Plain English Summary
Background and study aims
The purpose of this clinical trial is to verify whether the consumption of extra virgin olive oil (which has high levels of polyphenols) improves the inflammatory profile in people with low-grade inflammation, also known as meta-inflammation, and that it is common in people obese with prediabetes, compared to an olive oil with tiny amounts of polyphenols.
Likewise, other important aspects for health such as body weight and metabolic profile (fasting glucose, insulinemia, insulin resistance, beta cell functionality, glycosylated hemoglobin, lipidemia, etc.) will also be evaluated.
The improvement of these parameters is associated with a delay in the development of cardiovascular disease and diabetes, and could lead to the use of extra virgin olive oil, high in polyphenols, as a substitute for the natural source of dietary fat, as well as elaborate functional foods based on extra virgin olive oil.
Who can participate?
Adults (45 – 60 years old) who are obese (BMI 30 – 40) not diagnosed with diabetes
What does the study involve?
Participants will be randomly allocated to receive a one-month consumption of one type of olive oil (extra-virgin olive oil or refined olive oil) followed by a wash period of 15 days and a second one-month consumption of the second olive oil (refined olive oil or extra-virgin olive oil)
What are the possible benefits and risks of participating?
Expected benefits could include amelioration of metabolic alterations, such as fasting glucose, insulin resistance and weight loss. There are no expected risk for participants as they are just asked for substituting cooking oil at home for the one provided (blinded commercially available olive oil with low/high polyphenols content).
Where is the study run from?
Hospital Regional de Malaga, Spain
When is the study starting and how long is it expected to run for?
March 2018 to June 2019
Who is funding the study?
1. Consejería de Salud y Familias, Junta de Andalucía (Ministry of Health and Families, Junta de Andalucía), Spain
2. Instituto de Salud Carlos III, Ministerio de Sanidad, Gobierno de España (Carlos III Health Institute, Ministry of Health, Government of Spain)
Who is the main contact?
Dr Francisco-Javier Bermudez-Silva
Randomized double-blind cross-over interventional trial to assess the beneficial effects of extra-virgin olive oil versus refined olive oil in metainflammation
Extra virgin olive oil improves obesity-related meta-inflammation in obese people with pre-diabetes when compared to refined olive oil
Approved 29/11/2017, Ethics Committee for Clinical Research (CEI) of Malaga (Ethics Research Committee Provincial de Málaga, 7ª planta, Pabellón A, Hospital Regional Universitario, Avda Carlos Haya s/n, 29010-Malaga, Spain; + 34 951291977; firstname.lastname@example.org), ref:11/2017-PI1
Randomized single-centre double-blind cross-over interventional trial
Primary study design
Secondary study design
Randomised cross over trial
Patient information sheet
Not available in web format, please use contact details to request a participant information sheet
Obesity and pre-diabetes
One-month consumption of one type of olive oil (extra-virgin olive oil or refined olive oil) followed by a wash period of 15 days and a second one-month consumption of the second olive oil (refined olive oil or extra-virgin olive oil)
Randomisation process: 1:1 randomisation without stratification.
The nurse in charge of the study collects during each visit data on social status, habits, clinical, nutritional habits and semi-quantitative food frequencies, physical activity and anthropometrics. Fasting urine and blood samples are also collected, for measuring standard biochemical parameters, inflammatory parameters, oxidative stress markers, hormones, polyphenols levels. Patients are asked to bring with them a faeces sample for microbiota analysis.
Primary outcome measure
Inflammatory markers measured from serum/plasma samples by multiplex assay (IL-6, IL-1B, TNF-a, Leptin, adiponectin, CXCL-1, IFN-g, IL12p40, IL-4, IL-10, IL-13, IL-RA, hs-CRP) before and after each treatment
Secondary outcome measures
1. Body weight (kg) measured before and after each treatment
Measured from serum/plasma samples by multiplex assay before and after each treatment:
2. Metabolic status (fasting glucose, insulinemia, HOMA-IR, HOMA-B, HbA1C, lipid profile)
3. Standard biochemical analysis (Urea, uric acid, albumin, Fe2+, ferritin, bilirrubin, FA, Vit D, hemogram)
4. Oxidative status (LOOH, AOPP, TAS, Total thiol, Glutatione reductase)
5. Lipidomic profile by DOSY-NMR
6. Microbiota profile
Overall trial start date
Overall trial end date
Reason abandoned (if study stopped)
Participant inclusion criteria
1. Adult (40 - 65 years old)
2. Obese: BMI 30 - 40 kg/m²
3. Glycated hemoglobin (HbA1c): 5.7 - 6.4
4. Signed informed consent
Target number of participants
Total final enrolment
Participant exclusion criteria
1. Previous diagnosis of diabetes mellitus
2. Pregnant women
3. Diagnosis of some type of neoplasia
4. Inflammatory diseases in progress (Crohn's disease, ulcerative colitis, arthritis) and/or anti-inflammatory treatments
5. Women in hormone replacement therapy
6. Eat regularly more than 3 meals/week away from home (lunch or dinner, unless it is homemade food prepared with the provided oil)
Recruitment start date
Recruitment end date
Countries of recruitment
Trial participating centre
Hospital Regional de Malaga
Plaza del Hospital Civil s/n Pabellon 2 Sotano Lab Investigacion-Hormonas
Consejería de Salud y Familias, Junta de Andalucía
Funding Body Type
Funding Body Subtype
Instituto de Salud Carlos III
Funding Body Type
Funding Body Subtype
Results and Publications
Publication and dissemination plan
The results will be presented in national/international congresses in the field of obesity and diabetes.
The whole study will be published in a peer-reviewed international scientific journal.
The findinds will be disseminated to citizens through the official channels and social media of the sponsor's research institution and through the social media of the members of the research group.
IPD sharing statement:
The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request. Dr. Javier Bermudez-Silva, (email@example.com); specifically, raw data for published variables; data are expected to be available late 2020/early 2021 and during at least 10 years; data will be shared with researchers from public/non-profit research organizations upon reasonable request, allowing analysis of health variables related to the aims of this trial; consent from patients was obtained, patients were code converted, being the principal investigator the only person who guards the file (protected by password) encoding personal data of the participants; samples will be stored in the public biobank of the Consejeria de Salud de la Junta de Andalucía (Biobanco del Sistema Sanitario Público de Andalucía (BBSSPA), firstname.lastname@example.org) under specific MTA agreement between BBSSPA and the principal investigator and signed consent from patients; surplus samples will be available to other researchers from public/non-profit research organizations upon reasonable request to the principal investigator (Dr. Javier Bermudez-Silva, email@example.com); Biological samples and associated clinical data will be used in accordance to Ley 14/2007, of 3rd July, of Biomedical Research (Spain); Personal data collected will be considered confidential and managed according to Ley Orgánica 15/1999, of 13th December (Spain), of personal data protection.
Intention to publish date
Participant level data
Available on request
Basic results (scientific)