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The Sirens’ Song of Sugar

I must say: as a science person and an educator, there’s one quirk I find particularly annoying about Americans, and that is our strange ability to know things and still pretend that they’re not true. 

In other words—and if you’ll pardon my unavoidable French—Americans are good bulls**tters, and I am not smiling as I write this because it’s actually terrible news for our dietary health. 

Understand that the mark of a true bulls**tter is not dishonesty or a talent for lying per se. Rather, it is the ability to convincingly answer a question without necessarily knowing the answer—to make it seem like you’re speaking the truth whether your words are totally true, flagrantly false, or an educated guess. It’s a valuable (and sometimes amusing) social skill, but by definition it is unconcerned with the truth… and we Americans are so good at it that we can do it to ourselves without even noticing. 

We’re especially good at rationalizing dietary decisions. Feel like eating a Cinnabon? Well, now would be a good time to remember that you have a “fast metabolism”! Alternately, you can decide to run an extra mile on your next jog, or skip dessert that evening—or you can leave the realm of logic altogether and eat the Cinnabon because you did something nice for somebody, or because you’re traveling, or because… you get it. (This is part of the reason the USA is in trouble health-wise.)

Of course, this isn’t universally true of Americans. For one thing, we produce a lot of the world’s best scientists—and for another thing, we’ve collected some of the tastiest and most vibrant culinary traditions in the world. I just finished a two-year research tour around the country, and my brain is still ringing from all the wonderful people I met and unbelievable food I ate. 

With help from a few talented friends, I managed to re-discover the lost American diet for living to 100 years old… and my new book The Blue Zones American Kitchen is the culmination of that two-year tour. It’s tasty, it’s healthy, it’s backed by extensive science, and (if I may be so bold) it’s exactly the book I would have wanted for restoring my faith in the potential of American food. 

As much as I’d like to keep talking about that little beacon of dietary optimism, it’s time to get back to the business of undoing our favorite dietary BS. So let’s return to our favorite kind of unhealthy foods: simple carbs!


As I mentioned last time, the difference between complex carbs and simple carbs is like the difference between firewood and newspaper, respectively. They both “burn” to provide energy, but they burn in very different ways—and when it comes to our digestion, well, we’re built for the slow-burning stuff. 

Of course, our stomachs can handle small amounts of refined, fast-burning carbs like table sugar, much the same way that a little newspaper never hurt a campfire. (People living in the blue zones eat way less sugar, not none.) But imagine trying to build a campfire with nothing but newspaper, and you’ll have a better idea of why our bodies can’t function nearly as well after we’ve fed them piles of simple sugars and starches. 

Remember, too, that neither newspaper nor refined table sugar even existed until a few hundred years ago. Evolutionary changes take millions of years, if they happen at all, and—contrary to what the X-Men movies would have you believe—evolution doesn’t just magically “leap forward” at opportune times. 

So, alas, Nature isn’t going to adapt our stomachs to our diets for us; our bodies are stuck working the same way they have for thousands upon thousands of years. In the end, we have to change the things we want, because what we need isn’t going anywhere anytime soon. 

So here is the big question: why are we so drawn to refined sugars, like moths to flame, even when we know how bad they are for us? 

There are a handful of different answers, but for today, I’ll cover one that allows me to reminisce about my (unexpectedly) lovely time on the road researching The Blue Zones American Kitchen.

Today’s answer in a nutshell: Most of our favorite vices (including refined sugars) can cross the blood-brain barrier. That term is indeed a mouthful, but I’ll explain.

As you know, our circulatory system distributes important stuff like oxygen and glucose throughout the body, with blood cells acting like so many delivery trucks—and of course, our circulatory system “includes” the brain in the same basic way that America’s sprawling network of roads includes Washington, D.C. and even the White House in particular. 

But the brain, like our nation’s capital, is sensitive about fluctuations in that traffic, and it’s especially sensitive about potential threats (sometimes rightly, sometimes not). In both cases, they anticipate that a lot of those potential threats will simply follow the roads to get there—so, as you drive closer and closer to the capital, you’ll encounter more and more defensive measures like street cameras, security checkpoints, traffic stops, mandatory inspections, and guarded gates, all concerned with the same basic thing: keeping the capital safe from potential threats. ?️

I don’t know if Washington, D.C. has an official name for its system of road-based security measures, but in the case of the human body, it’s called the blood-brain barrier, or BBB for short (not to be confused with the Better Business Bureau). ?

Most substances we ever consume can’t cross the blood-brain barrier—and if such a substance is going to make it to the brain at all, it’ll do so indirectly, in tiny pieces, or once the body has broken the substance down into other substances.

