Fish, fish oil, and certain fruits and vegetables have all been found to lower the risk of developing dementia.  Of course, meat and saturated fats are bad.  

Blueberries Help Mice: Blueberries high in flavonoid pigments which are strong antioxidants. Mouse study found spinach, strawberries, and blueberries all helped reduce loss of test performance, e.g. mazes, balancing, but that only blueberries showed improvements in every test of motor coordination. James Joseph, Human Nutrition Research Center on Aging, Tufts, J Neuroscience 9/15/99. Amount equal to 1 cup blueberries per day. Recommends variety of pigmented fruits and vegetables as best since different anti-oxidants work in different ways.

Beta-carotene, Flavonoids, and Vitamins E and C Not Affect Dementia Risk in Honolulu-Asia Study: In a prospective study of 2,459 Japanese-American men ages 45-68 years in 1965-1968, and followed through 1999, there developed 235 cases of dementia (102 cases of Alzheimer's disease, 38 cases of Alzheimer's disease with contributing cerebrovascular disease, and 44 cases of vascular dementia). Intakes of beta-carotene, flavonoids, and vitamins E and C were not associated with the risk of dementia or its subtypes. Midlife dietary intake of antioxidants and risk of late-life incident dementia: the Honolulu-Asia Aging Study. Laurin D, Masaki KH, et al. National Institute on Aging. Am J Epidemiol. 2004 May 15;159(10):959-67.

Blueberries, Spinach Help Rats: Rats fed a diet rich in spinach reversed a normal loss of learning that occurs with age, according to a study by researchers at the University of South Florida. The study was presented at the Society for Neuroscience's annual meeting in San Diego. Rats fed a normal diet that contained 2 percent freeze-dried spinach. Blueberries are also rich in antioxidants. A study by researchers at the University of Houston at Clear Lake and the Universidad Nacional Autonoma de Mexico found that blueberries may help fight age-related declines in rats' memories. Aging rats that were fed a blueberry-supplemented diet for four months tested as well as younger rats in their abilities to recognize objects after an hour. Aging rats fed a normal diet failed to recognize the objects. This complete deficit was fully alleviated by diet. 11/13/01

Curcumin (Curry) Helped: Curcumin has potent antioxidant and antiinflammatory properties and reduces beta-amyloid and plaque burden in experimental studies. In a population-based cohort (n = 1,010) of nondemented elderly Asian adults ages 60-93, Mini-Mental State Examination (MMSE) scores for those who consumed curry "occasionally" and "often or very often" were significantly better than for those who "never or rarely" consumed curry. Curry consumption and cognitive function in the elderly. Ng TP, et al. National University of Singapore. . Am J Epidem 2006 Nov 1;164(9):898-906.

Folate Foods Helps Prevent Alzheimer's: From the Baltimore Longitudinal Study of Aging, 579 over 59 without Alzheimer's disease were followed for nine years.  Foods rich in folate include oranges, bananas, leafy green vegetables, asparagus, broccoli, liver, and many types of beans and peas, as well as fortified bread. During follow-up, 57 developed Alzheimer's disease. Those with a higher dietary intake of folate had a 60% lower rate of the disease compared to the lowest quartile. Older adults whose total folate intake (diet and supplement) equaled or exceeded the 400 microgram RDA reduced their chances of developing Alzheimer's disease by 55 percent. No association was seen between intakes of vitamin C, carotenoids, or vitamin B-12. Vitamin E and B-6 had no effect when controlling for folate. Maria Corrada, et al. University of California, Irvine. WebMD 8/15/05

Folate No Help in Chicago Study: In a 3.9 year follow-up study of 1,041 Chicago adults over age 64 and initially free of Alzheimer's disease, 162 persons developed incident Alzheimer's disease during follow-up. In logistic regression models adjusted for age, sex, race, education, cognitive activities, APOE-epsilon4, and dietary intakes of vitamin E in food and total niacin, there was no association between risk of developing Alzheimer's disease and quintiles of folate intake or of vitamin B-12 intake. The adjusted odds ratio was 1.6 for persons in the highest quintile of total folate intake (median of 752.7 microg/d) compared with persons in the lowest quintile of intake (202.8 microg/d). Compared with persons in the first quintile of total vitamin B-12 intake (3.1 microg/d) the odds ratio was 0.6 for persons in the fifth quintile of intake (20.6 microg/d). Intake of vitamin B-6 was not associated with incident Alzheimer's disease after control for dietary intakes of vitamin E and total niacin. Dietary folate and vitamins B-12 and B-6 not associated with incident Alzheimer's disease. Morris MC, et al. Rush University , Chicago. . J Alzheimer's Dis 2006 Aug;9(4):435-43.

