Obesity may cause Alzheimer’s-like brain changes, new study shows. Does losing weight help?

Being overweight in middle age has been linked to a higher risk of developing Alzheimer’s disease or dementia, and a new study shows that brain changes in obese people mirror some of those with Alzheimer’s.

Scientists at McGill University in Montreal analyzed the brain scans of more than 1,300 people in the first research to directly compare patterns of brain shrinkage in obese people and Alzheimer’s patients.

The scans revealed similar brain thinning in regions involved in learning, memory and judgment in both groups, according to the report published Tuesday in the Journal of Alzheimer’s Disease.

Obesity can cause changes in the body that are associated with increased risk of Alzheimer’s, including damage to blood vessels in the brain and the buildup of abnormal proteins, previous studies have found. The new research goes one step further.

“We have shown that there is a similarity between the brains of obese people and those with Alzheimer’s,” said first author of the study, Filip Morys, a postdoctoral neuroscience researcher at McGill University. “And it boils down to the thickness of the cerebral cortex.”

The cerebral cortex, which in humans is responsible for higher brain functions such as speech, perception, long-term memory, and judgment, is the outer layer of the brain.

The thinning in that region of the brain could reflect a decrease in the number of brain cells, Morys said.

The McGill researchers suspect that people who are obese, and possibly those who are overweight — a BMI between 25 and 25.9 — may be able to slow cognitive decline if they can get closer to a healthy weight.

Morys was unable to identify a target weight.

Why is obesity dangerous for the brain?

The science is not clear. Other brain-damaging conditions, including high blood pressure, high cholesterol and type 2 diabetes, are also linked to obesity, Morys notes.

To take a closer look at the impact of obesity on brain structure, Morys and his colleagues examined brain scans of 341 Alzheimer’s patients and 341 obese individuals with a BMI of 30 or more, along with scans of 682 healthy individuals.

All the brain scans and other information came from two large health databases: the UK Biobank and the Alzheimer’s Disease Neuroimaging Initiative, a program that recruits participants across North America and is funded in part by the National Institutes of Health.

Cognitive tests taken by the obese individuals in the study revealed no obvious mental deficits, but it’s possible that subtle changes in cognition related to the thinning seen on brain scans may not be detected on the types of tests used to assess mental status, Morys said .

The new research “has shown us something we didn’t know before,” said metabolism researcher Sabrina Diano, director of the Institute of Human Nutrition at Columbia Irving Medical Center.

“The study showed that obese individuals and those with Alzheimer’s disease have smaller common areas of the brain, possibly due to a neurodegenerative process,” meaning that nerve cells in these regions could be damaged and could die. Diano said.

The scans can’t show that obesity is causing these areas to thin, but it makes sense that weight control could be a way to reduce risk, he said.

“We know that if you take a mouse that has a genetic predisposition to develop Alzheimer’s and feed it a high-fat, carbohydrate-rich diet, similar to the Western diet, you can induce body weight gains in the animal, and as with weight gain, cognitive impairment and brain degeneration is accelerated,” Diano said.

Could weight loss reverse the damage?

The study opens the door for further exploration into whether weight loss may reverse some of the brain changes, said Dr. Joseph Malone, assistant professor of neurology in the University of Pittsburgh’s division of cognitive disorders. Malone was not involved in the study.

“We know that obesity is associated with other diseases that can affect blood vessels in the brain, such as type 2 diabetes, high blood pressure, high cholesterol and inflammation, which could lead to broken blood vessels in the brain and therefore contribute to the death of brain cells,” said Malone.

While the obese people in the study showed no memory declines, it’s possible that what the researchers are seeing is an early stage in the development of Alzheimer’s, Malone suggested.

One limitation of the research is that it doesn’t directly report what people eat, only that they are obese, said Linda Van Horn, chief of nutrition at Northwestern University Feinberg School of Medicine, who was not involved in the study.

“Given that, it leaves a lot of room for speculation and hypothesis generation,” Van Horn said. “Intuitively, you’d think it would impact various organs, including the brain.”

While the hope is that weight loss could stop or reduce brain degeneration, “unfortunately we’re finding more and more that there are some tipping points,” Van Horn said.

“I believe, based on examples like osteoporosis, that the chances of reversing the disease are less than preserving what’s there,” he said.

This article was originally published on NBCNews.com

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