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Hidden abdominal fat linked to Alzheimer’s disease

A new study suggests that an increase in visceral abdominal fat in middle age could be linked to the onset of Alzheimer’s disease. This fat, which surrounds internal organs in the belly, has been associated with brain changes that occur up to 15 years before Alzheimer’s disease’s earliest memory loss symptoms.

According to the Alzheimer’s Association, over six million Americans are currently living with Alzheimer’s, and this number is expected to rise to nearly 13 million by 2050. The disease disproportionately affects women, with one in five women and one in ten men likely to develop it in their lifetime.

Early Alzheimer’s risks 

Researchers aimed to identify early Alzheimer’s risks by assessing the association between brain MRI volumes, amyloid and tau uptake on positron emission tomography (PET) scans, and factors like body mass index (BMI), obesity, insulin resistance, and abdominal fat in a cognitively normal midlife population. Amyloid and tau are proteins believed to disrupt communication between brain cells.

“No prior study has linked a specific type of fat to the actual Alzheimer’s disease protein in cognitively normal people,” said study author Mahsa Dolatshahi, M.D., M.P.H., a post-doctoral research fellow at the Mallinckrodt Institute of Radiology (MIR) at Washington University School of Medicine in St. Louis. 

“Similar studies have not investigated the differential role of visceral and subcutaneous fat, especially in terms of Alzheimer’s amyloid pathology, as early as midlife.”

Focus of the study 

For the cross-sectional study, researchers analyzed data from 54 cognitively healthy participants, aged 40 to 60 years, with an average BMI of 32. They underwent various tests, including glucose and insulin measurements, glucose tolerance tests, and abdominal MRI to measure the volume of subcutaneous and visceral fat. 

Brain MRI measured cortical thickness in regions affected by Alzheimer’s, and PET scans examined disease pathology in 32 participants.

Critical insights 

The study found that a higher visceral to subcutaneous fat ratio was associated with increased amyloid PET tracer uptake in the precuneus cortex, a region affected early by Alzheimer’s. 

This relationship was more pronounced in men than in women. Researchers also found that higher visceral fat measurements relate to an increased burden of inflammation in the brain.

“Inflammatory secretions of visceral fat – as opposed to potentially protective effects of subcutaneous fat – may lead to inflammation in the brain, one of the main mechanisms contributing to Alzheimer’s disease,” explained Dr. Dolatshahi.

Study implications 

Senior author Dr. Cyrus A. Raji is an associate professor of Radiology and Neurology, and director of neuromagnetic resonance imaging at the Mallinckrodt Institute. Dr. Raji noted the implications of these findings for early diagnosis and intervention.

“This study highlights a key mechanism by which hidden fat can increase the risk of Alzheimer’s disease,” he said. “It shows that such brain changes occur as early as age 50, on average – up to 15 years before the earliest memory loss symptoms of Alzheimer’s occur.”

Dr. Raji suggested that targeting visceral abdominal fat could be a potential method to modify the risk of future brain inflammation and dementia.

“By moving beyond body mass index in better characterizing the anatomical distribution of body fat on MRI, we now have a uniquely better understanding of why this factor may increase risk for Alzheimer’s disease,” he concluded.

The study will be presented next week at the annual meeting of the Radiological Society of North America (RSNA).

Visceral abdominal fat 

Visceral abdominal fat, often referred to as visceral fat, is a type of body fat that’s stored within the abdominal cavity. It’s located near several vital organs, including the liver, stomach, and intestines, which makes its presence more concerning than subcutaneous fat, the fat that’s found under the skin.

Primary concerns

One of the primary reasons visceral fat is a health concern is due to its active nature. Unlike subcutaneous fat, visceral fat functions almost like an organ itself, releasing hormones and substances that can affect your body negatively. These secretions can lead to inflammation and can negatively impact insulin sensitivity, potentially leading to insulin resistance, a precursor to type 2 diabetes.

Moreover, high levels of abdominal fat are associated with a greater risk of serious health issues, such as heart disease, stroke, and certain types of cancer. It’s also linked to a higher risk of metabolic disorders and conditions like sleep apnea.

Diet and exercise 

Interestingly, visceral fat is also more responsive to diet and exercise than subcutaneous fat. This means that lifestyle changes, such as increased physical activity and a healthier diet, can be quite effective in reducing visceral fat levels. 

People often see improvements in their visceral fat levels and related health risks with weight loss, particularly when it’s achieved through a combination of diet and exercise.

Controlling visceral fat 

It’s important to note that while body mass index (BMI) is a common measure of body fat, it doesn’t differentiate between types of fat. Therefore, someone with a normal BMI could still have a high level of abdominal fat, making it important to focus on overall health and lifestyle rather than just weight or BMI numbers. 

Regular exercise, a balanced diet, adequate sleep, and stress management are key factors in controlling visceral fat levels.

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