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Why do we keep reaching for chips, cookies, and other junk food even when we’re not hungry? According to Dr. Chris van Tulleken in Ultra-Processed People, these foods are designed to override our body’s natural hunger and fullness signals, creating an addictive cycle that makes us overeat. Unlike whole foods that work with our internal regulatory system, ultra-processed foods (UPF) trick our brains into consuming more calories than we need.
This guide explores the science behind junk food addiction and provides practical strategies to break free from its grip. Drawing from research by van Tulleken, Michael Pollan (In Defense of Food), Michael Greger (How Not to Diet), and other nutrition experts, you’ll learn how to reconnect with your body’s natural eating cues and develop healthier relationships with food through mindful eating practices and strategic meal timing.
Table of Contents
Ultra-Processed Food Causes Us to Overeat
In Ultra-Processed People, Van Tulleken explains that we have an internal system governing our food intake, and it’s very good at self-regulating. But addictive junk food, or more specifically, ultra-processed foods (UPF), throws a wrench in that system, tricking us into eating more—and gaining more weight—even if we’re full or not hungry. Below, we examine each of these contentions in turn.
Humans Have an Internal System to Automatically Regulate Eating
Human life is fueled by food. Our bodies have adapted over millennia to allow us to effectively consume and use the calories food provides. As a result, we have an internal system capable of automatically regulating what and how much we eat so we can obtain exactly the right amount of energy and nutrients we need to thrive.
This system comprises our stomach, liver, pancreas, small and large intestines, and other organs that transmit signals to and from the brain via various nerves, blood vessels, and hormones, constantly telling our bodies when, what, and how much to eat.
(Shortform note: The brain region involved in regulating hunger and fullness is called the hypothalamus. Its primary function is to keep your body in balance by managing many important bodily functions, including blood pressure, mood, sex drive, and sleep. This link between our systems for sleep and eating may explain the many studies demonstrating that getting too little sleep is associated with overeating and weight gain. One explanation for this could be that lack of sleep activates the hedonic aspect of eating, driving the desire for salty, sugary, and fatty snacks in particular. Conversely, a 2024 study found that diets high in UPF lead to an increased risk of sleep problems.)
Just as we have a system that governs food intake for purposes of energy and nutrition, we also have a hedonic system, part of which governs eating purely for pleasure. One theory about why we find UPF appealing is that it causes our pleasure system to override our weight regulation system. However, an increasingly likely explanation for why we can’t stop eating UPF is that it short-circuits our weight regulation system completely.
(Shortform note: Experts who fault the hedonic system for overeating say ultra-processed foods in particular trigger “hedonic hunger”—a primal drive to eat anything delectable even if we’re not hungry. They say that the urge to eat these foods is centered in the brain’s reward system, which is also involved in addiction.)
UPF Interferes With Our Internal System
Van Tulleken argues that UPF is an addictive substance that deceives our brain and body into eating more of it. We’ll first examine an experiment van Tulleken conducted on himself that demonstrates how addictive UPF can be. Next, we’ll look at four characteristics of UPF that trick us into overeating: softness, calorie density, added flavorings, and additives.
Van Tulleken’s Experiment on Himself Points to UPF’s Addictiveness
Van Tulleken conducted an experiment on himself to study the effects of UPF. He began by eating no UPF for a month, and then for the next month he ate a diet consisting of 80% UPF.
Van Tulleken describes how his primarily UPF diet made him anxious, exhausted, achy, and less productive. At the end of the four weeks, he’d gained 13 pounds. Tests showed that the hormones in his body that are involved in eating weren’t functioning properly:
- the hormone that signals fullness (leptin) hardly responded to a large meal,
- the hunger hormone (ghrelin) was extremely high just after he ate, and
- the hormone that signals fat storage (also leptin) increased fivefold.
In addition, MRI scans showed increased connectivity between the parts of his brain involved in desire and reward and the parts involved in hormonal control of food intake. The brain pathways didn’t change, but the information flowing through them did—and over time, those brain circuits themselves could change, too.
All of this suggested that van Tulleken’s eating was increasingly governed by subconscious signals telling him to eat more.
