**5. Modulation of gut microbiota and inflammation by fatty acids: the role of diet**

As previously discussed, there are several actions of different types of FA in inflammatory pathways and in gut microbiota. Changes in the dietary quality of lipids can improve inflammatory markers and provide an intestinal balance, preventing the development of diseases [84]. In general, therapeutic protocols suggest that a lower intake of foods rich in saturated fats, trans fats, and sugars and an increase in dietary sources of bioactive fiber and lipids are considered beneficial [92]. Also, the intake of bioactive lipids, which include monounsaturated and PUFA, phytosterols, and medium-chain lipids is beneficial [85].

Regarding fat consumption, it has been reported that postprandial endotoxemia is influenced by the fatty acid composition of the diet and not by the fat content as a whole. Subjects consuming meals rich in omega-3 decreased serum levels of endotoxemia, unlike those who consumed omega-6-rich foods. The omega-6 fatty acids can increase serum triglyceride levels and also cause gut hyperpermeability, favoring the accumulation of fat in adipose tissue and stimulating the inflammatory processes [86].

The consumption of sardines and fish enriched in omega-3 caused a decrease in the *Firmicutes* filo and in the *Firmicutes*/*Bacteroidetes* ratio in patients with no DM2 treatment [87]. The adoption of a Mediterranean diet or low-fat and carbohydrate diet by obese individuals resulted in different changes in gut microbiota, with high

levels of the genus *Roseburia* and *F. prausnitzii*, respectively, demonstrating the protective effects of both diets on the development of DM2 [88]. The consumption of extra virgin olive oil enriched with phenolic compounds has been shown to have a cardio-protective effect, which could be mediated by the increase in the population of bifidobacteria, together with the increase in microbial metabolites and phenolic compounds, which has antioxidant activities [89].

Saturated fats, such as palmitic, lauric, and stearic acids, may be related to the activation of inflammatory processes. A study with healthy young people showed that a reduction in the palmitic acid/oleic acid ratio in the diet resulted in lower secretion of IL-1β, IL-18, IL-10, and tumor necrosis factor alpha stimulated by LPS [90]. A study conducted with subjects at risk of metabolic syndrome showed that the consumption of saturated fat increased the composition of pathogenic bacteria [41].

In infants, the percentage of fat in the complementary diet has been reported to be negatively correlated to the diversity of gut microbiota [91]. In infant formulas, lipids are typically added as vegetable oils, with long-chain fatty acids predominating [92]. However, human milk has a low content of n-6 fatty acids and a high content of medium-chain fatty acids, acting as a prebiotic [93]. Sources of SCFA may be useful for remodeling gut microbiota and reducing obesity.

The beneficial role of the fibers in a high-fat (HF) diet on inflammatory markers and gut microbiota was also verified [94]. A decrease in adipocyte size and IL-6 levels was observed when the fibers were administered as part of a HF diet over a period of 6 weeks. These fibers were able to alter gut microbiota and increase fermentation rates, mainly by stimulating the production of SCFA, demonstrating its role in the prevention of intestinal inflammation, and may increase the beneficial forms of microbiota diversity.

### **6. Conclusion and recommendations**

Determination of the fatty acid composition in the diet is essential for two reasons: first, to understand the pathogenesis and responsiveness of some diseases, such as obesity, and second, to address potential therapeutic interventions. In this chapter, we have demonstrated that there is a direct relationship between excessive fat consumption and microbiota composition. Obesity is closely associated to microbiota composition as well. In other words, an overconsumption of fat induces changes in microbiota composition, which, by its turn, becomes influential to obesity. These connections have been demonstrated both in obese people and in rodent models, that consume an excess of fat, have shown alteration in their microbiota composition. Increased intake of saturated fatty acids and LPS is negatively associated with this process, while a higher intake of food sources of short- and medium-chain fatty acids and n-3 PUFA has shown positive effects (**Figure 1**). It is evidently observed the relevant roles of these lipids in inflammatory processes, in the endocannabinoid system, brain functioning, and behavior, influencing the composition of gut microbiota and, therefore, the functioning of the gut-brain axis. All of these factors have significant implications for the reduction of meta-inflammation and, consequently, insulin resistance and the risk of DM2 and cardiovascular diseases in obese individuals.

As most studies have been conducted on animals and cell culture, we strongly recommend well-controlled, long-term clinical studies in humans, so that we can better understand this complex interaction among dietary fatty acids, gut microbiota, and obesity. Due to the strong anti-inflammatory activities of n-3 PUFA, as well as dietary fibers stimulating the production of SCFA and, therefore,

**61**

*Fatty Acids, Gut Microbiota, and the Genesis of Obesity DOI: http://dx.doi.org/10.5772/intechopen.80664*

influencing the composition of gut microbiota and the host health, we also recommend that dietary fiber and n-3 PUFA should be part of the diet of obese individu-

*Impact of dietary fatty acids in the gut microbiota composition and health. A healthy microbiota is associated with the balance between pathogenic and nonpathogenic bacteria that may reflect on systemic consequences. Dietary lipid profile can modulate its composition (yellow arrows). Excessive consumption of SFA (right yellow arrow) will cause negative outcomes to the metabolism and microbiota content (red boxes and arrows). On the other hand, SCFA and PUFA (left yellow arrow) reveal positive effects in inflammation, fat deposition, and microbiota (green boxes and arrows). The two-way arrow (in yellow) represents changes in gut microbiota ecology, depending on what type of FA has been consumed. The equilibrium among these factors seems to be another way to explain the obesity development. FIAF, fasting-induced adipose factor; LPS,* 

This work was supported by grants from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro, and Conselho Nacional de Desenvolvimento Científico e Tecnológico.

als and that dietary SFA and n-6 PUFA should be under control.

