Researchers say your waist-to-hip ratio, rather than BMI, can be an indicator of your chances for developing dementia.

The ultimate scientific puzzle as to what causes dementia remains unsolved.

However, a new cognitive decline study, focusing on a possible link between belly fat and the brain, may have brought us one puzzle piece closer.

The study, reported in the British Journal of Nutrition, analyzed the connection between obesity and cognitive abilities in adults 60 and older.

Scientists had previously investigated obesity and dementia and concluded that being overweight seem to be linked.

But the new study homes in on how older adults’ cognitive abilities are affected by obesity.

Dr. Howard Fillit is the founding executive director and chief science officer for the Alzheimer’s Drug Discovery Foundation.

Adults over 60 rank as the age group “most affected by cognitive impairment, mainly dementia, mainly caused by Alzheimer’s,” Fillit told Healthline.

That same age group contains a significant percentage battling their weight.

In actual numbers:

  • 10 percent of all individuals over 65 struggles with obesity, according to Fillit.
  • 5.7 million Americans have been diagnosed with Alzheimer’s disease. By 2050, that group is estimated to soar to almost 16 million.

Researchers say belly fat rather than body mass index (BMI) provides a more important indication that weight loss may help to prevent dementia.

Why is that?

“Central fat is an inflammatory tissue. Inflammation is a widely recognized risk for cognitive impairment,” explained Fillit.

To understand what it means to experience cognitive impairment, the Alzheimer’s expert suggested you think about your feelings when you’re ill.

For most of us, so-called “sickness behavior” makes us feel “tired, depressed, [and we find it] hard to concentrate.”

The study’s researchers also concluded that waist-to-hip ratio (WHR) offers a better way to measure central fat than BMI.

“Especially in older people who lose muscle mass with aging,” said Fillit. “BMI is a less reliable indicator of central obesity (i.e., belly fat).”

In addition, the research project supports theories that obesity boosts the risk of cognitive impairment in three ways:

  • inflammation
  • metabolic disturbances such as insulin resistance
  • lack of physical exercise

Fillit recommended that people view belly fat as a risk factor for poor health, including heart disease and diabetes as well as cognitive impairment and dementia.

Dr. Alexandra Sowa, a board-certified internist and obesity medicine specialist, founded SoWell Health, a weight loss and wellness practice in New York City. She also is a clinical instructor in medicine at New York University.

Sowa offered some insights into the difference between relying on BMI as a measuring tool versus WHR.

“BMI is a useful but inexact measuring guide. It only takes into account weight and height and isn’t always a reliable measure of body fat,” she told Healthline.

In contrast, WHR “puts more importance on visceral fat, an endocrine organ that secretes hormones and chemicals that are linked to the development of disease,” explained Sowa.

WHR is determined by dividing your waist circumference by your hip circumference. Be sure to measure the smallest part of your waist and biggest area of your hips.

The World Health Organization considers a healthy WHR to be 0.85 or less for women and 0.9 or less for men. A WHR of more than 0.85 in women or more than 0.9 in men is an indicator of obesity.

In the new study, researchers “hypothesized that the increase of C-reactive protein from belly fat was one of the factors leading to decline in cognitive function,” Sowa said.

“What it comes down to is this: Excess body fat leads to inflammation and inflammation leads to disease,” she explained.

Sowa views the results of the study as positive.

With the soaring rates of obesity and cognitive decline, she finds it “hopeful that evidence-based science is identifying a link between these two hugely burdensome diseases.”

Sowa emphasized that obesity is preventable and treatable.

Ultimately, preventing obesity “may prevent — or at the very least, lessen — the development of other disease, like dementia,” she added.

Bill Lagakos, who has a PhD in nutritional biochemistry and physiology, clarified that “normal weight” is defined as a WHR of less than 0.8 in women and less than 0.9 in men.

If your WHR is above these limits, you may be storing “disproportionately more weight in your belly region,” he noted. Based on the study, that would mean “you may have greater risk of cognitive decline.”

Lagakos, the author of “The Poor, Misunderstood Calorie,” recommended weight loss and exercise as the “most promising interventions” for those with excess belly fat.

To find the right weight loss plan, check with your healthcare provider and “find what works for you,” he added.

“For some, giving up industrial foods works,” Lagakos told Healthline. “Others require more restrictive plans such as ketogenic or low-fat diets. Find a diet and exercise plan you can stick to.”

Lagakos, who focused on inflammation, diabetes, and circadian biology during his postdoctoral studies, noted that follow-up research could offer even more information on how to prevent cognitive decline.

“A follow-up study would assess adiposity and cognition at baseline, then track them for a predefined amount of time. If the association remained, further studies to determine the mechanisms would be conducted to determine prevention, treatment, management, cure, etc.” he said.