Alzheimer's disease takes a devastating toll on thinking and memory power.
This leading form of dementia resembles heart disease in that each person's risk is affected by behavior, diet, and genetics.
When it comes to late-onset Alzheimer's disease – the most common kind by far – genetic factors play relatively small roles.
Instead, the evidence suggests that exercise (mental and physical) and diet affect the risk of Alzheimer's much more substantially.
Now, scientists from Chicago's Rush University Medical Center report that a hybrid of two diets appears to reduce the risk of Alzheimer's.
Better yet, the apparent risk reduction applies even if the diet is not followed to the letter.
A new hybrid of two healthy diets
Martha Clare Morris, Ph.D., and her Rush Center colleagues developed the new MIND diet plan.
It was designed to incorporate brain-healthy features of the Mediterranean diet and the DASH diet, which appear to delay the onset of Alzheimer's disease and other forms of dementia.
MIND is the acronym for their eating plan's full name: the "Mediterranean-DASH Intervention for Neurodegenerative Delay” diet.
Their new study compared all three diets in terms of their ability to delay Alzheimer's disease.
All three diets feature ample fruits and vegetables, relatively modest amounts of meat, and few refined grain or processed foods.
They also include eating fish or seafood at least once or twice a week ... but only the Mediterranean diet calls for people to eat fish six or more times a week.
There are the defining characteristics of the three diets:
The DASH Diet
DASH is an acronym for Dietary Approaches to Stop Hypertension:
- Fruits – 4 to 5 servings a day
- Vegetables – 4 to 5 servings a day
- Whole Grains – 6 to 8 servings a day
- Dairy – 2 to 3 servings a day of low fat or fat-free dairy foods
- Fish, poultry or lean meat – 6 or fewer servings a day*
- Nuts, seeds and legumes (i.e., beans, lentils, and peas) – 4 to 5 servings a week
- Fats and oils – 2 to 3 servings a day: Avoid trans fat, and limit saturated fat to less than 6 percent of total calories
- Sweets – 5 or fewer a week
- Sodium – less than 2,300 mg per day
*It seems a bit odd that the DASH diet recommends so many servings of meat or fish every day.
The Mediterranean Diet
This diet reflects the ancient eating patterns of long-lived rural Greeks, particularly those dwelling on Aegean islands like Crete:
- Fish – at least 6 times a week
- Fruits – 3-4 servings daily
- Vegetables – 3-4 servings daily
- Routine, modest consumption of beans, extra virgin olive oil, nuts, cheese, poultry, and whole grains
The MIND Diet
When they designed the hybrid MIND diet, Morris and her Rush Center colleagues considered past findings about the Mediterranean and dash diets, as well as the effects of specific foods and nutrients on the risk of developing dementia:
- Fish – once a week
- Beans – every other day
- Poultry – twice a week
- Berries – twice a week
- Nuts as a snack – most days
- Salad – daily
- Vegetables – daily
- Whole grains – 3 servings daily
- Glass of wine – daily
The MIND diet features 10 "brain-healthy” food groups: green leafy vegetables, other vegetables, nuts, berries, beans, whole grains, fish, poultry, olive oil, and wine.
And it minimizes intake of five "brain-unhealthy” groups – red meats, butter and stick margarine, cheese, pastries and sweets, and fried or fast food.
We're surprised by the diet's near-exclusion of red meats, butter, and cheese.
Although the available evidence links diets high in certain animal-source saturated fats to greater risk for early onset Alzheimer's in the small minority of people who carry the APOE4 gene variant, the evidence does not show that red meats, butter, and cheese raise the risk for folks outside that group.
And it's not the case that all saturated fats are equally concerning when it comes to brain or heart health. Much of the saturated fat in red meat is not associated with brain or vascular disease, nor are the saturated fats in coconuts or chocolate.
But the evidence on diet and brain health certainly does support a pretty dim view of margarine, pastries, sweets, and fried or fast foods.
Berries are the only fruit specifically designated as part of the MIND diet. "Blueberries are one of the more potent foods in terms of protecting the brain,” Professor Morris said, adding that strawberries also perform well in brain-health studies.
Prior Rush Center study found anti-Alzheimer's benefits from all three diets
This was the second Rush Center study to compare the effects of the three diets on the risk for Alzheimer's disease.
In a 2014 study, the Rush team found that close adherence to the MIND diet equaled or beat close adherence to the Mediterranean or DASH diets for delaying the development of Alzheimer's.
Specifically, the brain-health benefit of following the MIND diet most closely was equivalent to being 7.5 years younger than the one-third of the participants whose diets resembled the MIND diet least closely (Morris MC, et al. 2014).
And even moderate adherence to the MIND diet reduced the risk of Alzheimer's disease, suggesting that it may deter dementia even better than the Mediterranean or DASH diets do, despite prescribing much less fish than the the Mediterranean diet.
However, the findings of their new study suggest that it's best to eat as much fish as possible (see "Fish-rich diets conferred extra risk reduction", below).
Ten years ago, Professor Morris and her Rush Center colleagues linked higher fish takes to lower risk of Alzheimer's disease.
While they found no strong link between participants' estimated intake of omega-3 fatty acids and reduced cognitive decline, they did detect a substantial protective effect among those who'd eaten the most fish for the longest time.
New Rush Center study ranks the MIND diet and all fish-heavy diets highest
For their new study, the Rush researchers analyzed data from 923 participants in the Chicago Health and Aging Project.
All the volunteers were aged 65 or older, and were followed for an average of 4.5 years, to see how many would develop Alzheimer's disease (Morris MC et al. 2015).
Rather than assigning the volunteers to any of the three eating patterns – the MIND, Mediterranean, or DASH diet – they examined each participants' self-reported diet to see how closely it matched any of those.
As in their 2014 study, the results linked close adherence to any of the three diets to significant delays in the onset of Alzheimer's disease.
However, the MIND diet performed best in terms of reducing the risk of Alzheimer's disease among older people.
The results showed that the participants whose diets resembled the MIND diet most closely were 53 percent less likely to develop Alzheimer's during the 4 to 5 years the volunteers were followed.
As the authors noted, "The rate reduction [in risk for Alzheimer's disease] is the equivalent of being 3 to 4 years younger in age.”
Better yet, given the challenge of changing unhealthful food habits, even those whose diets only resembled the MIND diet moderately closely were about 35 percent less likely to develop Alzheimer's disease.
"People who adhered even moderately to the MIND diet had a reduction in their risk for Alzheimer's disease,” said Morris. "I think that will motivate people.” (RUMC 2015)
When the researchers in the new study excluded the participants who changed their diets somewhere along the line, they found that the association became stronger between the MIND diet and lower risk for Alzheimer's disease.
As Professor Morris said, "That probably means that people who eat this diet consistently over the years get the best protection.” (RUMC 2015)
Morris added a caveat: "The results need to be confirmed by other investigators in different populations and also through randomized trials.” (RUMC 2015)
Sadly, as well as being the only way to prove a link between a diet or nutrient and a drop in the risk for a disease, controlled clinical trials are costly and difficult to perform properly.
Fish-rich diets conferred extra risk reduction
The results showed that fish played a significant role in reducing the risk for Alzheimer's disease over four to five years of follow-up.
That fish-friendly finding was calculated after accounting for possible confounding factors, including the effects of other brain-healthy foods in each diet, and brain-healthy lifestyle habits.
The participants who ate fish once a week slowed their age-associated loss of mental function by 10 percent per year.
And those who ate fish twice a week slowed their loss of mental function by 13 percent per year.
Why would that be?
Omega-3s from fish are proven to boost brain capacities linked to mental performance.
This is especially true of omega-3 DHA, which plays major structural and functional roles in our brain cells.
Omega-3 DHA also regulates the expression of dozens of "working” genes in the brain, and stimulates and enables connections among brain cells.
Unsurprisingly, DHA is also essential to brain development ... which is why children accumulate DHA rapidly in the womb and during their first year of life.
Do omega-3s deter, delay, or lessen dementia?
We know that omega three DHA is critical to brain health.
But is it clear that diets rich in seafood-source omega-3s can prevent or alleviate Alzheimer's disease or other forms of dementia?
The available epidemiological evidence suggests that omega-3-rich diets can delay or diminish the extent of age-related mental decline.
Unfortunately, we still lack enough high-quality clinical evidence to draw clear, unambiguous conclusions.
Sadly, it is near-impossible to fund large, costly, high-quality clinical trials of non-patentable natural substances like fish oil ... so firm proof may be a long time coming.
In the meantime, given what we already know, it makes good sense to get plenty of seafood source omega-3s, either from fish or from fish oil supplements.
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