(Shortform note: Van Tulleken documented his experiment in video form for the BBC. The video shows that in addition to the other results, his BMI went up by two points, putting him into the overweight range, and his body fat went up by almost seven pounds. The hunger hormone in his blood increased by 30%, which explained why he felt hungrier and often kept eating even when he didn’t enjoy it.)
Besides van Tulleken’s experiment, there are many other indications that UPF is addictive, including:
- Brain imaging shows that UPF stimulates the brain’s reward system in the same way as addictive drugs.
- People consistently score UPF higher than real food on food addiction scales.
- UPF and addictive drugs are both modified from their natural state to allow for fast, easy delivery of the rewarding substance.
- A high UPF diet causes more deaths worldwide than tobacco.
(Shortform note: Critics of van Tulleken’s claim that UPF is addictive argue that for as long as there has been food, there have been food addictions. They point to sugar in particular as an example of a minimally processed ingredient that can result in addiction. Indeed, research increasingly shows that sugar may be as addictive as some illegal drugs; eating it releases dopamine and opioids in the body that lead to compulsive behavior. But the fact that sugar is addictive doesn’t undercut the claim that UPF is addictive. As van Tulleken notes, the large amount of added sugar in some UPF food may be one of the many factors contributing to its addictiveness.)
In addition, says van Tulleken, UPF has many characteristics that trick us into overeating.
UPF’s Softness Tricks Us Into Eating Faster
The chemical, physical, and heat processing UPF undergoes makes it much softer than whole foods. Softer food is easier to eat, so people eat UPF faster than other food. This means they end up eating more: Research shows that eating faster increases the risk of eating more, gaining weight, and having a metabolic disease.
Plus, our digestive system has evolved to break down the physical structure of whole foods—not to handle food so soft that it behaves in our bodies as if it’s already been chewed. The hormones that normally signal you’re full don’t know what to do with UPF. So not only is UPF’s softness causing us to eat more of it, but it’s also tricking us into not feeling full when we do.
(Shortform note: One reason UPF is so soft is that industrial processing destroys the natural fiber in foods. But fiber serves many important functions in the body. It slows digestion, reduces blood sugar spikes, delays the return of hunger after eating, and travels to the colon to nourish the microbes in the gut microbiome. As a result, people with high-UPF diets not only tend to eat more than people with diets high in unprocessed, fiber-rich foods, but they also appear to absorb significantly more calories when they eat.)
UPF’s Calorie Density Tricks Us Into Eating More
Whole foods like vegetables and meat have a high water content, but UPF needs to be dry so it doesn’t go bad. Because it lacks moisture, UPF is very dense in calories. This calorie density, when combined with softness, means that UFC will cause you to consume more calories, faster, than you would with unprocessed foods. Studies consistently show that foods with high calorie density promote eating and weight gain.
(Shortform note: In The Omnivore’s Dilemma, Pollan writes that humans have a biological preference for calorie-dense foods because our hunter-gatherer ancestors feasted whenever they could, to build fat reserves to last through future food shortages. UPF companies are taking advantage of this evolutionary preference to get us to buy and consume more.)
UPF’s Added Flavoring Tricks Us Into Thinking We’re Eating Something Nutritious
Van Tulleken says the added flavoring in UPF also tricks us into thinking we’re eating something nutritious, which may cause us to eat more. This happens because we associate certain flavors with nutritious foods, even though ultra-processing destroys the nutrients in whole foods.
When it comes to nutrition, there’s a big difference between whole foods and the components that make up whole foods. Research consistently demonstrates that eating whole foods protects against cancers, heart disease, dementia, and early death. Many studies show that nutrients like vitamins and minerals are only beneficial when consumed in whole foods containing them. When these same nutrients are consumed independently of whole foods, they’re not effective. In other words, multivitamins and supplements generally don’t work for healthy people (people without nutrient deficiencies). They don’t decrease the risk of disease or death.
(Shortform note: While experts agree that supplements are often ineffective for people without nutritional deficiencies, it’s also true that many people do have nutritional deficiencies and may benefit from certain supplements. More than two billion people worldwide are deficient in key vitamins and minerals, especially iron, iodine, zinc, and vitamin A. These deficiencies are especially prevalent in low-income countries and among pregnant and lactating women and young children. Doctors and scientists generally agree that the best way to address these deficiencies is through a healthy diet of whole foods; if that’s not possible, some supplements appear to be more effective than others. The more useful ones include vitamin B12, folic acid, vitamin D, and calcium.)
