High Fat and Sugar Foods May Rewire Your Brain — But You Can Reverse It

The human sweet tooth is a force to be reckoned with. It’s estimated the average American adult consumes about 77 grams of sugary goodness a day, a cumulative 60 pounds over the course of a year. While snacking on an extra slice (or two) of coffee cake is nothing to be ashamed of — nearly all animals, humans included, are hardwired to love sugar — researchers have become interested in how your brain circuitry might change in response to the constant influx of sugary, salty, and high-fat foods.

Consuming a diet high in certain fats puts the brain in harm’s way, stirring up neuroinflammation and potentially compromising cognitive function. With the double threat, then, of fat and sugar, it's not hard to imagine what sort of havoc the dynamic duo could do to our brains. According to new research, that delicious hit of fat and sugar on the tongue may, unfortunately, involve some neural reprogramming.

In a paper published Wednesday in the journal Cell Metabolism, scientists in Germany and the U.S. found that regular consumption of high-fat and sugar foods, even in small amounts, switches up the brain’s innate reward system such that it unconsciously hungers for those foods again, on a consistent basis.

“It’s like a one-two punch because you decrease preference for low-fat food and at the same time enhance the brain’s reward for high energy-dense food,” Dana Small, one of the paper’s senior authors and professor of psychology and psychiatry at the Yale School of Medicine, tells Inverse. “[Our findings suggest] being exposed to an unhealthy diet is enough to rewire your brain in such a way that could promote overeating.”

A taste for the finer, sugary, fatter things

Sugar and fat’s influence on the brain is no stranger to scientists. Over the years, research in animals like rats and mice has found that high-fat and sugar diets can shift the rodents’ dietary preference to the not-so-healthy side, which appears to occur alongside rewiring in the brain involved in reward, habit formation, and decision-making.

But does the evidence hold up for humans? That’s been a bit more complicated to tease apart. One’s predisposition or risk for obesity has been regarded as some parts genetic — anywhere from 40 to 70 percent depending on the individual — and it's hard to say whether being obese in the first place is what makes the brain susceptible or does the rewiring happen first. (A bit of the chicken or the egg conundrum.) Studies in the past do suggest that high-fat diets can reshape our taste buds, influencing our responses to fat and sugar that has us craving for more.

So that’s what Small and her colleagues set out to investigate. In their study, they recruited around 50 healthy, normal-weight adults in their mid-twenties. The participants were asked to eat two snacks per day — either a high-fat/high-sugar or low-fat/low-sugar yogurt (both around the same calories) — as part of their regular diet for the next two months.

After four and eight weeks of snacking on yogurt, these men and women would come into the laboratory to have their fasting blood glucose and insulin levels checked as well as their triglyceride, cholesterol, leptin, and hemoglobin A1C (a test which measures your blood sugar levels over the past two to three months).

The participants also performed a series of tests to see if there were any changes to their preference and perception of fat and sugar. For instance, they would eat four different puddings containing varying amounts of fat but the same sugar content, as well as drink unsweetened apple juice mixed with different concentrations of sucrose.

To track what changes, if any, were going on in the brain, the researchers had the volunteers sipping on milkshakes or a tasteless solution while inside a functional MRI scanner. (You can’t normally eat or drink in an MRI machine, so the researchers had to jerry-rig a special delivery system, which included a programmable syringe pump.) The milkshakes came in different flavors like banana, chocolate, vanilla, and strawberry, all prepared from either a flavored powder, milk, or cream.

During this time, both groups on the high fat/high sugar and low fat/low sugar didn’t really gain any weight or see any significant changes in their metabolic function, but the same couldn’t be said about what was going on in the brain. On the MRI scans, Small and her colleagues saw the high fat/high sugar participants’ brains lit up enthusiastically to the rich milkshakes compared to their low fat/low sugar counterparts, particularly activating neural regions involved in the dopaminergic system responsible for motivation and reward.

Alongside that, the high-fat/high-sugar folks weren’t so keen on the less fatty puddings and apple juices with less of a hit of sucrose. The low fat/low sugar group wasn’t too thrilled about drinking the apple juice with lower sugar content, as well. (Honestly, who could blame them?)

But what was more striking to see, says Small, was when the high fat/high sugar and low fat/low sugar participants did a basic learning task involving them predicting what visual stimulus would come after hearing a tone.

“What we found is that the fundamental learning circuits changed after the exposure to the high fat, high sugar snacks,” she says. “In fact, [in this group]... the circuits important for learning became sort of primed, and that’s interesting because it has nothing to do with food. It means this small dietary manipulation doesn’t just change how your brain responds to food, it changes how your brain works more fundamentally.”

Be aware of your eating habits

So what does this all mean? Well, for one, it shows that independent of gaining weight or experiencing any overt metabolic changes like spiking blood sugar or cholesterol levels, eating a high-fat and sugar diet consistently wires the brain in such a way that has you preferring energy-dense foods. And much like a cat who prefers her Fancy Feast above all else, this neural wiring may make you unconsciously picky, reaching out for high-fat and sugar foods continuously.

These results, therefore, suggest environmental factors contribute quite a bit, in addition to the genes you inherit, in setting you on course for overeating or, ultimately, obesity. And while our brains working against our better health interests isn’t good, there’s likely an evolutionary explanation, says Small.

“If you’re an organism and you live in an environment where there’s very little energy, you want to spend time and energy finding any source of food… [that’s] energy-rich,” she says. “You’d want to have a mechanism to change how you value foods, that you value high energy-dense foods and forget about the low energy-dense food. It makes good sense to tweak learning circuits and enhance learning in a way to learn how best to exploit this environment and remember where it is and maximize energy acquisition.”

There are some caveats to this study that are worth noting, such as the small number of people studied, the fact they were mostly healthy, normal-weight individuals, and snacking on yogurt (may be not at the top of everyone’s go-to snack list), all of which may not make the results generalizable to all folks such as those over or underweight.

But Small is hopeful that further research — “We’ve only scratched the surface,” she says — will shed more light on the connection between our guts and brain, encouraging policies that help individuals of low socioeconomic status gain access to fresh fruits and vegetables rather than processed, high fat and sugar foods.

“What we need to do is have changes at the level of government to incentivize [the food] industry to create healthier foods that are more available and less expensive,” says Small.

This is especially crucial considering obesity is a known risk factor for neurodegenerative diseases like Alzheimer’s, dementia, Parkinson’s, and overall poor cognitive function later in life.

The good thing is your brain is plastic — neuroplastic, that is. Small says even if you’ve been eating high-fat and sugar foods for a while, it’s possible to take charge of your unconscious eating habits and rewire your brain, as long as you do it soon enough before immutable changes happen.

“Having an unhealthy snack once in a while is probably not [too bad], but making a habit of it has consequences for how your brain functions,” says Small. “There’s clear evidence that diet affects the brain, and so you want to minimize your consumption of high energy-dense and processed foods.”

Eating your way to a healthy brain? Sounds easy enough.