Objective assessment of dietary nutrient content is essential in weight management and life-style interventions. Increasing evidence suggests that microRNAs (miRs) may be useful as biomarkers of nutritional status. The miRs are short non-coding RNAs that can be released by cells and circulate within the blood in a remarkably stable form. Modulation of circulating miR as well as tissue levels have been described in response to changes in intake of various specific nutrients.
In lean individuals, fat represents about 20 % of body mass, this percentage markedly increase in obese patients. As adipose tissue is an organ that releases various molecules including miRs, investigating the relationship between miRs and nutrients may benefit from studies on adipose tissue.
The general workplan of miRDiet was to perform profiling of adipose tissue miRs during nutritional interventions in order to discover miRs with relationship to dietary intake that circulate in blood and could be robust biomarkers of dietary content.
The miRDiet consortium focused on dietary calorie intake, protein content, glycemic index and polyphenol content of the diet. RNA was isolated from adipose tissue and plasma samples from patients undergoing various dietary interventions. The miRs levels were measured using two different techniques for discovery and for validation.
During the miRDiet project, circulating miRs were found as biomarkers for calorie restriction and polyphenol intake, but no potential biomarker was found for dietary glycemic index and protein content. It was observed that polyphenol supplementation tended to attenuate the increase in 2 circulating miRs, miR-22-3 and miR-378a-3p, that was found in the placebo arm. The miRs profiling revealed 3 miRs with lower concentrations after calorie restriction: miR22-3p, and miR-4324 and miR-4780, as biomarkers of calorie restriction in adipose tissue and plasma, respectively. These miRs are biomarkers of calorie deficit. Circulating miRs have potential clinical use in nutritional intake/status testing. Direct measurement of adipose tissue miRs is of interest in individuals with very high body fat in whom blood sampling is painful or impossible.