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10 Surprising Ways Game Theory Rules Your Daily Life

10 Popular (and Weird) Ancient Foods

Ten Bizarre Creatures from Beneath the Waves

10 Unexpected Things Scientists Made Using DNA

10 Surprising Things Found or Left on the Moon

10 Unique Ancient Peoples Whose Cultural Footprints Still Shape the World

10 Inventors Who Died Before Seeing Their Creations Succeed

10 Shocking Crimes Where the Perpetrator Walked Free

10 Unusual Facts About Calories

10 Days of Humiliation When the Person Should Have Stayed in Bed

10 Surprising Ways Game Theory Rules Your Daily Life
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Jamie Frater
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Jamie founded Listverse due to an insatiable desire to share fascinating, obscure, and bizarre facts. He has been a guest speaker on numerous national radio and television stations and is a five time published author.
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10 Popular (and Weird) Ancient Foods

Ten Bizarre Creatures from Beneath the Waves

10 Unexpected Things Scientists Made Using DNA

10 Surprising Things Found or Left on the Moon

10 Unique Ancient Peoples Whose Cultural Footprints Still Shape the World

10 Inventors Who Died Before Seeing Their Creations Succeed

10 Shocking Crimes Where the Perpetrator Walked Free
10 Unusual Facts About Calories
Calories—those tiny numbers printed on the backs of food packages—rule modern life. They determine how we eat, how we exercise, and often how we feel about our bodies. But for something so common, calories are deeply misunderstood. They are treated as absolute truths, yet the science behind them is full of quirks, loopholes, and downright bizarre history.
The term “calorie” didn’t even begin as a nutritional concept—it came from physics, where it described the energy needed to heat water. Over time, scientists borrowed the idea to measure how much energy our bodies could get from food. The problem is, humans aren’t machines, and our digestive systems don’t “burn” food with perfect efficiency. That means the calorie counts we see today are rough averages—sometimes accurate, sometimes wildly off.
From mislabeled snacks and deceptive gym machines to historical mix-ups and surprising metabolic tricks, the story of calories is stranger than most people realize. These small units of measurement have shaped diets, industries, and public health for over a century—all while resting on shaky scientific ground.
Here are 10 bizarre facts about calories—from their misunderstood origins to the surprising ways your body actually handles them.
Related: Top 10 Addictive Snacks and Why We Can’t Stop Eating Them
10 The Calorie Wasn’t Originally About Food at All
Before it became the dreaded number haunting dieters and nutrition labels, the calorie had nothing to do with food. It was actually a unit of heat energy used in physics and engineering. The term dates back to the early 19th century when French physicist Nicolas Clément introduced it as a way to measure the amount of energy needed to raise the temperature of one kilogram of water by one degree Celsius. Food scientists only borrowed the concept decades later when they began studying how much heat (energy) the human body could extract from various foods.
In other words, when you say a slice of pizza has 300 calories, what you’re really saying is that your body could, in theory, produce enough heat from digesting it to raise 300 kilograms of water by one degree Celsius. That’s not exactly the appetizing image most people have in mind when they count calories.
Even stranger, the calorie you see on food packaging isn’t technically a “calorie” at all. It’s actually a kilocalorie—1,000 real calories—but the food industry simply uses “Calorie” (with a capital C) for convenience. So when you read that a burger has 500 Calories, that’s actually 500,000 scientific calories.
This confusion between the “calorie” and “Calorie” has been debated for over a century. In 1948, the scientific community officially replaced the calorie with the joule as the unit of energy. However, the food industry refused to switch, likely because “this chocolate bar has 418,000 joules” doesn’t sound nearly as friendly on a label.
The next time you’re reading a nutrition label, remember—you’re looking at a relic of 19th-century physics, not just a measure of your next meal’s guilt factor.[1]
9 “Calorie Burn” Numbers on Machines Are Mostly Lies
You’ve probably seen it before—an elliptical machine proudly displaying that you’ve torched 500 calories after a sweaty 30-minute session. It feels satisfying, but here’s the bizarre truth: those numbers are wildly inaccurate. Studies have shown that most gym machines overestimate calorie burn by anywhere from 20% to 80%, depending on the brand and model.
