Human study: olive leaf supplement increases insulin sensitivity
They are great of course, all those animal studies in which researchers make mice and rats more sensitive for insulin, lose fat and build up more muscle by administering oleuropein. But that does not mean that this substance from green olives has the same effect in humans. To demonstrate this, you need human research. Like the study that New Zealand researchers from the University of Auckland, published in PLoS One in 2013.
For 12 weeks the researchers gave 46 healthy men, aged 35-55 years, with a BMI of 25-30, each day 4 capsules containing an extract of olive leaf. Every day the men consumed 51.1 milligrams of oleuropein and 9.7 milligrams of hydroxytyrosol. The researchers used a supplement from Comvita.
On another occasion, the men consumed a placebo for 12 weeks.
When the 12-week period was over, the researchers gave the men a portion of glucose. Then they watched how quickly the glucose disappeared from the men's blood, and how high their insulin levels rose. This enabled the researchers to determine how well the men responded to insulin.
Supplementation with the olive leaf extract limited the increase of both glucose and insulin levels after administration of glucose. This meant that insulin sensitivity increased.
"This is the largest and most comprehensive study to date examining the effect of supplemented olive leaf polyphenols alone on modifiable cardiovascular risk factors", the researchers write. "We showed improvements in insulin sensitivity in a cohort of overweight middle-aged men."
"Future research should evaluate the potential effects of olive leaf polyphenols on insulin sensitivity and glycaemic control (HbA1c) in patients with type 2 diabetes, and compare any such effects to conventional therapy (e.g. metformin)."
PLoS One. 2013;8(3):e57622.
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