The Truth About Calories and Why America Got Fat

Summary of an essay by Derek Thompson

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

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.

Calories in, calories out is the most important factor for long-term weight gain or loss.

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.

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.

The MAHA movement wants you to believe 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.

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. 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.

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 bar 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, 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 MAHA 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…

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—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. 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 work by slowing gastric emptying, increasing feelings of fullness, and reducing noisy thoughts about hunger—all of which reduce 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.

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 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 do 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?

Ultra-Processed Food Is a Huge Grab Bag of Food That Defies Easy ‘Good vs. Bad’ Categorization. There are four categories of food processing, according to the commonly used NOVA classification system.

Minimally processed food, like an apple or raw beans in your fridge.

Simple foods we might find in jars around the kitchen, like honey, sugar, extra virgin olive oil, or spices.

Processed foods: This is the stuff you can cook at home by combining minimally processed foods and simple foods. A boiled potato with olive oil or a chocolate chip cookie made from scratch would count as processed foods.

Ultra-processed foods require 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. 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 all ultra-processed foods. 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.

“If the MAHA 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.” 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.

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

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 overeating. 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.

Say True Things in a Simple Way. The “calories-in/calories-out” model of diet science is the best kind of conventional wisdom: It’s simple and true. Most diets and weight-loss drugs seem to work mostly because they put people in a steady caloric deficit. Ultra-processed food is too large a category to paint with one broad brush.

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.

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.

Modern media’s 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 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 overcomplicate it? Tell simple truths simply. Calories count; burning calories counts.