**3. Factors for weight regain after bariatric surgery**

It is difficult to outline current factors, leading to WR after B/MS. The role of those factors and their influence on patient's behavior, eating habits, and ability to keep his weight under control after the primary procedure are not well understood or investigated robustly. However, most of the published reviews confirm that they have been attributed to several surgical, biological, and behavioral factors [2, 16]. We can identify two groups of factors nowadays. The first group is of so-called non- modifiable factors as hormonal, metabolic, surgery-related [14, 17]. The second group is of so-called "modifiable behaviors," where patients should receive more support and care within 5 years after surgery by healthcare professionals. WR remains a major challenge in relation to the long-term success of B/MS [7, 8]. Although weight regain is a consistent finding among studies, there are considerable variations in the magnitude and rate of weight regain depending on factors ranging from behavioral, dietary, lifestyle, psychological, ethnic, and racial differences. Interestingly, there are studies that report an average of 56% WR weight within 10 years after primary surgery [10, 18]. A poor prognostic indicator for WR after B/MS is the slow weight loss in the first two postoperative years. Medical based evidence confirms that patients, who achieve 20–30% of total weight loss at one to 2 years postoperatively, can regain an average of 7% of their total body weight from their lowest postoperative weight over the course of 10 years [6–7, 9, 19, 20]. According to those studies, the estimated average WR is about 15% (between 2 and 5% of weight from their lowest reported postoperative nadir weight) within 2 years after Roux en Y Gastric bypass. Those studies have reported an increase to 70% of patients between 2 and 5 years after Sleeve Gastrectomy, and 85% increase of WR at over 5 years post-surgery [10, 21] after that procedure. The high prevalence of weight regain after B/MS has resulted in a significant increase in revisional bariatric surgery [2, 6], which is a cause for increase in surgical risk and adverse outcomes to the patient [22, 23]. Causes of WR following B/MS are multifactorial and can be categorized into patient and surgical-specific causes. The summary of all aforementioned factors could outline the importance of following about weight regain:

