To analyze the relationship between obesity and the brain across varying stages of cognitive health, brain images were collected from three participant groups: cognitive healthy, mild cognitive impairment, and mild Alzheimer’s disease. The team used two indicators of obesity, BMI and waist circumference, to investigate whether or not there were associations with brain structure.
In the early stage of Alzheimer’s disease, those affected typically exhibit brain structures with deceased levels of gray matter volume, white matter integrity, and blood flow. They are central to building neural connections and degradation can signal a loss of important brain functions, as often observed in those with AD.
This study found that those with mild Alzheimer’s disease with a healthy BMI may have retained some of these brain structures, as opposed to the cognitively healthy participants with obesity who exhibited potentially degenerating brain structures.
A key aspect of this study was that the three participant groups did not have a consistent distribution of BMI values. The cognitively healthy group fell within the obesity weight range, the MCI group fell within the overweight range, and the mild Alzheimer’s disease group fell within the “normal” range.
Weight loss is common both in old age and in people with Alzheimer’s disease. This is what likely drove these differences.
Brain structures and healthy weight ranges
When observing the indicators of obesity and brain structures, the researchers found the most notable associations between BMI and gray matter volume.
The group of participants with mild Alzheimer’s disease displayed a positive association between these two characteristics. The higher the BMI — but still contained within the healthy range — of the individual, the higher the levels of gray matter volume present in the brain. This group also displayed similar positive trends when the researchers looked at blood flow.
Degraded gray matter is a common characterization of Alzheimer’s disease onset. However, the participants with mild Alzheimer’s disease had higher volumes of gray matter in relation to the amount of body fat they had.
These results suggest that maintaining a healthy amount of body fat can preserve some gray matter volume that would otherwise have undergone degradation during dementia.
“We found that maintaining a healthy weight could help preserve brain structure in people who are already experiencing mild Alzheimer’s disease dementia,” explains study author Dr. Matteo De Marco.
A potential explanation for this result is that, even in progressed stages of dementia, healthy levels of body fat provide the brain with the adequate resources to mitigate brain damage.
Brain structures in overweight and obesity
On the other hand, the cognitively healthy participants and those with MCI displayed a negative association between obesity and both gray matter volume and blood flow. The changes in both groups resembled neural damage that is often present in those with Alzheimer’s disease. However, this was more pronounced in the cognitively healthy group in the obesity weight range.
Although obesity is not a direct cause of dementia, these trends show that having obesity during a cognitively healthy state may lead to negative consequences by worsening the cognitive decline that can occur later in life.
Importance of early prevention
Although maintaining a healthy body weight is beneficial (for physical health) at any age, this study suggests that the earlier, the better. Gaining a better understanding of these brain indications could also improve diagnoses to catch the symptoms and move toward intervention in the early stages of dementia.
According to Prof. Venneri: “[T]he diseases that cause dementia, such as Alzheimer’s and vascular dementia, lurk in the background for many years, so waiting until your 60s to lose weight is too late. We need to start thinking about brain health and preventing these diseases much earlier.”