The process of manufacturing UPF destroys the thousands of molecules that comprise whole foods, removing vitamins, reducing fiber and polyphenols, and generally ridding the food of micronutrients. UPF manufacturers are required by law to add certain vitamins and minerals to their food so we don’t develop deficiencies. However, the few that they add back in don’t make up for all the micronutrients lost in the course of processing. Those lost micronutrients might be precisely the ones that make whole foods so good for you.
In addition to removing micronutrients from food, ultra-processing destroys flavor molecules, so manufacturers also add flavoring. Van Tulleken explains that added flavorings in UPF affect both smell and taste. We link smells and tastes with our past experiences with food, so these senses can signal to us how nutritious a particular food is likely to be. This means that the added flavoring in UPF may convince our brains that what we’re eating is nutritious, even if it has been stripped of all its micronutrients. In short, added flavoring in UPF may be tricking our systems of smell and taste into thinking we’re eating something nutritious.
For example, van Tulleken notes that Pringles snack chips contain the flavor enhancers glutamate, guanylate, and inosinate—molecules that normally occur in easily digestible proteins such as cooked meats. When we eat Pringles, the added flavoring signals to our brain that we’re eating something akin to a home-cooked stew. Instead, all we get is starch and fats.
(Shortform note: Pringles fans may argue that while the snacks aren’t as nutritious as a stew, at least they contain potato. However, Pringles are only 42% “potato content,” and due to ultra-processing, they’re far less nutritious than a potato. Potatoes are a good source of potassium, vitamin C, folate, and vitamin B6, as well as many other micronutrients. Pringles contain none of those nutrients except vitamin C (in about half the amount found in potatoes). They’re also high in saturated fat and contain more calories than potatoes.)
Some scientists have theorized that we’re eating more in an attempt to make up for our increasing micronutrient deficiency. This may be why UPF diets can result in malnutrition and obesity simultaneously.
(Shortform note: Research shows that, although processing removes micronutrients from food and can’t possibly replace them all, some UPF is more nutritious than others. For example, soda is high in calories and contains no healthy nutrients, but a breakfast cereal that’s high in fiber, low in sugar, and fortified with nutrients that we might not otherwise get enough of, like folic acid, can be a nutritious choice.)
UPF’s Additives Damage Our Microbiome
Plus, additives in UPF may damage our microbiome, leading to overeating and other problems.
Our microbiome consists of all the microorganisms—such as bacteria, viruses, and immune cells—that live in our body, particularly in our gut. Van Tulleken calls the microbiome the body’s largest immune organ; it’s responsible for protecting us from harmful bacteria.
Manufacturers use thousands of additives in UPF, including emulsifiers, stabilizers, leavening agents, artificial sweeteners, and artificial flavors. Our gut microbiome turns some food into beneficial molecules, but food containing additives may harm the microbiome by leading to intestinal inflammation. This can result in overeating.
Even if additives don’t cause overeating, research suggests that they can alter the balance of bacteria in the gut. This imbalance can contribute to a variety of diseases, including rheumatoid arthritis, autoimmune diseases, and even cancer and mental illness.
(Shortform note: Van Tulleken only cites one study (on mice) linking additives to microbiome damage and overeating; critics note that human microbiomes are very different from the microbiomes of other animals. However, research linking microbiome damage to inflammation indicates that certain diets high in additives may cause chronic inflammation, which is associated with many serious diseases. Inflammation is your body’s immune response to a virus, bacteria, foreign toxin, or injury. Acute inflammation is a natural part of the healing process. Chronic inflammation occurs when your body continues sending inflammatory signals even when there’s no outside danger. Eating too much of certain UPF may increase chronic inflammation by causing a gut microbiome imbalance.)
How to Break Your Junk Food Addiction
To break the control that high-calorie, low-nutrient foods have over us, experts recommend reconnecting with our body’s natural hunger and fullness signals. Here’s how to break the junk food addiction.
