Post-surgical weight loss improves brain health

There are significant obesity-related differences in brain health - as measured by the difference between brain age and actual age (delta age) - between individuals with obesity and those with normal weight, as well as a marked improvement in brain age following bariatric surgery, according to researchers from McGill University, Montreal and Université Laval, Québec, Canada. The findings were reported in the paper, ‘Impact of weight loss on brain age: Improved brain health following bariatric surgery’, published in NeuroImage.

Figure 1: T-values comparing the adjusted delta age between baseline and 24 months post-surgery. Brain age prediction model was estimated based on each brain region separately in the CamCAN dataset and was applied to the bariatric surgery data to calculate the adjusted delta age across visits. The figure shows the T-values for the significant differences (after FDR correction) between adjusted delta age at 24 months post-surgery compared to baseline using an unpaired t-test. We found no significant differences between the adjusted delta age at 4 and 12 months post-surgery compared to baseline.

The authors stated that people living with obesity tend to have increased brain age, probably due to grey and white matter atrophy related to obesity. However, they noted that it is unknown whether older brain age associated with obesity can be reversed following weight loss and cardiometabolic health improvement. Therefore, they designed a study to assess the impact of weight loss and cardiometabolic improvement following bariatric surgery on brain health, as measured by change in brain age estimated based on voxel-based morphometry (VBM) measurements.

For their study, they used three distinct datasets: 1) CamCAN dataset to train the brain age prediction model, 2) Human Connectome Project (HCP) dataset to investigate whether individuals with obesity have greater brain age than individuals with normal weight, and 3) pre-surgery, as well as four, 12, and 24 month post-surgery data from 87 who underwent a bariatric surgery to investigate whether weight loss and cardiometabolic improvement as a result of bariatric surgery lowers the brain age.

For their study, they used three distinct datasets:

CamCAN dataset

Data used to train the brain age prediction model included participants with T1-weighted MRI data available from the second stage of the Cambridge Centre for Ageing and Neuroscience (CamCAN). In total, 640 participants (324 female), with age range between 18 and 88 and average BMI of 25.8+/-4.6 kg/m2 were included in the study. T1-weighted MRIs were acquired on a 3T Siemens TIM Trio.

Human Connectome Project (HCP)

Data used to assess the predicted brain age difference between individuals with obesity and those with normal weight included an independent sample from the HCP. All the participants from the HCP with a BMI higher than 35 kg/m2 were included in this sample. These participants (n=46) were individually matched (1:1) for age, sex, and ethnicity with a group of HCP individuals who had a normal body weight (n = 46). T1-weighted 3D MPRAGE sequence with 0.7 mm isotropic resolution images were acquired by the HCP using a 3T MRI scanner (Siemens Skyra).

Bariatric surgery-induced weight loss assessment dataset

Data used for the main analyses included 71 participants with severe obesity at four months post-surgery, 47 participants at 12 months post-surgery, and 34 participants at 24 months post-surgery. The researchers used T1-weighted MRIs of the participants. Most participants (n=46) underwent a laparoscopic sleeve gastrectomy (SG), laparoscopic biliopancreatic derivation with duodenal switch (BPD-DS) was performed in 12 participants and 13 participants underwent a laparoscopic Roux-en-Y gastric bypass (RYGB) surgery.

The researchers assessed grey matter density across cortical and subcortical regions as measured by voxel-based morphometry (VBM) to train the brain age prediction model and assess the relationship between predicted brain age, obesity, and weight loss.

Outcomes

The results revealed that participants living with obesity had significantly higher delta age values reflecting poorer brain health than the matched participants with normal weight (T-value =7.08, p<0.0001). There was a significant decrease in delta age 12-month post-surgery (p<0.0005) and 24-month post-surgery visits compared to baseline (p<0.0001), but not at four-months post-surgery (p=0.64) compared to baseline.

They also reported a significant effect of visits using a mixed effects model controlling for sex, age, and BMI at baseline as well as the surgery type. The results of the mixed effect model showed significant decreases in delta age 12-month post-surgery (p<0.0005) and 24-month post-surgery visits compared to baseline (p<0.0005), but not at four-months post-surgery (p=0.79) compared to baseline.

For participants that had completed all four visits (n=32), they found a significant association between adjusted delta age and BMI, systolic blood pressure as well as diastolic blood pressure, and HDL-cholesterol where higher BMI and blood pressure and lower HDL-cholesterol was related to higher delta age.

For all participants, they reported a significant association between adjusted delta age and BMI, systolic/diastolic blood pressure, and HOMA-IR where higher BMI, blood pressure, and HOMA-IR was related to higher delta age. They did not find any significant association between adjusted delta age and the rest of cardiometabolic variables in the complete sample. They did not find any significant differences at single region level at four months and 12 months post-surgery (Figure 1).

“These results suggest that obesity-related brain health abnormalities might be reversed by means of significant and sustained weight-loss, along with widespread improvements in cardiometabolic alterations,” the authors concluded.

Further information

To access this paper, please click here