Mastiha is a natural product from the tree Pistacia lentiscus var. Chia (Anacardiaceae) growing exclusively in the Southern part of Chios Island. It is the natural resinous exudate produced after longitudinal incisions made at close intervals from the base of the trunk up to the thicker branches of the tree. U.S. Food and Drug Administration has classified Mastiha as GRAS. Previous research demonstrates Mastiha's safety, as well as anti-inflammatory, antimicrobial and antioxidant properties. In addition, the European Medicine Agency has recently recognized Mastiha as a natural medicine and classified it to the category of traditional herbal medicines in diarrhea problems, mild dyspeptic disorders, skin inflammation and healing (EMA/HMPC/46758/2015).

However, the bioavailability of its microconstituents in human biological samples is still undetermined. To this end, the current study aims to investigate the whether Mastiha's compounds are bioavailable in healthy adults. Twenty apparently healthy men, aged 20-40 years old, will be enrolled based on certain inclusion and exclusion criteria. The staff of the study will provide detailed information regarding the aims, the methods, anticipated benefits and potential hazards of the study and all patients will receive the Patient Information Leaflet (PIL). Ample time (48 hours) will be provided in order to decide whether they want to participate in the protocol. Each patient agreeing to participate will sign an Informed Consent document and the staff will explain to patients that they are under no obligation to enter the trial and that they can withdraw at any time during the trial, without having to give a reason. A copy of the signed Informed Consent will be given to the participant.

After enrollment, the volunteers will undergo a medical and dietary assessment and their health status will be evaluated through a complete blood count. Then, they will follow a low-phytochemical diet for five days, meaning that they will exclude fruits, vegetables, legumes, coffee, tea, alcoholic beverages and chocolate. On the day of the experiment and after overnight fasting, the volunteers will consume 10g of natural Mastiha and blood samples will be obtained on timepoints 0h, 30min, 1h, 2h, 4h, 6h and 24h after Mastiha intake. Until timepoint 6h, they will be allowed to consume only water. Urine samples will also be collected on timepoints 0h, 4h, 8h and 24h.

After collection, the phenolic and terpenoid content or metabolites of Mastiha will be identified in plasma samples applying LC-HRMS. Additionally, the metabolomic profile will be assessed in plasma samples with LC-HRMS and in urine samples with NMR-based metabolomics. Oxidative stress will be evaluated through the CuSO4 technique and oxidised LDL levels in serum samples, as well as F-2 isoprostanes in urine samples.

Inclusion Criteria:

• Age: 20-40 years old
• BMI: 18.5-24.9 kg/m2

Exclusion Criteria:

• BMI > 25 kg/m2
• Alcohol or drug abuse
• Medication, vitamin or inorganic supplements
• Vegan or macrobiotic diet before and during the study
• Gastrointestinal diseases, such as IBD, peptic ulcer or GI cancer