As a person’s belly grows, the memory center of their brain shrinks and beta amyloid and tau plaques can appear, all of which occur as early as age 40 and 50, long before any cognitive decline is apparent, according to new research.
Both amyloid beta plaques and tau tangles are early signs of the brain’s march toward a possible diagnosis . Amyloid plaques usually appear first, while tau tangles appear later, as the disease progresses.
“The more amyloid or tau you have in your brain, the sicker you are,” said Dr. Cyrus Raji, senior author of the study and associate professor of radiology at Washington University School of Medicine in St. Louis.
“The way we can track a sicker-looking brain is lower blood flow,” Raji said. or a wasting away of gray matter, in a part of the brain’s memory center called the hippocampus.”
According to Dr. Richard Isaacson, a preventive neurologist and director of research at the Florida Institute for Neurodegenerative Diseases, reduced blood flow to the brain’s memory center may cause shrinkage, another key Alzheimer’s biomarker. He was not involved in the new research.
“Since the study found these relationships decades before cognitive decline and an expected diagnosis, having a laser-sharp focus on reducing belly fat may be one of our most powerful tools to fight this terrible disease,” Isaacson said in an email.
Obesity is a global epidemic , which estimates that more than half of the world will be overweight or obese within 10 years. In the United States alone, nearly 260 million Americans are projected to be overweight or obese by 2050 unless policymakers take immediate action.
“Conservatively, obesity as a risk factor for dementia affects at least 1% of American adults, meaning that more than 2 million individuals may have attributable to their obesity,” Raji said.
“It’s a huge public health problem,” Raji said. “We’re trying to understand how in midlife, between the ages of 40 and 50, is a risk factor for Alzheimer’s disease, which often doesn’t appear symptomatically until the age of 60, 70 or 80.”
Visceral fat is key
A pilot study by Raji and his team, published in November 2023, found that a type of deep abdominal fat, called visceral fat, was linked to inflammation and amyloid buildup in the brains of 32 men and women between the ages of 40 and 50. At this point in the research, the presence of tau had not been confirmed.
Visceral fat surrounds the body’s major organs and is completely distinct from the subcutaneous fat found in the rest of the body — subcutaneous fat typically makes up 90 percent of body fat.
“Most of a person’s body mass index (BMI) reflects subcutaneous fat, not visceral fat,” Raji explains. “So we measure visceral fat using abdominal MRI, and we have a specialized computer program that can measure the actual volume of visceral adipose tissue.”
The study also used positron emission tomography, or PET, scans to check for the presence of amyloid and tau in the brains of study participants, and magnetic resonance imaging, or MRI, to measure the levels of visceral fat that are produced when the waistline expands.
“The more visceral fat you have, the more inflammation you have in your body, and it’s actually much worse than the inflammation that you get with subcutaneous fat,” Raji said.
Visceral fat receives more blood flow due to its location close to organs and is more hormonally active than subcutaneous fat, Raji explained.
“We examined insulin resistance through fasting plasma insulin levels and glucose tolerance tests and found that the most abnormally high insulin was seen in people with the highest amounts of visceral fat,” he said. “Visceral fat is the most metabolically abnormal, the kind that induces diabetes.”
That study also found a link between deep belly fat and brain atrophy, or a wasting away of gray matter, in a part of the brain’s memory center called the hippocampus, Raji said. Brain atrophy is another biomarker for Alzheimer’s disease.
Tau tangles identified for the first time
The study continued with the recruitment of another 48 participants, for a total of 80. The average age of the study participants was 49 years old and the average BMI was 32. A BMI over 30 is considered a risk factor. Doctors consider a BMI over 30 to be obese.
According to Raji, summaries of the results obtained to date were presented at the 2024 American Society of Radiology.
“What is new is that we have shown for the first time that a higher amount of visceral or hidden fat is linked to abnormally elevated tau proteins in people up to 20 years before they might develop the first symptoms of Alzheimer’s disease,” Raji said. “Previously, we had only shown a link between visceral fat and amyloid.”
PET scans showed that as levels of visceral fat increased, so did levels of amyloid and tau, according to the new research.
“This work has great clinical significance and impact for the 47 million Americans, and hundreds of millions more around the world, who have early signs of Alzheimer’s that begin silently in their brains, but who have not yet developed symptoms,” Isaacson said.
Ways to combat visceral fat
There are smart ways to reduce belly fat that can reverse these trends, Isaacson said. First, you need to focus not just on body weight, but also on body composition.
“This can be easily done at home using a biometric scale or monitored by an annual DEXA scan ordered by a healthcare provider. This scan is also commonly used to track bone density as we age,” he explained.
Exercise is key, Isaacson added, but you need to train “smarter, not harder.”
“To burn fat most effectively and lose body fat over time, I suggest walking briskly, at a steady pace, for at least 45-60 minutes, two to three times a week,” she said.
You need to follow what experts call “Zone 2 training,” which can be controlled with a simple method: being able to hold a conversation while exercising, but just barely, Isaacson explains.
“Brisk walking on a treadmill with a slight incline, or walking with a weighted vest, are ways to get into the fat-burning zone more quickly and efficiently,” she said. “Tracking and increasing muscle mass is also key — the more muscle a person has, the higher their metabolism and the better they can burn fat throughout the day.”
If you have low muscle mass, try to do strength training for at least 30 minutes twice a week or more, and be sure to get adequate amounts of protein throughout the day, she added.