November 29, 2023
Hidden Belly Fat Tied to Alzheimer’s Risk 15 Years Before Symptom Onset
People in their 40s and 50s who have increased amounts of fat deep in their abdomens may be at increased risk of Alzheimer’s disease decades later, according to a new report. The study found that hidden belly fat in midlife was tied to brain changes typical of early Alzheimer’s disease. The link was particularly pronounced for men with increased belly fat, though women with excess belly fat also showed signs of Alzheimer’s disease changes.
Hidden belly fat, or visceral fat, is stored deep within the abdomen and surrounds the liver, intestines and other organs. It is not readily visible or “pinchable,” but as amounts increase, it may be marked by a bulging belly. Visceral fat makes up about 10 percent of the body’s fat stores in healthy individuals. Additional fat lies under the skin and is known as subcutaneous fat.
Earlier research had identified obesity and a high body mass index, or BMI, in middle age as a risk factor for Alzheimer’s disease. But this study found that people with increased amounts of hidden belly fat in middle age had higher levels of beta-amyloid in parts of the brain affected by early Alzheimer’s disease. As toxic beta-amyloid builds up in the brain it clumps together to form plaques, a hallmark of Alzheimer’s disease.
The researchers also found that people with high levels of belly fat had signs of brain atrophy, or a wasting of the levels of gray matter, in the hippocampus. The hippocampus is critical for memory formation and is one of the brain areas first affected by Alzheimer’s disease. Earlier studies have also tied brain shrinkage to a higher risk for Alzheimer’s disease.
“Even though there have been other studies linking BMI with brain atrophy or even a higher dementia risk, no prior study has linked a specific type of fat to the actual Alzheimer’s disease protein in cognitively normal people,” said study author Dr. Mahsa Dolatshahi, of 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.”
For the study, presented at the annual meeting of the Radiological Society of North America, the researchers analyzed brain scans from 32 men and women who ranged in age from 40 to 60. Their average BMI was 32, indicating many were overweight, though all were free of memory problems or other signs of Alzheimer’s disease.
The researchers measured levels of visceral and abdominal fat, conducted brain scans to look for signs of beta-amyloid buildup and brain wasting, and performed blood tests for markers for diabetes. They found that increased levels of visceral fat were tied to Alzheimer’s-related brain changes as well as higher levels of body-wide inflammation. Visceral fat is more metabolically active than subcutaneous fat and secretes chemicals that are tied to higher levels of inflammation. Scientists increasingly recognize inflammation as a marker for various chronic diseases of aging, including heart disease and Alzheimer’s.
“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,” Dr. Dolatshahi said.
“This study highlights a key mechanism by which hidden fat can increase the risk of Alzheimer’s disease,” added study author Cyrus A. Raji, of Washington University. “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.”
The study was small, and further research is needed to better understand how belly fat may contribute to dementia. But the authors note that targeting visceral fat may be one way to help reduce the risk of developing Alzheimer’s disease years down the road. Other studies indicate that having a waist size exceeding 40 inches in men or 35 inches in women is a sign of excess visceral fat. But even people who are not overweight may have excess levels of this “hidden” abdominal fat.
The good news is that visceral fat responds well to diet and exercise measures, Dr. Raji said, because visceral fat is more easily metabolized and burned than subcutaneous fat. Eat a heart-healthy diet rich in whole grains, fruits, vegetables and lean meats, and avoid ultra-processed foods and snacks and sugary drinks. Alcohol, too, can contribute to “beer belly,” or excess abdominal fat. Aim to get regular exercise, including both cardio and strength training. All these measures have been tied to lower levels of abdominal fat, lower rates of obesity, and a reduced risk for Alzheimer’s disease.
By ALZinfo.org, The Alzheimer’s Information Site. Reviewed by Eric Schmidt, Ph.D., Fisher Center for Alzheimer’s Research Foundation at The Rockefeller University.
Source: Dolatshahi M, Commean PK, Rahmani F, et al: “Alzheimer Disease Pathology and Neurodegeneration in Midlife Obesity: A Pilot Study.” Aging and Disease, August 3, 2023, presented at the Radiological Society of North American conference November 21, 2023.