Your brain needs glucose (sugar) for energy. But to build cells, to produce chemicals necessary for nerves to communicate, and to repair damage, you need the basic building blocks of cells, proteins.

The proteins you eat do not go directly into the brain because a filter, called the ‘blood-brain barrier,’ protects the brain. Even though the level of some substances might be quite high in your blood, this filter keeps them from getting into your brain.

Otherwise rapid fluctuations and surges of substances that might be helpful at low levels, but harmful at higher levels, would pummel your brain. The blood-brain barrier excludes from the brain many substances, including protein from the foods you eat and medications, such as antibiotics.

In contrast, other substances, such as glucose, pass freely into the brain. The more glucose in your blood, the more there is in your brain. Other substances do get into the brain but at slow, controlled rates.

Since proteins cannot pass directly into the brain, your brain makes its own, using the substances that do cross the blood-brain barrier, namely, amino acids. Amino acids are the basic structural units of proteins, which connect together like beads on a string. When you eat protein in, say, soybeans or steak, your intestinal tract and liver digest it, breaking the protein’s long strings of amino acids into individual amino acids. These amino acids then circulate in your blood. Like glucose, these lone amino acids can enter the brain, which then assembles them to make the specific proteins it needs. At this level it does not make any difference to your brain if the source of the protein is beef or soybeans.

Of course, the other parts of the food consumed, like fat, do make a difference in your overall health, so a good quality diet rich in protein but not excessive amounts of animal protein is recommended.

Fish has often been touted as ‘brain food’ due to its high protein content, and other very good minerals known to affect the brain, such as zinc.  It also has a good calories to protein ratio, and protein helps you feel full after eating (as does fat, but again, we want to limit it in the diet).

More studies need to be done on the role of fish in a brain-healthy diet, but one things is for sure, fish is generally a healthy food choice, though with increasing levels of mercury in the world’s oceans,  you should do your research on which types of fish are considered least risky.