AMPK adenosine monophosphate-activated protein kinase

The authors declare no conflicts of interest.

2-AG 2-arachidonoylglycerol

CB1 type 1 cannabinoid receptor CB2 type 2 cannabinoid receptor

DM2 type 2 diabetes mellitus

AEA anandamide

CoA coenzyme A

BMI body mass index

**Acknowledgements**

*lipopolysaccharides; TLR4, Toll-like receptor 4.*

**Figure 1.**

**Conflict of interest**

**Abbreviations**

#### **Figure 1.**

*Biochemistry and Health Benefits of Fatty Acids*

bacteria [41].

forms of microbiota diversity.

**6. Conclusion and recommendations**

compounds, which has antioxidant activities [89].

levels of the genus *Roseburia* and *F. prausnitzii*, respectively, demonstrating the protective effects of both diets on the development of DM2 [88]. The consumption of extra virgin olive oil enriched with phenolic compounds has been shown to have a cardio-protective effect, which could be mediated by the increase in the population of bifidobacteria, together with the increase in microbial metabolites and phenolic

Saturated fats, such as palmitic, lauric, and stearic acids, may be related to the activation of inflammatory processes. A study with healthy young people showed that a reduction in the palmitic acid/oleic acid ratio in the diet resulted in lower secretion of IL-1β, IL-18, IL-10, and tumor necrosis factor alpha stimulated by LPS [90]. A study conducted with subjects at risk of metabolic syndrome showed that the consumption of saturated fat increased the composition of pathogenic

In infants, the percentage of fat in the complementary diet has been reported to be negatively correlated to the diversity of gut microbiota [91]. In infant formulas, lipids are typically added as vegetable oils, with long-chain fatty acids predominating [92]. However, human milk has a low content of n-6 fatty acids and a high content of medium-chain fatty acids, acting as a prebiotic [93]. Sources of SCFA

The beneficial role of the fibers in a high-fat (HF) diet on inflammatory markers

and gut microbiota was also verified [94]. A decrease in adipocyte size and IL-6 levels was observed when the fibers were administered as part of a HF diet over a period of 6 weeks. These fibers were able to alter gut microbiota and increase fermentation rates, mainly by stimulating the production of SCFA, demonstrating its role in the prevention of intestinal inflammation, and may increase the beneficial

Determination of the fatty acid composition in the diet is essential for two reasons: first, to understand the pathogenesis and responsiveness of some diseases, such as obesity, and second, to address potential therapeutic interventions. In this chapter, we have demonstrated that there is a direct relationship between excessive fat consumption and microbiota composition. Obesity is closely associated to microbiota composition as well. In other words, an overconsumption of fat induces changes in microbiota composition, which, by its turn, becomes influential to obesity. These connections have been demonstrated both in obese people and in rodent models, that consume an excess of fat, have shown alteration in their microbiota composition. Increased intake of saturated fatty acids and LPS is negatively associated with this process, while a higher intake of food sources of short- and medium-chain fatty acids and n-3 PUFA has shown positive effects (**Figure 1**). It is evidently observed the relevant roles of these lipids in inflammatory processes, in the endocannabinoid system, brain functioning, and behavior, influencing the composition of gut microbiota and, therefore, the functioning of the gut-brain axis. All of these factors have significant implications for the reduction of meta-inflammation and, consequently, insulin resistance and the risk of DM2 and cardiovascular diseases in obese individuals. As most studies have been conducted on animals and cell culture, we strongly recommend well-controlled, long-term clinical studies in humans, so that we can better understand this complex interaction among dietary fatty acids, gut microbiota, and obesity. Due to the strong anti-inflammatory activities of n-3 PUFA, as well as dietary fibers stimulating the production of SCFA and, therefore,

may be useful for remodeling gut microbiota and reducing obesity.

**60**

*Impact of dietary fatty acids in the gut microbiota composition and health. A healthy microbiota is associated with the balance between pathogenic and nonpathogenic bacteria that may reflect on systemic consequences. Dietary lipid profile can modulate its composition (yellow arrows). Excessive consumption of SFA (right yellow arrow) will cause negative outcomes to the metabolism and microbiota content (red boxes and arrows). On the other hand, SCFA and PUFA (left yellow arrow) reveal positive effects in inflammation, fat deposition, and microbiota (green boxes and arrows). The two-way arrow (in yellow) represents changes in gut microbiota ecology, depending on what type of FA has been consumed. The equilibrium among these factors seems to be another way to explain the obesity development. FIAF, fasting-induced adipose factor; LPS, lipopolysaccharides; TLR4, Toll-like receptor 4.*

influencing the composition of gut microbiota and the host health, we also recommend that dietary fiber and n-3 PUFA should be part of the diet of obese individuals and that dietary SFA and n-6 PUFA should be under control.
