5: The Benefits of Protein, Brain Food
THE BUILDING BLOCKS OF PROTEIN
Proteins come third in the lineup of top brain-healthy nutrients. Proteins are complex molecules that do most of the work in our cells and are required for the structure, function, and regulation of the brain’s networks. They are made up of smaller units called amino acids that are attached to one another in smaller or longer chains. The number and sequence of amino acids used to build a protein determine that protein’s unique shape and properties.
Amino acids are essential for just about every function that takes place within the body and brain. This includes maintaining healthy tissues, assembling hormones, and powering all sorts of chemical reactions, for starters. But even more important for the brain, amino acids have long resided in the minds of all creatures on Earth. In fact, many of these nutrients act as neurotransmitters, the chemical messengers that our brains use for signaling, communicating, and processing information. Neurotransmitters are responsible for how you think, talk, dream, and remember. They spur the impulses that wake you up, make you sleepy, keep you focused, and even cause you to change your mind.
Adequate amounts of amino acids, and therefore of the proteins that supply them, must be provided to the brain on a daily basis for all these cognitive functions to be carried out. However, the human brain has figured out how to manufacture some amino acids on its own, while importing the rest from the diet. So even though all amino acids are needed for overall health, the brain alone doesn’t require all of them.
Just like fats, amino acids can be essential or non-essential. Amino acids that can be produced directly by the brain are labeled as non-essential, while those that cannot be made internally and must be supplied by the diet are labeled as essential.
When you eat a meal that contains protein, essential amino acids like tryptophan (the molecule found in turkey that facilitates sleep) enter the brain very rapidly thanks to special passageways embedded in the blood-brain barrier. Instead, non-essential amino acids (such as the asparagine found in asparagus) are markedly restricted from entry into the brain.
In general, proteins are not hard to come by. Several foods contain complete, well-balanced proteins, which means that they provide all essential amino acids. These foods are generally of animal origin and include fish, milk, eggs, chicken, pork, and beef. Many plant-based foods such as legumes, grains, soybeans, and some nuts and seeds also contain good amounts of protein. In the next pages we’ll see which proteins are specifically needed for a healthy, active brain and which foods provide the best amino acid content to support mental clarity and sharpness throughout a lifetime.
STARS, TREES, SPIDERS, KITES, AND CARROTS . . . OH MY!
The most immediate way to appreciate just how intrinsically dependent our cognitive abilities are on the right combinations of brain-essential amino acids is to look at those very mechanisms that enable our thoughts to take shape in the first place. We will now look at how brain cells communicate with one another, transmitting information throughout the brain to form ideas, memories, and feelings—and how much, if not most, of this process is literally based on protein.
If you were to gaze into the brain through a microscope, you would witness a peculiar sight. The human brain is packed with an incredible array of brain cells, each one a different shape and size.
Some might look like stars and others more like trees, each one sporting its own signature branch structure. Another grouping might look more like spiders, while others appear more like kites trailing their long tails. Some even look like carrots, with their leafy tops. These stars, trees, spiders, kites, and carrots are all working diligently to carry messages back and forth, keeping the communication going among all the various brain regions before further branching out to share the information with the rest of your body.
The orchestra of our central nervous system, for which the brain is the conductor, is composed of over 80 billion brain cells called neurons. Neurons are unique among all the cells that make up our bodies because of their ability to send signals to other cells no matter how far the distance. It’s precisely these varying shapes and sizes that enable them to do so.
Throughout this amazing electrical relay, our neurons do not actually touch. Their bodies, or axons, end in several synapses, which are the tiny gaps that separate one neuron from the next and act as connection points. Every neuron has between 1,000 and 10,000 synapses, totaling an astounding 100 trillion connections overall.
Each electrical impulse traverses many synapses as it makes its way through the nervous system. This “neurotransmission” is carried out by neurotransmitters, the chemical messangers of the brain. Neurotransmitters are in charge of dispatching information from cell to cell. The continued, incessant influx of neurotransmitters is precisely what gives birth to our thoughts, memories, and words—and even gives us a good night’s sleep—setting the stage for healthy mental functioning. The human brain relies on the well-orchestrated action of over one hundred neurotransmitters, each with its own specialty and particular chemical makeup. Some of these neurotransmitters have a profound effect on our cognitive performance and mental capacities. One, called serotonin, influences your emotional stability and sleep patterns, but also memory and appetite. Another, called dopamine, is responsible for reward-motivated behavior, movement control, and cravings. Additionally, there’s glutamate, a neurotransmitter responsible for provoking you to spring into action, and its alter ego, gamma-aminobutyric acid (GABA), that inhibits you from acting at all. We can all imagine just how deeply these molecules affect our brainpower and mental abilities.
