**6. Influence of probiotics in the development of obesity**

The development of obesity is not caused by one specific factor. On the contrary, it is the result of an interaction of genetic, environmental, social, lifestyle factors, etc., which transforms it into a multifactorial disorder, which explains how quickly it has become more prevalent throughout all age groups in developed countries and shows that traditional theories are not adequate to explain the complex phenomenon of gaining body weight [27].

In recent decades and as a result of advances in science, research for 'nontraditional' etiological factors involved in an individual's excessive weight gain has begun [28]. One of these new factors is highlighted in a study on the role of probiotics and their influence on gut microbiota. It should be noted that even now few studies have been carried out on humans to elucidate the effect of these microorganisms on body weight, and existing studies still show contradictory results; the available literature arises from findings found in animals (rats) [4].

However, several ways in which probiotics may influence adiposity and weight gain have been identified. These range from extracting calories from nutrients, generating specific metabolites, to modulating the behaviour of the brain-intestine axis [27].

These hypotheses arise from research suggesting that obese individuals have a different composition of gut microbiota to subjects of a normal weight. For example, in people with obesity, they have observed a decrease in members of phylum *Bacteroidetes* (*Prevotella* and *Bacteroides* genera) and an increase in members of phylum *Firmicutes* (*Clostridium*, *Enterococcus*, *Lactobacillus*). It has been suggested that the aforementioned microorganisms have a greater capacity to extract energy from the undigestible waste products of nutrients that pass through the large intestine. These alterations are normalised with both phyla, when the subjects lose weight (increase of *Bacteroidetes* and decrease of *Firmicutes*) [29]. It has been observed that obese and inactive people have greater adiposity and insulin resistance but also less diversity and microbial composition (**Figure 3**) [4].

A study conducted at Laval University in Canada evaluated the effect of *Lactobacillus rhamnosus* probiotic (LRP) supplementation on weight reduction, appetite control and eating behaviour in a group of obese men and women. The results showed that, in the group of women, the consumption of this microorganism provides beneficial effects on mood and behaviour linked to dietary intake, compared to the group of men and those who received the placebo. This opens up a series of possibilities for health professionals with regard to the implementation of successful obesity programmes, especially considering that many individuals experience great difficulties when trying to sustain their weight loss. This is mainly due to poor appetite control and not taking the necessary action to lead a healthy lifestyle. Based on the findings of this research, it has been suggested that some probiotic strains could be included as environmental factors with regard to body weight loss and maintenance [27].

Corroborating these findings, a multicentre, randomised, double-blind study conducted on 29 men and 14 women, using the microorganism *Lactobacillus gasseri* and administered through a probiotic yogurt for 12 weeks, demonstrated, in the individuals analysed, a 4.6% decrease in areas of abdominal and subcutaneous fat, as well as a decrease in BMI, waist and hip circumference [4].

Nevertheless, and contrary to these results, several investigations using a similar model maintain that administering yogurt with other species of probiotics such as

**101**

*Gut Microbiota and Obesity: Prebiotic and Probiotic Effects*

*Bacillus lactis* Bb 12 and *Lactobacillus acidophilus* La5 has no effect on body weight, BMI and serum lipid levels. This is also the case with *Streptococcus thermophilus* in

As previously mentioned, the impact of consuming probiotics in relation to obesity and a variety of parameters has been widely documented. This is, thanks to studies on rats, used when administering different strains of the *Lactobacillus* and *Bifidobacterium* genera; various hypotheses have emerged from these investigations. More specifically, one of these arose from observing axenic mice (without gut microbiota). Despite consuming 30% more food than conventional animals of the same age and weight, they have 42% less total body fat. However, once the microbiota from conventional mice was transplanted into the digestive tract of the axenic mice, these latter experienced a 57% increase in total body fat. The mechanism associated with this increase is linked to the increased activity of the enzyme lipoprotein lipase, which inhibits the fasting-induced adipocyte factor (FIAF) hormone due to the effect of the gut microbiota. This explains why axenic mice do not show weight gain even when consuming a high-calorie diet. Various studies carried out on rats show that the 'antiobesity' effect is determined by differences

