Is Olive Oil an Indispensable Part of a Mediterranean Diet?

Plant-based diets, including the Mediterranean diet, are leading the pack in the popularity of healthy diets.  There is, however, continuing debate about which aspects of a Mediterranean diet are the most important.  Is it the olive oil that is mainly responsible for the heart health benefits of the Mediterranean diet for health?

 

ABOUT HEALTH BENEFITS AND RISK FACTORS (1,2):

When we talk about health benefits, what do we really mean?  How do we know that a specific action such as a lifestyle change like altering the components of a diet, exercising more or stopping smoking will be beneficial?  And in what ways does health improve?

Perhaps not surprisingly, over decades of study, scientists have discovered an array of circumstances that lead to worsening health.  These circumstances are known as risk factors for disease.  When it comes to cardiovascular health, the risk factors are very well known and, fortunately, many of these risk factors are within our own personal power to change.

Cardiovascular risk factors include;

• High cholesterol and other lipids (fats)
• Eating a diet high in saturated fats, trans fat, and cholesterol
• High blood pressure
• High blood glucose (sugar) and/or diabetes
• Obesity
• Lack of physical activity
• Smoking
• Drinking too much alcohol
• Age
• Family history
• Ethnic background

A person with one or more of the above cardiovascular risk factors has a higher chance of  experiencing a cardiac event with the amount of risk increasing with the number of risk factors they have.

Cardiac events that are the consequences of having cardiovascular risk factors include;

• Atherosclerosis (build-up of harmful plaque inside blood vessels)
• Angina (chest pain indicating that blood flow and oxygen coming to the heart are low)
• Heart attack (damage to the heart due to a severe reduction or blockage of the flow of blood to the heart)
• Heart failure (difficulty of the heart to pump blood and oxygen throughout the body)
• Stroke and Transient Ischemic Attack (TIA) (a disruption or a blockage of the blood supply to the brain)
• Peripheral artery disease (damage to the blood vessels of the arms or legs which can cause muscle cramping, pain when trying to use the muscles in the arms or legs, difficulty walking any distance, trouble with walking upstairs and leg/arm numbness or weakness)
• Disease of the aorta such as an aortic aneurysm (a bulge in the wall of the aorta, the main artery coming out of the heart, which results in a weak area that may rupture)
• Damage to the arteries in other organs such as the kidneys (so that they can no longer perform their important functions of filtering the blood, eliminating waste and regulating electrolyte and fluid levels in the body) and the eyes (damage to the network of blood vessels in the eye which can lead to impaired vision)

We can’t change our age, family history or ethnic background, but the rest of the risk factors are open to our alteration.  We can stop smoking lose weight and control our alcohol intake.  We can increase our exercise….even just a daily walk can make a difference.  But the most powerful way to reduce the risk of cardiovascular disease is through the food that we eat.  Food choices can bring about remarkable positive outcomes such as lowering blood pressure, supporting healthy blood vessels, decreasing levels of cholesterol and other lipids in the blood, reducing excess weight and preventing and even reversing high blood sugar and diabetes.

 

A FIRST-OF-ITS-KIND STUDY:

Though olive oil is a highly touted part of a Mediterranean diet, this dietary pattern is made up of much more than just olive oil.  It emphasizes mainly plant-based foods – fruits; vegetables including potatoes, salad, legumes and beans; bread and whole grain cereals; nuts; seeds; and olive oil; with small amounts of fish, dairy, eggs and alcohol; and red and processed meat and sweets consumed only rarely.  (3)  Many studies looking at Mediterranean diets in general illustrate that eating this predominantly plant-based diet that includes extra virgin olive oil (EVOO) is healthier than eating an animal-based diet.  (4)  This makes sense because olive oil is high in monounsaturated fat which, when it is replacing fats sourced from animals such as dairy and meat which are higher in saturated fat, is indeed linked to better heart health.

However, a Mediterranean diet can also be comprised exclusively of whole plant-based foods (no fish, meat, dairy or eggs).  Such whole-food plant-based vegan diets have also been extensively studied and have consistently revealed their wide-ranging health benefits.   (5,6,7,8)

In a new study from July 2024, researchers set out to compare the risk factors of cardiovascular disease related to eating a whole-food plant-based vegan diet high in EVOO with those related to eating a whole-food plant-based diet containing little to no EVOO.  (9)  This is the first study to directly compare the health effects of high and low amounts of EVOO in a Mediterranean diet.