If a substance can cross the BBB, it is (by definition) psychoactive—which basically means that the substance is able to interact directly with the brain without having to be filtered or broken down by other parts of the body first.

With essentials like glucose and oxygen, this “direct interaction” just means allowing supplies to be delivered where they’re needed; they’re able to cross the BBB because they pass every security check.

In other cases, a substance is able to cross the BBB because it bypasses security, rather than passing through it legitimately. It could take seconds, minutes, or the better part of an hour—but once a substance is across the barrier, it’s free to do its thing from inside the brain. 

This is where things officially become fun and dangerous. 

In case you’re curious, substances that can cross the blood-brain barrier (BBB) include…

? Alcohol 

? Nicotine 

☕ Caffeine 

? Opiates (painkillers, heroin, etc.) 

? Cannabis (THC specifically; CBD doesn’t cross) 

?‍? Virtually all other recreational drugs, and… 

? Refined sugar 

Refined sugar really does belong on this same list with drugs and vices, even though no two substances above work in exactly the same way. But if you’re thinking refined sugar is “harmless” just because its effects aren’t as dramatic as the others’, think again.  

The million-dollar question is what a substance does after it’s crossed the BBB. More than anything else, that’s what dictates the substance’s perceived effects and any imbalances or damage caused in the background.

Let’s consider two contrasting examples—one benign and the other extreme—to better understand why refined sugar’s ability to cross the BBB helps explain America’s undying sweet tooth:

CAFFEINE ☕ Caffeine works by pulling a little sleight-of-hand trick on the brain. At the molecular level, caffeine is shaped just like adenosine, a neurotransmitter that makes us feel sleepy; caffeine does what it does by temporarily blocking adenosine receptors so that the brain can’t absorb the “sleepy juice.” Hence, we feel more awake and alert. 

Caffeine is definitely habit-forming because we really like being able to counteract that sleepy feeling. But it wouldn’t be quite right to say that caffeine is addictive (in the fullest sense of the word) because it doesn’t directly interfere with the brain’s reward system.

By stark contrast…

HEROIN ? As long as we’re personifying things, heroin is like the unholy love child of Robin Hood and a terrorist commando. Once heroin gets through the BBB (almost instantly), it drives straight to the brain’s reward center, marches into the bank vault, empties out the dopamine, then carries it into the middle of the nearest crowd and throws it straight up in the air, scattering everything to the wind. 

The problem with drugs like heroin, explained one way, is that a person using it is both the empty bank vault AND the crowd of people gleefully gathering cash off the street. They can’t help but enjoy the rush—dopamine gives you that heck yeah! feeling and reinforces whatever behaviors led you there—but they did need the dopamine in the vault to keep business running smoothly, and now it’s gone. That’s a major disruption to the body and mind, especially considering how temporary the fun is. 

So where does sugar fall on this continuum of disruption and danger?

Obviously, sugar is nowhere near as potent or dangerous as heroin. Having said that, what refined sugar does on the other side of the blood-brain barrier isn’t all that different. Refined sugar doesn’t clean out the vault and throw all the money in the air, but it does tamper with the brain’s reward system; its presence drips more and more dopamine into the system that the brain wouldn’t have dripped otherwise, in large part because the energy is far more concentrated than it would be in nature. 

This steers not only how we feel, but also how we think and behave. It’s just a finger, but make no mistake: refined sugar will put a finger on the steering wheel if you let it. 

To summarize and wrap things up: we’re drawn to the sirens’ song of refined sugar because it has a unique ability to get in our heads, both literally and figuratively. Unlike so many other things we eat and drink, sugar represents and rewards itself in our brains… and I think that’s an excellent reason to be wary of it. 


In the past, I’ve mentioned the importance of the dinner table—how people who eat meals together tend to eat better diets and enjoy better overall health. That’s an observable fact.

Scientists can’t account for the exact reasons just yet; conducting dietary studies is tricky because so many elements of life (“variables,” to a scientist) overlap and interact with our diets. But it’s still an observable fact that there are health benefits to eating with other people.

I want to revisit this subject because this podcast episode from ZOE with Jonathan Wolf and Dr. Sarah Berry did a great job of expanding what I’ve said and adding some hard science (citations with links!) to the discussion.

The link above has the complete set of info: podcast audio, transcript, links to several scientific studies, and more. For my part, I’ll provide a tidy recap of the health benefits of eating with others (and the hazards of eating alone): 

? Eating alone is associated with disordered eating behaviors, depressive symptoms, obesity, and high blood pressure compared to social eating. This is especially true for those who didn’t eat with others (as often) during childhood, since eating behaviors (good or bad) are learned. 

