Researchers break down how, exactly, a healthy diet
might lower dementia risk
by Hallie Levine, AARP, July 24, 2018
En español | Last year’s Alzheimer’s Association
conference made headlines with the release of studies showing that a healthy
diet, along with other lifestyle factors, can slash your risk of dementia by
a third. To find out why exactly that might be the case, researchers have
hunted for answers, among other places, in the gut microbiome, the trillions of
microorganisms that live in our digestive tracts. Certain changes in these
bacteria have been linked to various inflammatory and autoimmune conditions,
such as obesity, diabetes and inflammatory bowel disease. But scientists also
discovered that some types of microbiome bacteria can promote buildup in the
brain of specific proteins known as amyloid and tau proteins, which are linked
to Alzheimer’s disease. In mouse studies, dietary changes that alter the
microbiome in turn reduce amyloid plaques, lower inflammation and — bingo —
improve memory.
Research released at
today’s conference suggests another link along the digestive tract: that a
person’s ability to metabolize certain lipids — fatlike substances found in
blood and body tissue that actually make up most of your brain — also can
affect the risk of developing Alzheimer’s and other dementias. “If your body
has trouble producing or moving lipids around, it may impact your brain
structure and its function,” explains Heather Snyder, senior director of
Medical and Scientific Operations at the Alzheimer’s Association.
While this research is
still in its infancy, it has the potential to be game-changing. “It may help us
develop better diagnostic tests for the disease in the future, as well as to
better understand why some people progress rapidly over a year, and some more
slowly over 15 years,” says Jagan Pillai, a neurologist at Cleveland Clinic.
What the Studies Show
Two of the studies
looked at the impact of lipids on Alzheimer’s risk. One study, by researchers
at the University of Pennsylvania and Duke University, found that low levels of
a certain type of lipids, plasmalogens, are linked to higher Alzheimer’s risk. (Some
of these plasmalogens also contain two omega-3 fatty acids that are vital for
brain health.) The second study, done at the University of California, Davis,
looked at 800 older adults, some healthy, some with mild cognitive impairment
and some with full-blown Alzheimer’s. They also found that people with
Alzheimer’s had many problems with lipid metabolism, such as difficulty
absorbing lipids that contain EPA and DHA. In addition, giving these patients
fish oil supplements failed to bring these lipids back to normal.
“These studies seem to
show that if, for whatever reason, your body has trouble producing certain
lipids, it impacts what’s going on in your brain,” explains Snyder. This may
also explain why fish oil supplements have had mixed results in clinical trials
when it comes to warding off dementia. “Some people just aren’t able to absorb
them, for unknown reasons,” Snyder says.
A third study, at
Indiana University, examined the bile acids — substances made by your liver
that help break down fat — in older adults who either had early-stage
Alzheimer’s or were at increased risk of the disease. They found that high
levels of certain bile acids were increased in people with Alzheimer’s and were
linked to cognitive decline, reduced brain glucose metabolism and greater brain
atrophy, as well as higher levels of amyloid and tau proteins. “We still have a
lot to tease out: Are these changes in bile acids causing changes in the brain,
or is it the other way around — that something happening in the brain leads to
alterations in digestion?” says Snyder. “But information like this could
ultimately be used to develop better diagnostic testing for Alzheimer’s.”
There are more than 40
different risk genes associated with Alzheimer’s. The last study, out of
Erasmus Medical Center in Rotterdam, looked at some of these genetic variations
and found that two — including the strongly associated APOE-e4 — were
significantly associated with lower levels of cholesterol components that help
keep brain cell membranes healthy and strong. Other genes were associated with
higher or lower levels of certain bile acids. “Alzheimer’s researchers haven’t
paid much attention to these sorts of markers in the past, but this research
suggests that perhaps we should,” says Gary Small, professor of
psychiatry and biobehavioral sciences at the David Geffen School of Medicine at
UCLA. “This may help us understand how these underlying mechanisms contribute
to Alzheimer’s disease, and thus unlock strategies for more effective
treatments.”
The Takeaway
While much of this
research is intriguing, it’s still in its infancy, cautions Small. In the
meantime, “the microbiome is certainly a very interesting area of study
right now, not just for Alzheimer’s but for brain health and mood,” he notes.
In the meantime, you can help keep all your organs, including your liver, GI
tract — and yes, brain — in tiptop shape by eating a diet high in fruits,
veggies, whole grains and healthy fats such as fatty fish and olive oil, while
limiting saturated fats and sugars.
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