As it turns out, many cognitive issues arise as a consequence of neurotransmitter abnormalities. For example, a marked reduction of the neurotransmitter serotonin (the one essential for mood, memory, and appetite) is a typical finding in patients with depression, which in turn can affect memory and attention.
What could be causing this depletion of our neurotransmitters?
You guessed it—a poor diet.
Our neurotransmitters are created from one source: our food.
A closer look at the neurotransmission process reveals a surprising fact—neurotransmitters are not sitting around waiting to shuttle their next signal. They are actually produced each and every time there is a need to carry one of the brain’s various messages. They report for duty when a message presents itself and disappear again once their mission is complete. This incredibly sophisticated and yet delicate process is intrinsically dependent on several nutrients extracted from the foods we eat day after day. Consequently, the production of neurotransmitters inside the brain responds quite rapidly to changes in our diet—especially our protein intake.
SLEEP, DAYDREAM, AND REMEMBER WITH SEROTONIN
Serotonin has been mainly associated with our moods, as this neurotransmitter signals our brains when we are feeling relaxed and happy. When the brain produces low levels of serotonin, happy signals become much less frequent and short-lived, eventually producing diseases such as depression and anxiety. Serotonin is also largely acknowledged for its role in sleep and appetite regulation. Less well-known is that its depletion can also be responsible for some aspects of the memory impairments associated with advancing age and dementia.
Food is the essential impetus for serotonin production. In fact, the production of serotonin in the brain is based on the presence of the amino acid tryptophan, and is critically dependent on how much tryptophan is available to the brain. Tryptophan is an essential amino acid, meaning it cannot be produced in the body at all. Consequently, the only way we can make it available to our brains is through the foods we eat on a daily basis.
What foods provide us with tryptophan? And how can we get enough of it?
According to current dietary guidelines, the average adult, man or woman, needs 5 mg of tryptophan per kilogram of body weight daily. For example, the recommended dose for a 175-pound (79 kg) adult is 395 mg of tryptophan per day.
This brain-essential nutrient is not too difficult to come by. Several foods contain tryptophan, especially those rich in animal- or plant-based protein. But there’s a catch: tryptophan generally takes a backseat to other amino acids in terms of how often and how easily it is absorbed by the brain. Additionally, less than 10 percent of all the tryptophan that we import from our diet is used to make serotonin. Consequently, it’s even more important that we consume enough tryptophan-rich foods every day to reach a level that makes a difference in our brains.
Table 3 provides examples of common foods that are good sources of tryptophan. It’s interesting to note that although popular lore leads us to believe that tryptophan is responsible for the drowsiness we feel after a turkey dinner, turkey ranks quite low on the list of tryptophan-rich foods. So low that it didn’t even make it into Table 3.
Chia seeds instead rank at the top. Chia is one of Nature’s powerhouse plant-based foods. These tiny brown seeds have long been known for their high nutritional value and ability to provide sustainable energy. Chia is the ancient Mayan word for “strength.” In fact, ancient Aztec and Mayan warriors literally survived on rations of chia at times, as did long-distance runners and messengers. Two tablespoons of chia seeds contain over 200 mg of the tryptophan your brain needs to make serotonin, as well as a good amount of omega-3 PUFAs, minerals, and fiber.
