As the size of a person’s belly grows, the memory center of their brain shrinks and beta amyloid and tau may appear — all of this occurring as early as a person’s 40s and 50s, well before any cognitive decline is apparent, according to new research.
Both beta amyloid plaques and tau tangles are early signs of the brain’s march toward a possible Alzheimer’s disease diagnosis. Amyloid plaques typically appear first, with tau tangles arriving later as the disease progresses.
“The more amyloid or tau you have in the brain, the sicker the brain becomes,” said senior study author Dr. Cyrus Raji, 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. “We also saw brain atrophy, or a wasting away of gray matter, in a part of the brain’s memory center called the hippocampus.”
Less blood flow in the memory center of the brain may cause shrinkage, another key biomarker for Alzheimer’s, said preventive neurologist Dr. Richard Isaacson, director of research at the Institute for Neurodegenerative Diseases in Florida. He was not involved in the new research.
“Since the study found these relationships decades before cognitive decline and an expected diagnosis, having laser sharp focus on reducing belly fat can be one of our most powerful tools to fight this terrible disease,” Isaacson said in an email.
Obesity is a worldwide epidemic, according to the World Health Organization, which estimates more than half the world will be overweight or obese within 10 years. In the United States alone, it’s estimated nearly 260 million Americans will 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 so that means over 2 million individuals could have dementia from Alzheimer’s disease attributable to their obesity,” Raji said.
“It’s a big public health issue,” Raji said. “We’re trying to understand how obesity at midlife, in the 40s and 50s, is a risk factor for Alzheimer’s disease, which doesn’t usually appear symptomatically until the 60s, 70s or 80s.”
Visceral fat is key
A pilot study by Raji and his team, released in November 2023, found a type of deep abdominal fat called visceral fat, was linked to inflammation and amyloid buildup in the brains of 32 men and women in their 40s and 50s. At this point in the research, the presence of tau was not confirmed.
Visceral fat wraps itself around the major organs of the body and is completely different than the subcutaneous fat on the rest of the body — subcutaneous fat typically makes up 90% of the body’s fat, according to the Cleveland Clinic.
“Most of a person’s body mass index (BMI) reflects subcutaneous fat, not visceral fat,” Raji said. “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 gold-standard amyloid positron emission tomography, or PET, scans to verify the presence of amyloid and tau in the brains of study participants, and magnetic resonance imaging, or MRI, to measure levels of visceral fat that occur when waistlines expand.
“The more visceral fat one has, the more inflammation happens in the body and it’s much worse, in truth, than the inflammation that occurs with subcutaneous fat,” Raji said.
Visceral fat receives more blood flow due to its placement near organs and is more hormonally active than subcutaneous fat, Raji said.
“We looked at insulin resistance via fasting plasma insulin levels and glucose tolerance tests and found the most abnormally high insulin was seen in people with higher amounts of visceral fat,” he said. “Visceral fat is the more metabolically abnormal, diabetes-inducing fat.”
That study also found a relationship 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 of Alzheimer’s disease.
Tau tangles identified for first time
The study has continued, adding an additional 48 participants to make a total of 80. The average age of those in the study was 49, and the average BMI was 32. A BMI of over 30 is considered obese by the medical establishment.
Updates on the findings so far were presented in abstracts at the Radiology Society of North America’s 2024 conference on Monday, Raji said.
“What is new is that we demonstrate for the first time that higher amounts of visceral or hidden fat is related to abnormally high tau proteins in persons up to 20 years before they could develop the earliest symptoms of Alzheimer’s disease,” Raji said. “Previously, we had only showed a link between visceral fat and amyloid.”
The PET scans showed that as visceral fat levels went up, so did levels of both amyloid and tau, according to the new research.
“This work is highly impactful and clinically relevant for the 47 million Americans, and hundreds of millions more globally, who have early signs of Alzheimer’s starting silently in their brains, but have not yet developed symptoms,” Isaacson said.
Ways to fight visceral fat
There are smart ways to reduce belly fat that can reverse these trends, Isaacson said. First, don’t focus just on body weight, but also body composition.
“This can be done easily at home by using a biometric scale or can be monitored by using an annual DEXA scan ordered by a healthcare provider. This scan is also commonly used to track bone density as we age,” he said.
Exercise is key, Isaacson added, but do it by working out “smarter — not harder.”
“To more efficiently get into ‘fat burning’ mode and lose body fat over time, I suggest taking a brisk walk, at a steady pace, working up to at least 45 — 60 minutes two to three times per week,” he said.
You want to follow what experts call “Zone 2 training,” which can be tracked using a simple method — being able to carry on a conversation while exercising, but just barely, Isaacson said.
“Walking fast on a treadmill at a slight incline, or walking with a weighted vest, are ways to get into the fat burning zone more quickly and efficiently,” he said. “Tracking and building muscle mass is also key — the more muscle a person has, the higher their metabolism and the better they can burn fat through the day.”
If your muscle mass is low, try strength training for at least 30 minutes twice a week or more, and be sure to eat adequate amounts of protein intake throughout the day, he added.