The Microbiome as a Modifiable and Predictive Factor in Obesity Treatment: Impact of Nutritional Intervention With Probiotics and Prebiotics.

Obesity: The Epidemic of the 21st Century and a Public Health Concern. Obesity is one of the most severe and prevalent non-communicable diseases of the 21st century, representing a global public health problem that affects all age groups. In Spain, it is estimated that over 39% of adults (aged 25-60) are overweight and 20% are obese, with Andalusia being one of the regions with the highest rates, which continue to rise. Obesity is a multifactorial, recurrent, and progressive disease associated with significant physical and psychological complications, as well as considerable morbidity and mortality. It is a key risk factor for numerous chronic conditions, including metabolic syndrome (type 2 diabetes mellitus, hypertension, dyslipidemia) and the associated elevated risk of cardiovascular diseases.

Moreover, obesity can increase the risk of other diseases, including digestive, respiratory, and joint disorders, as well as various types of cancer (esophagus, colon, pancreas, prostate, and breast). Although the pathogenic mechanisms underlying obesity are not fully elucidated, it is understood that obesity is linked to a state of chronic low-grade systemic inflammation. Dysregulated adipose tissue functionality in obese individuals leads to elevated free fatty acid levels and increased production of inflammatory cytokines, establishing a vicious cycle that promotes the hypertrophy and hyperplasia of adipocytes, hallmarks of obesity.

The excessive production of these mediators and their release into the bloodstream have a profound impact on other organs and systems, contributing to the metabolic (e.g., diabetes) and cardiovascular (e.g., endothelial dysfunction, atherosclerosis) alterations that almost invariably accompany obesity. Consequently, obesity is associated with reduced quality of life and has a significant negative socioeconomic impact. It is also a determinant of several "intermediate risk factors," leading to increased mortality and reduced life expectancy.

The treatment of obesity involves lifestyle and dietary changes, often supplemented by pharmacological therapy, including appetite suppressants and fat absorption inhibitors. However, these strategies may be insufficient, and for severe obesity (BMI >35) or morbid obesity (BMI >40), surgical intervention is often necessary. Bariatric surgery, despite its effectiveness in reducing metabolic and cardiovascular comorbidities and improving survival and quality of life, involves significant complications due to patient characteristics and high costs. Moreover, over the last 30 years, there has been a marked increase in the prevalence of morbid obesity and, consequently, a greater demand for bariatric surgery.

While surgery reduces comorbidities and enhances patient outcomes, its effects on the gut microbiota remain suboptimal. As such, specific dietary interventions before and/or after surgery are needed to improve microbial gene richness and ensure long-term metabolic health.