Cardiometabolic and immunological impacts of extra virgin olive oil consumption in overweight and obese older adults: A randomized controlled trial

Olive oil, a major component of Mediterranean diet (Med-diet), is known as a functional food with various beneficial effects. The impact of olive oil on immune functions has not been clearly defined as the limited numbers of studies have reported contradictory results. In addition, to our knowledge, there has been no human study that reported the impact of olive oil on immune responses of overweight or obese older adults.;We investigated the effects of olive oil compared to oil consumed in a typical American diet on in vivo indices of immune response including delayed type hypersensitivity skin response (DTH), and immune cell phenotype, and ex vivo indices including T cell proliferation, and cytokine production. The effects of olive oil consumption on cardio-metabolic factors including lipid profile and blood pressure were also determined.;In this randomized placebo controlled clinical trial, 41 eligible overweight or obese participants (age≥ 65 y) who consumed a typical American diet, were randomized into either the control (N=21) or experimental group (N=20) in a 1:1 ratio. Both groups were provided study oils and spreads. The control group was provided with a mixture of corn and soybean oil, and butter to use as spread, while the experimental group was provided with extra virgin olive oil to use as oil and spread. Both groups were asked to continue consuming a typical American diet but to replace substitutable oils in their diet with the study oils provided to them. The participants used the oil freely (ad libitum) in their cooking, as a spread and dressing for 3-mo. At baseline and 3-mo, overnight fasted blood samples were collected on two consecutive days for measurements of immune and cardio-metabolic factors, and DTH implants were administered on the second day after the blood draw and evaluated 24 and 48 hours later. Blood pressure was also measured.;After 3-mo of supplementation, the olive oil group showed a significant decrease in systolic blood pressure (P = 0.04), and a marginally significant increase in HDL-C compared to the control group (P = 0.06). While T cell proliferation increased significantly at 3-mo in both groups compared to their respective baseline levels (P between 0.001 and 0.04), the olive oil group had a significantly larger increase in T cell proliferation stimulated by anti-CD3/anti-CD28 compared to the control group (P No significant difference was found in the mean change between baseline and 3-mo in either T cell phenotype or cytokine production between the two groups. Although DTH response (skin induration) increased at 3-mo from the respective baseline within each group (P between 0.001 and 0.04), there was no significant difference in the mean change between the two groups.;In conclusion, substitution of oils used in a typical American diet by overweight and obese older adults with extra virgin olive oil may have cardio-metabolic and immunologic benefits as manifested by decreased systolic blood pressure, increased HDL-C, and increased T cell proliferation.