The Boring Truth About Why America Got Fat

The truth about calories, ultra-processed food, and why “myth-busting” media sometimes makes more myths

Photo by Fábio Alves on Unsplash

Americans don’t just want facts about diet and health. They want stories. They want to know who’s wrong, who’s evil, and, best of all, who’s hiding something. They demand the busting of myths, the spilling of secrets, the tasting of forbidden truths.

This desperation for health news that is also a particular kind of darkly delicious entertainment swings open a wide door for media companies and social-media influencers to serve up contrarian takes that are often disconnected from the underlying evidence. The podcast and YouTube space is filled with audacious claims about lying scientists and dubious diets. To add irony to insult, these segments are often sponsored by bullshit supplements with no evidence of efficacy.

The paranoid style of diet science—this obsessive emphasis on myth and conspiracy that confuses basic facts and misleads viewers—is not the exclusive domain of himbo podcasters. Even trustworthy and high-quality news organizations can sometimes fall into the trap of being contrarian rather than clear.

Take, for example, a New York Times article that recently caught my eye while circulating on the website’s Most Popular page: “10 Nutrition Myths Experts Wish Would Die.” One of the purported myths stunned me. I’ll reproduce the section in its entirety, so I can’t be accused of taking anything out of context.

Myth No. 3: ‘Calories in, calories out’ is the most important factor for long-term weight gain.

It’s true that if you consume more calories than you burn, you will probably gain weight. And if you burn more calories than you consume, you will probably lose weight — at least for the short term.

But the research does not suggest that eating more will cause sustained weight gain that results in becoming overweight or obese. “Rather, it’s the types of foods we eat that may be the long-term drivers” of those conditions, said Dr. Dariush Mozaffarian, a cardiologist and professor of medicine at Tufts University.

Ultraprocessed foods — such as refined starchy snacks, cereals, crackers, energy bars, baked goods, sodas and sweets — can be particularly harmful for weight gain, as they are rapidly digested and flood the bloodstream with glucose, fructose and amino acids, which are converted to fat by the liver. Instead, what’s needed for maintaining a healthy weight is a shift from counting calories to prioritizing healthy eating overall — quality over quantity.

You might wonder: Derek, you were enraged by this mere swell in the sea of words? Yes, I was. I hate this framing. Despite its respectable presentation, this passage perfectly captures the way that myth-busting contrarianism can pull food-science coverage away from reality. To my eye, the section above offers three claims:

1. The “calories in, calories out” model isn’t so important in the long run.

2. The entire category of “ultra-processed foods” is the better enemy.

3. To the extent that ultra-processed foods are bad for us, they’re bad in a way that doesn’t have much to do with calories.

All three claims are wrong. Before we dive into the weeds on an issue I’m passionate about, I want to be clear about what’s true, right here at the top:

The passage above makes it seem like ultra-processed foods are bad for us in ways that have nothing to do with calorie consumption. But one of the most famous randomized studies of ultra-processed foods is, literally, named "Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain." That is, junk food is probably bad for us precisely because its energy density and rapid digestion lead to more calorie consumption. So, the New York Times’ effort to bust a diet myth just reinforces the fact that there’s no myth to bust.

But let’s back all the way up. I want to talk a bit about why diet science is hard, what we know about food, and what we think we know about ultra-processed food.

1. Diet Science: Very Important, Very Messy

Americans are unhealthy. We die younger and faster than the residents of just about every rich country. A 30-year-old in the U.S. is four-times more likely to die in the next 12 months than a similarly aged person in Australia, Austria, Switzerland, Germany, France, the UK, or Japan.

When you decompose America’s premature death gap, a few culprits become immediately obvious. Americans are much more likely than other rich countries to die of gun violence, drug overdoses, and car crashes. We also have higher rates of chronic disease, especially heart disease and metabolic diseases, such as diabetes. We eat more and worse food. We're arguably exposed to more environmental toxins. We move around less, too. According to one study, Americans take at least 30 percent fewer steps a day than people do in Australia, Switzerland, or Japan. We have altogether too much energy going into our bodies and too little energy going out. The result is that the U.S. has the highest prevalence of obesity among industrialized countries.

To the extent that you and I want to understand the all-important question of how to survive, and why Americans die faster than residents of other countries, it really is essential to scrutinize diet and to understand why Americans are heavier and less healthy than residents of other countries.

