Obesity is a global problem. It affects every age group and is associated with many negative health effects. As an example, there is a relationship between obesity and allergic and immunological diseases, such as asthma, psoriasis, food allergies, allergic rhinitis and atopic dermatitis. Obesity undeniably affects their development. In addition, it causes adverse changes in the course and response to therapy in relation to patients without excessive body weight. The treatment of diseases associated with obesity is difficult; drugs are less effective and must be used in higher doses, and their use in patients with obesity is often associated with higher risks. The main form of treatment of all obesity-related diseases is a change in eating habits and increased physical activity, which leads to a decrease in body fat mass. The positive effect of reducing BMI has been confirmed in many independent studies. This paper reviews various types of research documents published since 2019. It aims to systematize the latest knowledge and highlight the need for further research for effective and sustainable treatment options for obesity, its complications and obesity-related diseases.