Additionally, plant-based foods like raw cacao (chocolate!), wheat, oats, spirulina, and sesame and pumpkin seeds figure prominently among the richest natural sources of tryptophan on the planet. Animal foods like milk, yogurt, chicken, and fish like tuna and salmon are also a good start. In particular, yogurt is an excellent protein source with many health benefits, especially for the digestive system. However, I am not talking about the sugary, creamy, fruity, yogurt-like substances you find in bright packages on supermarket shelves. Those products are full of artificial sweeteners and colorants, not to mention preservatives, and will do nothing to help your brain stay healthy over time. When I say yogurt, I mean organic, plain, tart yogurt—preferably full-fat and from goat’s milk for an extra protein kick. If you don’t like tart flavors, I recommend you sweeten the yogurt yourself with raw honey, maple syrup, or fresh fruit.
|Food item||Unit (imperial)||Unit (metric)||Tryptophan (mg)||Sum of CAAs (mg)||Tryptophan/ CAA ratio|
|Chia seeds||1 ounce||28 g||202||1,270||0.159|
|Milk, whole||1 quart||946 mL||732||8,989||0.081|
|Sesame seeds||1 ounce||28 g||189||2,330||0.081|
|Yogurt, whole, plain||1 cup||245 g||49||3,822||0.078|
|Pumpkin seeds||1 ounce||28 g||121||1,615||0.075|
|Prunes (dried plums)||1||26 g||2||27||0.074|
|Seaweed, Spirulina||1 ounce||28 g||260||3,768||0.069|
|Raw cacao||1 ounce||28 g||18||294||0.061|
|Wheat bread||1 slice||50 g||19||317||0.060|
|Edamame||1 cup||118 g||236||2,354||0.057|
Table 3. Top ten tryptophan-rich foods, ranked by the ratio of tryptophan to competing amino acids (CAAs). This ratio provides the best indication of tryptophan availability for transport across the blood-brain barrier for use in serotonin synthesis.
In general, tryptophan is found in many common foods, so deficiencies are unlikely. However, too little protein in the diet can cause a deficit. If you are vegan or eat very little animal protein, your tryptophan levels might be low. In that case, make sure you are eating enough of the richest vegetarian sources. Additionally, tryptophan (in the form of 5-Hydroxytryptophan, or 5-HTP) can be taken as dietary supplements.
Here’s another trick. Research has shown that eating carbohydrates with or immediately after tryptophan-rich foods helps increase its absorption, thereby increasing serotonin production. This observation is at the heart of many nutritionists’ recommendations to eat some carbs for dinner to promote tryptophan absorption and facilitate sleep. When I was little, my mamma would make me a cup of warm milk with honey before bed to help me fall asleep. Little did she know that this simple practice helps tryptophan get through to the brain, boosting serotonin production and, therefore, sleep.
Finally, sometimes the problem is not tryptophan availability as much as a vitamin deficiency. Although tryptophan is indispensable for serotonin production, vitamin B6 is also needed to convert tryptophan into serotonin. As we’ll see in the next chapters, this vitamin truly is a brain must, as it is crucial not only for serotonin production but also for several other neurotransmitters.
DOPAMINE: MIND YOUR STEP
Although serotonin gets a lot of mainstream attention and most of the hype, dopamine has been gaining increasing popularity due to its role in cognitive function. Dopamine impacts our reward, motivation, and attention functions, as well as problem solving and motor control, not to mention allowing us to feel pleasure in the first place.
Dopamine abnormalities are involved in several medical conditions including Parkinson’s disease, attention deficit hyperactivity disorder (ADHD), schizophrenia, and drug addiction.
This neurotransmitter is manufactured in the brain by breaking down the amino acid tyrosine. Tyrosine is a non-essential amino acid, which means our bodies are capable of producing this nutrient on their own. But there’s a catch. Tyrosine needs to be produced from another amino acid called phenylalanine, which happens to be an essential amino acid, meaning it must be obtained from our diet instead. What this all boils down to is that without eating foods containing phenylalanine, we might as well kiss good-bye our pleasurable strolls in the park or playing our favorite games—let alone enjoying the thrill of winning them.
In order to be sure you’re getting enough of these nutrients, keep an eye on the recommended dose of phenylalanine and tyrosine. We all need 33 mg per kilogram of body weight per day. For example, the recommended dose for a 175-pound (79 kg) adult, man or woman, is 2.6 grams per day.
As shown in Table 4, phenylalanine is found in many high-protein animal products such as chicken, beef, eggs, and fish (particularly fatty fish like salmon, striped bass, and halibut), as well as dairy products such as milk and yogurt. Plant-based foods are also excellent sources, particularly legumes like soybeans and peanuts, nuts like almonds, and once again, chia, pumpkin, and sesame seeds. Oh, and don’t forget spinach.