Pomegranate Juice Helped Mice: Richard Hartman et al of Loma Linda University found that feeding mice who were genetically prone to develop an Alzheimer's-like disease the equivalent of 1-2 cups per day of pomegranate juice from young adulthood reduced the build up of beta-amyloid plaques in their brains. The mice did much better in maze and other tests than mice given sugar-water supplements. Antioxidants were thought to be preventing the damage. Sci News 2/3/05. Neurobiol Dis 2006 Dec;24(3):506-15.

Soy Protein No Help for Post-Menopausal Bones, Lipids, or Mental Functioning: In a DB PC study of 202 postmenopausal women given 25.6 g of soy protein containing 99 mg of isoflavones (52 mg genistein, 41 mg daidzein, and 6 mg glycetein or total milk protein as a powder on a daily basis for 12 months, cognitive function, bone mineral density, or plasma lipids did not differ significantly between the groups after a year. Effect of soy protein containing isoflavones on cognitive function, bone mineral density, and plasma lipids in postmenopausal women: a randomized controlled trial. Kreijkamp-Kaspers S, Kok L, et al. University Medical Center Utrecht, The Netherlands. JAMA. 2004 Jul 7;292(1):65-74

Spinach, Spirulina Help, Apples Help Some, Cucumbers Not at All: Two studies published 7/15/02. J Neurosciences found rats 6 weeks on spinach at 2% of chow had reversal of aging effects. Aged rats fed either spirulina-or apple-enriched diets for two weeks demonstrated improved neuron function, a suppression of inflammatory substances in the brain, and a decrease in malondialdehyde (MDA), a marker for oxidative damage. In fact, spirulina reversed the impairment in adrenergic neural function normally associated with aging. U S. Fla.

Corn: Cooking Corn Longer Increases Anti-Ox Values: Sweet corn and cooked the kernels in batches at 115 degrees Celsius (239 degrees Fahrenheit) for 10, 25 and 50 minutes. Liu says that the cooking increased the antioxidants in sweet corn by 22, 44 and 53 percent, respectively. Ferulic acid, a phenolic normally bound to cell in corn, released by cooking longer. Liu, Cornell, Aug. 14, 02, Journal of Agriculture and Food Chemistry

Omega-3

So far, 10 of the 12 studies on fish consumption that I have found have documented decreases in dementia.  None have found harmful effects.  Fish, fish oil, and other sources of omega-3 fatty acids are also good for the heart and other parts of the body.

47% Decrease in Dementia with High DHA and Fish Intake: Docosahexaenoic acid (DHA) is an abundant fatty acid in the brain. In the diet, DHA is found mostly in fatty fish. The content of DHA has been shown to be decreased in the brain and plasma of patients with dementia. In a prospective 9.1-year follow-up study of 899 adults free of dementia at baseline, median age 76, there were 99 new cases of dementia (including 71 of Alzheimer disease) occurred during follow-up. After adjustment for age, sex, apolipoprotein E epsilon4 allele, plasma homocysteine concentration, and education level, subjects in the upper quartile of baseline plasma PC DHA levels, compared with subjects in the lower 3 quartiles, had a relative risk of 0.53 of developing all-cause dementia (P=.04) and 0.61 of developing Alzheimer disease (P=.14). Subjects in the upper quartile of plasma PC DHA levels had a mean DHA intake of 0.18 g/d and a mean fish intake of 3.0 servings per week (P<.001) in a subset of 488 participants. Plasma phosphatidylcholine docosahexaenoic acid content and risk of dementia and Alzheimer disease: the Framingham Heart Study. Schaefer EJ, et al. Tuffs University. . 

Omego-3 and Arachidonic Claimed to Help Cognitive Impairment: In a study of 21 mild cognitive dysfunctional adults, 12 were given arachidonic and docosahexaenoic acids 240 mg/day and 9 were given olive oil placebo for 90 days. The treatment group showed a significant improvement of the immediate memory and attention score. Dietary supplementation of arachidonic and docosahexaenoic acids improves cognitive dysfunction. Kotani S, et al. Ishikawa, Japan. Neurosci Res 2006 Oct;56(2):159-64. Ed: This study is too small to tell anything.

