Next to water, protein makes up most of the weight of our bodies. Muscles, organs, hair, nails and ligaments are all composed of protein, so it's obvious why protein is an important part of the diet.
But it gets more complex with the brain. The brain and its long spidery neurons are essentially made of fat, but they communicate with each other via proteins that we eat. The hormones and enzymes that cause chemical changes and control all body processes are made of proteins.
Have you ever noticed that a high carbohydrate lunch can make you feel sluggish? Or that eating protein in the middle of the day keeps you more alert through the afternoon? Brain cells communicate with one another via chemical messengers called neurotransmitters, which are usually made of amino acids, the building blocks of protein.
What you eat affects which nerve chemicals will be dominant in your brain, which affects how you feel. Carbohydrates can make you feel tired because they increase the brain's level of the amino acid tryptophan, which in turn spurs the brain to make the calming neurotransmitter serotonin. Serotonin is important for normal sleep patterns, learning, blood pressure and appetite, among many other functions.
Eating protein raises the levels of another amino acid called tyrosine, which prompts the brain to manufacture norepinephrine and dopamine, other kinds of chemical messengers in the brain. Not as well known as serotonin, norepinephrine and dopamine can keep you energized because they promote alertness and activity.
This isn't to say that to stay alert, you ought to eat mostly protein. A healthy brain produces hundreds of neurotransmitters needed for regular maintenance of the brain and needs proteins to do so. But the brain also needs carbohydrates for fuel and other nutrients for repair and maintenance of brain cells.
You don't need to load up on protein. Most Americans eat far more protein than they need and as a consequence end up consuming too much fat and cholesterol as well. The USDA recommends only two to three small servings of protein a day, or about 12 percent of total calories—and that's more than what most of the world consumes. Poultry, seafood and lean meat are the richest sources, as are dairy products, legumes, nuts and seeds. Grains and vegetables have protein too, albeit in lesser amounts but without the fat.
However, watching your diet isn't always enough. Some neurotransmitters, like dopamine, essential to feelings of pleasure and reward, are also depleted by stress and a lack of sleep. Alcohol, caffeine and sugar all appear to lessen the effects of some neurotransmitters in the brain. In addition to a healthy, varied diet, the brain also needs healthy everyday living habits.