This study aims to investigate the potential effects of the administration of hydroxytyrosol, which is an extra virgin olive oil phenolic compound, in doses 15 milligrams and 5 milligrams daily versus placebo for 6 months in anthropometric parameters such as body weight, body fat and visceral fat, in combination with diet, in overweight and obese women.

Hydroxytyrosol is an extra virgin olive oil phenolic compound which has known protective effects in LDL oxidation and reduces oxidative stress. Olive oil has been associated with enhanced weight loss, and hydroxytyrosol could have a potential role in this.

Participants entered the study after signing the informed consent document. Detailed medical and family history was taken at baseline visit, and measurement of height, body weight, body fat and visceral fat were also made. Each participant visited a dietitian the same day and written consultation concerning the diet to be followed was given, based on Mediterranean diet and 500 kilocalories below their estimated Basal Metabolic Rate. The above measurements and dietitian consultation were repeated in each visit during the intervention (4,12 and 24 weeks).

Baseline laboratory testing was made including urea, creatinine, aminotransferases and fasting lipids and glucose, while serum and plasma were stored in -80 Celsius degrees for future analyses. Blood samples were also taken at 4, 12 and 24 weeks of the intervention.

All participants had an identical meal test at baseline, at 12 and 24 months and blood samples were collected at times 0, 30, 60, 90, 120, 150 and 180 minutes after meal consumption. Samples were also stored in -80 Celsius degrees for future analyses.

Each participant received in each visit prepackaged the quantity of capsules until the next scheduled visit, and the used empty blisters were returned in the following visit in order to assess compliance in capsules consumption. 24-hour diet recalls were used to assess compliance to diet.

In each visit an investigation concerning potential adverse events was made and data were recorded.

A communication was obtained with each participant who discontinued the study before 24 weeks, the reasons for discontinuation were recorded and data obtained until their last visit before study discontinuation were used in analyses.

Paired analyses were made using the system Statistical Package for the Social Sciences comparing all study groups before and after the intervention.

Inclusion Criteria:

Overweight and obese women. Stable body weight (<5% variation) during the past 3 months before enrollment. Stable hypolipidemic treatment for at least 3 months before enrollment.

Exclusion Criteria:

• Diabetes mellitus
• Neoplasms
• Autoimmune conditions
• Psychiatric disorders (excluding stable depressive disorder)
• Hyper/hypo-thyroidism with recent changes in medical treatment during the past 6 months before enrollment
• Renal impairment, defined as estimated Glomerular Filtration Rate (MDRD) <60millilitres/min
• Heart failure, defined as left ventricle Ejection Fraction <40%, use of diuretics or other treatment due to heart failure (antihypertensive medications allowed)
• Impaired liver function, defined as liver transaminases values twice above the upper normal range
• Malabsorption status (inflammatory bowel disease, previous bariatric surgery, chronic pancreatitis)
• Medical treatment known to influence body weight (steroids, oestrogens/ progesterone, topiramate, mirtazapine or anti-obesity treatment)
• Unwillingness to participate to the study
• Baseline waist circumference >130cm due to technical difficulties in visceral fat measurement
• Pregnancy, lactation