Trend Favoring Polyunsaturated Fatty Acids: In a 2.6 year follow-up study of adults ages 65-84, 18 new events of mild cognitive impairment were diagnosed. High polyunsaturated fatty acids (PUFA) intake tended to be a protective factor (age, sex, education, Charlson comorbidity index, and total energy intake controlled), (HR: 0.62, =0.12). The Italian Longitudinal Study on Aging. Solfrizzi V, et al. University of Bari, Italy. . Exp Gerontol 2006 Jun;41(6):619-27.

Weekly Fish Meal Lowers Alzheimer's and Stroke Risk: In a study of 3718 people over age 64 and followed for 6 years with repeated testing, thos who ate one fish meal a week had a 10% slower decline in thinking than a control group; those eating two fish meals a week showed a 13% slower decline. Archive Neurol 10/10/05 epub.

Fatty Fish Linked to Better Brain Function in Middle Age: In a cross-sectional Dutch study of 1613 adults ages 45-70, researchers found those eating fatty fish and those getting more omega-3 seafood fatty acid EPA and DHA had significantly better cognitive scores and mental speed even after correcting for common risk factors (OR = 0.81 and OR = 0.72).  Dietary intake of fatty acids and fish in relation to cognitive performance at middle age. S. Kalmijn, M. P.J. van Boxtel, M. Ocké, W. M.M. Verschuren, D. Kromhout, L. J. Launer. Neurol 1/24/05

Moderate Drinking and Seafood Prevented Dementia: In the PAQUID study of 2,950 initially non-demented adults over 65, at follow-up moderate drinkers had a decreased relative risk of developing a dementia in the subsequent 8 years (RR=0.56) compared to non-drinkers. In a sub-sample of 1416 subjects, those who ate fish or seafood at least once a week had a significant reduced risk of incident dementia adjusted for age and sex (RR=0.66). Nutritional Factors and Risk of Incident Dementia in the PAQUID Longitudinal Cohort. Larrieu S, Letenneur L, Helmer C, Dartigues JF, Barberger-Gateau P. Universite Victor Segalen Bordeaux. J Nutr Health Aging. 2004;8(3):150-4

Omega-3 Levels Not Associated with Less Dementia: An analysis of the Canadian Study on Health and Aging cross-sectional data on those over 65 found no significant difference in omega-3 polyunsaturated fatty acid concentrations between controls and cases of cognitive impairment and dementia. In the prospective analysis, a higher eicosapentaenoic acid (p < 0.01) concentration was found in cognitively impaired cases compared to controls while higher docosahexaenoic acid (p < 0.07), omega-3 (p < 0.04) and total polyunsaturated fatty acid (p < 0.03) concentrations were found in dementia cases. Omega-3 fatty acids and risk of cognitive impairment and dementia. Laurin D, Verreault R, Lindsay J, Dewailly E, Holub BJ. J Alzheimers Dis. 2003 Aug;5(4):315-22

Fish Prevents Dementia: 5,386 subjects. High fat, high sat fat, and high cholesterol was associated with an increased risk of dementia. Increased fish strongly linked with decreased Alzheimer's with a RR of 0.3. Kalmijn, Erasmus U, Netherlands, Ann Neurol ’97, 4:776-82;

Fish Decreases Risk of Dementia: 1,674 French age 68 and older followed for 7 years found eating fish at least once a week had a risk ratio of RR 0.69 after adjust for age and sex and education for a 30% decrease in dementia. Meat harmful only to a non-significant extent.  The highly educated also had less dementia. BMJ 2002;325:932-933 Fish, meat, and risk of dementia: cohort study. Pascale Barberger-Gateau. 