 

HOW THE STUDY WAS DONE: (9)

This analysis used a randomized crossover trial approach.  This means that all participants received both interventions (high EVOO and low EVOO) in random order and each participant served as his/her own control in determining the effect of the intervention.  A washout period between trials  was used to prevent any carry-over effects of EVOO from the previous intervention.

Adults aged 18 to 79 years with borderline to high risk for atherosclerotic cardiovascular disease (at least a 5% risk of developing cardiovascular disease) were chosen as participants.  Possible participants were declined if they had a history of coronary artery disease, heart attack, heart failure, or a high calcium score; if they had kidney disease or active cancer; if they were planning to become pregnant; or if they were already following a Mediterranean or a whole-food plant-based vegan diet.  A total of 40 participants completed the study.

Weekly virtual group cooking classes led by a dietitian/chef were provided during the diet trials.    Weekly gift cards were also supplied to support grocery purchases.

All EVOO was given to the participants at no cost and they were instructed to consume EVOO only in its raw state.

Data was collected before and after each diet trial.

Participants were split into two groups which consumed two different diets for four weeks each. The base diet was whole-food plant-based vegan.  The difference in the diets was in their content of EVOO.  One diet included 4 tablespoons of EVOO daily and the other contained little to no (up to 1 teaspoon daily) of olive oil consumption.

 

Group 1:  During each 9-week trial, these participants followed a high EVOO (4 tablespoons per day) diet for the first 4 weeks; followed by no EVOO consumption for a 1-week washout period; then finally a low EVOO (less than 1 teaspoon per day) diet for 4 more weeks.

Group 2: This group did the opposite, following a low EVOO (less than 1 teaspoon per day) diet for 4 weeks; followed by no EVOO consumption for a 1-week washout period; then finally a high EVOO (4 tablespoons per day) diet for 4 more weeks.

 

Before and after each phase of the trial, the researchers measured several aspects of cardiovascular health through observing changes in the levels of risk factors in the blood.

The primary measure was the change in low-density lipoprotein cholesterol from baseline.

Secondary measures were alterations in the levels of other lipids (total cholesterol, high-density lipoprotein cholesterol, apoliprotein B and triglycerides); glucose; and high sensitivity-C-reactive protein.  (More information on these components below)

Other measurements taken were body weight, blood pressure, heart rate and waist and hip circumference.

 

OTHER DETAILS OF THE TRIAL DIETS (9):

During the high-EVOO phase, fat content of the diet was 48% with EVOO contributing most of the dietary fat.

During the low-EVOO phase, sources of fat came from unrefined whole plant‐based fats such as avocados, nuts, seeds and olives and the fat content of the diet was 32%. Whole plant-sourced foods are also rich in dietary fiber which has its own well-known cholesterol-lowering effects, and in phytonutrients which have shown significant benefits in the prevention and management of chronic diseases such as heart disease.  (10)

Carbohydrate content of the diets was 42% during the high-EVOO phase and 56% during the low-EVOO phase.

No differences in physical activity of the participants were observed between the diet phases.

Both diets were low in saturated fats and trans fats.

The fats found in whole-plant foods are mainly polyunsaturated and monounsaturated fats with very small amounts of saturated fats. (11)

The fats found in EVOO are 75% monounsaturated fats, 14% saturated fats and 11% polyunsaturated fats. (12)

 

THE NITTY GRITTY STUDY RESULTS:  (9)

First of all, let’s try to clarify this data by using some abbreviations:

Low density lipoprotein cholesterol = LDL-C (sometimes dubbed “bad cholesterol”)

High density lipoprotein cholesterol = HDL-C (sometimes dubbed “good cholesterol”)

Total cholesterol = TC (total of all cholesterol types)

Apolipoprotein B = ApoB (the main protein in LDL-C.  High levels indicate lower clearance of cholesterol from the blood and are associated with higher risk of heart disease)

High sensitivity C-reactive protein = hs-CRP (a measure of inflammation that can predict the risk of cardiovascular disease) 

Glucose = sugar level in the blood. A high level can indicate pre-diabetes or diabetes.   

