Major Weight Loss Alters Brain Structure in People With Obesity, One-Year Study Finds
Key Takeaways:
- Adults with obesity who lost at least 40% of their excess weight over one year showed greater increases in subcortical grey matter volume than those who lost less, alongside significant improvements in blood sugar control, cholesterol, liver enzymes and inflammation.
- Greater excess weight loss was associated with reductions in cortical and subcortical T1 relaxation times, a possible marker of improved grey matter tissue health, although the between-group difference in subcortical volume did not survive correction for multiple comparisons.
- Cognitive performance did not differ significantly between groups after one year, and the researchers say longer, larger studies are needed to establish whether early structural brain changes lead to measurable cognitive benefits.
Weight loss and the brain: a growing question
People with obesity who lost at least 40% of their excess weight over one year showed measurable gains in brain structure, particularly in subcortical grey matter volume, according to a prospective cohort study conducted at New York University Grossman School of Medicine’s Brain, Obesity & Diabetes Laboratory. These changes were accompanied by substantial improvements in blood sugar control, cholesterol and inflammation.
The findings, published in Obesity Science & Practice, arrive at a time when the use of weight-loss medications in the United States doubled from 0.76 million to 1.51 million users between 2017 and 2024. As more people undergo major weight loss, understanding how it affects the brain has become an increasingly urgent question.
How the study was designed
The study enrolled 84 adults with obesity from weight-loss programmes at NYU Langone Medical Center and NYU Langone Brooklyn between 2018 and 2023. Each participant was followed for approximately one year, with identical evaluations carried out at baseline and at follow-up.
Participants were aged between 33 and 59 and had body mass index (BMI) values between 30 and 50 kg/m², with diagnoses of type 2 diabetes, prediabetes or insulin resistance. Rather than randomising participants to a specific treatment, the researchers categorised them after the fact according to how much weight they lost. In total, 54 people who achieved 40% or greater excess weight loss formed the weight-loss group, while 30 people who lost less than this threshold formed the non-weight-loss group.
Excess weight was calculated as the difference between each participant’s actual weight and the weight corresponding to a BMI of 25 kg/m². On average, the weight-loss group lost 64.39% of their excess weight and 23.62% of their total body weight, falling from a mean of 245.42 pounds at baseline to 186.51 pounds at follow-up. By comparison, the non-weight-loss group lost an average of 9.71% of excess weight and 3.38% of total body weight.
Treatment approaches varied considerably. Across the overall cohort, 57 participants underwent bariatric surgery, mostly sleeve gastrectomy, while 27 received behavioural or medical interventions. A total of 25 participants used GLP-1 receptor agonists as adjunctive therapy across both approaches.
Comparing the two groups at baseline
At the start of the study, the two groups were closely matched. They did not differ significantly in age, education, socioeconomic status, weight, waist circumference or the prevalence of metabolic syndrome, which affected 83.3% of the non-weight-loss group and 68.5% of the weight-loss group. Around three-quarters of the cohort were female, reflecting the clinical population seeking obesity treatment.
A small number of baseline differences emerged, with the weight-loss group showing higher BMI, LDL cholesterol, cholesterol ratio and alanine aminotransferase (ALT). However, most of these differences disappeared after adjustment for multiple comparisons, leaving only LDL cholesterol and ALT statistically distinct between the groups.
Assessments and brain imaging
Each participant underwent a physical examination, fasting blood tests, a five-sample oral glucose tolerance test, cognitive testing and a standardised 3T MRI session that included a structural MP2RAGE scan.
The researchers processed the images using FreeSurfer software, measuring regional brain volumes and generating quantitative T1 maps, a technique sensitive to changes in tissue. They paid particular attention to regions vulnerable to Alzheimer’s disease, including the inferior parietal and inferior temporal cortices, the posterior cingulate cortex and the hippocampus. These areas were selected because they are sensitive to the metabolic, vascular and inflammatory insults that are also common in obesity.
