All around the world, severe chronic diseases are rapidly growing and one of the root causes of these is obesity; it has been a major health concern for the last few decades (Gentile and Weir, 2018; Wilkins et al., 2019).
However, various methods are being used to treat excessive weight gain, yet obesity still remains a public health problem that now requires nutritional or medical solutions.
BMI (body mass index) that ranges between 25-30kg or higher than 30kg/m2 can cause diseases such as cardiovascular diseases, cancer, and diabetes. These diseases can be the leading causes of death.
Obesity can be a concerning matter; researchers are working hard to find efficient treatments for these conditions. (Wilkins et al., 2019).
Usually, people who regularly intake high-calorie diet face obesity, which can induce different changes in the functioning of the gut microbiome (Guirro et al., 2019).
Besides other factors such as genetic, nutritional, or lifestyle, it has been noted that obesity might be due to perturbation of the gut microbiome that affects the overall metabolic function and energy homeostasis (Guirro et al., 2019).
There are approximately 1014 bacteria and archaea of over 1,000 species that exist in the human gastrointestinal tract; these are also known as the gut microbiota (Lv et al., 2019).
Over the last few decades, scientists and researchers have been trying to deduce the impact of the gut microbiome as good gut microbiota and the use of probiotic supplements that are showing positive results in reducing many health problems (Mohajeri et al., 2018; Valdes et al., 2018).
The gut microbiome plays an essential role in the well-being of the human body, this is helping researchers in finding new treatments for various health conditions such as weight gain, or -weight loss. It has been noted that the relationship between gut flora and diet plays an important role in regulating the structure of the gut microbiota.
Microbes in the human intestines directly impact the breakdown, absorption, and storage of nutrients that affect host physiology (Gentile and Weir, 2018).
It has been researched that the overuse of antibiotics can cause an onset of obesity (Podolsky, 2017; Leong et al., 2018). Gut dysbiosis (an imbalance of gut microbiota composition) can be caused by dietary or environmental changes that result in an overgrowth of pathogenic organisms causing inflammation; they play a vital role in the pathology of chronic metabolic and intestinal diseases (Turroni et al., 2014).
Gut microbiota is also known to play an essential role in the connection of the brain with the central nervous system, which helps explain the direct link of the gut microbiota with overall health (Lankelma et al., 2015).
Scientists have come up with the research that the microbiota in humans is composed of 5 various categories/types of microbiota such as Bacteroides, Firmicutes, Actinobacteria, Proteobacteria, and Verrucomicrobiai, of which the Bacteroidetes and Firmicutes make up 90% of the species of bacteria (Lv et al., 2019).
The link between the gut microbiome and Obesity
The role of gut microbiota is the physiological functions such as vitamin synthesis, digestion, and regulating metabolism. Scientists have proven that gut microbiota is responsible for energy production derived from food, provides low-grade inflammation, and impacts fatty acid tissue compositions. These functions or mechanisms directly or indirectly link the gut microbiome with obesity (Baothman et al., 2016; Duca et al., 2018).
A diverse microbial shows a preventative measure of long-term weight gain in healthy humans (Menni et al., 2017). The gut microbiome differs from individual to individual; some studies have noted that the ratio of Firmicutes to Bacteroidetes is significantly higher in obese individuals (John and Mullin, 2016).
As per previous studies, scientists have noted correlations between increased Bacteroidetes in stools and weight loss and between Firmicutes and the development of obesity (Ley, 2010; John and Mullin, 2016).
A famous study was conducted to note the differences in gut microbiome between non-obese and obese Japanese subjects. The obese subjects were reported to have a significantly reduced number of Bacteroidetes and higher Firmicutes to Bacteroidetes in comparison to the ratios of the non-obese subjects.
Apart from a higher number of Firmicutes in obese subjects, another study reported that if overweight and obese individuals start therapy with high Firmicutes/Bacteroides, then the ratios have significantly better health outcomes due to following a whole grain and high-fiber diet in comparison with low Firmicutes/Bacteroides ratios (Hjorth et al., 2018).
The gut microbiome also has the ability to alter bile acid signaling and can produce distinct pathophysiological bile acid profiles (Sanmiguel et al., 2015).
It has been scientifically reported that approximately 5-10 % of bile acids are bio-transformed by anaerobic gut microbiota (Bacteroides, Eubacterium, and Clostridium), with the rest deposited in the stool. This proves that the gut microbiome plays an important role in the digestion and metabolism of dietary fat (Mazloom et al., 2019).
Scientists have reported that the use of probiotics has shown a significant reduction in an individual’s BMI and total body fat, especially visceral fat (Osterberg et al., 2015; Mazloom et al., 2019).
A scientific clinical study conducted by Osterberg et al. (2015) indicated that probiotics play an essential role in preventing any increase in body weight or body fat in 20 healthy males who were on a high-fat diet for 4 weeks along with the intake of probiotics.
Another study through meta-analysis was conducted to note the effects of probiotics on an individual’s body weight and glycaemic control in overweight or obese adults.
Overweight and obese adults that participated in the intake of probiotics showed a significant reduction in their body weight, BMI, waist circumference, and fat mass percentage compared to adults in the control group (Wang et al., 2019b).
As many research studies have shown that probiotics help the gut microbiome to reduce weight and ensure that the overall physical health remains healthy and maintain a balance.