Following starch ingestion, blood glucose levels are influenced by genetically-determined differences in an enzyme called salivary amylase, says a new study.
Specifically, higher salivary amylase activity is related to lower blood glucose.
The findings, by researchers from the Monell Center, are the first to demonstrate a significant metabolic role for salivary amylase in starch digestion, suggesting that this oral enzyme may contribute significantly to overall metabolic status.
Other implications relate to calculating the glycemic index of starch-rich foods and ultimately the risk of developing diabetes.
"Two individuals may have very different glycemic responses to the same starchy food, depending on their amylase levels," Abigail Mandel, lead author of the study, said.
"Individuals with high amylase levels are better adapted to eat starches, as they rapidly digest the starch while maintaining balanced blood glucose levels. The opposite is true for those with low amylase levels. As such, people may want to take their amylase levels into account if they are paying attention to the glycemic index of the foods they are eating," Mandel said.
Starch from wheat, potatoes, corn, rice, and other grains is a major component of the United States diet, comprising up to 60 percent of our calories.
Amylase enzymes secreted in saliva help break down starches into simpler sugar molecules that can be absorbed into the bloodstream. In this way, amylase activity influences blood glucose levels, which need to be maintained within an optimal range for good health.
A previous study had demonstrated that individuals with high salivary amylase activity are able to break down oral starch very rapidly. This finding led the researchers to ask how this "pre-digestion" contributes to overall starch digestion and glucose metabolism.
In the current study, amylase activity was measured in saliva samples obtained from 48 healthy adults. Based on extremes of salivary amylase activity, two groups of seven were formed - high amylase (HA) and low amylase (LA).
Each subject drank a simplified corn starch solution and blood samples were obtained over a two hour period afterwards. The samples were analysed to determine blood glucose levels and insulin concentrations.
After ingesting the starch, individuals in the HA group had lower blood glucose levels relative to those in the LA group. This appears to be related to an early release of insulin by the HA individuals.
"Not all people are the same in their ability to handle starch," Paul Breslin, senior author of the study, said.
"People with higher levels of salivary amylase are able to maintain more stable blood glucose levels when consuming starch. This might ultimately lessen their risk for insulin resistance and non-insulin dependent diabetes," he said.
The study has been published online in published online in The Journal of Nutrition.