? Those who eat alone tend to eat faster, which sharpens the blood-sugar spike (and subsequent crash) following a meal. This effect is compounded for those who eat alone and distracted, since distractions tend to increase the amount we eat over the course of a meal. 

? Those who eat alone are likelier to eat processed and ultra-processed foods (in other words, the kinds you couldn’t possibly make in a home kitchen) like frozen meals. One big explanation for this, and I’m sorry if the familiarity of this stings: it’s a lot of effort (and often waste) to cook for just one person. So we don’t. 

? In general, social eating is slower than solitary eating. There are a number of reasons for that—manners and conversation, to name two—but eating slower means a steadier rise and fall in blood sugar. It also means you’re likelier to eat all of the food groups on your plate, including the green veggies, lest you feel judged by your fellow diners.

? Teenagers who regularly eat with their families avoid the pitfalls mentioned in the first hazard (red dot), but they also just eat better, healthier things. They take in more fruits and veggies, they drink fewer sugary soft drinks and eat less fast food, and they outstrip their solitary peers in their intake of a number of essential nutrients—protein, calcium, iron, folic fiber, and vitamins, to name a few.

? People with more close relationships actually have more diverse, and thereby healthier, microbiomes than people with fewer close relationships; for instance, married people tend to have fewer gut issues than single people. Because they cook together—and, in the first place, bring enough people to justify a proper meal—they eat a greater diversity of ingredients, especially healthy ingredients like vegetables, which has been shown to correlate with the health of the gut microbiome. 

? People who eat socially feel happier and more satisfied with life, not to mention more trusting of others and more engaged with their communities. A dinner table is a place for social bonding—and as I mentioned before, it’s appropriate that the word companion literally means “someone you share bread with.”

?  There’s even some evidence that eating with others can make the food taste better to you! After all, taste is one of those areas where perception is reality.


The Blue Zones American Kitchen is available now! If you haven’t ordered your copy yet, you can do so from any retailer where books are sold. Each week, we’re celebrating some of the incredible chefs who have shared their brilliance with us in this lost American Diet of Longevity.

Adán Medrano is a chef, food writer, filmmaker, and author of Truly Texas Mexican: A Native Culinary Heritage in Recipe and Don’t Count the Tortillas: The Art of Texas Mexican Cooking. He returned to the US in 2010 to focus on the culinary traditions of the Mexican-American Community after more than 23 years traveling and working throughout Latin America.

A graduate of the Culinary Institute of America, Adán celebrates indigenous traditions in both his food and his educational courses. He’s also the founder of the CineFestival San Antonio, the longest-running Latino film festival in the US. ⁠

His cooking insight? ⁠

The best way to know if people like your cooking is not their compliments (“wow, that’s delicious”), but their appetites (“can I have some more?”).⁠


Mama’s Zucchini Pupusas

Salvadoran chef Claudia Lopez and her mom, Norma, watched the Forks Over Knives documentary about plant-based eating and had an epiphany. Their restaurant, Maria’s International Tamales in downtown Los Angeles, is now an oasis of healthy food in a jungle of fast food. Claudia’s excellence and skill mean that her pupusas and tamales are in high demand and well loved by veggie and meat lovers alike.

Her pupusas are filled with zucchini and easy to make at home. Once you get the hang of whipping up the dough, you can experiment with alternative fillings like beans, jackfruit, and other vegetables. Masa harina, used in the dough, is a finely ground cornmeal that is made from nixtamalized, dried corn.


For the Dough:
3 cups masa harina
1 cup warm water, plus additional as needed
Pinch of salt

For the Filling:
2 zucchini, grated on the large holes of a box grater, sprinkled with a pinch of salt, and squeezed to remove excess water

For Serving:
Hot sauce
Curtido (pickled cabbage)

The Method

To make the dough, in a large bowl, add all the ingredients and mix to combine.

You may need to add a bit more water, 1 tablespoon at a time, to get the dough to come together. Let stand for about 10 minutes before forming the pupusas.

Wet your hands with a bit of water and/or oil to keep the dough from sticking.

Make a ball of dough about the size of an ice-cream scoop and flatten it between the palms of your hands into a round that’s about 1⁄4 inch thick. Add 2 to 3 tablespoons of the zucchini filling to the center of the dough. Wrap the dough around the filling and then flatten it again between the palms of your hands, until it is about 1⁄4 inch thick and 4 inches across. Repeat with the remaining dough and filling.

To cook, heat a nonstick skillet over medium-high heat. Cook each pupusa until lightly browned, about 5 minutes per side.

Serve with the hot sauce, salsa, and curtido.

Click here to download a printable PDF of this recipe.


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