Does your brain age match your chronological age?

As you age, you gradually lose muscle mass and accumulate visceral fat, a type of fat deep inside your body that surrounds your heart, kidneys and other organs. Now scientists say your visceral fat to muscle ratio can provide 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 to be 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 be the same as their chronological age,” said senior study author Dr. Cyrus Raji. “It turns out that the age of their organs may also not correspond to their chronological age.”

One of the reasons these results are so important is that chronological age – and therefore aging brain “by far” is a major risk factor for Alzheimer's disease and other forms of dementia, said Raji, assistant professor of radiology and neurology at the Mallinckrodt Institute of Radiology at Washington University School of Medicine in St. Louis.

“The risk of disease extends to organ systems,” Raji said. “The disease does not just clearly respect the anatomical boundaries of one organ system.”

Previous studies including Raja's ownstudied the relationship between visceral fat and health outcomes such as loss of brain volumecognitive impairment and structural changes in the brain.

The study involved 1164 healthy people with an average chronological age of 55.17 years. About 52% were women and 39% were non-white. All underwent full-body MRIs that examined the brain, fat and muscle tissue.

To determine the age of the participants' brains, Raji and his colleagues used an algorithm that was trained on MRI scans of 5,500 healthy adults aged 18 to 89 years. The average brain age of study participants was 56.04 years—older than their average chronological age. The researchers called this difference the “brain age difference.”

The average difference in brain age was 0.69 years, meaning the participants' brains looked a little older than they should have. However, this figure was not statistically significant.

Just as higher muscle mass and a lower visceral fat-to-muscle ratio corresponded to younger brain age, lower muscle mass and a higher visceral fat-to-muscle ratio corresponded to older brain age.

This relationship between body fat and brain age only holds true for visceral fat, which is also known as latent fat, active fat, or deep belly fat. The study found that subcutaneous fat, the layer of fat beneath the surface of the skin, was not associated with brain age.

“Visceral fat, really terrible fat, [is] associated with higher rates of diabetes, insulin resistance, prediabetic conditions, high cholesterol– said Raji. – This leads to higher inflammatory state in the body, which over time affects the brain. This is the primary mechanism by which we think obesity may influence the risk of Alzheimer's disease.”

BMI doesn't tell you much about body composition

From a clinical perspective, the study results are in line with the expectations of Dr. Zhenqi Liu, a professor of diabetes at the University of Virginia School of Medicine.

“When people are very young and healthy, they tend to have more muscle mass and will have [a] younger brain age,” said Liu, who was not involved in the study.

Elderly peopleon the other hand, especially those who live with chronic diseases such as diabetes or obesity“They tend to have less muscle mass,” Liu added. “I wouldn’t be surprised if their brain size decreases.”

However, the study confirms that muscle health is vital to overall health, Liu said.

Restrictions body mass index or BMIas an indicator of health is also demonstrated in this study, Liu said. BMI is a standardized measure of body fat that is nearly 200 years old. calculated using your height and weight. But it's fallen out of favor in recent years, namely because it doesn't take into account how your fat—neither visceral nor subcutaneous—is distributed throughout your body.

A BMI of 30 or higher is classified as obese. Raja says his latest work demonstrates how a low BMI can mask poor brain health.

“If you have more visceral fat and less muscle, your brain may look older,” Raji said. “It makes sense from the perspective that Alzheimer's disease is a big risk factor—regardless of what the BMI shows.”

Liu favors two other approaches to assessing body composition. Firstly, this is your waist circumference. According to the National Heart, Lung, and Blood Institute, body measurements greater than 35 inches for women or 40 inches for men increase the risk of heart disease and type 2 diabetes. The second measurement is the waist-to-hip ratio, which involves dividing your waist circumference by your hip circumference. According to the World Health Organization, this ratio should not exceed 0.85 for women and 0.9 for men.

However, you won't be able to accurately measure your own visceral fat unless your doctor refers you to an MRI, which can evaluate the amount of fat under the skin and around organs. Optional full body scan can cost up to $5,000.

The good news is that there are steps you can take to increase muscle mass and reduce visceral fat without spending a dime.

How to build muscle and burn visceral fat

If it's been a long time since you touched the dumbbell or went for a long walk“Don’t be afraid,” said Siddhartha Angadi, Liu’s colleague and assistant professor of kinesiology in UVA’s School of Education and Human Development.

“Anyone can play sports — regardless of their age,” said Angadi, who was not involved in the study. “There is excellent data on life expectancy, health and various diseases showing that exercise is incredibly safe.”

Angadi recommends following American College of Sports Medicinerecommendations for physical activity. At least twice a week, healthy adults age 65 and younger are recommended to perform muscle-strengthening exercises that work all major muscle groups.

“Do 10 to 15 different exercises,” says Angadi. “You want to do one to three sets; you want to have eight to 12 reps on each set. Use machines if you're not familiar with weight training, which is a fancy way of saying weightlifting.”

According to Angadi, aerobic exercise is especially effective for combating visceral fat. Recommendations suggest 150 minutes of moderately intense aerobic activity each week.

“There is nothing that can reverse brain aging,” Angadi said. “You can just slow down.”

Glenn Gesser, a professor of exercise physiology at the College of Health Solutions at Arizona State University, says baby steps can help build muscle and burn visceral fat.

“A lot of people think it takes a long time to get any health benefits from exercise, and that's not necessarily true,” said Gesser, who was not involved in the study. “The biggest return on investment comes in the first few minutes of exercise.”

For example, if you aim to do the recommended 150 minutes of aerobic exercise per week, your body will benefit the most during the first 30 minutes, says Gesser.

“It’s the same thing with weight training,” Gesser said. “A lot of people might not want a gym membership, they might not want to walk and lift weights, but you can do weight training even with your own body weight.”

While Raja's study 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, Gesser said. When you exercise, your muscles release chemical signals that are thought to have a positive effect on the brain and other tissues.

“That's why people who exercise regularly tend to have a lower risk of cognitive decline, dementia, Alzheimer's disease and the like,” Gesser said. “If you want a healthy brain, you need healthy muscles.”

Gesser added: “It's not surprising that the single best predictor of whether you're going to spend the last years of your life in a nursing home or assisted living facility is physical fitness.”

Strength training is critical for healthy weight loss

Michael Snyder turned 70 in October, an age when muscle mass and strength naturally decline. He also accepts GLP-1 drug to help maintain a healthy weight.

As the use of GLP-1 has increased dramatically in recent years, so has awareness of the decline in muscle mass that can accompany significant weight loss, said Snyder, the W. Asherman Professor of Genetics at Stanford University School of Medicine. He did not participate in the study.

“If you're on [GLP-1s]“You should do strength training,” Snyder said. “I lift weights every day.”

Dr. David D'Alessio, director 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 through calorie restriction, that is, dieting, or if you lose weight through bariatric surgery, or if you lose weight by taking Ozempic, you will lose some fat and muscle mass,” said D'Alessio, who was not involved in the study. “It would be about 30% muscle mass and 70% fat. About half of the muscle mass by these measures is muscle.”

Even for people who aren't trying to lose weight, strong muscles are essential to living a long, healthy life, Snyder says.

“There’s a huge interest in longevity these days,” Snyder said. “Everyone wants to live forever, and to do that you need to maintain your mass.”