Antidiabetic Effect of Olive Pomace Oil

This clinical trial aims at assessing whether consumption of olive pomace oil in the diet may benefit persons with type 2 diabetes mellitus or persons at risk of developing the disease (prediabetic persons).

The main questions the study aims to answer are:

* May olive pomace oil prevent a high increase of blood glucose levels when consumed in a meal together with carbohydrates in diabetic/prediabetic patients?
* May olive pomace oil decrease fasting blood glucose levels of diabetic/prediabetic patients after consuming it daily?
* May daily consumption of olive pomace oil improve glucose homeostasis and other alterations like elevated blood lipids or inflammation, which also affect persons with diabetes or prediabetes?

Researchers will compare the effect of consuming olive pomace oil to the effects of a comparison oil (high-oleic acid sunflower oil).

Participants will:

In different days, they will consume white bread alone or the oils (olive pomace oil, high-oleic acid sunflower oil or extra virgin olive oil) spread on white bread and blood will be collected at different times during 2 h. This study to observe the increase of blood glucose after a carbohydrate-rich breakfast will be part of the so-called "postprandial" study, and will be conducted during 3 weeks, during which participants will consume corn oil on a daily basis.

Participants will also take part in the "chronic" study, that will last 22 weeks in total. During this study, they will firstly "wash" the effects of the oil they normally consume in their diets by consuming corn oil during 3 weeks. It is during these weeks when they will attend the Human Nutrition Unit (HNU) of ICTAN to carry on the "postprandial" study described in the previous paragraph.

After the initial 3 weeks, participants will consume olive pomace oil as the only oil in their diets during 8 weeks, "wash" its effects again by consuming corn oil during 3 weeks and then change to consume the other oil (high-oleic acid sunflower oil) during 8 weeks.

During the chronic study, they will visit the clinic once every 4 weeks for checkups and tests. They will refrain from eating other oils or specific fat-rich foods. Participants will also attend our phone calls to ask them what they ate the day before on different weeks during the study, and wear an accelerometer during 1 week to record their physical activity. They will keep a diary of the doses of insulin/metformin used and the blood glucose levels they measured at home.

This trial comprises 2 studies in parallel, a postprandial study and a chronic intervention.

In the postprandial study, participants will attend the Human Nutrition Unit (HNU) of ICTAN in different days. During these visits, they will consume white bread (50 g) alone or with 10 g of extra virgin olive oil (EVOO), olive pomace oil (OPO) or high-oleic acid sunflower oil (HOSO). A nurse will insert a catheter in the non-prevailing arm and collect fasting blood (0 h) and blood samples 1 and 2 h after consuming the bread/oil to measure the postprandial glycemic/insulinemic response, as well as incretins (GLP-1, GIP). Blood lipids will also be determined. These visits will be carried out during the 3-week run-in period prior to the chronic intervention, when the EVOO and control (white bread) tests will be carried out (weeks 1 and 2, respectively). Then, coinciding with the first day of the chronic intervention, participants will consume either OPO or HOSO as corresponding to the randomized allocation to each oil. The other postprandial test will be carried out at the beginning of the second intervention after crossover and wash-out, thus avoiding additional visits and discomfort to the participants.

The chronic study is a crossover, randomized, blind, clinical trial. After a 3-week run-in during which participants will consume corn oil as the only dietary oil, they will be randomly allocated to one of each intervention arms, OPO or HOSO, each lasting 8 weeks. Then, a 3-week wash-out period with corn oil will follow before changing to consuming the other oil.

During the study, participants should avoid other oils and fats such as olives, sunflower seeds, butter, margarine, nuts or avocados.

During the chronic intervention, participants will visit the HNU at the beginning (week 1), middle (week 4) and at the end (week 8) of each intervention arm. A nurse will collect a fasting blood sample and measure blood pressure. An analysis of body weight and body composition (anthropometric and bioimpedance measurements) will be performed. Participants should maintain their habitual diet and exercise level throughout the study; diet will be monitored by periodic 24-h recall questionnaires (a trained member of the team will phone participants on 3 different days (including a festive one) before each visit to the HNU to enquire what they ate the previous day). In addition, a physical activity questionnaire will be completed at the beginning of the study and, on each intervention arm, participants will carry during 7 days an accelerometer to monitor real physical activity.

Biochemical, hormonal and inflammatory markers will be measured in blood samples to assess the potential effect of olive pomace oil on different outcomes of relevance in the management of blood glucose in diabetic/prediabetic persons, including glucose homeostasis, insulin resistance, blood lipid levels, liver function, different hormones, incretins, adipokines, pro- and anti-inflammatory cytokines, on integrity of the intestinal barrier.

Eligibility Criteria:
Inclusion Criteria:

* Fasting blood glucose between 100-126 mg/dL and/or
* Glycated haemoglobin (HbA1c) between 5.7-6.4% and/or
* Diabetic persons with Fasting blood glucose \>126 mg/dL and/or
* Diabetic persons with Glycated haemoglobin (HbA1c) \> 6.4%

Exclusion Criteria:

* Kidney or liver diseases
* Gastrointestinal diseases (irritable bowel syndrome, Crohn disease, chronic bowel inflammation)
* Food allergies/intolerances
* Vegetarians/vegans
* Smoking
* Pregnant or lactating women
* On prescription drugs other than for hypertension/thyroid/dyslipidemia/glucose control, or changes in dosage in the last 3 months
* Consumption of vitamins, dietary supplements or nutraceuticals