This week’s blog is all about a staple of the Mediterranean diet - extra virgin olive oil.

We’ll take you through some it’s impressive health benefits - attributed largely to its unique composition of monounsaturated fats and phenolic compounds. And also describe some of it’s interactions with the gut microbiome.

This is a blog packed with science…if that’s not your thing, we recommend you skip to the end for our six big take aways.

What is Extra Virgin Olive Oil?

Extra virgin olive oil or EVOO is the highest grade of olive oil – you could describe it as the fresh juice of the olive. Regular olive oil is heated to extract the oil and refined, while extra virgin olive oil is cold-pressed and left unrefined.

EVOO and Metabolic Health

Metabolic syndrome is a cluster of conditions that occur together, increasing your risk of heart disease, stroke and type 2 diabetes. These conditions include increased blood pressure, high blood sugar, excess body fat around the waist, and abnormal cholesterol or triglyceride levels. The syndrome is on the rise, but a Mediterranean diet with a good dose of EVOO can help improve your metabolic health and reduce your risk of cardiovascular disease and diabetes.

Heart Health

The cardiovascular benefits of EVOO consumption have been demonstrated in a range of studies including high quality, randomized controlled trials. Most notable was the PREDIMED trial with over 7,000 participants with type 2 diabetes and at least 3 risk factors for coronary heart disease. The participants were split into three groups – one group on a Mediterranean diet plus 4 tbsp of EVOO a day, one on a Mediterranean diet plus 30g of nuts per day, and one group on a low-fat diet. The participants were followed for around 4.8 years. Those on the diets supplemented with EVOO or nuts had a 30% lower risk of developing a of major cardiovascular event, including a heart attack, stroke, or death from cardiovascular causes compared with the group eating a low-fat diet.

The EVOO and nuts groups also had lower blood pressure and total cholesterol.

Risk of Diabetes

The PREDIMED trial also demonstrated that consumption of EVOO and nuts resulted in lower fasting blood glucose levels compared with the control participants after 1 year. A side-study with participants without diabetes at the start found that fewer of the participants in the group went on to develop type II diabetes than the group instructed to follow a low-fat diet. Indeed, there was a 40% relative risk reduction in diabetes risk.  

Similarly, in an Italian randomized, cross-over study of 25 participants, the addition of 10 g of EVOO to a Mediterranean-type meal produced significant changes in a range of biomarkers linked to a reduced risk of metabolic disease (decreased 2-hour post prandial glucose, LDL-C, and dipeptidyl peptidase-4 levels, and significantly increased GLP-1 and gastric inhibitory peptide (GIP) levels in circulating blood). You may have heard of GLP-1. It is a hormone that enhances the production and release of insulin by the pancreas. GLP-1 agonists like the drug Ozempic mimic it’s effects and are increasingly being prescribed for diabetes treatment.

Mechanisms for the Positive Effects of EVOO on Metabolic Health

The positive effects on metabolic health are linked to both the phenols and the particular fatty acids found in EVOO.

For example, the major fatty acid in EVOO, oleic acid, assists in balancing blood glucose levels by activating receptors, leading to intestinal GLP-1 release and widespread anti- inflammatory effects in a variety of tissues.

Olive oil phenolic compounds demonstrate cholesterol binding activity and can impair cholesterol absorption in the intestine, as well as reducing oxidation of LDL (low-density lipoprotein) or “bad” cholesterol via their antioxidant effects.

Short chain fatty acids produced by gut bacteria boosted by EVOO consumption also play a role (see below).

Brain Health

An off-shoot of the PREDIMED study - The PREDIMED-NAVARRA randomized trial demonstrated that intake of the Mediterranean diet supplemented with either EVOO or nuts can also improve cognitive function compared with a low-fat diet. The researched examined cognitive performance using standard tests – the Mini-Mental State Examination (MMSE) and the Clock Drawing Test (CDT) after 6.5 years of nutritional intervention in elderly patients with a high risk of cardiovascular disease. They found small but significant improvements in both.

Studies in mice and rats have also indicated that EVOO, especially the phenolic compound oleocanthal found in EVOO may the prevent and halt the progression of Alzheimer’s disease.

EVOO and Ulcerative Colitis

A small-scale randomised trial published in 2020 demonstrated that the addition of 50 ml of EVOO per day over 20 days led to decreased inflammatory markers and improved gastrointestinal symptoms in patients with ulcerative colitis.

Lab and animal studies indicate that much of the effect is due to the effect of the phenol Oleuropein (OLE) found in EVOO and it’s breakdown product hydroxytyrosol (HT).

It seems that EVOO is a useful add-on to medical treatment for ulcerative colitis.

The Role of the Gut-Microbiome in EVOO Health Effects

There are many interactions between the fatty acids and phenolic compounds in EVOO, bacteria in the gut-microbiome, the immune system in the gut and even interactions with the gut-brain axis.

