High Endogenous Salivary Amylase Activity Is Associated with Improved Glycemic Homeostasis following Starch Ingestion in Adults

Abstract

In the current study, we determined whether increased digestion of starch by high salivary amylase concentrations predicted postprandial blood glucose following starch ingestion. Healthy, nonobese individuals were prescreened for salivary amylase activity and classified as high (HA) or low amylase (LA) if their activity levels per minute fell 1 SD higher or lower than the group mean, respectively. Fasting HA (n = 7) and LA (n = 7) individuals participated in 2 sessions during which they ingested either a starch (experimental) or glucose solution (control) on separate days. Blood samples were collected before, during, and after the participants drank each solution. The samples were analyzed for plasma glucose and insulin concentrations as well as diploid AMY1 gene copy number. HA individuals had significantly more AMY1 gene copies within their genomes than did the LA individuals. We found that following starch ingestion, HA individuals had significantly lower postprandial blood glucose concentrations at 45, 60, and 75 min, as well as significantly lower AUC and peak blood glucose concentrations than the LA individuals. Plasma insulin concentrations in the HA group were significantly higher than baseline early in the testing session, whereas insulin concentrations in the LA group did not increase at this time. Following ingestion of the glucose solution, however, blood glucose and insulin concentrations did not differ between the groups. These observations are interpreted to suggest that HA individuals may be better adapted to ingest starches, whereas LA individuals may be at greater risk for insulin resistance and diabetes if chronically ingesting starch-rich diets.

Anomalous association of salivary amylase secretion with the postprandial glycaemic response to starch

“…The findings of the present study have confirmed in Malaysian subjects the results of the study by Mandel et al Legend: As several of the highest and lowest ranked subjects were unavailable for participation in this phase of the study, additionally more medially ranked subjects were recruited as listed above with North American subjects [5] which have shown that the cohort who are high salivary amylase producers, have an improved glucose tolerance to starch (i.e. lower AUC) compared to subjects who are low salivary amylase producers.…”

“…This enzyme is important for the process of starch digestion, because it has long been established that swallowing a starch meal without premixing it effectively with saliva leads to a generally lower glycemic response [4]. While a 2013 study showed no significant correlation between salivary amylase and glycaemic response to starch [2], a study by Mandel et al 2014 has shown counterintuitively that subjects who are high salivary amylase producers, have a better glucose tolerance to starch than subjects who are low salivary amylase producers [5]. A coherent explanation for this finding is not readily apparent.…”

“…Each participant fasted overnight for a minimum of 8 h. To minimise circadian variability in the salivary secretory rates, saliva collection was undertaken between 7 a.m. and 9 a.m. on the following morning, After rinsing the mouth with water (to reduce contamination of the collected sample with solid particulates) each subject's non-stimulated saliva sample was collected in a weighed polypropylene tube by the passive drool method [5] for exactly 2 min. Subsequently a stimulated saliva sample was collected for 2 min in a similar manner.…”

“…With the statistical level of significance set at 5 % and power at 80 %, 31 subjects were required, in order to evaluate the averaged salivary amylase with a desired precision of 4 U/mL, assuming a standard deviation of 11 U/mL [5]. 50 subjects were recruited for sampling in order to account for potentially incomplete data.…”

“…The relationship between salivary amylase activity and glycaemic response to starch has not been undertaken in SE Asian subjects. In earlier reports of this topic, the participants were Americans [5] or South Americans [9], both (presumably) largely of European origin. E Asians generally consume a diet rich in rice and have a higher prevalence of glucose intolerance then is evident in people of European origin [2,10].…”