May 3, 2023
Getting plenty of fiber is recommended for digestive health. But a high-fiber diet may also be good for your brain. Two new studies found that the more fiber people tended to eat, the lower their risk of developing Alzheimer’s disease and other forms of dementia in old age.
One study, published in Nutritional Neuroscience, looked at 3,739 Japanese men and women who ranged in age from 40 to 64 at the start. They filled out detailed surveys about what they ate, including how much fiber they typically consumed.
Researchers tracked their health over 20 years. During that time, 670 of them developed Alzheimer’s disease or another form of dementia.
The researchers found that the more fiber someone tended to eat, the lower their risk of disabling dementia. The group that ate the most fiber — 18 to 65 grams of fiber a day, on average — had a 26 percent lower risk of dementia than the group that ate the least — 2 to 10 grams of fiber a day. Soluble fiber, found in foods like oat bran, beans, nuts, and some fruits and vegetables, appeared to offer more protection than the insoluble fiber found in whole grains. But all forms of fiber seemed to provide protective benefits.
The second study, in the journal Age and Ageing, looked at 848 men and woman age 65 and older in two areas of Tuscany, Italy. All had undergone genetic tests to see whether they carried the APOE-E4 gene, a risk factor for Alzheimer’s disease. Inheriting APOE-E4 from a parent is one reason that Alzheimer’s disease tends to run in some families, though not everyone who has the gene variant will develop dementia. Other forms of the APOE gene lower the risk of developing Alzheimer’s.
Over the next 15 years, researchers tracked their typical eating habits, including how much fiber they got. They also underwent regular tests of memory and thinking skills.
The researchers found in those who carried the APOE-E4 gene variant, the more fiber they tended to eat, the better their cognitive skills tended to be in old age. A high-fiber diet did not seem to have a protective effect on cognitive skills for those who carried other forms of APOE.
Fruits and vegetables are high in fiber, and other research has shown that a diet high in these heart-healthy foods are good for brain health. A high-fiber diet can also reduce the risk of developing diabetes and heart disease and help to keep weight and blood pressure in check, which have likewise been shown to increase the risk of developing Alzheimer’s disease. Fiber also feeds the billions of “healthy” bacteria in our gut, which in turn improves the health of our digestive and immune systems and lowers body-wide inflammation.
But most of us don’t get enough fiber in our diets. The American Heart Association and other medical groups recommended we get at least 25 to 30 grams of dietary fiber a day, but most Americans consume about half that amount.
Whole fruits, vegetables, beans, legumes, nuts, seeds and whole grains are all high in fiber. Choose brown rice over white ice, and whole-grain breads or pastas over white breads or regular pasta.
Top sources of fiber include lentils (18 grams of fiber in a cup of cooked lentils); black beans or pinto beans (15 grams per cup); artichoke hearts (14 grams per cup); chickpeas (12 grams per cup); raspberries (8 grams per cup); blackberries (7.5 grams per cup); barley (6 grams per cup); pears (6 grams per medium pear); almonds (6 grams per 23 almonds); oats (5 grams per cup cooked); broccoli (5 grams per cup); avocadoes (5 grams per half avocado); apples (4.5 grams per medium apple); and Brussels sprouts (4 gram per cup).
Diets high in fiber include the Mediterranean diet, which has also been linked to a lower risk for Alzheimer’s disease.
By ALZinfo.org, The Alzheimer’s Information Site. Reviewed by Eric Schmidt, Ph.D., Fisher Center for Alzheimer’s Research Foundation at The Rockefeller University.
Sources: Kazumasa Yamagishi, Koutatsu Maruyama, Ai Ikeda, et al: “Dietary fiber intake and risk of incident disabling dementia: the Circulatory Risk in Communities Study.” Nutritional Neuroscience, February 2023
Andrea Union-Caballero, Tomas Merono, Cristina Andres-Lacueva, et al: “Apolipoprotein E gene variants shape the association between dietary fibre intake and cognitive decline risk in community-dwelling older adults.” Age and Ageing, January 2023