Increases in apo A-IV may contribute to the therapeutic effects of gastric bypass
Roux-en-Y gastric bypass (RYGBP) surgery not only promotes rapid weight loss but also helps treat comorbidities associated with obesity even before significant postsurgical reduction of body weight, although the processes underlying this effect have not been elucidated. Observations suggest that increased secretion of gut-derived hormones after gastric bypass surgery may play a role in regulating weight loss and energy metabolism. A proteomic study of severely obese patients who underwent RYGBP indicates that apolipoprotein A-IV may be linked to the additional health benefits of the surgery. Analysis of fasting plasma samples from these patients before and after surgery revealed marked increases in this protein after gastric bypass. This glycoprotein inhibits gastric emptying and acts as a satiety factor, but it also inhibits inflammation and atherogenesis through actions on cholesterol metabolism and transport. These findings, together with the overall health benefits observed after RYGBP, suggest a possible therapeutic role for this peptide that merits further research. See page 46
PET scans highlight the effect of BMI on prefrontal glucose metabolism and cognition
Research indicates that obesity may impair cognition, including executive function, attention, and memory. Comorbidities associated with obesity, such as diabetes and hypertension, probably contribute to these observations, but a high BMI per se is linked to decrements in cognition and executive function even in the absence of comorbid conditions, although the underlying processes remain largely unknown. Suspecting the role of prefrontal activity in mediating the effects of BMI on cognition, researchers have examined the relationship between BMI and brain metabolism using positron emission tomography with 2-deoxyglucose tracer to quantify regional glucose metabolism at baseline and during cognitive testing. Such measures of metabolism have been shown to correlate with brain function and performance. At baseline, the scans revealed that subjects with high BMI exhibited lower levels of glucose metabolism in the prefrontal cortex and cingulate gyrus when compared with leaner individuals. Regional brain metabolism also correlated with performance on tests of memory and executive function. In contrast, changes observed in regional brain activity that were measured when subjects performed cognitive tasks were not associated with BMI. Although these results suggest that BMI does not affect glucose metabolism during cognitive tasks, obesity does seem to reduce baseline prefrontal metabolism and in turn impairs executive function. See page 60
Modest weight loss found to help sleep-disordered breathing
Sleep apnea is a common disorder among individuals with obesity, but even obese individuals without this condition are less likely to sleep soundly than those who are not obese. Both mechanical changes and circadian and metabolic abnormalities attributed to obesity are posited to contribute to sleep disruption. Obese persons tend to sleep less efficiently and wake more often at night, making excessive daytime sleepiness a common complaint. New research suggests that in severely obese individuals, even modest weight loss can yield substantial improvements in sleep dynamics. Participants in a weight-reduction program underwent testing before and after weight loss to assess pulmonary function, score on the apnea/hypopnea index, oxygen consumption and carbon dioxide production, and sleep quality. Modest weight loss resulted in a substantial decrease in the apnea index. In particular, subjects with more severe sleep-disordered breathing prior to weight loss actually exhibited the greatest improvement in the index. Oxygen consumption and carbon dioxide production also decreased after weight loss. Although pharyngeal patency did not improve, minimum and mean oxygen saturation increased when body weight was reduced. These results indicate that in severely obese subjects, even modest weight loss can yield significant benefits in sleep quality and amelioration of sleep-disordered breathing. See page 84
