How sugar and fat affect your brain

Sweets, like these candies at La Boqueria Market in Barcelona, release dopamine in our brains on levels similar to nicotine and alcohol. (Image: Getty Images via National Geographic)

Much of our food is increasingly manufactured to be irresistible to us. Experts say this trend has long-term health consequences.

We often think of smoking and drinking when it comes to addiction—but there’s another compulsion affecting as many as 14 percent of adults and even 12 percent of kids: food addiction.

Indulgent dishes enticing us with fat and sugar can feel impossible to avoid, especially during the holidays. Experts confirm it’s more than a feeling: Half a century of food trends has created an environment where more than half the food consumed by American adults is ultra-processed, often optimized to hit the body’s fat and sugar sensors to release dopamine.

These processed food products capitalize on our biology to keep us reaching for more. “We don’t realize that these are really killing people on par with what we’re seeing with things like alcohol and tobacco, leading to preventable deaths,” says Ashley Gearhardt, an associate professor of psychology at the University of Michigan and a member of a research team that assessed the latest figures for the prevalence of food addiction in March 2022.

Experts are rewriting what we know about food addiction and asking new questions about what we can do to curb it—and save lives.

What food does to our brains

Food affects our brains in many complex ways, and one particularly important response is the release of dopamine, a neurotransmitter. Like addictive drugs, eating food releases dopamine. Contrary to popular belief, dopamine doesn’t increase pleasure. It encourages us to repeat behaviors that help us survive—like eating nutritious food and reproducing. The more dopamine that’s released, the more likely we’ll repeat that behavior.

When we eat fat and sugar, sensors in the mouth send a message to release dopamine in the striatum, a section of the brain associated with movement and rewarding behavior. But that oral sensory process is only part of the story, says Alexandra DiFeliceantonio, an assistant professor at Virginia Tech’s Fralin Biomedical Research Institute. There’s also a secondary sensor in the gut that registers fat and sugar, signaling the brain to release dopamine in the same region.

Although researchers are still mapping out how exactly the presence of sugar is signaled from the gut to the brain, the way that fat is signaled from the gut to the brain has been well documented. When fat is detected in the upper intestine, the message is carried up the vagus nerve (which controls several unconscious functions like digestion and breathing) through the hindbrain to the striatum.

Foods rich in fat and sugar can increase dopamine in the striatum as much as 200 percent above normal levels—a similar bump to what’s observed with nicotine and alcohol, the two most common addictions in the U.S. Specifically, one study found sugar increased dopamine levels by 135 to 140 percent, and fat increased them by 160 percent in another study, although it takes longer to kick in. Other drugs work very differently—cocaine can triple normal dopamine levels while methamphetamine can multiply normal dopamine levels 10-fold.

How the food we eat has changed

As we learn more about how food affects our brains, it has become increasingly manufactured to be irresistible to us. Our bodies are inundated with foods that have higher concentrations of certain nutrients, like fat and sugar, and more combinations of nutrients than ever before. These are combined with sensory properties—like a pleasingly smooth and velvety ice cream—that make eating more enjoyable than ever.

Traditionally, humans made food with whole foods: for example, pie crusts were made from flour and butter. In contrast, industrially processed foods are composed of substances extracted from foods, like starches and hydrogenated fats. Additives like artificial flavors, emulsifiers (which keep oil and water mixed together), and stabilizers (which preserve the structure or texture of food) make food more appealing—but ultimately to our own detriment.

Experts like DiFeliceantonio believe we should make the distinction between highly processed foods and those made from scratch. Being aware of those differences is the first step in avoiding a long list of diet-related health issues.

“We’ve been eating homemade versions of cakes, cookies, and pizzas for a very long time. But, it wasn’t until the rise in production of ultra-processed foods in the 1980s that we’ve seen this increase in diet-related mortality and disease,” DiFeliceantonio says.

Highly processed foods can qualify as clinically addictive, both Gearhardt and DiFeliceantonio argue. According to what’s known as the rate hypothesis, the faster something affects your brain, the more addictive that substance will be. Many processed foods are essentially pre-digested to maximize the speed of dopamine release.

Finally, it’d be impossible to extricate social and psychological forces from the equation. Processed foods have been accessible, affordable, and aggressively advertised for generations. That perfect storm has created generations of people who know processed foods aren’t healthy but are still compulsively drawn to them.

“The cues that surround these foods start to take on a life of their own,” says Gearhardt. “When you see a fast food sign or a vending machine, that has such power and drive for us that even if you’re not hungry, or even if your doctor just told you have diabetes, you might want to have these processed foods you know aren’t good for you. They’re everywhere; we’re constantly on the defensive against doughnuts at the morning meeting, and the late-night advertisement for pizza.”

How are perspectives changing? What are the questions left unanswered?

In recent years, experts have begun to ask new questions about food addiction as some of their early assumptions have proven false.

Take tolerance and withdrawal for example. These were once considered major elements of addiction. It was once believed people with food addiction continued to eat compulsively in order to avoid withdrawal, the unpleasant physical and mental repercussions (like anxiety, nausea, and headaches) that appear when a person decreases or stops using a substance.

“That’s actually not true,” DiFeliceantonio says. “Most theories of drug addiction have a lot more to do with habitual use, or with an intense craving. That’s what’s sustaining drug use.”

Tolerance is almost the opposite of withdrawal—the consequences of continuing to use a substance. As a person’s tolerance of a substance grows, they need to consume increasing amounts to get the same effect. In the case of food, the dopamine deficit hypothesis posits that if we eat something and don’t get enough pleasure from it, we’ll eat more until we feel good.

“I have some trouble with that hypothesis, because everything we do releases dopamine. So eating broccoli, because it is delivering nutrients to the gut, releases dopamine,” DiFeliceantonio says. “People don’t do things that they only kind of like, such as eating broccoli, a lot just to get more dopamine.” She adds there’s also no indication there’s a threshold to reach to earn that dopamine reward.

As research progresses, scientists are left with more questions than answers about how our bodies become addicted to food. We know that dopamine doesn’t tell the full story, because it’s not what makes eating food pleasurable. Researchers have found evidence that might actually have a different cause: A 2012 study showed that eating food stimulates our opioid receptors, which increase feelings of pleasure. But scientists know very little about how the process works, because it’s difficult to measure opioid levels in a living organism.

Some experts suspect a sensor in the upper intestine may play a role in our food likes and dislikes. Others wonder whether there may be something at play in the hypothalamus, a critical part of the brain that regulates everything from your body temperature to your sense of hunger.

Researchers also want to learn which combinations of nutrients trigger different levels of dopamine release. Studying humans, unfortunately, requires expensive scans and a dose of radiation. “You can’t scan the same person 20 times with all different tastes and combinations and things, so we’re really more limited in what we can do,” DiFeliceantonio says.

As for a solution, Gearhardt says the answer is clear—but far from easy. We can look to the major societal changes that were imposed to limit smoking—making cigarettes less affordable and less widely marketed—and do the same with addictive food, she says.

There are other ways to fight food addiction, too.

“Don’t hate yourself for not being able to avoid addictive foods because it isn’t easy. It’s using our biology against us,” she says. Learn what makes you turn to these foods, whether it’s certain emotions, places or even a time of day. “Just try to be aware of that so you can prepare yourself to have alternative ways of coping or strategizing in those moments of temptation.”

Source: National Geographic (29 December 2022)