The problem starts with the assumptions these machines make. Most don’t take into account your unique weight, metabolism, or fitness level. They rely on standardized formulas based on an “average” person—usually a 154-pound (70-kilogram) male. So if you’re smaller, older, or metabolically different, the calorie reading could be fantasy.
Harvard Medical School once tested multiple cardio machines and found treadmills overestimated calories by about 13%, stair climbers by 12%, and ellipticals by an astonishing 42%. Even smartwatches and fitness trackers aren’t immune. A 2017 Stanford University study found that no wearable accurately measured calories burned during exercise—some were off by as much as 93%.
The deception isn’t entirely malicious. Manufacturers tend to err on the optimistic side to keep users motivated. After all, who wouldn’t want to believe they’ve earned that post-workout smoothie? But the downside is psychological: people often overcompensate by eating back the calories they think they’ve burned, sabotaging their fitness goals.
The most accurate way to measure energy expenditure involves sophisticated equipment that tracks oxygen intake and carbon dioxide output—hardly practical for your neighborhood gym. So, while your treadmill might tell you you’ve “burned” 500 calories, you might want to mentally knock off at least a third of that number.
In the end, it’s better to see those glowing digits as guidelines, not facts. They might help you gauge effort—but they’re far from the truth about what’s actually happening inside your body’s metabolic system.[2]
8 Ice Water Technically Helps You Burn Calories (Barely)
If you’ve ever heard someone claim that “drinking ice water burns calories,” they’re not entirely wrong—just wildly optimistic. The logic is rooted in physics: your body must use energy to warm that icy liquid to your internal temperature of about 98.6°F (37°C). The process is real, but the results are hilariously underwhelming.
Here’s how it works. Suppose you drink a tall glass of ice water—say, about 16.9 oz (500 milliliters)—at 32°F (0°C). To warm that to body temperature, your body expends roughly 17.5 calories. That’s it. You’d need to drink about 70 glasses of ice water just to burn the calories from a single chocolate-chip cookie.
This phenomenon is known as thermogenesis, the process of generating heat through metabolic effort. The same principle is why you might shiver when cold—your body’s muscles contract to produce heat, which burns energy. Some diet trends have tried to capitalize on this by recommending “cold exposure” tactics, from ice baths to chilly walks. While such methods do slightly boost metabolism, the effect is modest unless combined with broader lifestyle changes.
In truth, the “ice water diet” is more of a myth. A 2006 study from the Journal of Clinical Endocrinology & Metabolism found that drinking cold water did increase calorie burn—but only by about 4% for a short time. That’s not even enough to offset a small bite of an apple.
So yes, technically, chugging ice water does force your body to use a bit of energy. But calling it a “weight loss trick” is like calling a paper airplane a “flight vehicle.” The science checks out—but the impact barely registers.
If you enjoy cold water, drink it. It’s refreshing, hydrating, and calorie-free. Just don’t expect it to replace your treadmill anytime soon.[3]
7 Labels Can Be Off by 20%—and That’s Totally Legal
When you pick up a snack labeled “100 calories,” you probably assume it contains 100 calories. But here’s the strange truth: that number could legally be as high as 120 or as low as 80, and the manufacturer wouldn’t be breaking any rules.
According to the U.S. Food and Drug Administration (FDA), nutrition labels are allowed a margin of error of up to 20%. This means a “low-calorie” meal with 250 calories could actually have 300. And because companies often use the most flattering estimates to make products seem healthier, most of those discrepancies lean upward—meaning you’re probably consuming more than you think.
This variance happens because the calorie counts on food labels aren’t measured directly. They’re estimated using something called the Atwater system, developed in the late 1800s. This method assigns standard values—4 calories per gram of protein, 4 for carbs, and 9 for fat—regardless of how the food is processed or how your body digests it. But digestion isn’t uniform. For example, whole nuts and fibrous foods often pass through the digestive system partially unabsorbed, meaning their true caloric impact is lower than the label suggests.
On the other hand, heavily processed foods—like potato chips or instant noodles—tend to deliver more usable energy than Atwater’s method predicts because they’re easier for your body to break down. Ironically, your body might absorb nearly all the calories from junk food but far fewer from raw vegetables or nuts of the same calorie count.
In 2012, scientists from the U.S. Department of Agriculture discovered that almonds, long thought to be calorie-dense, actually contain 20% fewer digestible calories than labels claim. Yet, the labeling system hasn’t changed.
