GI of white wheat bread) and a GP of 94. In the same study, boiled wheat kernels had a GI of 68 but a GP of 51. The results suggest that the rye kernels produce a more stable blood sugar profile,” Rosén writes.⁴

 

This GP system added to glycemic index scores may be a more accurate predictor of response to meals. Flattening out the sudden spikes in glucose level and insulin production may have more value in preventing and treating metabolic syndrome than glycemic indexes alone. High glycemic profile foods may keep people feeling ‘full’ longer increasing satiety.⁵

 

Törrönen’s studies taken together should leave us fairly certain that adding berries to either sugar or bread will actually improve glycemic control.

 

Berries provide significant amounts of polyphenols that are linked to a wide array of health benefits. Yet patients, particularly those with blood sugar problems, are often resistant to our suggestions to eat berries in quantity or with frequency out of fear of the fructose the berries contain. These studies provide the data to respond to this concern. While berries may contain some sugar, they contain other chemicals that change they way the body responds, slowing the rise in blood sugar, so that neither the sugar in the berries nor the starches eaten with them are quite as bad for you as they might normally be.

 

Adding berries to a high-carbohydrate breakfast such as corn flakes or oatmeal should lessen the mid-morning hypoglycemic crash these meals often trigger.

 

Does this mean that bread eaten with jam is better than plain bread alone? Not exactly, but almost; if the jam were made from berry puree without further added sucrose, then yes, apparently it would yield a better glycemic profile. Would a sucrose-sweetened berry jam be better than no jam at all? This is where it gets complicated.