Food cravings are quite common—according to this study of a thousand college students, 97% of women and 68% of men experience them, on average two to four times per week. (Chocolate was the most commonly craved food, if you were wondering—especially among the women. Shocking, I know.)

But why do cravings happen in the first place? Should we listen to our cravings, or fight them?

Can We Trust Our Food Cravings?

The idea that our bodies intuitively know what micro or macronutrients they’re lacking (and that our cravings reflect this) goes back to a classic experiment from the 1920s and 1930s by a pediatrician named Clara Davis.

Over a period of six years, Davis studied babies aged 6 to 11 months, and exposed them to 34 different foods in a controlled environment, ranging from bone marrow to peas. With no prompting from the researchers, and no prior exposure to solid foods that might sway their tastes, the babies were free to develop their own preferences and eat whatever they wished.

Perhaps surprisingly to those of us in the Western world familiar with the typical toddler diet (white bread, macaroni and cheese, and perhaps the occasional peanut butter and jelly sandwich), the babies tried every one of the foods presented to them, and usually more than once. Many of the babies began the study malnourished (this was the 1920s, and many came from orphanages). Yet by the time the study ended, they were all healthy and robust.

The conclusion was that the babies instinctively “knew” which foods contained the nutrients they most needed, and gravitated toward that one or those several. For a short period of time, many of them ate quite an imbalanced diet, greatly favoring one food over the others—but it all evened out in the end, as nutrient status improved.

Are Our Cravings Today Really About Nutrition?

However, one major difference between the study and the variables present in the “real world” was that the babies were given a choice between 34 nutrient-dense foods—they didn’t have the option of choosing to eat junk. Even if this innate sense of nutritional wisdom exists, the obesity epidemic implies that other factors are yet much stronger. (After all, when was the last time you had an uncontrollable urge for bone marrow?)

The evolutionary explanation for why we crave fat, sugar, and salt (and note: I’m talking microevolution here, or the changes within our species over a relatively short period of time, in response to external pressures) is that back in the hunter-gatherer days, our ancestors didn’t always know where their next meals were coming from. So they developed a taste for calorically dense food, to pack on the pounds in order to help them make it through to their next feast. Such adaptations were appropriate in that world; not so much in ours, where there’s a fast food joint on every corner and we can indulge cheaply, several times per day if we like. So it may be that while our bodies innately crave the nutrients they need, they also crave calories—the more, the better. From the standpoint of microevolution, the latter would probably be stronger: especially because in that world, there was yet no such thing as “empty calories”. Calorically dense foods were, back then, also packed with micronutrients. 

According to the book The Dorito Effect, there’s another possible explanation for why we now crave junk as a culture more than nutrient dense foods: the innate wisdom of our cravings has been hijacked by artificial flavors. In other words, if you’re craving Vitamin C, as far as your cravings are concerned, an orange-flavored popsicle will do just as well. As big industrial food processing has resulted in less nutrient dense food, such artificial flavors have become increasingly necessary. These can add back the lost flavor, and even to some extent the lost nutrients (that’s what the food label “enriched” means). But it’s still a far cry from the original whole foods consumed by our ancestors—or by those babies in Dr. Davis’s study.

What About Stress Eating?

Another proven (and very common) cause of our cravings is stress, particularly for sweets. There are a few possible explanations for this.

The first has to do with cortisol: the stress hormone. One of the jobs of cortisol is to mobilize sugar from the liver in between meals via gluconeogenesis (the process of creating new glucose) once the liver’s glycogen stores have been depleted. Basically, when you’re stressed, you need more energy to do the same things you normally do. But if you eat more sugar when you’re stressed, you spare the body this additional burden: hence the craving. (A healthier solution to this, by the way, is to eat complex carbohydrates with protein at your meals, which will give your body a steady source of glucose hours after you eat, rather than the spike-and-crash process that occurs with simple sugars. But when stressed, your body wants sugar, and it wants it now. So in the moment, given the choice between a cinnamon roll and an apple with nut butter… it’s no contest.)

The second explanation for sweet cravings during stress has to do with how stress affects our moods.  Long-term stress depletes both dopamine and serotonin, the neurotransmitters associated with positive feelings. Eating sugar can help to raise both of these, because in addition to helping glucose get into cells, insulin also allows amino acids from the protein in our diet (such as the precursors to serotonin and dopamine: tyrosine, phenylalanine, and tryptophan) to cross the Blood Brain Barrier (BBB). A craving for sugar may therefore really be a desire to raise insulin, in order to raise dopamine and/or serotonin.

Who Has The Craving: You, or Your Gut Flora?

According to this study, your cravings might not have anything to do with what’s best for your body, either presently or historically—but they may instead come from the needs of the bacteria and fungal species in your gut!

I’ve certainly seen in practice that those with an overgrowth of candida often experience strong sugar cravings—though this is correlation, not necessarily causation. It may be that those with candida overgrowth have it because they eat a lot of sugar already (due to a preexisting habit), rather than because the organism causes them to crave sugar. But I wouldn’t rule it out. 

Other Influencing Factors

One might suppose that cravings also tend to arise due to a desire for variety: if you eat the same thing over and over for a long time, you’ll simply crave something different. But this study shows that is not the case. (I can also attest that patients who adhere to a strict diet generally experience fewer cravings over time, rather than more. They might get bored of their routines, but this boredom does not seem to translate into cravings, per se.)

Or, is it your genes? Will you end up preferring the same foods your parents and siblings like? Apparently not: according to this study, any such similarities are based upon environmental rather than genetic factors, as they disappear when the environment changes. (So surrounding yourself with people who eat healthier than you do will likely rub off over time!) 

The Upshot

Your body is intelligent. It craves what it does for good reason.

Unfortunately, those reasons might not always take into account all the possible consequences of our highly processed, fast food world. Our bodies have been “tricked” into craving foods that aren’t truly in our best interests anymore.

The good news is, it’s possible to “re-train” your instincts and cravings by eating real, whole foods, the way God created them. Here’s a good primer on how to eat for health in 2018.