Deficiencies of both amino acids are rare, but any medical condition or dietary regimen that reduces intake of these amino acids would consequently affect dopamine production in the brain.
|Animal sources||Phenylalanine (mg/100 g food)||Plant sources||Phenylalanine (mg/100 g food)|
|Organ meat||1200||Sesame seeds||959|
|Pork, leg||1030||Pumpkin seeds||924|
Table 4. Top ten food sources of phenylalanine, ranked by phenylalanine density, which is a convenient way to compare different foods and the relative amounts of phenylalanine they make available to our brains.
Supplements for these amino acids are also available. In this case, I recommend supplementing with the natural form L-phenylalanine, as opposed to D- and DL-phenylalanine, which are synthetic forms. Always ask your health-care provider for advice before taking any supplements.
GLUTAMATE: READY, SET, GO . . . OR WAIT, HIT THE BRAKES!
I once read an interesting analogy about how the brain handles decision making. Picture this: someone walks into the room holding a steaming slice of hot pizza, and you think, “Wow, I want that pizza and I want it NOW!” The neurons responsible for initiating your acting on that thought are about to send impulses skyrocketing across your brain to achieve your aim, when suddenly another thought comes to mind. “Maybe I shouldn’t eat pizza because, truth be told, I am trying to lose weight.” A different group of neurons immediately sends a counter impulse to put everything on hold. But then you smell that pizza again and decide that you’ll eat a little bit of it anyway. Just as the Team Pizza neurons start firing in all directions ready to celebrate their win, you discover that you don’t have any cash on you. The Team Don’t Do It neurons respond by putting an end to the discussion once and for all. You sigh and go about your business, if a little disappointed at the outcome.
The point is that your brain can both initiate an action and constrain the same action, all at an incredible speed. This is possible due to the fact that we possess different neurotransmitters to achieve differing goals. There are excitatory neurotransmitters, which push neurons to transmit signals, and inhibitory neurotransmitters, which make signal transmission less likely. Consider it the yin and yang of neurotransmission—or a devil and an angel on each of your shoulders.
Glutamate is the main excitatory neurotransmitter of our entire nervous system from head to toe. It’s the one that makes you reach for your wallet to buy the pizza. To get a better sense of how important this little molecule is, consider that more than 90 percent of all your brain synapses are primed to release glutamate. That makes for a lot of glutamate action going on.
At the same time, glutamate is also used by the brain to produce its alter-ego, gamma-Aminobutyric acid (GABA), the major inhibitory neurotransmitter of our nervous system. So not only does glutamate prompt you to get that slice of pizza—it can also stop you from having that slice in the first place.
But it doesn’t end here. As it turns out, glutamate features prominently in yet another crucial area of brain health. It also assists in learning and memory.
Here’s the story. The connections between two or more neurons are strengthened or weakened depending on how often those neurons are activated in tandem. According to the theory of Hebb (one of the most famous theories in the field of neuroscience), “neurons that fire together, wire together,” while those that fire out of sync . . . lose their link. It is widely believed that this process, called long-term potentiation (LTP), is based on glutamate, or a slightly different version of glutamate that goes by the rather impressive name of N-methyl-D-aspartate, or NMDA for short. NMDA possesses its own specific set of receptors in the memory centers of the brain. These receptors act as gates, which are generally kept locked. Glutamate (in the form of NMDA) is the key to opening these locks. When the neurotransmitter arrives, the gates open, allowing information to flow into the neuron. Over time, the more frequently this happens, the longer the gates will stay open. The feedback loop that ensues forms the basis of synaptic plasticity, which is the biological equivalent of memory formation.
But let’s put all this information into a brain-food context. Our ability to initiate an action, to refrain from doing something, and to form long-term memories are all dependent on the amino acid glutamate.
Glutamate (or glutamic acid) is a non-essential amino acid, which means that the brain is capable of producing it on its own. However, once again, there is a catch. The brain needs the sugar glucose to make glutamate. Glutamate is formed when the brain breaks down glucose in a process called metabolism, which is the very same process the brain uses to make energy. This makes most of our mental activities highly dependent on our dietary choices, and specifically on our intake of carbohydrates.