Multicomponent lifestyle interventions achieve good results in the management of obesity among the adult population. However, their implementation in certain populations poses difficulties. A good level of nutritional knowledge enables people to make changes in their diet that improve their health. This study aims to assess the relationship between nutritional knowledge and nutritional parameters such as dietary intake, anthropometric parameters and biomarkers. A before-after, non-randomized interventional study involving a two-monthly nutritional educational intervention was carried out over 8 months. Anthropometric and biomarker data were collected, and nutritional knowledge was evaluated using the Bach questionnaire and food frequency questionnaire (FFQ). The study comprised 66 overweight and obese adults with mean age of 50.23 years. Females predominated (84.8%). At the end of the intervention, nutritional knowledge increased significantly, with a significant reduction in the consumption of sweets, soft drinks, high-fat products, and processed meats, and an increase in the intake of lean meat and poultry. A 3% decrease in body weight was observed. An intervention for the management of obesity in the adult population based on nutritional education achieves weight loss, modifications in eating habits and reduction of fat intake. Increased nutritional knowledge is associated with healthier eating habits and a decreased cardiovascular risk.