Why Are Certain Individuals More Prone to Vomiting? Research on Gut Bacteria

The gut microbiome comprises trillions of microorganisms, including bacteria, viruses, fungi, archaea, and eukaryotes, residing in the human gastrointestinal tract. These microbes metabolize undigested food residues, digestive mucus, and dead cells present in the intestines. In return, they generate numerous beneficial compounds such as short-chain fatty acids, vitamins, and anti-inflammatory agents. However, certain microorganisms produce harmful substances, including neurotoxins, carcinogens, and immunotoxins. In healthy individuals, bacteria from the Firmicutes and Bacteroides genera predominate. Disruptions in gut microbiota balance (dysbiosis) can adversely affect metabolic and immune processes, contributing to the development of various conditions, including obesity (J. Miyamoto et al., 2019).

Groundbreaking animal experiments provided initial evidence linking gut microbiota to obesity. It was demonstrated that after microbiome transplantation into germ-free mice, there was a marked increase in fat tissue and reduced insulin sensitivity, despite unchanged food intake. Obese mice also exhibited decreased Bacteroides populations and elevated Firmicutes levels, with the Firmicutes-to-Bacteroides ratio correlating positively with BMI (C. M. Dos Santos Pereira Indiani, 2018). However, these findings were not replicated in human clinical trials (T. Wu et al., 2020).

Scientific research confirms that the composition of the gut microbiome directly influences body weight. It turns out that different bacterial strains, even within the same species, can have varying effects on metabolism. Among the microorganisms that support maintaining a healthy weight are Akkermansia muciniphila and bacteria from the Christensenellaceae family. Akkermansia muciniphila is often used as a dietary supplement in overweight individuals to improve metabolic parameters (C. Depommier et al., 2019). Studies have also shown that different species of the Lactobacillus genus have varying associations with obesity. The abundance of L. paracasei is negatively correlated with obesity, while L. reuteri and L. gasseri show a positive correlation (L. Crovesy et al., 2017). Additionally, a deficiency in Bifidobacterium bacteria is linked to an increased BMI (I. N. Sergeev et al., 2020).

Regarding body weight, the most significant mechanisms associated with a balanced gut microbiota involve variations in energy absorption among different bacterial strains. Research indicates that bacteria in the intestines of overweight individuals absorb energy from food to a much greater extent, facilitating its storage as fat tissue. A well-balanced gut microbiota also ferments difficult-to-digest carbohydrates into short-chain fatty acids like acetate, propionate, and butyrate, which play a crucial role in the host's energy metabolism. These compounds reduce levels of pro-inflammatory cytokines and inhibit lipid breakdown, thereby enhancing fat oxidation and energy expenditure (M. A. González Hernández et al., 2019). However, an excess of these acids has been linked to increased body weight, waist circumference, and other markers of metabolic syndrome (J. De la Cuesta-Zuluaga et al., 2018). The gut microbiota also influences the nervous system via the gut-brain axis, indirectly affecting eating behaviors. Short-chain fatty acids produced by gut bacteria enhance postprandial satiety. Additionally, the microbiota regulates the secretion of anorexigenic hormones such as peptide YY, GLP-1, and pancreatic polypeptide, which lower glucagon levels, slow gastric emptying, stimulate insulin synthesis, and reduce food intake (J. F. Cryan et al., 2019). The use of antibiotics is also significant, as they disrupt gut microbiota balance. Dysbiosis caused by these medications has been associated with substantial weight gain and elevated LDL cholesterol levels, which are detrimental to cardiovascular health (C. I. Le Roy et al., 2019). Antibiotic use before the age of two is a strong predisposing factor for obesity development (C. M. Stark et al., 2019). Imbalance in gut microbiota promotes inflammatory states, increasing the risk of obesity and its complications. Certain bacteria produce pro-inflammatory substances like lipopolysaccharides or cytokines, whose excess harms the organism. A healthy microbiota strengthens the intestinal barrier, whereas dysbiosis can weaken it and increase permeability, thereby promoting inflammation (H. Tilg et al., 2020).

Emerging research indicates that genetic factors significantly shape the gut microbiome composition. Genetic studies have identified 20 genes in the human genome that govern microbial diversity in the gastrointestinal tract. Certain genes are pivotal in modulating host-microbiome interactions, including immune responses and metabolic processes (T. A. Suzuki et al., 2019). Additionally, the gut microbiota can be transmitted from mother to child via the placenta, amniotic fluid, umbilical cord blood, and colostrum. Consequently, maternal obesity and associated dysbiosis may predispose offspring to obesity (H. M. Tun et al., 2018).

While genetics plays a role in shaping the microbiome, its significance is considerably smaller compared to the influence of environmental factors. Gut-residing microorganisms are highly dependent on the host's diet, emphasizing the critical importance of proper nutrition. Research conducted on mice has demonstrated that a high-fat diet leads to a reduction in the population of beneficial Bacteroidetes bacteria and an increase in less beneficial Firmicutes and Proteobacteria species (M. T. Liu et al. 2019). Additionally, both the quality and quantity of sleep significantly impact microbiome diversity. Chronic sleep disturbances are associated with excessive consumption of processed foods, which results in an increase in Lachnospiraceae and Ruminococcus bacteria and a decrease in Lactobacillaceae, promoting dysbiosis and serving as a risk factor for inflammation and insulin resistance (V. A. Poroyko et al. 2016). Another crucial factor influencing gut microbiota is stress. Excessive stress also contributes to the development of dysbiosis (J. P. Karl et al. 2016).

Research conducted in 2021 demonstrated that the flexitarian diet most effectively supports a healthy gut microbiome. The study compared various dietary patterns, including plant-based, flexitarian, the standard Western diet, low-carbohydrate, and the so-called 'conscious Western diet,' which, despite being based on healthy principles, remains high in sugar and low in vegetables. The flexitarian approach proved most beneficial as it provides a balanced intake of all food groups, is rich in fiber, and reduces meat consumption without eliminating it entirely. Primary protein sources include legumes and their derivatives. This diet is ideal for individuals seeking to reduce meat intake but who are not ready for a fully vegetarian lifestyle. Additionally, it encourages the reduction of processed foods and sugar, which is advantageous for gut health. Environmental concerns often drive this dietary choice (A. Cotillard et al. 2022). Beyond flexitarianism, other strategies to enhance the microbiome include increasing fiber, probiotic, and prebiotic intake, as well as limiting sugar and processed foods. Adequate hydration is also crucial to fostering an environment conducive to beneficial bacteria (A. Beam, E. Clinger, L. Hao 2021).

The gut microbiome represents a complex ecosystem of microorganisms that coexist with the human body, performing essential functions such as digestion, vitamin synthesis, immune system support, and metabolic regulation. Imbalances in the microbiome composition may elevate the risk of obesity, as certain microorganisms can enhance energy absorption from indigestible food components. Additionally, the microbiome influences metabolic regulation, affecting hormonal responses and fat tissue accumulation. Intestinal dysbiosis can induce inflammatory states that hinder weight management. To maintain microbial diversity, a balanced diet rich in whole, fiber-containing foods is recommended. Adequate rest and mental well-being are also crucial factors.