Certain chemicals in onions have an antioxidant effect that may boost the brain's ability to store memories and fight degenerative brain diseases. However, the healthiest diet is a balanced diet, which includes a variety of vegetables, fruits and other items from all food groups. Always check with your doctor before changing your dietary habits, especially if the change overtly favors one food over all others.

A 2005 study by Hokkaido Tokai University scientists concluded that di-n-propyl trisulfide, a sulfur compound found in onions, improves memory impairment. The group hypothesized that oxidative stress produces a primary oxidation product, called brain lipid hydroperoxide, which may lead to neurodegenerative disease. The results showed that the antioxidant onion extract, including the sulfur compound, improved learning and memory functions in mice.

Red onions contain anthocyanin and quercetin, and white and yellow onions contain substantial levels of quercetin. Anthocyanins are part of the bioflavonoid phytochemical group, and they are widely known for their antioxidant capabilites. Several studies indicate that anthocyanins help to improve neural and age-related deficits, cognitive performace and may help prevent neurodegenerative disorders. Quercetin also is a flavonoid antioxidant, and it combats particles -- called free radicals -- that damage cell membranes. Research suggests that quercetin may help prevent or improve a myriad of physical ailments including high cholesterol, hypertension and more.

Whereas some research demonstrates that eating onions will boost your memory, a greater body of research suggests that onions may more directly relate to the prevention of illnesses like certain cancers. The breadth of studies both supports and refutes the health benefits of the phytochemicals found in onions, and clearly more research needs to be done to learn the full effects of a high intake of onions. Consult your doctor before you include high quanitites of onions or any particular food item in your diet.

Try putting some variety in your diet with other foods that also may contain memory-boosting substances. For example, blueberries, red beets, red, purple and black grapes, and eggplant also contain anthocyanin, while apples and broccoli contain quercetin. Additionally, foods that contain folic acid, like spinach, also may protect you from memory loss. These foods are part of a healthy diet that also contains whole grains, lean protein, nuts and seeds, low-fat dairy products and healthy fats. Following a healthy diet will ensure that you get everything your mind and body needs.