Pathophysiology of Malabsorptive Bariatric Procedures

Abstract

The pathophysiology of biliopancreatic diversion is strictly combined with energy malabsorption which occurs when part of the ingested calories are not absorbed. The presence of malabsorption can be measured either by estimating the energy content or the fat content of the stools. Alternatively, malabsorption can also be observed in the imbalance of energy intake and expenditure. One of the types of malabsorptive procedures currently in use is biliopancreatic diversion (BPD). The procedure is characterized by selective and permanent malabsorption. The absorption capacity threshold for fats and starches are selective. Therefore, the daily energy absorption is constant for every patient in spite of the fact that the usual daily energy intake by the patient is generally higher than the surgically-induced absorption capacity threshold. Consequently, weight loss is unavoidable and independent of both the preoperative weight and the energy intake when the energy absorption is constant. The most interesting specific effects of BPD are the lifelong normalisation of serum glucose and serum cholesterol in the majority of patients without medication and on an unrestricted diet. The negative effects of malabsorption consist essentially of the reduced absorption of iron and calcium with the consequent risk of anaemia and bone demineralisation. There is also a risk of increased loss of endogenous nitrogen with the consequence of protein malnutrition, increased colonic fermentation and putrefaction. This will inevitably result in side effects of bloating, flatulence and foul-smelling stools. Finally, it is important to emphasise the relationship between malabsorption and gastric restriction in that BPD should not be combined with a strong gastric restriction. That pathophysiological status could lead to the situation where only one mechanism would be active, while the negative effects of both mechanisms could be present.