Some animal products contain aluminum, copper and arsenic that have been linked to Alzheimer’s and neuropathy. Harmane, a neurotoxin found in chicken, pork, salmon, and cigarette smoke, is linked to a higher risk of essential tremor, which is associated with cognitive impairment. The incidence of Parkinson’s disease, another degenerative disease responsible for cognitive impairment, is linked to dairy consumption. Cadmium contamination impairs neurocognitive performance, while increasing the risk of certain hormonal cancers. A plant-based diet may inhibit cadmium and lead absorption. Glycotoxins (found mostly in chicken) and the neurotoxin, BMAA, (found mostly in fish) may increase risk of Alzheimer’s disease. Poor cardiovascular health may clog cerebral arteries, cutting off blood flow to the brain and leading to the development of Alzheimer’s disease.

Supplement intake has been associated with cognition in both positive and negative ways. Iron supplements seem to increase the risk of Alzheimer’s (an update here), whereas vitamin B12 is essential for brain health (see also here). Creatine can boost cognitive functioning in some, but may be unsafe in supplement form. Homeopathy, however, seems to have no effect at all (beyond placebo).

Eating healthfully is even more critical for pregnant women. Numerous studies have shown that industrial pollutants such as flame retardant chemicals and mercury found in fish (such as tuna) may impair a baby’s cognitive development, and is associated with reduced cerebellum size in newborns; methylmercury contamination in fish generally outweighs DHA benefits on brain development measured as children IQ. The use of algae-based DHA supplements may offer the benefits without the risks. To stay on the safe side, mothers-to-be would have to stop eating fish at least one year before pregnancy. Licorice has also been shown to be harmful at excessive doses to the developing child. Raising the child on a plant-based diet has been associated with increased intelligence, but potentially confounding variables prevent firm conclusions.

Many nutrients present in plant foods can have a positive effect on cognition. Green leafy vegetables and soy beans may help improve memory. Both coffee and tea (and the caffeine they contain) are linked to positive cognitive benefits, but should probably be consumed without milk because it can block phytonutrient absorption. Anthocyanidins from berries may slow brain aging and improve memory; lavender extracts may alleviate generalized anxiety disorder and help with performing mental tasks; and flaxseed may contribute to better cognition in older adults. A plant-based diet (low in saturated fat from animal sources) may effectively treat multiple sclerosis, including its cognitive symptoms. Lifestyle changes including plant-based diets could also help prevent Alzheimer’s disease. A Mediterranean diet, rich in fruits, vegetables and grains, was shown to prolong the life of Alzheimer’s patients. The rates of Alzheimer’s disease are very low in rural India, where the diet is largely plant-based; this could also be due to the spice turmeric, present in curry, which, unlike its isolated component curcumin, may both prevent and treat symptoms of Alzheimer’s disease. One plant-derived product that might not help with Alzheimer’s disease is coconut oil.

There may be a quick, non-invasive, cheap test involving smelling peanut butter which may help diagnose Alzheimer’s early on, which is good considering neurodegenerative brain changes may begin by middle age.

In addition to choosing the right foods, there are cognitive benefits to limiting calories altogether, and of course, getting plenty of exercise (see here, here). Even just a glass of water before school may help children perform cognitively better!

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