Evolutionary Reward Systems and Food Preferences (Nutrition For Health and Hypertrophy Part 18)

Continued from part 17.

In the previous part of this series, we ended up with an unanswered question. To understand the answer to that question, we need to understand what makes you want to eat anything in the first place.

You Evolved to Live And Breed

As covered previously in this series, life is a fight against entropy.

Because we aren’t immortal and don’t have perfect restoration (damage is not repaired perfectly and thus accumulates and eventually kills us), the way all species survive is to produce a copy of themselves before we die.

The “priority” genetics that pass down to the next generation are the ones that compel you to breed and keep you alive long enough to make sure that your children survive.

If a creature didn’t have the genes to make them want to breed, they would get kicked out of the gene pool until only creatures who really want to breed were left.

Again, this is all obvious stuff but how does it all actually work? What compels you to do anything?

Simple organisms like cells and bacteria are closer to machines than they are to living objects. They have no “thoughts”, their machinery just works in a certain way that gets them to multiply.

Some structures find food (behavior called positive chemotaxis) and avoid toxins (behavior called negative chemotaxis), some structures turn the food to usable energy (mitochondria), and some structures produce a copy of the cell (DNA/RNA, etc.).

For complex organisms like ourselves, our cells do not have the ability to go find and absorb the energy they need on an individual level.

As animals evolved to have multi-cellular bodies, we also evolved systems to find and consume substances that can be broken down to provide us with energy (food) and to make sure that all of our cells are working together in sync so we stay alive and breed.

In our species and many of our ancestors, this task is handled by our nervous system including our brain and our endocrine system.

Much of our “primitive whole body” communication is done by the endocrine system (hormones) because it evolved much before the nervous system. However it is quite inefficient because the endocrine system requires:

• Something to produce a hormone that communicates something (when some condition is met)
• A bloodstream or some other mechanism to transport the hormone to the cell that needs to receive the communication
• The cell that needs the communication to have receptors for that hormone (something covered in great detail in the piece on soy in this series)

An example that I’ve already covered before is the Thyroid hormone. The thyroid gland produces hormones that tell the cells in the body how fast they should do their processes.

Almost every cell in the body has receptors for the thyroid hormones and when they receive more thyroid hormones, they work faster.

As you can see, this means that the endocrine system is slow (a hormone has to be produced, then transported across the blood, and then fit into a receptor in the target cells).

Also every unique communication requires a new hormone to be produced by the body (which is more complex than it seems because then you also need machinery for all those new hormones, and all the cells need more receptors for every unique hormone).

This is why the evolution of more complex organisms was only possible along with the breakthrough evolution of the nervous system. Cells that can send messages up and down the chain using electrochemical signals instead of hormones.

Eventually a central hub of nervous system cells developed to manage even more complex organisms. This is what we call the brain. Humans are from the line of organisms that developed brains.

This is not a series on the nervous and the endocrine system so I’m going to keep references simple and only tell you what is absolutely necessary. I will not go in depth into what each hormone and signal does and how it does it.

There will also be some oversimplifications. For example, when I say the “brain does something”, often the act is a combination of the brain, the brain stem, the nervous system as a whole, the endocrine system, etc. all working together. However for our purposes, referring it all as the “brain” is enough.

I want this to be useful series on practical nutrition and not to turn it into a science book. All the background information is purely to help you understand the WHY behind the recommendations.

How Your Brain Gets You to Do Things

It should be fairly obvious that animals with a brain more attuned to getting energy effectively and efficiently and seek opportunities to breed are more likely to pass on their genes to the next generation. Over time, these preferences have been hardwired into us.

But how does the brain actually compel you to do anything?

It does so by using motivation and reward systems.

When you do something positive* your brain makes you feel good and learn to do that behavior more often. When you do something negative* your brain makes you feel bad and learn to avoid that behavior.

* The terms “positive” and “negative” are used roughly here and should be understood in the context of our ancient evolutionary environment.

Things like eating, making children, working with your tribe, avoiding risks, sexual promiscuity, etc. were generally positive behaviors and the brain rewards you for doing so.

Not getting any sex, eating things that make your stomach upset, doing things that lead to injury, eating non-nutritious items like dirt and poop, etc. were generally negative behaviors and the brain makes you suffer for doing them (For example, the feelings you know as “pain” and “loneliness” are created by the brain as a dis-incentive for doing something that is not good for your survival and/or reproduction).

