The Evolution of the Sweet Tooth

From the very first time that your mother admonished your grandmother for letting you have a bunch of candy when you were under her care, you’ve been aware that sugar isn’t good for you.

Maybe you didn’t fully understand why… You’ve probably heard it all. “You’ll get a sugar rush!” “You’ll get pimples on your skin.” “You’ll grow a spare tire around your mid section.”

And while all of those things are true

Our collective knowledge of the dangers of sugar (especially refined sugar cane, and less of the natural sugars occurring in fruits) has not stalled the growth of the more than $90 billion global sugar industry. 

Now, there are several circulating theories.

First, consuming sugar, especially from a young age, creates an open feedback loop because sugar in itself has addictive properties. Eating it is yummy. So a hit of dopamine gets released upon consumption. You like dopamine. You want to do the thing again that gave you the dopamine. And so on.

Another theory is that some people literally aren’t coded with a sweet tooth gene. (More on that later.)

But to really understand why humans have retained the interest in sweet foods when, say, birds and cats hate sweet flavors, we’ve got to go back in time.

Our Ancestors and Sweet Things 

Many moons ago, fruit was hard to come by. Vegetables, on the other hand, were much more accessible.

However, fruits contain more energy-giving nutrients than vegetables do. We know that processed refined sugar is an energy-killer

But sugar in its natural form converts to energy in the body. So finding an apple locked high up on a tree branch had to catalyse an ignition in the brain. That reaction had to be stronger than the reaction from seeing an almond cluster high on a branch, or the tell-tale leaves of carrots in the ground. The stronger the reaction, the stronger a human being’s desire to climb a tree and snatch the apple. 

Now, not everybody figured that out. Our primate ancestors who had the best chance of fighting off starvation were the ancestors who found the fruit and ate it. 

Those genes got passed on to their children, eventually leading to a genetic mutation that reminded humans to search for fruit because they were craving sugar.

Makes sense, right?

If your body didn’t tell you to search for food rich in calories, energy, and nutrients, you didn’t do it. 

And then? We changed. We evolved. We lived in societies, grew fruit trees on purpose, set up an agriculture industry whereby fruit became available in huge quantities to the masses.

Today… if you’ve got a craving for sweets, you’re far more likely to snag a candy bar at your local convenience joint than you are to grab a banana from that same store.


The Liver Gene

Turns out that just like some of our ancestors had the desire for sweets coded into their genes, we have a genetic mutation today that appears more strongly in some of us than in others.

It’s called the FGF21 hormone. 

Basically, it starts in the liver, and regulates sugar cravings by sending messages to the brain that we need sugar.

People with this gene variation have a 20% higher chance of loving sweets than people without it. 

And once again, we see the effects of a positive feedback loop. The more sweet food we eat, the more FGF21 is released in the liver where it travels through the bloodstream to the brain. The brain registers the FGF21 as a sugar craving, and tells the body it needs sugar.

Except in this case, you don’t need sugar. You want it.

So if this gene is present in your body, and your desire for sugar is already higher than that of your average compatriot, you eat more sugar. Eating more sugar produces more of the hormone, which tells you again to eat more sugar.

And so on, and so forth.

How Much Do We Really Need?

The presence of FGF21 isn’t a death sentence – it’s not the endgame. 

Since we’re capable of higher reasoning via our prefrontal cortex, and since we’ve evolved (at least in the Western world) beyond our barest survival instincts due to the vast abundance of food and supplements available…

We need to remember that not every craving requires us to pay heed.

In fact, most of the time, they’re the result of our habits burrowing well-trodden neural pathways to pleasure centers in our brains.

There’s nothing wrong with the sugar in fruit – or even in the sweetness of a square of dark chocolate. Or cookies and milk once in a while.

But really, we only need between 25 and 35 grams of sugar per day. 

And those of us with a sweet tooth are definitely eating more than that. 

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Dr. Pedram Shojai

NY Times Best Selling author and film maker. Taoist Abbot and Qigong master. Husband and dad. I’m here to help you find your way and be healthy and happy. I don’t want to be your guru…just someone who’ll help point the way. If you’re looking for a real person who’s done the work, I’m your guy. I can light the path and walk along it with you but can’t walk for you.