Beta-glucan and Insulin Sensitivity in Obese Humans

Obesity is an important health problem of modern civilization. In Western societies, almost half of the adult population has problems with an increased body weight. In Europe, obesity occurs in 10-20% males and 15-25% females. In Poland, obesity is present in about 20% of population.

Products containing nutritional fiber has been used by humans for thousands of years. However, beta-glucan as biologically active compound, present in these products, has been identified relatively lately. This substance is a polymer of glucose and is present in two forms: 1,3D-1,6D and 1,3D-1,4D.

Water-insoluble beta-glucan (1,3D-1,6D) has immunomodulatory properties. It stimulates host defense against viral, bacterial and parasitical infections through binding with the specific receptors located on the immune system cells surface in many animal models. There are data that beta-glucan 1,3D-1,6D affects both innate and acquired immune response also in humans.

The aim of the study was the assessment of the influence of beta-glucan 1,3D-1,6D added to the low-calorie diet on insulin sensitivity and the expression of selected proinflammatory cytokines in adipose tissue and peripheral blood mononuclear cells (PBMC) in obese humans with normal glucose tolerance.

The study group consisted of 40 subjects with marked overweight or obesity (body mass index, BMI > 28 kg/m2), without serious concomitant diseases not taking drugs affecting glucose or lipid metabolism, nonsmokers. Only volunteers, who gave written informed consent, after receiving a full information about the aim and the design of the study by the research personnel were recruited.

At the beginning of the study, after subjects' qualification to the project and before the dietary intervention, the investigators assessed:

• anthropometric measurements: BMI, waist-to-hip ratio (WHR), full physical examination.
• body composition with Tanita TBF-511 Body Fat Analyzer.
• glucose tolerance with the oral glucose tolerance test.
• insulin sensitivity with the euglycemic hyperinsulinemic clamp technique.
• before and after the clamp, additional 6 ml of blood was collected, and PBMC isolation was performed.
• before the clamp, a biopsy of subcutaneous adipose tissue was performed.
• isolation of mRNA from PBMC and adipose tissue was performed. Then, the expression of the selected genes with the Real Time PCR In adipose tissue was measured measured.
• additionally, serum concentrations of ghrelin, peptide Y-Y3-36, citruline and intestinal fatty acid-binding protein was assessed.

After the initial visit, participants received detailed instructions about low-calorie diet, with the aim of reduction of 5-7% of body weight and the examples of menu for 14 days.

Then, participants were randomly assigned to a group receiving or not beta-glucan preparation, as a addition to the low-calorie diet. Each group consisted of 20 subjects. Subjects assigned to a group receiving beta-glucan, received the preparation (BETA GLUCAN 1,3-1,6 Laboratoria Natury 500mg) together with the detailed instruction of its usage. This preparation is used as a non-prescription diet supplement, and the dose of 500 mg daily is indicated by the manufacturer.

Analysis of the compliance to the dietary indications and analysis of body composition was performed every 2 weeks.

After 12 weeks of low-calorie diet, without or with beta-glucan, all the examinations performed at the beginning of the study were repeated.

Inclusion criteria

• marked overweight or obesity (BMI above 28 kg/m2)
• normal glucose tolerance

Exclusion criteria

• morbid obesity (BMI above 40 kg/m2)
• impaired glucose tolerance or diabetes
• cardiovascular diseases
• other serious disease
• smoking
• usage of drugs known to affect carbohydrate or lipid metabolism