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Fiftysomething Diet: Your Brain on Fat and Sugar

These baddies can spur changes in gut bacteria that harm cognitive health

By Maureen Callahan

A daily donut break, a few chocolate chip cookies with lunch, a bowl of ice cream after dinner — everyone knows that splurging too often on high-fat, high-sugar treats isn’t great for the waistline or heart.

But new research suggests it could be damaging to your brain health as well.

Perhaps even more intriguing is the way it happens: through the gut. Studies are finding that not only do gut bacteria communicate with the brain and influence its function, but the mix of these bacteria is partly determined by what you eat.

Do you want to keep mental ability high in later years? Then here’s what you need to know:

Of Mice and Men and Women

Right now, the most intriguing research with gut and brain health is happening in mice. Before you dismiss studies done on mice as not applicable to your fiftysomething body, take note: Oregon State University (OSU) researcher Kathy Magnusson says these rodents are actually good models and relevant to humans when it comes to things like spatial memory, aging and obesity.

In a 2015 study published in Neuroscience, Magnusson and her colleagues wrote that feeding mice diets rich in fat and sugar can cause changes in gut bacteria that damage cognitive flexibility.

In fact, after just four weeks on a high-fat or high-sugar diet, the ability of mice to complete a battery of tests used to detect mental and physical function deteriorated. The biggest change was in cognitive flexibility, or the ability to adapt to change.

“Think about driving home on a route that’s very familiar to you, something you’re used to doing,” Magnusson says. “Then one day that road is closed and you suddenly have to find a new way home.” Mice on the high-fat, high-sugar diet had more trouble with that kind of change (tests like a water maze) than mice on a normal control diet.

“It’s increasingly clear that our gut bacteria, or microbiota, can communicate with the human brain,” says Magnusson, a professor in the OSU College of Veterinary Medicine and principal investigator with the Linus Pauling Institute.

“Bacteria can release compounds that act as neurotransmitters, stimulate sensory nerves or the immune system and affect a wide range of biological functions,” she says.

Your Brain on Fat

While the Oregon researchers noticed that both fat and sugar impact cognitive function, an earlier 2014 paper published in the journal Biological Psychiatry focused on the damaging effects of a high-fat diet alone.

To do that, scientists at Louisiana State University transplanted gut microbes from donor mice (eating either a high-fat diet or a control diet) into normal-weight adult mice and observed both groups for behavioral and physical changes. Mice receiving microbiota from donors on the high-fat diet showed increased anxiety, impaired memory and markers of inflammation in the brain.

"This paper suggests that high-fat diets impair brain health, in part, by disrupting the symbiotic relationship between humans and the microorganisms that occupy our gastrointestinal tracts," Dr. John Krystal, editor of Biological Psychiatry, said in a statement.


Your Brain on Sugar

In a 2012 Mayo Clinic study, scientists noticed that people 70 and older who ate diets rich in carbs were four times as likely to develop mild cognitive impairment as people who let the bulk of their diet come from protein and fats.

They had a theory. "A high carbohydrate intake could be bad for you because carbohydrates impact your glucose and insulin metabolism," said Dr. Rosebud Roberts, epidemiologist and lead researcher on the study.

"Sugar fuels the brain — so moderate intake is good. However, high levels of sugar may actually prevent the brain from using the sugar — similar to what we see with type 2 diabetes,” Roberts said.

The Big Picture

As researchers work to tease out all the mechanisms by which diet impacts brain health, OSU’s Magnusson shifts the focus to problems with the overall American diet. It dishes up plenty of fats, sugars, and refined carbs — sometimes all three in one food — via typical indulgences like a donut, a super-sized candy bar, or a snack of sugary soda and refined chips.

“We’ve known for a while that too much fat and sugar are not good for you,” Magnusson says. Their work “suggests that fat and sugar are altering your healthy bacterial systems… It’s not just the food that could be influencing your brain, but an interaction between the food and microbial changes.”

In other words, go easy on fatty and sugary foods. Your brain, and probably the rest of your body, will thank you.


Maureen Callahan is a registered dietitian, recipe developer and lead author of the diet book review series. She is a two-time James Beard Award winner. Read More
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