Kyoto researcher: olive oil first cut glucose rise in mice

Olive oil taken 15 minutes before a glucose drink led to a smaller early rise in blood sugar in mice than the same oil taken 15 minutes after, ScienceDaily reports. The experiments also point to glucagon, a hormone best known for pushing blood sugar up, as part of the system that holds it down. All of the work was done in mice. The same effect has not been shown in people.

How the experiment ran

The researchers fasted the mice overnight and sorted them into three groups, ScienceDaily reports. The first got water, then glucose. The second got olive oil, with glucose arriving 15 minutes later. The third got glucose first and olive oil 15 minutes after that.

They measured blood sugar and four hormones that matter to it: insulin, glucagon, GIP and GLP-1. GIP and GLP-1 help the body handle glucose after a meal. Glucagon usually works in the other direction, prompting the liver to release stored glucose.

To estimate how quickly the stomach was emptying, the team gave the mice acetaminophen, a common pain reliever, and checked how much of it reached the bloodstream.

Other groups repeated the test, including mice with type 2 diabetes and mice missing the receptor that GLP-1 needs. The team also blocked glucagon or GLP-1 signaling, interrupted the vagus nerve on both sides beneath the diaphragm, and tried other dietary fats. The vagus nerve links the brain and the gut.

Fat first, then glucose

When the oil came before the glucose, the early blood sugar rise was smaller than when the oil came after, ScienceDaily reports. Fat first also slowed gastric emptying, so glucose left the stomach for the intestine more gradually, and it set off an early increase in glucagon, GIP and GLP-1.

The effect held in mice with type 2 diabetes and a severe insulin deficiency. That suggests the response can still work when the body's insulin regulation is badly damaged.

A hormone that usually does the opposite

Glucagon is known for raising blood sugar by telling the liver to put stored glucose back into the blood. Here it contributed to a response that limited the rise instead.

Blocking glucagon signaling on its own did not remove the benefit of taking oil first, and blocking GLP-1 on its own did not either, ScienceDaily reports. Block both at once and the effect was reduced. The vagus nerve experiments added a third thread: nerve signaling is part of how the body reacts to the order in which nutrients arrive.

What it means at the table

Earlier clinical studies in people found that a meal which starts with vegetables, protein or fat produces a gentler rise in blood sugar afterward, ScienceDaily reports. Reordering a meal is easier to keep up than dropping a food group, which is what makes the idea worth testing further.

"Meal-sequencing is appealing because it merely changes how a meal is eaten rather than requiring people to avoid entire food groups," said Daisuke Yabe of Kyoto University, the corresponding author, in comments carried by ScienceDaily.

"Our findings suggest that the order in which nutrients reach the gut can engage a coordinated hormone-nerve response that changes how quickly the stomach delivers glucose to the intestine," Yabe said, in comments carried by ScienceDaily.

The catch is the species. None of these experiments involved a person, and this research has not established that what happened in the mice happens in us. The team says more clinical studies are needed to learn whether the same mechanisms can help control blood sugar in people who have diabetes and in those who do not. This is one study, not a consensus, and it is a mouse study at that.

• blood sugar
• GLP-1
• glucagon
• Kyoto University
• mouse study
• olive oil