To date, no drug therapy has been approved for primary (PPMS) & secondary (SPMS) progressive multiple sclerosis. The urgent need to find new therapies - if possible with minimal side effects - led us to the search for the potential therapeutic effects of early harvest olive oil. The positive effect of phenol-rich, flavonoid and lignin-based olive oil on the modification of intestinal microbe populations and their by-products of metabolism is well known, such as the extent of gut-associated lymphoid tissue immune-stimulation due to antioxidants, anti-inflammatory and immunoregulatory properties. The aim of this Greek, Randomized Clinical Trial, is to evaluate the effect of Early Harvest Extra Virgin Olive Oil on cognition and mental health of patients diagnosed with PPMS or SPMS. The patients will be evaluated once at the beginning of treatment, after 6 months of treatment and after twelve months of treatment, in order to specify the eficacy of extra virgin olive oil in holistic treatments for SPMS and PPMS

Study Type: Randomized Clinical Trial. Primary Purpose: Prevention OBJECTIVES OF THE TRIAL The objectives of this study are:To investigate the efficacy of Early Harvest EVOO as a disease course modifying treatment for primary (PPMS) or secondary (SPMS) progressive multiple sclerosis in a phase III randomized controlled clinical trial study in objective measurements in patients with primary (PPMS) or secondary (SPMS) progressive multiple sclerosis.

STUDY DESIGN This is a Greek, randomized controlled study group of Early Harvest EVOO to a control group, in which the patients will receive only their symptomatic medication. Qualifying patients will be randomly assigned to receive 50mL of Early Harvest EVOO or not on a daily basis for 24 months. Patients undergo assessments at baseline, 6 and 12 months +/- 7 days after beginning treatment.

Duration: The total study duration will be 12 months. Patients will receive study interventions for 12 months.

Number of Subjects 30 subjects total will be enrolled; 20 in the experimental group (Early Harvest EVOO); 10 in the Control group

Inclusion Criteria:

• Confirmed diagnosis of primary (PPMS) or secondary (SPMS) progressive multiple sclerosis
• EDSS≥ 5
• No response to any given treatment for MS or interruption due to side effects
• Progressive aggravation in the disease's progression estimated by: deterioration in EDSS-plus disability scale, Timed 25-Foot Walk or 9-hole peg test.
• Progressive aggravation in the disease's progression estimated by: new lesions in MRI scan and neuropsychological tests
• Progressive aggravation in patient's neuropsychological status
• Progressive aggravation in patient's Quality of life, estimated with MuSIQol - Greek 3.01 MS and SF-36
• Years of education: >= 5
• Proficient language fluency
• Have a study partner with 10+ hr/wk contact (can be in person and telephone), accompanies to visits
• Compliance

Exclusion Criteria:

• Enrollment in other trials or studies not compatible with MSOIL
• Visual and auditory acuity inadequate for neuropsychological testing
• History of significant other neurological or psychiatric illnesses or presence of other diseases precluding enrollment.
• Use of forbidden medications (listed below)
• Ferromagnetic implants and devices (including implants or devices held in place by sutures, granulation or ingrowth of tissue, fixation devices, or by other means) not eligible for MRI scanning. Brain malformation or other conditions that may complicate lumbar puncture
• Any significant or uncontrolled medical condition or treatment-emergent
• Clinically significant laboratory abnormality

Medications across the study

Excluded Medication:

• Immunosuppressant or immunomodulating agents, corticosteroids, or investigational drugs within 3 months of study initiation
• Antibiotics in general, at least one month prior assessment of specific inflammatory markers (faecal levels of calprotectin, metabolomic profile, gut microbiota)
• Use of neuroleptics or within 4 weeks of screening
• Participation in any other investigational drug study within 4 weeks of screening (individuals may not participate in any drug study while participating in this protocol).