But nutrition science is hard. The best tool in medicine is the randomized controlled trial, or RCT. But while you can randomize people to take a pill for months or years, you can’t easily randomize thousands of people to stick with rigid diets for years. They’ll sneak an ice cream here, a snickers bars there, and throw off the findings. As a result, nutrition evidence often comes from two sources. There are large observational studies, which follow tens of thousands of people (with imperfect dietary surveys and lots of confounds) and smaller short-term randomized trials that control every bite. Larger RCTs tend to be rare, expensive, and hard to sustain. One of the best things that the Make America Healthy Again movement could do—after restoring funding to infectious disease, mRNA, and experimental cancer research—is to invest in food science and diet research to teach us more about our food. But I suspect it will mostly prove the following…

2. The “Calories In, Calories Out” Model Is Fundamental and True

The most straightforward rule in diet science is the so-called energy balance model (EBM) of nutrition. This is also known as the calories in, calories out (CICO) model. Whatever you want to call it—EBM, CICO, WIGWAM (When I Gorge, Weighty Adiposity Materializes)—the gist is that when calories in exceed calories out, weight goes up; if calories out exceed calories in, weight goes down.

This isn’t a quirky hypothesis awaiting confirmation. It’s a law of physics. “Everyone accepts that there is an energy imbalance occurring where you have what we call positive energy balance, where our caloric intake is above our energy expenditure and that is leading ultimately to rates of body weight gain,” Kevin Klatt, a nutritionist and research scientist at UC Berkeley, told me. “So the most basic consensus in nutrition is that if people consistently eat more calories than they burn, weight goes up.”

Diets and weight-loss drugs, from Atkins to Zepbound, mostly work because they get people to consume fewer calories. Mediterranean diets work in large part by getting people to eat whole foods, which are more filling. GLP-1 drugs seem to work by slowing gastric emptying, increasing feelings of fullness, and reducing noisy thoughts about hunger—all of which reduces total calories. Intermittent fasting might take advantage of the body’s superior insulin sensitivity earlier in the day, but it mostly works because narrowing the eating window reduces calories.

If this were a podcast I would say the next part very loudly, but it’s an article, so I’ll put it in bold, instead: Just because the energy balance model is simple doesn’t mean that losing weight is easy. Many people with extraordinary conscientiousness, and who desperately want to get thinner, struggle to lose weight their entire lives. This is not a mere failure of willpower or lack of effort. Obesity almost certainly has a genetic component that makes some people much more susceptible to weight gain in today’s food environment. Everybody has friends who annoyingly seem to melt fat by just sitting in a chair and others who cycle desperately through diets and exercise routines without success¹. But even the research that controls for genes upholds the calories-in/calories-out model. A 1990 study purposefully overfed 12 pairs of identical male twins. While researchers noted "wide differences” between individuals in the study, they found “significant similarity within pairs in the response to overfeeding.” That is, if you take two people with exquisitely similar genes, their weight gain or loss is overwhelmingly determined by their caloric balance. This is consistent with the idea that caloric surplus leads to weight gain—but also, that the amount of weight gain is dependent on other factors, such as genetic variation.

I’ve never spoken to a nutritionist who says “calories in, calories out” is the only thing that they ever talk to their patients about. I think what we eat matters. I even think when we eat matters. But while macronutrients and meal timing probably matter at the margin, they aren’t as important in the long run as our caloric balance. This is particularly true when we look at “junk food”—or, more specifically, what we’ve increasingly taken to call Ultra-Processed Food. So, what is that?

3. Ultra-Processed Food (UPF) Is a Huge Grab Bag of Food That Defies Easy ‘Good vs. Bad’ Categorization

There are four categories of food processing, according to the flawed but commonly used NOVA classification system.

• Group 1 is minimally processed food, like an apple or raw beans in your fridge.

• Group 2 is simple foods we might find in jars around the kitchen, like honey, sugar, extra virgin olive oil, or spices.

• Group 3 is “processed foods.” This is the stuff you can cook at home by combining Group 1 and Group 2 foods. A boiled potato with olive oil or a chocolate chip cookie made from scratch would probably count as Group 3 foods.

• Group 4 is ultra-processed foods. If Group 3 is stuff anybody can make from scratch in a kitchen, Group 4 requires industrial food-chemistry technology, including preservatives, flavors, colors, and emulsifiers. The addition of any of these ingredients technically makes a food “ultra-processed.”

When responsible nutritionists talk about how you shouldn’t eat ultra-processed foods, they’re often referring to things like sugar-sweetened beverages, grain-based desserts, meals cooked in oils with tons of industrial-grade salty ingredients, and frozen pizza. You can’t make any of that stuff at home. It’s cooked up in labs and engineered to be deliciously calorie-dense.

The ultra-processed food category is enormous. “Within it, you can have an unsweetened almond milk that has an emulsifier, which makes it an ultra processed food,” Klatt told me. “Protein powders that have gone through intense industrial extraction are ultra-processed.” Whole-grain bread with one preservative? Technically, that’s ultra-processed, too.