Marked improvements in metabolic health
The metabolic results were striking. Compared with the non-weight-loss group, participants who lost the most weight showed significantly greater reductions in BMI, waist circumference, HbA1c, fasting glucose, fasting insulin, HOMA-IR and C-reactive protein. They also showed improved insulin sensitivity, measured by QUICKI and ISI, a healthier lipid profile with higher HDL and lower LDL cholesterol, and improved liver enzymes. Most of these effects remained significant after correction for multiple comparisons.
At follow-up, the prevalence of metabolic syndrome was significantly lower in the weight-loss group than in the non-weight-loss group. Blood pressure, however, did not change significantly between groups, probably because many participants were already taking antihypertensive medications at baseline.
For healthcare professionals supporting people living with obesity and related metabolic conditions such as type 2 diabetes and insulin resistance, findings like these highlight the wide-ranging benefits of effective weight management. CCH’s Obesity Essentials course offers a grounding in supporting people living with obesity, helping clinicians place evidence like this in the context of everyday practice.
Changes in brain structure
The brain findings were more nuanced. The clearest signal appeared in subcortical grey matter volume. After adjusting for age and the interval between scans, the weight-loss group showed significantly greater increases in subcortical grey matter than the non-weight-loss group, and this effect persisted when T1 relaxation time was added as a covariate.
Within the weight-loss group, subcortical grey matter increased significantly over the year, while the non-weight-loss group showed a significant decline in the composite volume of Alzheimer’s-vulnerable regions. However, the between-group difference in subcortical volume did not survive correction for multiple comparisons, and the researchers stress that the within-group changes in Alzheimer’s-vulnerable regions should be regarded as preliminary.
T1 relaxometry offers further evidence
T1 relaxometry provided a second line of evidence. Longer T1 relaxation times are generally interpreted as a marker of tissue damage. In this study, higher percentage excess weight loss was associated with greater reductions, indicating improvements, in both cortical and subcortical T1 relaxation values. This aligns with earlier findings in adolescents with obesity.
Taken together, the authors write, the results suggest that weight loss is associated with improvements in the volume and possibly the health of grey matter, particularly in subcortical regions. This is consistent with existing literature showing that higher BMI is linked to grey matter atrophy.
No clear effect on cognition yet
Cognition told a different story. Cognitive performance did not differ between the groups at baseline or at follow-up. Although the weight-loss group showed numerically greater improvements in memory composite scores, these did not reach statistical significance and were highly variable.
The authors suggest that a one-year follow-up may be too short for subtle structural changes to translate into measurable cognitive benefits, and that detecting such effects is likely to require larger, adequately powered cohorts with longer follow-up periods.
Limitations and next steps
The study has several important limitations. It was non-randomised, and group assignment was determined post hoc based on weight loss, meaning unmeasured confounding cannot be fully ruled out. The modest sample size prevented subgroup analyses, including any examination of sex-dependent effects, and the one-year follow-up was designed to capture short-term changes rather than long-term trajectories.
The researchers note that longer studies will be needed to determine whether weight loss alters the course of cognitive decline and neurodegenerative risk, and whether the structural brain changes observed precede measurable cognitive benefits.
Even so, the parallel improvements in peripheral metabolic markers and central neuroimaging measures raise the possibility that weight loss may influence neurobiological pathways relevant to neurodegenerative risk before cognitive changes emerge. According to the authors, this provides a rationale for extended follow-up to test the durability and functional significance of these early structural signals.
CCH insight
Weight loss in this study was achieved through a range of approaches, from bariatric surgery to behavioural and medical interventions, and the benefits extended well beyond the scales. Obesity Essentials from The College of Contemporary Health helps healthcare professionals build the knowledge and confidence to support people living with obesity across these different pathways.
Explore Obesity Essentials and enrol today →
Source: Obesity Science & Practice
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