As you age, you gradually lose muscle mass and gain visceral body fat, a type of fat located deep inside your body and surrounding your heart, kidneys, and other organs. Now, scientists say the ratio of visceral fat to muscle can reveal clues about your brain health.
People with higher muscle mass and a lower visceral fat-to-muscle ratio tend to have younger brains, according to a study presented next week at the annual meeting of the Radiological Society of North America.
“We know that a person’s age, in terms of appearance, may not correspond to their chronological age,” said Dr. Cyrus Raji, lead author of the study. “It turns out that the age of their organs might not match their chronological age either.”
One reason these findings are so important is that chronological age — and therefore brain aging — is “by far” the leading risk factor for developing Alzheimer’s disease and other forms of dementia, said Raji, an associate professor of radiology and neurology at the Mallinckrodt Institute of Radiology at Washington University School of Medicine in St. Louis.
“Disease risk passes through organ systems,” Raji said. “Disease does not only respect the anatomical boundaries of an organ system.”
Previous research, including Raji’s, has studied the relationship between visceral fat and health problems such as brain volume loss, cognitive impairment and structural changes in the brain.
The study included 1,164 healthy people whose average chronological age was 55.17 years. About 52% were women and 39% were non-white. All underwent a full-body MRI that examined the brain, fat and muscle tissue.
To determine participants’ brain ages, Raji and colleagues used an algorithm that had been trained on the MRI scans of 5,500 healthy adults aged 18 to 89. The average brain age of study participants was 56.04 years, higher than their average chronological age. Researchers have called this difference the “brain age gap.”
The average difference in brain age was 0.69 years, meaning the participants’ brains looked slightly older than they should. However, this measure was not statistically significant.
Just as higher muscle mass and lower visceral fat-to-muscle ratio corresponded to younger brain age, lower muscle mass and higher visceral fat-to-muscle ratio corresponded to older brain age.
This link between body fat and brain age was only true for visceral fat, also known as hidden fat, active fat, or deep abdominal fat. Subcutaneous fat, the layer of fat just below the surface of the skin, was not associated with brain age, the study found.
“Visceral fat, which is the really terrible fat, [is] “This leads to a higher rate of diabetes, insulin resistance, prediabetic states and high cholesterol,” Raji said. “This leads to a higher inflammatory state in the body, which over time affects the brain. This is the main mechanism by which we think obesity may affect the risk of Alzheimer’s disease.
BMI reveals little about body composition
From a clinical perspective, the study results are about what Dr. Zhenqi Liu, the James M. Moss Professor of Diabetes at the University of Virginia School of Medicine, would expect.
“When people are very young and healthy, they tend to have more muscle mass and they will have [a] younger brain age,” said Liu, who was not involved in the research.
In contrast, older people, especially those living with chronic illnesses such as diabetes or obesity, generally have lower muscle mass, Liu added. “I wouldn’t be surprised if their brain volume decreased.”
Despite this, the study reinforces that muscle health is vital to overall health, Liu said.
The limitations of body mass index, or BMI, as a measure of health are also highlighted in this research, Liu said. BMI is a standardized measurement of body fat, almost 200 years old, calculated based on your height and weight. But it has fallen out of favor in recent years, in part because it doesn’t take into account how your fat – neither visceral nor subcutaneous – is distributed throughout your body.
A BMI of 30 or more falls into the obese category. For Raji, his latest work demonstrates how a low BMI could mask poor brain health.
“If you have more visceral fat and less muscle, you may have an older brain,” Raji said. “This makes sense as Alzheimer’s disease is a significant risk factor, regardless of what BMI would show.”
Liu favors two other approaches to assessing body composition. The first is the waistline. Measurements beyond 35 inches for women or 40 inches for men increase your risk of heart disease and type 2 diabetes, according to the National Heart, Lung, and Blood Institute. The second measurement is the waist-to-hip ratio, which involves dividing your waist measurement by your hip measurement. According to the World Health Organization, this ratio should not exceed 0.85 for women or 0.9 for men.
