Effect of a high-protein diet with β-cryptoxanthin supplementation on metabolic risk factors, oxidative and inflammatory biomarkers in non-alcoholic fatty liver disease (NAFLD): study protocol for a randomized controlled clinical trial

BACKGROUND: Excessive hepatic fat is associated with increased metabolic risk factors, production of inflammatory factors, and oxidative stress. High protein intake might trigger an increased hepatic lipid oxidation through an increase in hepatic energy expenditure. Furthermore, the majority of randomized controlled trials (RCT) in humans have failed to show whether carotenoids can be used to prevent and treat non-alcoholic fatty liver disease (NAFLD). However, it is notable and contradictory that NAFLD is rapidly escalating in Iran and other countries with lower intakes of fruit and vegetables (as sources of β-cryptoxanthin [β-CX] and carbohydrates) and higher intake of carbohydrates (as an agent of NAFLD); and the effects of β-CX and a high protein diet (HPD) on NAFLD need to be investigated further. METHODS/DESIGN: This study will be conducted as a randomized, double-blind, placebo-controlled clinical trial for 12 weeks to receive daily β-CX 6 mg supplementation combined with a HPD on levels of metabolic factors, β-CX, glycemic and lipid profiles, inflammatory factors, adipocytokines, and body composition. Ninety-two eligible patients, aged 18–60 years, of both genders, who are obese and overweight (body mass index [BMI] 25–40 kg/m(2)) will be randomly assigned to four groups as follow: HPD + placebo; normal protein diet + β-CX (NPD + β-CX); HPD + β-CX; and NPD + placebo (control group). Two populations will be analyzed in this work. The intention-to-treat (ITT) population includes all patients who will be randomized, while the per-protocol (PP) population includes all individuals who complete the 12- week intervention (i.e. study completers). DISCUSSION: Our findings from this trial will contribute to the knowledge of the relationship between β-CX supplementation and a HPD on NAFLD patients and determination of optimal macronutrient ratios without energy restriction. TRIAL REGISTRATION: Iran clinical trials registry, IRCT2017060210181N10. Registered on 20 June 2017. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s13063-018-3014-8) contains supplementary material, which is available to authorized users.