Episode 7 - How processed starches affect metabolic responses
The first paper discussed is from 1989 and is called “Insulin and glycemic responses in healthy humans to native starches processed in different ways: correlation with in vitro alpha-amylase hydrolysis”
18 subjects eat 35g of starch that is either raw, gelled (boiled & cooled) or made into a paste (via mechanical extrusion).
In vitro α-hydrolysis with α-amylase of differently processed starches correlate strongly (r2 = 0.95, p < 0.0001) with the glycemic and insulin responses of 18 human subjects ingesting these starches.
Contrary to popular belief, fiber is not a strong predictor of the glycemic or insulin responses in human subjects.
The ‘access’ α-amylase has to hydrolyze the starch in the plants cells appears to be the main determinant of the subjects glycemic and insulin response to the food (beyond its basic carbohydrate content).
For example, “extruded white flour gives a higher increase in glucose and insulin plasma responses than does boiled white flour”
The second paper discussed is from 2015 and is called “Postprandial glucose, insulin and incretin responses to different carbohydrate tolerance tests”
191 subjects aged 16 to 17-years of age are assessed as either normal glucose tolerant (NGT), impaired glucose tolerant (IGT) and type 1 or 2 diabetic according to WHO criteria. They then drank 75g of glucose (OGTT) or ate a 75g equivalent amount of starchy noodles (SNTT).
Insulin, glucose and the incretin GLP were measured.
Overall, lower glucose and insulin was seen in the SNTT interventions than in the OGTT ones.
SNTT AUCs accounted for 82.7% of glucose AUCs.
The iAUC (incremental AUC) is the ratio of insulin iAUC to GLP iAUC. It showed that the only difference was between the NGT and T2DMs, meaning the NGTs did better on SNTTs than on OGTTs whilst T2DMs did worse on SNTTs and better on OGTTs. For the IGTs there was no difference.
SNTTs could be used to replace OGTTs in certain populations, such as T2DMs, since it amplified the incretin effect.