## 1 Introduction  
The growing phenomenon of overweight and obesity has led to a global problem. Current data estimate that 650 million people are obese worldwide, while 1.9 billion are overweight [1]. The latest trend analyses show that the number of obese or overweight people is steadily increasing both in Europe and around the world [2, 3]. The obesity disease is characterized by excessive fat accumulation, which is a consequence of a long-term energy surplus. The reasons given for this state are primarily seen in excessive energy consumption, reduced energy expenditure, or both at the same time. Additionally, changes in eating habits and the increased availability of high-calorie foods have made overweight and obesity one of the most severe health problems of our era. Obesity is a multifactorial disease caused by both environmental and genetic determinants. Importantly, overweight and obesity positively correlate with other chronic diseases such as type 2 diabetes, cardiovascular diseases, some types of cancer, and infertility. Annually, nearly 2.8 million deaths in the world are a consequence of excess weight [1, 4, 5]. Scientific reports from the last several years have investigated the relationship between the composition of the intestinal microbiota and the development of obesity [6]. People with excessive body weight have a higher positive proportion of _Firmicutes_ to _Bacteroidetes_ than normal-weight people. It seems that significant variation within _Firmicutes_ may contribute to more efficient energy extraction from food sources and increase energy storage in host fat tissue [7,8]. Intestinal bacteria ferment indigestible carbohydrate residues, synthesize short-chain fatty acids and amino acids, and thus can contribute to an increase in the amount of energy supplied to the host. However, it is not determined whether this process is of clinical importance [9,10]. On the other hand, by-products of bacterial fermentation can reduce appetite and increase satiety [11] as well as decrease body weight and Body Mass Index (BMI) [12]. Consequently, the intestinal microbiota is a potentially modifiable factor associated with the prevention and treatment of excessive body weight. Probiotic bacteria are described as 'live microorganisms which when administered in adequate amounts confer a health benefit on the host' [13]. Probiotic food supplementation has grown in popularity in recent years [14]. The best known probiotic microorganisms include strains belonging to the genera _Lactobacillus_ and _Bifidobacterium_[15]. _Bifidobacterium animalis_ subsp. _lactis_ BB-12 has been used in clinical trials alone and with other bacteria such as _Lactobacillus acidophilus_ LA-5 or _Streptococcus thermophilus_[16]. The results of human experiments provide the basis for attributing several beneficial effects to LA-5 and BB-12. They show, among others, prophylactic activity against children rotavirus diarrhea infection in children [17], and also reduce the incidence of skin eczema [18]. Many studies were carried out with the use of probiotic preparations, although probiotic food products containing LA-5 and BB-12 strains were also studied. Consumption of the above-mentioned products reduced inflammation markers [19] and improved blood lipid profile [20]. In this context, probiotics can be a useful tool in the treatment of obesity and its complications. Regular intake of drugs or dietary supplements containing probiotics can be problematic due to their often high price, the pharmacotherapy used by the patient, or frequent irregularities on the dietary supplement market [21]. For this reason, it is worth focusing on widely available food enriched with probiotic strains. The probiotic product should contain at least \(10^{6}\)-\(10^{7}\) of viable probiotic bacteria cells per one ml of product [22].