1. Slow Down
In In Defense of Food, Michael Pollan writes that it takes 20 minutes for our stomachs to signal to our brains that we’re full. Unfortunately, many of us eat our meals at a much faster rate, meaning we continue to gorge on food before our bodies have time to react. Pollan recommends eating slowly, allowing your stomach to properly signal your brain when you’ve eaten enough.
2: Eat More Earlier in the Day
In How Not to Diet, Michael Greger writes that eating junk food leads to a catch-22 scenario where we crave ever more junk food: When your body digests healthful foods, it releases a steady stream of nutrients from that food into your bloodstream, creating hormonal changes that make you feel full. Because junk food lacks nutrients, this process of satiation isn’t triggered, and you end up feeling hungry again soon after you’ve eaten—and craving more junk food.
To break this damaging cycle, Greger recommends working with your body’s natural digestive clock. The amount of time and effort your body spends digesting food decreases during the day—in other words, you burn more calories digesting food in the morning than you do in the evening. Thus, if you eat your largest meal in the morning and your smallest in the evening, you’re aligning your eating with the rhythm of how your body wants to receive food.
3: Listen to Your Body’s Cues
In Intuitive Eating, Evelyn Tribole and Elyse Resch write that after spending years with a “clean your plate” mentality, you’ll likely have to work at getting back in touch with your body’s natural hunger and fullness cues. You may not even recognize comfortable fullness, having become accustomed to feeling “stuffed.”
To reacquaint yourself with these cues, Tribole and Resch recommend eating mindfully by assessing your hunger levels before, during, and after each meal. This means pausing in the middle of a meal to check in with your stomach and your taste buds—if you’re still feeling hungry and the food still tastes good, keep eating. If you’re starting to detect emerging fullness and the food isn’t as pleasurable anymore, stop.
4. Practice Intermittent Fasting
In Fast. Feast. Repeat., Gin Stephens writes that to eat well, you must reacquaint yourself with your natural hunger cues, noting that as infants, we naturally sense the hormonal signals our body puts out indicating when we’re hungry and when we’re satisfied, but as we get older, we lose touch with these signals, leading us to overeat. She argues that the best way to reverse this process is by practicing intermittent fasting, in which you cycle between periods of fasting and periods of “feasting,” or eating.
Fasting is not dieting, Stephens writes. Dieting is limiting your overall calorie intake consistently and permanently, whereas fasting is incorporating periods of no-calorie intake into your day or week. Dieting doesn’t work because long-term calorie restriction, though it might be temporarily successful, leads to metabolic adaptation, where your body burns fewer calories and produces more hormones to increase your hunger because it thinks you’re starving. This is why, after dieting for a while, people often end up binging on junk food, undoing any results of dieting they’ve achieved. Fasting, in contrast, works with the way our bodies have adapted to periods of scarcity and abundance, and thus doesn’t trigger a starvation response.
| The Western Diet Problem According to Michael Pollan in In Defense of Food, to change your habits away from the Western diet, you must differentiate the theories from the problem and work to address the latter. Regardless of the theory, the problem remains the same—eating a Western diet leads to Western diseases. The “how” and “why” are less important than the “what,” meaning you have to treat the whole problem, not just the symptoms. The following rules can help you cut ties with the Western diet. What to eat: Eat only real food, meaning whole foods or food with ingredients your great-grandmother would recognize. – Eat more green plants, and make meat a side dish to vegetables. – Eat a variety of fruits and vegetables to consume a variety of nutrients. – Eat wild plants and game, which are high in nutrients. What not to eat: – Don’t eat food with more than five ingredients or containing high-fructose corn syrup. – Avoid foods with health claims. Real food doesn’t typically come in packages, and when it does, it often doesn’t need a label expressing how healthy it is. – Avoid industrialized meats and produce. How to eat: – Eat slowly and with other people. – Eat meals at tables. Don’t eat snacks. – Eat smaller portions and listen to your body to know when you’re full. Where to get food: – Shop at farmers’ markets or join a community-sponsored agriculture group. – Grow a garden and cook your meals at home. When you understand where food comes from and prepare it yourself, you become part of a healthier food chain. When the whole food chain is respected and supported, your health and the health of the natural world will be, as well. |
Learn More About the Dangers of Junk Food
If you want to learn more about why junk food is so addictive, with additional context and science, you can read the full guides to the books mentioned throughout this article here:
