The main objective is to study the effect of polyphenol supplementation on hepatic steatosis as measured by hepatic ultrasound, hepatic magnetic resonance imaging and on intima-media thickness and vascular elastography in obese adolescents known for hepatic steatosis as diagnosed by liver biopsy

1. Evaluate the feasibility of a larger, open-label, randomized, controlled trial on the effects of polyphenol supplementation:

   Recruitment, compliance to polyphenol supplementation and the visit roadmaps Duration of the radiological exams and participants' satisfaction and point of view on the experience. Test the relevance of using a food diary. Test the effectiveness of the data collection procedure during the visits. Explore the obstacles encountered while performing the radiological exams and the rate of adverse events (AE). Calculate the sample size of the future randomized clinical study

2. Effects of polyphenols IMT and vascular elastography. Anthropometric measurements, insulin resistance, inflammation, lipid/lipoprotein profile, gut microbiome and liver function

3. Evaluated different imaging modality for steatosis Different imaging modalities will be compared between children

Inclusion Criteria:

• Aged 12 to 18 years
• BMI percentile > 85th for age and sex
• Diagnosis of hepatic steatosis on imaging (ultrasound or MR).
• Diagnosis of hepatic steatosis, NASH, or fibrosis on liver biopsy.
• Elevated alanine aminotransferase (ALT) enzyme level.
• Index of hepatic steatosis 8xALT/AST + BMI (+2 for girls) > 30.

Exclusion Criteria:

• Known chronic systematic diseases
• Any other serious conditions which, according to the doctor's judgment, would prevent compliance and safe participation in the study until completion.

Exclusion criteria to be validated when contacting the participants and their parents/tutors:

• Being pregnant.
• Taking all kinds of prescription or over-the-counter natural health products/natural supplements/vitamins on an ongoing basis or within the next four months, excluding vitamin D.
• Weight loss of 5% to 10% of the usual weight in the last six months before recruitment or weight change of 5% in the last three months.
• Alcohol consumption > two drinks/day or > one day/week.
• Known peanut allergy and/or to the medicinal ingredients contained in the active polyphenol supplement: elderberry, haskap, black chokeberry, blueberry, blackcurrant.
• Any contraindications for MRI.