Nutritional Status in Obesity: A Comprehensive Narrative Review of Dysbiosis, Micronutrient Deficiencies and the Effects of Probiotics/Synbiotics.

Obesity is a chronic, relapse-prone disease often associated with comorbidities such as type 2 diabetes, dyslipidemia, and non-alcoholic fatty liver disease. Intestinal dysbiosis, defined as an imbalance in the composition and function of the gut microbiota, is commonly observed in individuals with excess body weight and plays a key role in the development of related metabolic complications. Moreover, dysbiosis can disrupt nutrient metabolism, leading to imbalances in energy homeostasis. Those affected by excess weight frequently exhibit deficiencies in essential vitamins and minerals, which further exacerbate metabolic and inflammatory dysfunctions, accelerating the progression of comorbidities. Studies have shown that the gut microbiota in individuals with obesity differs significantly from that of healthy, normal-weight individuals. Obesity often shows alterations in the relative abundance of Firmicutes and Bacteroidetes (F/B), with individual variability and reduced bacterial diversity, although the F/B ratio alone may not consistently reflect dysbiosis. Prolonged or repeated antibiotic use can further disturb the microbiota, worsening dysbiosis and contributing to the development of excess body weight by impairing energy metabolism and promoting systemic inflammation. Recent evidence suggests that probiotics are a safe and promising therapeutic approach for managing metabolic disorders. Several in vivo and clinical studies have reported a potential causal relationship between probiotic supplementation and the improvement of weight-related conditions. This narrative review aims to explore the alterations of gut microbiota in obesity and their impact on nutritional deficiencies. Additionally, it highlights the potential role of probiotics in restoring microbiota balance and improving metabolic dysfunctions related to excess body weight.