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.