Fish Prevents AD: A Rush-Presbyterian study of 815 Chicagoans age 65 and up found that those eating fish at least weekly had 60% lower risk of AD vs. those rarely eating it. Total omega-3 and DHA associated with benefit but not EPA. Results were adjusted for age, heart condition, and other fats. Consumption of fish and n-3 fatty acids and risk of incident Alzheimer disease. Morris MC, Evans DA, Bienias JL, Tangney CC, Bennett DA, Wilson RS, Aggarwal N, Schneider J. Arch Neurol. 2003 Jul;60(7):940-6

Fish Protective in Zutphen Study: A Dutch prospective study of 476 adults found a high linoleic acid intake was associated with cognitive impairment (OR=1.8). A high fish consumption tended to be inversely associated with cognitive impairment and decline (RR=0.5). J Nutr Health Aging. 2000;4(4):202-7

Fish Good, Beans Maybe Not: A diet rich in fish may ameliorate AD, possibly by lowering homocysteine, but more vegetarian diets do not. In fact, eating beans correlated with worse cognition in AD patients. Further studies should test if restricting the intake of beans slows the progression of AD. Germany. Study of vegetarian and meat-eating AD patients. J Gerontol A Biol Sci Med Sci 2002 Dec;57(12):M797-802

Omega-3 Helps Improve Alzheimer's: Supplement to a 4:1 balance omega-6:omega-3 in DB PC study of 100 AD patients with 60 on fatty acid supplement found incr qual life, mood, coop, appetite, sleep, short memory after 28 days. 49 of 60 showed some overall improvement. Previous rat studies by same researches with same supplement found incr in learning, thermoregulation, neurotoxin recovery, and seizure protection. Yehuda, Bar-Ilan Univ, Israel, Int J Neurosci 11/96 87:141-9

Omega-3: EFA and Anti-oxidants Help: 36 patients with Alzheimer's disease in a DB PC study. Those  who were treated with essential fatty acids (fish oil) and anti-oxidants showed greater improvement vs. placebo in 20 wk study. Corrigan, Scotland, Ann NY Acad Sci ’91;640:250

Omega-3, Trans Fats, Sat Fat in the Rotterdam Study: At 6 year follow-up of 5,395 elderly with 167 cases dementia, high intake of total, saturated, and trans fat and cholesterol and low intake of MUFA, PUFA, n-6 PUFA, and n-3 PUFA were not associated with increased risk of dementia or its subtypes. Diet and risk of dementia: Does fat matter?: The Rotterdam Study. Engelhart MJ, Geerlings MI, Ruitenberg A, Van Swieten JC, Hofman A, Witteman JC, Breteler MM. Neurology 2002 Dec 24;59(12):1915-21; However, earlier data from the Rotterdam Study at 2.1 years showed that high intakes of the following nutrients were associated with an increased risk of dementia after adjustment for confounders: total fat (RR=2.4), saturated fat (RR=1.9), and cholesterol (RR=1.7). A high fish consumption, an important source of n-3 PUFAs, reduced the risk of dementia (RR=0.4)in a 2000 report. Ann Neurol. 1997 Nov;42(5):776-82

EFA and DHA Low in AD: Serum cholesteryl ester-eicosapentaenoic acid and DHA levels were significantly lower (P<0.05 and P<0.001 respectively) in all MMSE score quartiles of patients with Alzheimer's disease compared with control values. Serum cholesteryl ester-DHA levels were progressively reduced with severity of clinical dementia. DHA levels did not differ in patients with Alzheimer's disease across age quartiles: all were consistently lower than in control subjects. Step-wise multiple regression analysis showed that cholesteryl ester-DHA and total saturated fatty acid levels were the important determinants of MMSE score and CDR. Dublin. Low serum cholesteryl ester-docosahexaenoic acid levels in Alzheimer's disease: a case-control study. Tully AM, Roche HM, Doyle R, Fallon C, Bruce I, Lawlor B, Coakley D, Gibney MJ. Br J Nutr 2003 Apr;89(4):483-90

Animal Fat and Cholesterol are Bad; Fish Good: Prospective Zutphen Elderly Study (n=476) and the Rotterdam Study (n=5,386). Rotterdam Study showed that high intakes associated with an increased risk of dementia after adjustments: total fat (RR=2.4 (95%CI: 1.1-5.2)), saturated fat (RR=1.9 (95%CI: 0.9-4.0)), and cholesterol (RR=1.7). A high fish consumption, an important source of n-3 PUFAs, reduced the risk of dementia (RR=0.4). In the Zutphen Elderly Study a high linoleic acid intake was associated with cognitive impairment (OR=1.8). A high fish consumption tended to be inversely associated with cognitive impairment and decline (RR=0.5). J Nutr Health Aging 2000;4(4):202-207

Low DHA Risk factor Alzheimer’s: Ernst Schaefer, Tufts Univ