 

Now, on to the trial results:

Both diets resulted in reductions in LDL-C, HDL-C, TC, ApoB, glucose and hs-CRP.

Larger LDL-C reductions occurred after consumption of the low EVOO diet.

LDL-C was decreased by 25.5 mg/dL after the low EVOO diet.

LDL-C was decreased by 16.7 mg/dL after the high EVOO diet.

The low EVOO diet also created greater decreases in the following measurements compared to the high EVOO diet;

TC (decrease of 33.8 mg/dL after the low EVOO diet compared to 19 mg/dL after the high EVOO diet)

HDL-C (decrease of 10.5 mg/dL after the low EVOO diet compared to 5 mg/dL after the high EVOO diet)

ApoB (decrease of 14.8 mg/dL after the low EVOO diet compared to 5.5 mg/dL after the high EVOO diet)

Glucose (decrease of 17.8 mg/dL after the low EVOO diet compared to 8.8 mg/dL after the high EVOO diet)

 

Substantial differences were also detected when the order of the two trial diets was reversed;

Eating high EVOO during the first 4 weeks and low EVOO during the last 4 weeks of the trial resulted in a 12.7 mg/dL decrease in LDL-C and lowering of other lipid levels, glucose and hs-CRP.

Eating low EVOO during the first 4 weeks and high EVOO during the last 4 weeks of the trial resulted in a 15.8 mg/dl increase in LDL-C along with increases in glucose of 15.3 mg/dL, TC of 29.4 mg/dL, HDL-C of 9.8 mg/dL. Increases were also observed in hs-CRP and triglycerides.

Raising EVOO levels after following a low-EVOO intake pattern appeared to hinder further reductions in lipids.

 

Body weight decreased after both the high and low EVOO diets, with greater weight loss observed after the low EVOO diet compared to the high EVOO diet.  Weight decreased from 89 kg to 83.8 (for the high EVOO diet) and to 83.1 kg (for the low EVOO diet).

 

 

OTHER FACTORS THAT MAY BE PLAYING A ROLE IN THESE OBSERVED RESULTS (9):

• The higher intake of saturated fat during the high-EVOO diet may be contributing to the differences in LDL levels in the different diet periods. Olive oil contains about 14% saturated fat.
• In both groups participating in this study, intake of dietary fiber increased by 8 to 9 gm/day through the consumption of plant-sourced foods. Every extra gram of soluble fiber has been shown to result in up to 1 mg/dL reduction in LDL‐C concentrations.
• In addition, each 1 mmol/L (38.67 mg/dL) reduction in LDL-C is associated with reducing the risk of major vascular events by at least 25% through increasing the activity of LDL receptors in the elimination of cholesterol from the body.
• Because of the lack of animal-sourced foods with their higher levels of saturated fats in the study diet, this investigation corroborates the positive health impact of minimizing saturated fats. Saturated fats reduce the action of LDL receptors leading to decreased clearance and increased levels of circulating LDL particles.  Conversely, the effects of monounsaturated fats and polyunsaturated fats enhance LDL receptor activity thus increasing the removal of LDL from the blood.

 

DISCUSSION:

Olive oil, similar to any other vegetable oil, is a processed and concentrated fat with the nutritional value of the olives mostly lost during its processing.  EVOO has the advantage of undergoing only a single process that presses the olives (indicated by terms on the bottle like “cold-pressed” and “first pressed”).  The resulting mash is not refined any further with chemicals or heat, unlike regular olive oil and other vegetable oils.  After filtering, some of the olive material will be preserved including its phytonutrients (healthful plant compounds) and its antioxidants (components that fight against free radicals that can damage cells).  EVOO is higher in these healthful components than most other oils including regularly processed olive oil.  However, the amount of phytonutrients and antioxidants found in a healthy plant-based diet, which, on its own, is very rich in both components, far outweighs the amount available from any oil, even if the oil is EVOO.  Removing olive oil from a plant-based diet would be unlikely to result in any diminishing of the healthfulness of the whole diet pattern.  To obtain the nutritional value offered in olives, it is best achieved through eating whole olive, not by consuming its extracted oil form. (13)

This latest study shows us not only that olive oil added to a whole-food plant-based vegan diet does not increase the healthfulness of the diet, but also that the more olive oil in the diet, the fewer benefits for heart health the diet will have.

