According to findings published in the Nutrition Journal, a dietary supplement derived from the white kidney bean, when consumed by volunteers, in both capsule and powder form, decreased the GI of white bread.
The GI index measures how quickly certain foods release carbohydrates into the body, which then raise consumers' blood glucose levels. High GI foods cause blood sugar levels to rise more rapidly whereas a low GI rating, that takes longer to digest and release sugar into the bloodstream, provides consumers with the satiety, 'full' sensation.
The researchers, based at the UCLA School of Medicine, say that epidemiological studies suggest that low GI diets decrease the risk of developing type II diabetes and coronary heart disease, while controlled clinical trials indicate that low GI diets lowers cholesterol.
Hypothesis
According to the scientists, during in-vitro analysis, the white kidney bean derived supplement called Phase 2 was shown to inhibit the digesting enzyme alpha-amylase, which is secreted in the saliva and by the pancreas and is responsible for breaking down starches into sugars that are consequently absorbed in the small intestine.
“Since the GI is a function of the rate of absorption of glucose in the gut, inhibition of alpha-amylase may result in the lowering of GI,” they hypothesised.
The authors said the objective of this study was to thus determine whether the addition of Phase 2 in-vivo would lower the GI of a commercially available high glycemic food such as white bread.
The study
Predicting the GI through the in-vivo method involved feeding the test food to a number of human volunteers and taking regular blood samples to monitor changing blood sugar levels.
They researchers explained that they conducted an open-label 6-arm crossover study with 13 randomized subjects aged between 24 and 44 and a BMI between 18 and 25 (kg/m2).
And they said that standardized GI testing was performed using white bread with and without the addition of Phase 2 in capsule and powder form.
Subjects with any active eating disorders, gastrointestinal illness or history of gastrointestinal surgery, diabetes or other endocrinologic disorders were excluded, continued the authors.
They said that the study population received 50g net carbohydrates in the form of white bread with butter either by itself or with a form of Phase 2 in seven different sessions at the testing facility.
“Although fat may affect the GI of foods there was consistency in the study in that it was included in both the control and test groups,” stressed the researchers.
They said that the dietary supplement was given at dosages of 1500mg, 2000mg, and 3000mg in capsule form and 1500mg, 2000mg, and 3000mg in powder form, with the powder form of the test product mixed into the butter which was spread on the bread.
“The capsules were taken immediately prior to the ingestion of food. During each visit subjects had their capillary blood glucose measured nine times over two hours,” explained the authors.
Statistical analysis was performed by one-way ANOVA of all seven treatment groups, they added.
Results
The researchers found that the data demonstrated significant decreases in the GI of white bread with the powder form of Phase 2 at the dosage of 3000mg, while the capsule formulation at the 1500mg dose had no effect on the GI and both the 2000mg and 3000mg capsule doses caused insignificant reductions in GI.
"The data suggests a possible dose dependent effect with a preference for the powder form.The lesser effect with the capsule formulation may reflect a reduced bioavailability of the white bean extract, perhaps due to the time required for capsule dissolution,” they said.
The authors conclude that their results merit further research with a larger number of volunteers, and they suggest it would be beneficial to determine if 2000mg and 3000mg doses of powder and/or capsule forms of Phase 2 can reduce the GI's of other high GI foods such as pasta or rice.
Source: Nutrition Journal
Published online ahead of print: doi:10.1186/1475-2891-8-52
Title: Lowering the glycemic index of white bread using a white bean extract
Authors: J K Udani, B B Singh, M L Barrett and H G Preuss