There is not much research on the effect of probiotics and their relationship with obesity; however, the findings that are available indicate that the changes caused by gut microbiota could be useful as another strategy in the current quest to combat obesity. However, it is necessary to continue researching in this area, with more emphasis on investigations on humans and populations with a representative

Currently, obesity is a major public health problem worldwide. There is no specific cause that determines the development of this disease; on the contrary, it is the result of numerous factors that interact, including genetic, environmental, food, lifestyles, etc. [27]; however, the study of intestinal microbiota and its implication in obesity has aroused curiosity among scientists. The current information obtained

Although much of the research indicates that there are differences in the composition of the intestinal microbiota of obese and normal subjects, there is still

As indicated in this chapter, the development of these intestinal bacterial communities depends to a large extent on the host and can be modified by exogenous and endogenous influences. Ghosh et al. in 2011 talked about the direct relationship

In 2013, Devaraj et al. established the existing association in the imbalance of the microbiota where the composition of this is affected producing an increase of the *Firmicutes* genus and a decrease of the *Bacteroidetes*; this instability would affect the metabolism of the human being and as a consequence the appearance of various metabolic diseases among which obesity stands out [21]. In the same way, several publications continue confirming this situation, for example, the study of Jameel Barkat of the year 2018 relates the role of the microbiota in the regulation of energy balance, food absorption and its relationship with the appearance of various diseases: diabetes, metabolic syndrome and obesity, among others [30]. A study was conducted in 36 adults analysing the faecal bacterial composition, finding a decrease in *Firmicutes* and *Clostridia* in diabetic patients compared to the control group. This same research reaffirms that among the factors that alter the stability

comes mainly from the work done in rats and, exceptionally, in humans [17].

number of subjects so that results can be valid and extrapolated.

between food patterns and the microbiota composition [18].

*DOI: http://dx.doi.org/10.5772/intechopen.86672*

between microbial species and strains [20].

**7. Discussion**

controversy about it [4].

fermented milk for 8 weeks [4].

**Figure 3.** *Gut microbiota imbalance between healthy and obese individuals.*

*Gut Microbiota and Obesity: Prebiotic and Probiotic Effects DOI: http://dx.doi.org/10.5772/intechopen.86672*

*Bacillus lactis* Bb 12 and *Lactobacillus acidophilus* La5 has no effect on body weight, BMI and serum lipid levels. This is also the case with *Streptococcus thermophilus* in fermented milk for 8 weeks [4].

As previously mentioned, the impact of consuming probiotics in relation to obesity and a variety of parameters has been widely documented. This is, thanks to studies on rats, used when administering different strains of the *Lactobacillus* and *Bifidobacterium* genera; various hypotheses have emerged from these investigations. More specifically, one of these arose from observing axenic mice (without gut microbiota). Despite consuming 30% more food than conventional animals of the same age and weight, they have 42% less total body fat. However, once the microbiota from conventional mice was transplanted into the digestive tract of the axenic mice, these latter experienced a 57% increase in total body fat. The mechanism associated with this increase is linked to the increased activity of the enzyme lipoprotein lipase, which inhibits the fasting-induced adipocyte factor (FIAF) hormone due to the effect of the gut microbiota. This explains why axenic mice do not show weight gain even when consuming a high-calorie diet. Various studies carried out on rats show that the 'antiobesity' effect is determined by differences between microbial species and strains [20].

There is not much research on the effect of probiotics and their relationship with obesity; however, the findings that are available indicate that the changes caused by gut microbiota could be useful as another strategy in the current quest to combat obesity. However, it is necessary to continue researching in this area, with more emphasis on investigations on humans and populations with a representative number of subjects so that results can be valid and extrapolated.