The difference is in the source of the fat.  (9,13)

• When 10 grams of EVOO was tested as a substitute for 10 grams of animal-based dietary fats such as dairy, butter, mayonnaise, lard and animal meats, studies have demonstrated lower risks of early death by 8% to 34% (14).
• When EVOO replaces other vegetable oils, there is no resultant lowering of mortality risk. (14)

This study concluded that, while both inclusion and exclusion of EVOO within a whole-food plant-based diet can reduce cardiovascular risk factors and support cardiovascular health, low amounts of EVOO seem to be more optimal for decreasing the risk of cardiovascular disease and appear to lead to better health outcomes than high EVOO intake.

 

BOTTOM-LINE:

Olive oil is not a whole food. Only whole fruits and vegetables can show decades of study supporting their role in lowering cardiovascular risk factors and attaining better heart health.  This study shows us that, while both plant-based diet patterns used in the study improved cardiovascular risk factors, lower EVOO levels were associated with larger decreases in LDL-C and in many other markers of cardiovascular risk.

This leads us to the conclusion that EVOO is likely not a necessary part of a Mediterranean diet.

The major players in the health benefits to be gained from eating such a diet are the many varieties of plant-sourced foods that it is made up of.

 

SOURCES:

1  https://www.cdc.gov/heart-disease/risk-factors/index.html

2  https:/www.nhs.uk/conditions/cardiovascular-disease/

3  Mazzocchi ,A., Leone, L., Agostoni, C., Pali-Schöll, I. The Secrets of the Mediterranean Diet. Does [Only] Olive Oil Matter? Nutrients. 2019 Dec 3;11(12):2941. Doi: 10.3390/nu11122941. PMID: 31817038; PMCID: PMC6949890.

4  Zong, G., Li, Y., Sampson, L., Dougherty, L.W., Willett, W.C., Wanders, A.J., Alssema, M., Zock, P.L., Hu, F.B., Sun, Q.  Monounsaturated fats from plant and animal sources in relation to risk of coronary heart disease among US men and women,  The American Journal of Clinical Nutrition. 2018; 107(3): 445-453.  ISSN 0002-9165.  https://doi.org/10.1093/ajcn/nqx004.

5  https://news.stanford.edu/stories/2021/05/embracing-plant-based-diet

6  https://www.health.harvard.edu/blog/what-is-a-plant-based-diet-and-why-should-you-try-it-2018092614760

7  https://www.heart.org/en/healthy-living/healthy-eating/eat-smart/nutrition-basics/how-does-plant-forward-eating-benefit-your-health

8  https://www.who.int/news-room/fact-sheets/detail/healthy-diet

9 Krenek, A.M., Mathews, A., Guo, J., Courville, A.B., Pepine, C.J., Chung, ST., Aggarwal, M.  Recipe for Heart Health:  A Randomized Crossover Trial on Cardiometabolic Effects of Extra Virgin Olive Oil within a Whole-Food Plant-Based Vegan Diet.  Journal of the American Heart Association.  13(15);  https://doi.org/10.1161/JAHA.124.035034.

10  Monjotin, N., Amiot, M.J., Fleurentin, J., Morel, J.M., Raynal, S. Clinical Evidence of the Benefits of Phytonutrients in Human Healthcare. Nutrients. 2022 Apr 20;14(9):1712. Doi:10.3390/nu14091712. PMID: 35565680; PMCID: PMC9102588.

11  https://www.canada.ca/en/health-canada/services/nutrients/fats.html

12  https://www.fatsecret.com/calories-nutrition/usda/olive-oil

13  https://www.forksoverknives.com/wellness/why-olive-oil-is-not-healthy-for-your-heart/

14  Guasch-Ferré, M.,  Li, Y., Willett, W.C., Sun, Q., Sampson, L., Salas-Salvadó, Martínez-González, M.A., Stampfer, M.J., Hu, F.B.  Consumption of Olive Oil and Risk of Total and Cause-Specific Mortality Among U.S. Adults, Journal of the American College of Cardiology.  2022; 79(2):101-112.

https://doi.org/10.1016/j.jacc.2021.10.041.