So next time you meticulously count every calorie, remember that the numbers on the box might be lying—legally. The precision you think you’re achieving could just be an illusion wrapped in FDA-approved fine print.[4]
6 Calories Aren’t the Same Everywhere—Even for the Same Food
It sounds bizarre, but a slice of bread in one country might technically have a different calorie value than an identical slice somewhere else. That’s because calorie labeling isn’t a globally standardized system. Each nation calculates calories slightly differently—depending on local regulations, measurement methods, and rounding rules.
For instance, in the United States, calorie counts are often rounded to the nearest five or ten, and companies can ignore anything below five calories per serving by labeling it as “zero.” That’s how something like cooking spray or artificial sweetener can boast “0 calories” even when several servings might add up to a small meal. In Europe, on the other hand, calorie counts are typically listed in both kilocalories and kilojoules, with stricter rounding standards—but even then, small discrepancies persist due to different testing techniques.
In Japan, calories are measured using a unique method that estimates digestible energy instead of total energy content. That means a Japanese nutrition label might show fewer calories for the same portion of food compared to an American label—simply because Japan’s system accounts for the fact that not everything you eat is fully absorbed by your body.
Things get even stranger when you consider how food processing affects absorption. Toasting bread, for example, slightly reduces its water content, which increases the number of calories per gram—even though you haven’t added a single new ingredient. The same is true for dehydrated fruits, roasted nuts, and fried foods: they become more calorie-dense simply by losing moisture.
Then there’s the human factor. People digest food differently based on their gut bacteria, age, and even sleep patterns. Two people can eat identical meals, but one might absorb more calories than the other, up to a difference of 10% or more.
So while you might think calories are an absolute measure, they’re really a moving target—shifting depending on geography, labeling laws, and biology. That “200-calorie” snack bar might not mean the same thing in London, Tokyo, or Los Angeles—and it might not even mean the same thing for you and your friend sitting right next to you.[5]
5 The Human Body Wastes a Lot of the Calories It Takes In
We often think of calories like money—what you “spend” through exercise versus what you “earn” by eating. But here’s the weird part: your body is a terribly inefficient spender. In fact, a surprising amount of the calories you eat are never converted into usable energy for movement or storage. They’re simply lost in the messy chaos of digestion, metabolism, and heat production.
When you eat, your body doesn’t just “absorb calories.” It has to break down the food, transport nutrients, and rebuild molecules. All of that takes energy, too. Scientists call this the thermic effect of food (TEF)—the energy cost of processing what you eat. Protein, for example, is the most expensive macronutrient to digest, burning about 20–30% of its calories during digestion. Fat, on the other hand, is lazy—it only costs your body about 0–3% to process.
That means a 300-calorie steak doesn’t actually give you 300 usable calories. After digestion, your body might only get around 210 to 240. Fiber-rich foods waste even more, as some of their calories pass through undigested. Nuts are a classic example—studies show that almonds provide up to 20% fewer calories to your body than their labels suggest because much of their fat remains trapped in fibrous cell walls.
Then there’s heat loss. Your body constantly gives off warmth just by existing, a process called diet-induced thermogenesis. Even sitting quietly after a meal, you’re burning calories—about 10% of your daily total—simply because your metabolism is turning food into fuel inefficiently.
In a sense, humans are built with built-in “energy leakage.” That inefficiency is one reason why two people with identical diets and activity levels can still gain or lose weight differently. Genetics, hormones, gut bacteria, and muscle mass all change how much energy actually gets extracted from your food.
So while calorie math might look simple—”calories in versus calories out”—the biology behind it is anything but. Your body is less a calculator and more a leaky furnace, burning and wasting energy in unpredictable ways. The next time you see a 200-calorie snack, just remember: your body’s not keeping perfect score.[6]
4 You Can Survive on Zero Calories—but Only for a While
