Millions of younger Americans suffer from less obvious mental impairments, including mild memory loss and diminished alertness, as well as brain-related disorders, such as depression and chronic anxiety.

Neurologists now believe that most mental impairments are caused by lifelong exposure to toxic agents, including pollution and tobacco, and to naturally occurring molecules that damage brain tissue and impair circulation to the brain.

Research clearly shows that some foods can improve mental performance and help prevent long-term damage. Best choices…

Sardines. They have two to three times more omega-3 fatty acids than most other fatty fish. Our bodies use omega-3s for the efficient transmission of brain signals. People who don’t get enough omega-3s in their diets are more likely to experience learning disabilities, dementia and depression.

Bonus: Omega-3s reduce inflammation and inhibit blood clots, the underlying cause of most strokes.

Fatty fish also are high in choline, a substance used to manufacture one of the main neurotransmitters (acetylcholine) involved in memory.

Recommended: Three cans of sardines a week. Sardines are less likely to accumulate mercury or other toxins than larger fish.

Caution: Many people believe that flaxseed is an adequate substitute for fish. Although it contains alpha-linolenic acid (ALA), a type of omega-3, only about 10% of ALA is converted to docosahexaenoic acid (DHA) or eicosapentaenoic acid (EPA), the most beneficial forms of omega-3s and the ones that are plentiful in fish oil.

If you don’t like sardines, you can take fish oil supplements (1,000 mg twice a day).

Omega-3 eggs. They’re among the best foods for the brain because they contain folate along with omega-3s and choline. Folate is a B vitamin that’s strongly linked to mood and mental performance. A Finnish study of 2,682 men found that those with the lowest dietary intakes of folate were 67% more likely to experience depression than those with adequate amounts.

Recommended: Up to eight eggs a week. Only buy eggs that say “Omega-3″ on the label. It means that the chickens were given a fish meal diet. Eggs without this label contain little or no omega-3s.

Low-glycemic carbohydrates. The glycemic index ranks foods according to how quickly they elevate glucose in the blood. Foods with low glycemic ratings include legumes (beans, lentils) and whole-grain breads. They slow the release of sugars into the bloodstream and prevent sharp rises in insulin.

Why it matters: Elevated insulin is associated with dementia. For example, diabetics with elevated insulin in the blood have four times the rate of dementia as people without diabetes. Elevated insulin damages blood vessels as well as neurons. The damage is so pronounced that some researchers call Alzheimer’s disease “type 3 diabetes.”

Recommended: Always eat natural, minimally processed foods. They’re almost always low on the glycemic index. For example, eat apples instead of applesauce… whole-grain bread instead of white bread… or any of the legumes, such as chickpeas, lentils or soybeans.

Nuts. They’re among the few plant foods that contain appreciable amounts of omega-3 fatty acids. They also contain antioxidants, which reduce brain and arterial inflammation that can lead to cognitive decline.

Most of the fat in nuts is monounsaturated — it lowers harmful LDL cholesterol without depressing beneficial HDL cholesterol — important for preventing stroke.

Recommended: One to two handfuls daily. Walnuts and macadamia nuts are among the highest in omega-3s, but all nuts are beneficial. Avoid highly salted and roasted nuts (the roasting changes the composition of the oils). Lightly toasted is okay.

Cruciferous vegetables, such as broccoli, brussels sprouts, cauliflower and kale. They contain detoxifying compounds that help the liver eliminate toxins that can damage the hippocampus and other areas of the brain involved in cognition.

Recommended: One cup daily is optimal, but at least four cups a week. Cooked usually is easier to digest than raw.

B-12 foods. Meat, dairy products and seafood are our only source (apart from supplements) of vitamin B-12 in the diet. This nutrient is critical for brain health. A study published in American Journal of Clinical Nutrition found that older adults with low levels of vitamin B-12 were more likely to experience rapid cognitive declines. Older adults have the highest risk for B-12 deficiency because the age-related decline in stomach acid impairs its absorption.

Recommended: Two to three daily servings of organic lean meat, low-fat dairy (including yogurt) or seafood. Also important: I advise everyone to take a multi-nutrient supplement that includes all of the B vitamins.

Green tea. It’s a powerful antioxidant and anti-inflammatory that also stimulates the liver’s ability to break down toxins. New research indicates that green tea improves insulin sensitivity — important for preventing diabetes and neuro-damaging increases in insulin.

Recommended: One to two cups daily.

Berries, including blueberries, raspberries and strawberries. The darker the berry, the higher the concentration of antioxidant compounds. In studies at Tufts University, animals fed blueberries showed virtually no oxidative brain damage. They also performed better on cognitive tests than animals given a standard diet.

Recommended: One-half cup daily. Frozen berries contain roughly the same level of protective compounds as fresh berries.

The new findings come from a Dutch research group and were reported in the July 2009 issue of The American Journal of Clinical Nutrition. In this report healthy elderly subjects were assigned to either 1.8 grams daily of fish oil, 0.4 grams daily of fish oil or 0.4 grams daily of high oleic sunflower oil (control) for 26 weeks. At base line and the end of the intervention subjects blood samples were taken and immune cells (peripheral blood mononuclear cells) were analyzed for changes in 17,699 genes. The research group found that a high fish oil intake changed the expression of 1040 genes, whereas sunflower oil intake changed the expression of only 298 genes. Specifically fish oil resulted in “a decreased expression of genes involved in inflammatory- and atherogenic-related pathways, such as nuclear transcription factor kappaB signaling, eicosanoid synthesis, scavenger receptor activity, adipogenesis, and hypoxia signaling.” Leading the authors to conclude that intake of fish oil can alter the gene expression profiles of immune cells to a more antiinflammatory and antiatherogenic status.

Guy’s Comment: Nutrigenomic discovery (how nutrition effects the reproduction of DNA) is continuously highlighting the profound impact of small dietary molecules on cellular function and the development of disease. The finding that eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from fish oil can positively influence the expression of over a thousand genes in a single cell type, in this case human immune cells, speaks to the immense and often under appreciated role of nutrition in medicine.

This is not to mention the profound effects that fish oil has been shown to exert on the behavior of children and lengthening of attention their spans.

Click here for effective Fish Oil supplementation

Sources: Bouwens M et al. Fish-oil supplementation induces anti-inflammatory gene expression profiles in human blood mononuclear cells. Am J Clin Nutr. 2009 Jun 10.