So, you can see the problem with demonizing the entire Group 4 category. A breakfast of Mountain Dew and Twinkies is an ultra-processed breakfast. A breakfast of whole cereal with one preservative and almond milk can be equally an ultra-processed breakfast. No nutritionist is going to tell you that those are equivalent meals. So what’s the point of talking about ultra-processed foods as a homogenous category?

“If the policy remedy is to slap the label of WARNING: ULTRA-PROCESSED FOOD on all of the almond milk and half the tofu and protein powder, and it’s the same label as what we’ve got on the Pop-Tarts, people are going to become numb to this stuff,” Klatt said. The boogeyman-ification of UPF is distracting us from one big thing that we know for certain, which is that people in Western food cultures are in chronic caloric surplus, and it’s making many of us chronically unhealthy.

4. Bad Ultra-Processed Foods Are Bad Mostly Because They Cause Overeating

In 2019, a team of nutrition researchers led by the acclaimed food scientist Kevin D. Hall published a landmark paper entitled "Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake."

In an NIH lab setting, 20 adults were randomly assigned to eat either a fully ultra-processed diet or a diet without ultra-processed food. All meals and snacks were carefully measured and weighed, and participants were told they could eat as much as they wanted. The researchers tracked appetite, eating rate, glucose levels, and other hormones. The unmistakable result was that people in the ultra-processed food category ate much more food—about 500 more calories per day!—and gained more weight, whereas people in the other group ate more slowly and felt full faster.

Many ultra-processed foods melt in our mouth. They’re broken down incredibly quickly by the body before we have a sensation of fullness. All of this can lead to over-eating. When I think about Twinkies, Cheeto Mac ’n Cheese, or microwavable pizzas, I think about food that, on contact with my tongue, practically dissolves into a glycemic goo that goes down in a flush. What is easy to eat is easy to overeat.

There’s more research to be done on why the worst ultra-processed foods are bad and why we overeat certain types of food. Maybe certain foods trigger an insulin response that wrecks the body’s metabolism. Maybe some foods trigger a dopamine response (“MOAR Twinkie!”) that overrides our satiety cues (“Oof, I’m stuffed”). But one thing you absolutely cannot say about ultra-processed food is that it overturns the calories-in/calories-out physics of food science. Ultra-processed diets cause excess calorie intake is right there in the name of the study.

5. Say True Things in a Simple Way

Let me summarize everything I just told you with four basic truths (as best we know! science evolves!) about food and diet.

1. The “calories-in/calories-out” model of diet science is the best kind of conventional wisdom: It’s simple and true.

2. Most diets and weight-loss drugs seem to work mostly because they put people in steady caloric deficit.

3. Ultra-processed food is too large a category to paint with one broad brush.

4. Some ultra-processed foods are associated with weight gain, but this seems largely attributable to the fact that energy-dense foods that melt in your mouth and are rapidly absorbed by your digestive system cause excess calorie intake … which leads us right back to Point 1.

Some folks say we should talk about food quality rather than food quantity. I’m sympathetic to the idea that it’s easier for some people to conceptualize high-quality foods than it is to count every calorie in their diet. But it’s good to be honest with people, too. If you tell a patient “please replace all the brownies in your diet with celery,” you are technically suggesting a qualitative diet change. But you shouldn’t tell that person that calorie quantity doesn’t matter. If that patient loses weight, it will be significantly due to the fact that if swapping brownie for celery every weekday will remove hundreds of calories from their daily diet. We shouldn’t tell people “quantity doesn’t matter” when quantity might matter most.

One of my closely held theories of modern media is that the most fundamental bias in news is toward negativity. Journalists and editors like negative frames to raise alarms, and readers and viewers gravitate to negative frames because our attention is drawn to high-arousal emotions, such as outrage and catastrophe. Myth-busting media is a sly form of negative framing, which offers audiences the promise that something they believe might be dangerously incorrect. I have no problem with attracting audience attention to important stories, nor am I averse to the busting of myths. I do, however, object to journalism that puts the allure of contrarianism over the virtue of honest clarity.

Health is complicated. Diet is complicated. Food is complicated. So why overcomplicated it? Tell simple truths simply. Calories count.

1. In fact, I think the success of GLP-1s pretty much explodes the idea that people who fail with diets suffer predominantly from a lack of willpower. GLP-1s essentially reprogram our gut-brain axis to trick the body into controlling caloric intake. That some people don’t need GLP-1s isn’t a sign that they’re better or more conscientious people. It’s more likely a sign that they came into this world genetically “pre-loaded,” so to speak, to burn calories easily, rarely feel hungry, and infrequently suffer from the food noise that so many of us feel.