Nutritional approach has been intensely investigated in inflammatory bowel disease (IBD) patients, but, despite many sparse reports, at present, there is not a universally accepted specific diet. In fact, nutritional requirements and, therefore, the ideal diet, may vary according to disease type, extension and activity. Among nutritional related issue in IBD, obesity has become a relevant one. In fact, obesity and IBD are both increasing in prevalence in last decades, and more and more IBD patients are overweight or obese. These two conditions present common metabolic pathways, leading to dysbiosis and mucosal barrier dysfunction, but the real clinical relationship and the potential reciprocal relative influences are not clear. In order to control weight, many IBD patients follow different weight loss diets, often without any specialized medical advice. Among those, low carb, intermittent fasting, paleolithic, and low-fat diets are some of the most popular, and plant based and Mediterranean diet, even though they are not just strictly weight loss diets, are followed by many IBD patients even for weight control. All the diets mentioned above have been effectively associated with weight loss, reduction in waist circumference and body mass index. However, there are still conflicting data regarding safety in IBD patients and potential experimental and clinical anti-inflammatory effect. In the present review, we described potential relations between obesity and IBD, and we analysed available evidence on efficacy and safety of weight loss diets in IBD patients, in order to provide a practical guide to physicians.