Energy balance after bariatric surgery

Obesity and its associated comorbidities have spread worldwide and cause significant burden to patients, and health-care systems. The most effective treatment of obesity is bariatric surgery but the underlying mechanism of weight loss are not well understood. In this thesis, we investigated that whether ileal transposition (IT) and Roux-en-Y gastric bypass (RYGB) creates negative energy balance thus contributing to the observed weight loss in rats. Negative energy balance can occur either when food intake is lower than the energy expended (physical activity) or if the expenditure is higher than the intake. Different diets (High fat – HF, High protein – HP and High carbohydrate – HC) were utilized to document if diet influences weight loss and energy balance following these surgeries.
We found that the primary cause of weight reduction after IT was decreased food intake and not increased energy expenditure. Only ingestion-related energy expenditure (IEE) increased, which could lead to higher satiety thus, contributing to weight loss. Energy efficiency (how much weight is gained after eating certain amount of food) was decreased after both surgeries, but for longer time after RYGB probably contributing to the greater and more sustained weight loss compared to IT.
HP diet seems to be the most effective to reduce weight either with or without surgery, meanwhile HF diet had a biphasic effect: before surgery HF diet led to weigh/fat gain but shortly after both surgeries resulted in the most weight loss and reduced energy efficiency. Interestingly HF diet after RYGB seemed to alleviate the postsurgical stress.