Entry #: 26
Date: 11 December 2017
Section: Insulin resistance
Topic: Olive oil and insulin resistance and liver inflammation
Type: In vivo model
OliveNetTM Journal Club
Expert review of literature related to olives and olive oil
D. Elizabeth McCord, Nancy B. Ray and Tom C. Karagiannis
Polyphenol-rich virgin olive oil reduces insulin resistance and liver inflammation and improves mitochondrial dysfunction in high-fat diet fed rats
Lama et al
Citation / Year
(1) / 2016
Polyphenol-rich olive oil, olive oil phenolics, inflammation, insulin resistance, mitochondrial dysfunction
Whereas early research focussed on the beneficial health effects of the major mono- and poly-unsaturated fatty acid component of extra-virgin olive oil, it is now evident the minor phenolic content is important for the potent anti-inflammatory and antioxidant effects of extra-virgin olive oil (2-5). In this study, the authors have utilised a conventional in vivo model to highlight the importance of the phenolic fraction of virgin olive oil in producing anti-inflammatory and antioxidant effects. A well-controlled experiment using four groups of animals (n = 6 per group) was performed. Group 1 received a standard pellet diet (control group; 17% fat, 23% proteins, 60% carbohydrates; 16.1 kJ/g), group 2 received a high fat diet (58.1% fat, 16% proteins, 25% carbohydrates), group 3 received the high fat diet with 1.3% virgin olive oil rich in polyphenols and tocopherols, and group 4 received the high fat diet with a virgin olive oil with tocopherols but not polyphenols. The polyphenol-rich olive oil contained 404.1 mg/kg of polyphenols whereas the oil for group was completely devoid of polyphenols. This experimental design allowed the authors to at least in part, de-lineate the effects attributable to the polyphenolic content. The experiment was performed over a six week period with an oral glucose tolerance test conducted at five weeks.
Key points and implications
The authors have methodically evaluated the anti-inflammatory and antioxidant effects of polyphenol-rich diet compared to the control, high fat diet and high fat diet without polyphenols groups. Firstly, the high fat diet increased serum alanine transaminase – a marker of liver damage – and triglycerides and these were reduced by the polyphenol-rich diet. Similarly, the oral glucose tolerance test, fasting serum glucose levels, and homeostatic model assessment for assessing β-cell function and insulin resistance, highlighted improvements with the polyphenol-rich diet which were more pronounced than the virgin olive oil diet
without polyphenols. This was confirmed by Western blot analysis of: 1) phosphorylated AKT, 2) GLUT2, 3) AMPK, and 4) PPAR-α in the liver. In addition, the polyphenol-rich diet positively modulated the serum levels of pro-inflammatory (TNF-α and IL-1), and anti-inflammatory (IL-10) mediators. Effects on liver inflammation and oxidative stress were also measured by examining mRNA levels of TNF-a and the cyclooxygenase-2 levels, investigating reactive oxygen species and reactive nitrogen species-induced liver damage, by measuring malondialdehyde levels as a marker of lipid peroxidation. The findings indicated that polyphenol-rich diet improved all of the above parameters more effectively than the virgin olive oil diet without polyphenols diet. Finally, improved fatty acid oxidation with the polyphenol-rich diet was observed in isolated hepatic mitochondria. Overall, using a well-controlled experiment and wide array of conventional biochemical and molecular methodologies this study re-iterates the importance of the polyphenolic content of virgin olive oil in producing potential health benefits.
- A. Lama et al., Polyphenol-rich virgin olive oil reduces insulin resistance and liver inflammation and improves mitochondrial dysfunction in high-fat diet fed rats. Molecular nutrition & food research 61, (2017).
- L. Parkinson, S. Cicerale, The Health Benefiting Mechanisms of Virgin Olive Oil Phenolic Compounds. Molecules 21, (2016).
- S. Cicerale, X. A. Conlan, A. J. Sinclair, R. S. Keast, Chemistry and health of olive oil phenolics. Critical reviews in food science and nutrition 49, 218-236 (2009).
- P. Reboredo-Rodriguez et al., State of the Art on Functional Virgin Olive Oils Enriched with Bioactive Compounds and Their Properties. International journal of molecular sciences 18, (2017).
- F. Visioli, A. Poli, C. Gall, Antioxidant and other biological activities of phenols from olives and olive oil. Medicinal research reviews 22, 65-75 (2002).