Basic Mechanisms Behind Why You Do Anything

The exact mechanism of how this works is well out of the scope of this series, but here is a quick (and simplified) version because I might use the terms later in this series:

1) Basal Ganglia

This is the part of the brain that selects what your present instinct is from all the options available to it, before your conscious brain even realizes it.

Every part of the body is sending signals to do something e.g. your body is saying “eat”, “have sex”, “jump up and down”, “walk”, etc. and this part of the brain decides what is the strongest signal and tells the rest of the brain to do that (e.g. if you’re on the footpath, it’s probably best to walk than to have sex).

All of this happens before the idea of doing it even enters your conscious brain (i.e. your free will exists in the conscious part of your brain and you need to use your willpower to resist the decisions made by the basal ganglia)

2) Dopamine

This is a neurotransmitter that does a whole bunch of things but in our context, its importance is in its big role in learning and motivation.

When you do something good for your survival, the brain releases dopamine which makes you “learn” to do that activity again when the same stimulus is present (behavioral reinforcement).

Next time the same situation arises, the body will send a stronger signal to the Basal Ganglia making that choice be more likely to be picked.

E.g. When you smell cookies, you feel hungry to eat it. This is because many times in your life, you smelled cookies before you ate them. The brain liked it (getting calories is positive) and released dopamine, “teaching” your body that the smell of cookies means it should stimulate your appetite because eating them is going to lead to something good.

The more (and the faster) dopamine that is released, the stronger the learning effect (especially when the outcome you get is better than expected).

Addictive substances like drugs release so much dopamine that the basal ganglia starts picking the option to have that substance even at inappropriate times. A drug addict could be driving a car and be thinking of drugs.

The presence of dopamine is also what gets the basal ganglia to make a decision from all the available options it has. When lab mice are dopamine deficient, they do nothing. They will die of starvation even when food is right in front of them. They have no motivation to eat. When their dopamine is restored, they start eating again.

3) Endorphins (and other things in the “endogenous opioids” category which I will just call “endorphins” in this series)

These are neurotransmitters that make you feel good (blunt stress, reduce feelings of pain, and enhance your mood). When you do something that releases endorphins, it makes you feel better (this is why people feel good after eating “comfort foods”).

Food Preferences

Humans in general have the following innate food preferences and aversions (that is to say that these things when consumed make our brains release dopamine and reinforce our behavior of eating them when the same cues/stimulus are present):

Innate preferences:

• Caloric density (we have a very strong preference for high calorie foods)
• Fat
• Carbohydrates
• Protein
• Sweet flavor
• Salty flavor
• Meaty flavor (umami)

Innate aversions:

• Bitter flavor
• Odor of decay
• Anything that causes digestive distress (although this is a conditioned taste aversion and not a true innate preference)

(Credit: This list is taken from the extremely well researched book The Hungry Brain (USA, India) by Stephan J. Guyenet, PhD in neuroscience)

All of these preferences are largely innate and built into your DNA by millions of years of evolution. My infant loved his decongestant drops when he was sick because it had a sweet flavor added to it, and hates taking his multivitamin drops because of the foul smell and taste of the B vitamins in it.

Did anyone tell him that sweet taste is good and bitter taste is bad? No. He already knows that, thanks to evolution.

When we started feeding him solids, he was happy to eat them.

His brain detected the calories in the feeding cup and said “Nice, I like that. Here is some endorphins so you feel good and some dopamine so you learn to do that again.”

As that happened a few times, he learned that seeing the feeding cup and smelling his food means it’s time to eat. Now he gets really excited and gets ready to eat when shown his feeding cup (my wife has to hold him back from pushing his face into the cup).

He learned that from the dopamine he got from his previous meals.

When rats are injected with fats, carbs, or protein substances directly into their stomachs, they get more dopamine from it than when entirely non-nutritious substances are injected directly into their stomachs. The more calories that are injected, the stronger the dopamine response (i.e. more learning).

They have no idea what they ate nor did they ever taste it, but their bodies still recognize “more calories” as a better outcome and release more dopamine.

Likewise dopamine is released when you eat something that has little to no calories but has salty flavor (like a salty drink), sweet flavor (like Pepsi Black or Coke Zero), or umami flavor (soy sauce and many teas).

Now that you know all this, we are ready to begin answering the big unanswered question in the previous part of this series.

See you in the next piece.

– Harsh Strongman

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