Supplements containing Olive Leaf Extract, according to the manufacturers, reduce the rate at which aging takes place and protect the skin against UV radiation. Ten years ago researchers at the King Saud University in Saudi Arabia published an animal study, which suggests that Olive Leaf Extract may also help weight loss. According to the Saudis, this phenol-rich extract boosts the concentration of active thyroid hormones in the blood.
The fruits and leaves of the olive tree, Olea europaea, are packed with compounds like hydroxytyrosol [shown below, formula 1], oleuropein [formula 2] and oleocanthal [formula 3]. These are all antioxidants. If you give them to mice exposed to UV radiation, then they delay the skinís aging. [Phytother Res. 2010 Jul; 24(7): 995-1003.] Moreover, the olive phenols have been shown to inhibit the development of skin cancer in similar experiments. [Int J Cancer. 2011 Apr 15;128(8):1955-65.]
In a study published in 2002 in Phytotherapy Research, the researchers looked at another effect of the phenols in Olea europaea. Because administration of Olive Leaf Extract in animal experiments had led to a reduced glucose level and less lipids in the blood, the Saudi researchers wondered whether Olive Leaf Extract, by raising the amount of thyroid hormones in the body, boosted metabolism.
The researchers gave male rats weighing 125-150 g homemade water-based Olive Leaf Extract orally for 14 days. The maximal dose was 0.5 mg per day. That works out at 4 mg per kg bodyweight. For humans, that would be about 50 mg extract per day. That's not a lot. Drug stores sell capsules containing 150 mg Olive Leaf Extract.
In the rats that were given 500 micrograms Olive Leaf Extract, the concentration of the T3 hormone rose by a factor of 2.5. This would be enough to make people wanting to lose weight faster notice a change.
The researchers suspect that the phenols in Olive Leaf Extract make the enzyme 5'-deiodinase work harder. This enzyme converts the less active thyroid hormone T4 into the more active T3.
Phytother Res. 2002 May;16(3):286-7.