Still, you can’t accurately measure your own visceral fat unless your doctor recommends an MRI, which can assess the amount of fat under the skin and around organs. An optional full-body scan can cost up to $5,000.
The good news is that there are steps you can take to increase your muscle mass and reduce your visceral fat without spending a dime.
How to build muscle and burn visceral fat
If it’s been a while since you’ve picked up a dumbbell or taken a long walk, fear not, said Siddhartha Angadi, Liu’s colleague and associate professor of kinesiology in UVA’s School of Education and Human Development.
“Anyone can exercise, regardless of age,” said Angadi, who was not involved in the research. “There is excellent data across the lifespan, across the health span, and across multiple diseases, demonstrating that exercise is incredibly safe.”
Angadi recommends following the American College of Sports Medicine’s physical activity guidelines. At least twice a week, healthy adults ages 65 and younger are encouraged to engage in muscle-strengthening activities that work all major muscle groups.
“Do 10 to 15 different exercises,” Angadi said. “You want to do one to three sets; in each set you want to have eight to 12 reps. Use machines if you’re not familiar with resistance training, which is a fancy way of saying weightlifting.”
Aerobic exercise is particularly effective at targeting visceral fat, Angadi said. Guidelines suggest 150 minutes of moderate-intensity aerobic activity each week.
“Nothing can reverse brain aging,” Angadi said. “You can just slow down the pace.”
Glenn Gaesser, professor of exercise physiology at Arizona State University’s College of Health Solutions, said small steps can help build muscle and burn visceral fat.
“A lot of people think it takes a lot for exercise to produce some health benefit, and that’s not necessarily true,” said Gaesser, who was not involved in the study. “The greatest return on investment is obtained from the first minutes of exercise. »
For example, if you strive to do the recommended 150 minutes of aerobics per week, your body will benefit the most in those first 30 minutes, Gaesser said.
“Same with resistance training,” Gaesser said. “A lot of people might not want to get a gym membership, they might not want to go lift weights, but you can do resistance training even with your own body weight.”
Although Raji’s research does not conclude that higher muscle mass and a lower visceral fat-to-muscle ratio guarantee better brain health, it does shed light on the relationship between the brain and the musculoskeletal system, Gaesser said. When you exercise, your muscles release chemical signals that are thought to positively influence the brain and other tissues.
“That’s why people who exercise regularly tend to have a lower risk of cognitive decline, dementia, Alzheimer’s, etc.,” Gaesser said. “If you want a healthy brain, you have to have healthy muscles.”
Gaesser added, “It’s no surprise that the best indicator of whether or not you’re going to spend the final years of your life in a nursing home or assisted living facility is physical fitness. »
Strength training is essential for healthy weight loss
In October, Michael Snyder turned 70, an age when muscle mass and strength are naturally in decline. He also takes a GLP-1 medication to help him maintain a healthy weight.
As the use of GLP-1 has increased in recent years, so has awareness of the decline in muscle mass that can accompany significant weight loss, said Snyder, a professor of genetics at Stanford University who was not involved in the study.
“If you are sure [GLP-1s]you should be weight training,” Snyder said. “I lift weights every day.”
Dr. David D’Alessio, chief of the division of endocrinology, metabolism and nutrition at Duke University School of Medicine, emphasized that muscle loss is not unique to people taking GLP-1.
“If you lose weight by restricting calories, that is, by dieting, or if you lose weight through bariatric surgery, or if you lose weight by taking Ozempic, you will lose fat mass and lean mass,” said D’Alessio, who was not involved in the study. “It will be about 30% lean mass and 70% fat. By these measurements, about half of lean mass is muscle.”
Even for people who aren’t trying to lose weight, strong muscles are necessary for a long, healthy life, Snyder said.
“There’s a lot of interest in longevity these days,” Snyder said. “Everyone wants to live forever, and to do that you’ll need to maintain your mass.”
