Several components of the diet are involved in the aetiology and development of obesity and resistance to insulin. Among the dietary-therapeutic measures used to treat these pathologies are the moderate reduction of calorie intake, the reduction of the energy density of the diet and the intake of a quantity of dietary fiber that covers recommended needs.

Dietary fiber may have beneficial effects on these diseases by decreasing the energy intake, delaying and reducing the absorption of energy nutrients and/or modifying the metabolic response by reducing the resistance to insulin. However, there is little scientific evidence to suggest that dietary fiber has a healthy effect on these pathologies, and the evidence that does exist is generally derived from short-term epidemiological or experimental studies. Very few control studies have been made of the long-term therapeutic effect of dietary fiber.

For all these reasons, we decided to do the present doctoral thesis, which is structured as follows:

1) We analyzed epidemiological data from the Examen de Salut Catalunya 2002 (Catalonia Health Examination 2002) about dietary fiber intake in our geographical area in order to be able to make plans and decisions about the amounts of fiber to be administered in the subsequent experimental studies on the healthy effects of dietary fiber supplementation.
2) We studied the acute effect of an association of soluble dietary fibers (plantago ovata and glucomannan) on the post-prandial glycemic response in healthy individuals in comparison with the isolated administration of glucomannan. This enabled us to decide what type of fiber supplementation to administer in the medium-long term experimental study.
3) We studied the medium-long term therapeutic effect of supplementation with dietary fiber on overweight or obese patients with type 2 diabetes. The data provided by the epidemiological study show that the amount of fiber used as a supplement in the experimental study would lead to 95% of the population studied in Examen de Salut Catalunya 2002 respecting the intake recommended by the Spanish Society of Community Nutrition for the Spanish population (Serra-Majem, 2001).