Introduction
Overweight and obesity have reached epidemic proportions worldwide, posing significant public health challenges. In Taiwan, the prevalence of overweight adults is substantial, with obesity-related conditions placing a considerable burden on the healthcare system. While excessive caloric intake and decreased physical activity are primary drivers of obesity, the role of gut microbiota, particularly Helicobacter pylori (H. pylori), has gained increasing attention. H. pylori is a gram-negative bacterium colonizing the human stomach, and chronic infection can trigger immune responses leading to gastritis or systemic effects. Recent studies suggest associations between H. pylori and extradigestive diseases, including insulin resistance, metabolic syndrome, and obesity. However, the exact nature of this relationship remains a subject of debate, with conflicting findings reported in various studies.
H. pylori and Its Potential Influence on Body Weight
The potential mechanisms linking H. pylori infection to obesity involve gastritis or peptic ulcers, immunological cytokines, and the hormone leptin. H. pylori-related gastritis or peptic ulcers can lead to dyspepsia and reduced appetite, potentially affecting body weight. Successful eradication of H. pylori has been observed to result in weight gain in some patients.
Tumor necrosis factor-alpha (TNF-α), a key inflammatory mediator, is implicated in obesity-related insulin resistance. Leptin, an adipokine, regulates body weight by influencing appetite and food intake. H. pylori strains, particularly cytotoxin-associated gene A (cagA)-positive strains, can induce significant gastric inflammation. In Taiwan, the prevalence of H. pylori infection is high, with most strains being cagA-positive. H. pylori infection can alter leptin and TNF-α levels in the gastric mucosa, potentially influencing body weight.
Conflicting Results from Cross-Sectional Studies
Cross-sectional studies investigating the association between H. pylori infection and BMI have yielded inconsistent results. Some studies have reported a positive correlation, while others have found no association or even a negative correlation. These discrepancies may arise from variations in study populations, H. pylori detection methods, BMI criteria, and failure to account for confounding factors like socioeconomic status, education, occupation, and mental health.
To accurately assess the relationship between H. pylori infection and BMI, it is crucial to control for these potential confounders. It has been hypothesized that H. pylori colonization is associated with changes in BMI due to chronic inflammation and insulin resistance, with cytokines (TNF-α and C-reactive protein) and adipokines (adiponectin and leptin) playing a role. Additionally, the timing of H. pylori infection (early vs. late life) may influence its impact on body weight.
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Research Examining the Association Between H. Pylori Infection and BMI
One study aimed to evaluate the association between H. pylori infection and BMI using data from three districts in Taiwan, incorporating age, inflammatory cytokine and adipokine levels, and detailed demographic data. The study enrolled 2604 subjects, categorized into normal weight, overweight, obese 1, and obese 2 groups based on BMI.
The results revealed that over half of the subjects were overweight or obese. Overweight and obese subjects were more likely to be male and had a higher prevalence of diabetes mellitus, hyperlipidemia, hypertension, and metabolic syndrome. They also exhibited higher mean HOMA-IR, HS-CRP, leptin, TNF-α, and WBC values, along with lower mean adiponectin values.
The prevalence of H. pylori infection varied across the BMI groups, with a trend towards higher prevalence in overweight and obese subjects. Specifically, subjects with H. pylori infection in the 40-49 and 30-39 age groups had higher mean BMI values than those without the infection. However, among subjects older than 50, no significant differences in mean BMIs were observed between those with and without H. pylori infection.
Correlation analyses indicated that BMI level was positively correlated with age, male gender, marriage status, diabetes mellitus, hypertension, dyslipidemia, mental component summary (MCS) score, leptin, TNF-α, HS-CRP, HOMA-IR, and WBC count. It was negatively correlated with the physical component summary (PCS) score and adiponectin value. H. pylori infection was positively correlated with age, diabetes mellitus, the MCS score, and WBC, and negatively correlated with marriage status.
Logistic regression analyses, adjusting for confounding factors, showed that H. pylori infection increased the risk of being overweight. Subgroup analysis revealed that among subjects younger than 50, H. pylori infection was associated with a higher risk of being in the obese 2 category (BMI ≥ 30).
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Discussion of Research Findings
These findings suggest a complex relationship between H. pylori infection and body weight, with the association potentially being more pronounced in younger individuals. The study's results align with previous research indicating that overweight and obese individuals are more likely to be male and have a higher prevalence of insulin resistance, diabetes mellitus, dyslipidemia, and metabolic syndrome.
The associations between H. pylori infection and overweight/obesity remain a subject of ongoing debate. Inconclusive results may stem from variations in subject populations, H. pylori detection methods, and BMI criteria. Some studies have reported a higher prevalence of H. pylori infection among overweight and obese subjects, while others have found no association.
The P value for the difference in the incidence of H. pylori infection among the normal, overweight, obese 1, and obese 2 groups was marginally significant in the study. This marginal difference may be attributed to the close H. pylori infection rates between the overweight, obese 1, and obese 2 groups. However, when comparing the H. pylori infection rate between the normal and overweight groups separately, the difference was statistically significant.
The age distribution may also contribute to the observed differences. The most significant difference in mean BMI value between subjects with and without H. pylori infection was found in the 40-50 age group. This suggests that the influence of H. pylori infection on BMI may be more prominent in younger individuals.
The study found an association between H. pylori infection and overweight after adjusting for confounding factors. Moreover, among subjects younger than 50, H. pylori infection was associated with obese 2 (BMI ≥ 30 kg/m2). This aligns with previous findings that H. pylori infection increases insulin resistance and metabolic syndrome in individuals younger than 50.
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Additional Research and Perspectives
Other studies have explored the relationship between H. pylori infection and obesity, with varying results. Some studies have found an association between H. pylori infection and abdominal obesity, particularly in individuals younger than 50. However, H. pylori seropositivity has not been consistently associated with obesity as defined by BMI.
One study analyzed data from the National Health and Nutrition Examination Survey (NHANES) and found that abdominal obesity, as defined by waist-height ratio (WHtR), was associated with H. pylori seropositivity. This association was significant in subjects younger than 50 but not in those aged 50 or older.
Another study retrospectively analyzed data from five universities and found that H. pylori eradication (HPE) did not significantly affect BMI or lipid profile in H. pylori-positive patients. However, patients with low BMI showed a tendency to gain weight after HPE.
Potential Mechanisms and Considerations
H. pylori colonization is often associated with chronic active gastritis, which can interfere with gastric hormone regulation, including ghrelin and leptin. H. pylori eradication can increase serum ghrelin levels, potentially leading to increased appetite and food intake.
Epidemiological studies on the correlation between H. pylori colonization and BMI and obesity have yielded conflicting results. Some studies have reported increased BMI after H. pylori eradication therapy, while others have found no association.
The Gut Microbiome and Its Role
Research suggests that the gut microbiome plays a crucial role in obesity and related metabolic disorders. Studies have explored the composition and diversity of the gastric microbiome in patients with and without H. pylori infection, revealing differences in the relative abundance of various bacterial taxa.
One study found that Firmicutes were prevalent in all groups, but their relative abundance varied. Actinobacteriota were more common in H. pylori-negative groups, whereas Campilobacterota were more common in H. pylori-positive groups. The genus Cutibacterium was predominant in the H. pylori-negative group, whereas Helicobacter was predominant in the H. pylori-positive group.
These findings highlight the complex interplay between H. pylori infection, the gut microbiome, and metabolic health.