Effect of a Low-calorie Diet With a Prebiotic Supplement on Health of Overweight-obese Subjects.

The main objective of this project is to evaluate the effect of prebiotic supplementation on weight loss and other physiological and metabolic parameters related to excess weight in overweight/obese adult men and women, as well as to determine the changes in the gut microbiota associated with these changes. Specific objectives are focus on evaluate the effect of the intervention on the following parameters: * Weight and body composition. * Changes in the gut microbiota (metagenomics). * Changes in urinary and serum metabolites. * Complete blood count, routine biochemical variables related to glucose and lipid metabolism, as well as liver health parameters. * Specific markers involved in obesity pathology (insulin, leptin, adiponectin, and cytokines MCP1, TNF, CRP, and IL10). * Satiety-related variables using a visual analog scale. * Adherence to the assigned intervention, both to the hypocaloric diet and to the supplement provided in the study. * Physical activity level. * Changes in gastrointestinal health through self-reported questionnaires. * Mental health and quality of life of participants through self-reported questionnaires. * Chronotype of participants through a self-reported questionnaire. For this purpose, a randomized, double blind parallel study has been designed. Target sample size is 156 subjects. Participants will be allocated in two groups for 8 weeks: * Experimental group (n=104): hypocaloric diet + prebiotic supplement. * Placebo group (n=52): hypocaloric diet + placebo supplement. Participants will visit nutritional intervention unit at week 1 and week 8. At week 4 they will receive a phone control call.