For example, most of the phenols in EVOO are present as ‘conjugates’, i.e., linked to other molecules, or in long strings of phenols. They largely pass through the small intestine without being absorbed, but are broken down by the bacteria found in the large intestine, so that they can be absorbed. For example, Oleuropein (OLE), the major phenolic secoiridoid found in EVOO is rapidly broken down by the bacteria in the colon into its active metabolite hydroxytyrosol (HT). HT fights free radicals, and has antioxidant and anti-inflammatory effects (see the section on ulcerative colitis above), plus likely beneficial effects toward diabetes, and possibly even anti-cancer effects.

The phenols are effectively a form of prebiotic. They are used by good bacteria in the body to produce beneficial products.

Studies in rodents have demonstrated that the phenols and the oleic fatty acid found in EVOO increase the abundance of beneficial bacteria: Faecalibacterium prausnitzii, which promotes anti-inflammatory action, and Roseburia, Lactobacillus and Bifidobacteria strains, which produce beneficial short chain fatty acids (acetate, butyrate and propionate). Short chain fatty acids (SCFAs) cross the gut wall where they induce activity in dendritic cells that promotes a cascade of anti-inflammatory and an immune regulating effects (increased T-reg cells and production of anti-inflammatory cytokines).

SCFAs are also an important source of fuel for the colon cells. SCFAs are also important in helping to strengthen the gut barrier by improving the tight junctions between colon cells. This stops bacteria and a compound derived from the cell wall of bacteria (LPS) from crossing into the blood triggering inflammation.

Other positive effects of SCFAs are observed in other body systems. Experiments in mice have demonstrated that SCFAs, are also potent activators for GPR43, a receptor that plays an important role in regulation of blood glucose levels, via the secretion of the hormones GLP-1, GIP, and peptide YY.

The bacteria boosted through EVOO supplementation – may have other beneficial effects. Some Lactobacillus strains can help lower absorption of cholesterol in the gut, whilst other strains produce gamma-aminobutyric acid gamma-aminobutyric acid (GABA), an inhibitory neurotransmitter that has been shown to reduce anxiety and depressive-like symptoms and behaviours (in mice at least).  More research is needed to understand these effects.

The fatty acids and the phenols found in EVOO not only boost good bacteria in the microbiome, they may also reduce harmful bacteria. Mouse studies have shown that they reduce Desulforibrionaceae and Blautia spp. associated with obesity and inflammation. And lab studies have demonstrated antibacterial effects of Turkish EVOO against cultures of the food borne pathogens E. coli, Listeria and Salmonella.

Key Take Aways

• EVOO can help improve your heart health, brain health, immune system and reduce your risk of diabetes – this is the closest thing to ‘food as a medicine’ that there is.

• This is due to the healthy fats and the phenol compounds found in EVOO

• ·There is a two-way interaction between EVOO and your gut microbiome. EVOO promotes healthy gut bacteria. The bacteria help to make the beneficial phenols bioavailable, and may underpin some of the benefits.

• Effects are seen when you consume 4 tablespoons a day – yes, it’s a lot!

• ·Ensure it is Extra Virgin Olive Oil

• ·It works best in combination with a Mediterranean diet. There appears to be a synergistic effect between the phenols and other plant chemicals found in the olive oil, tomatoes, leafy vegetables, fish oil and the fibre found in legumes.

We have plenty of recipes with olive oil on our recipe page https://www.noisyguts.com/recipes- One of our favourite salads is this one, with EVOO used to roast the sweet potatoes and in the dressing. Also check out our latest dessert recipe that includes both nuts and EVOO.

References:

Millman, J. F., et al. (2021). Extra-virgin olive oil and the gut-brain axis: influence on gut microbiota, mucosal immunity, and cardiometabolic and cognitive health. Nutrition reviews, 79(12), 1362–1374. https://doi.org/10.1093/nutrit/nuaa148

D'Archivio, M., et al. (2022). Dietary EVOO Polyphenols and Gut Microbiota Interaction: Are There Any Sex/Gender Influences?. Antioxidants (Basel, Switzerland), 11(9), 1744. https://doi.org/10.3390/antiox11091744

Morvaridi, M., et al. (2020). The effects of extra virgin olive oil and canola oil on inflammatory markers and gastrointestinal symptoms in patients with ulcerative colitis. European journal of clinical nutrition, 74(6), 891–899. https://doi.org/10.1038/s41430-019-0549-z

Blog written by: Noisy Guts co-founder Dr Mary Webberley. Mary has a background in biology, with two degrees from the University of Cambridge and post-doctoral research experience. She spent several years undertaking research into the diagnosis of IBS and IBD. She was the winner of the 2018 CSIRO Breakout Female Scientist Award.