Brain Health Following Bariatric Surgery to Treat Obesity
Post by Lani Cupo
The takeaway
“Brain age” refers to how old a brain appears when compared to normative trajectories of development across the lifespan. Obesity increases brain age, however, bariatric surgeries can reduce the impact of obesity on brain age.
What's the science?
The brain age gap is defined as the difference between a person’s predicted age based on biological features (in this case brain grey matter density) and a person’s actual chronological age. Advanced brain age — when the predicted age is greater than the chronological age — in adults has been associated with various disorders and reliably predicts cognitive impairment. While obesity has been linked to increased brain age in the past, it was previously unknown whether weight-loss interventions can reduce brain age and improve brain health. Recently in NeuroImage, Zeighami and colleagues investigated brain age in individuals with obesity and the impact of bariatric surgery on brain and cardiovascular health.
How did they do it?
The authors used three different large magnetic resonance imaging (MRI) datasets for this study. They derived a measure of volume at each voxel, (like a 3D pixel) in the brain images, allowing them to examine volume across the entire brain. The first dataset (640 participants, 324 females) was used to construct a model that describes how the brain’s grey matter changes with age in healthy participants. Based on the model from the first dataset, brain age was predicted for the second data set (92 participants, 46 with obesity). In this “test” dataset, the authors compared the brain age gap for participants with and without obesity. The final dataset (87 at baseline, 65 females, 34 at last visit, 25 females) was used to examine brain age in subjects with obesity at baseline (before surgery) and then 4, 12, and 24 months after surgery. Lastly, in this dataset, brain age was also compared with improvement in “cardiometabolic metrics” including body mass index (BMI), blood pressure, triglycerides, cholesterol, glucose, and a measure of insulin resistance (HOMA-IR).
What did they find?
First, the authors found that compared with individuals who did not have obesity, those with obesity had an increased brain age gap, reflecting poorer brain health. On average, the brains of those with obesity appeared about 5 years older than those of controls. Second, the authors found that compared with baseline, participants who completed all four visits demonstrated improved brain age (reflected in a reduced brain age gap) 12 months and 24 months after the surgery. At 12 months, the decrease in brain age was about 2.9 years, and at 24 months it was about 5.9 years compared to baseline, reducing the gap almost to control levels.
In the participants who completed all four visits, the authors found an association between higher brain age and cardiometabolic metrics, including higher BMI and blood pressure, and lower HDL cholesterol (the so-called “good” cholesterol). When participants who did not complete all four visits were included, the authors found an association between higher brain age and higher BMI, blood pressure, and HOMA-IR. The discrepancy between the two samples could reflect some systematic difference between the participants who remained in the study and those who dropped out. At 24 months post-surgery, the reduction in brain age was driven by a global change across brain regions, however, the somatomotor, visual, and ventral attention networks were strong contributors to this reduction.
What's the impact?
This study is the first to show that surgeries that target weight-loss and cardiometabolic health can improve brain health and reduce the brain age gap. These results could suggest that improved brain health following bariatric surgery may result from increased cerebral blood flow and greater insulin sensitivity. Ultimately, these findings reinforce the benefits of bariatric surgeries in patients with obesity, not only in terms of cardiovascular health but for brain health as well.