It sounds impossible, but history has repeatedly shown that humans can survive for astonishing lengths of time without consuming a single calorie. The record for medically supervised fasting goes to a Scottish man named Angus Barbieri, who, in 1965, lived on nothing but water, tea, coffee, and vitamin supplements for 382 days—more than a year—without any solid food.
Barbieri began his fast at 456 pounds (207 kg) and ended it weighing just 180 pounds (82 kg). Doctors closely monitored him at the University of Dundee in Scotland, ensuring his electrolyte balance and vitamin intake stayed safe. What kept him alive wasn’t magic—it was his body’s immense fat reserves. Fat is essentially stored energy, and each pound of it holds around 3,500 calories. That means Barbieri’s body had more than one and a half million calories to draw from before starvation truly began.
During prolonged fasting, the body enters a state called ketosis, where it burns fat for fuel instead of carbohydrates. Once the fat reserves are depleted, the body begins breaking down muscle tissue, eventually leading to organ failure. That’s why starvation beyond the body’s energy stores becomes fatal.
What’s fascinating—and a little eerie—is how adaptable the human metabolism can be. Barbieri reported feeling surprisingly energetic during his fast, though doctors noted occasional weakness and dizziness. He resumed eating gradually, and remarkably, he kept most of the weight off for years afterward.
Today, his case remains one of the most extreme demonstrations of human endurance and metabolic flexibility ever documented. It also serves as a grim reminder of how many calories we truly store in our bodies—enough to sustain life for months.
Of course, such fasting is incredibly dangerous without medical supervision and is never recommended. But it proves one bizarre fact: the human body can, under extraordinary conditions, survive on zero calories by becoming its own buffet.[7]
3 Your Brain Burns More Calories Than Any Other Organ
It might not feel like it when you’re sitting still, but your brain is one of the hungriest organs in your body. Despite accounting for only about 2% of your total body weight, it consumes around 20% of your daily calories—even when you’re doing nothing physically demanding.
That means if you eat a 2,000-calorie diet, roughly 400 of those calories are spent powering your thoughts, emotions, memory, and even your daydreams. The reason is that your brain is an energy-intensive machine. Every neuron (and you’ve got about 86 billion of them) uses electrical impulses and chemical signals that require constant fueling from glucose—your body’s primary energy source.
In fact, thinking hard literally burns more fuel. When scientists used brain imaging to study people solving complex math problems, they noticed a measurable uptick in glucose consumption in regions responsible for reasoning and focus. The increase isn’t massive—maybe a few extra calories per hour—but it’s proof that “mental effort” has a physical cost.
Babies and young children take this to an extreme. During early development, a child’s brain can consume up to 60% of their total energy intake, which explains why toddlers tire easily and need constant refueling. Even during sleep, the brain remains a metabolic powerhouse, performing maintenance tasks like memory consolidation, which still require significant energy.
But here’s the twist: using your brain more won’t make you lose weight. While intense mental work can raise calorie expenditure slightly, the effect is too small to offset any snack cravings it might trigger. In fact, some studies suggest that mental fatigue can increase hunger, leading people to eat more afterward—a cruel biological irony.
Still, the next time someone tells you that sitting and thinking isn’t real work, remind them that your brain burns calories just to keep you sane, focused, and breathing. Every idea, decision, or daydream costs energy—proof that even doing “nothing” can make you hungrier than you’d think.[8]
2 A Calorie from One Food Isn’t the Same as a Calorie from Another
“Calories are calories,” right? Not quite. While the term measures energy, not nutrition, your body doesn’t treat all calories equally. In fact, two foods with the exact same calorie count can have completely different effects on your metabolism, hunger levels, and fat storage.
Take, for instance, 100 calories of soda versus 100 calories of chicken breast. Both technically deliver the same amount of energy, but the soda’s sugar causes a rapid spike in blood glucose and insulin, encouraging fat storage and leaving you hungry again within minutes. The chicken, on the other hand, digests slowly, promotes satiety, and burns more calories during digestion thanks to its high protein content.
This difference stems from something called the metabolic pathway—the route your body uses to convert nutrients into usable energy. Protein takes a long and energy-demanding path (burning up to 30% of its calories in digestion), while refined carbohydrates like sugar are absorbed almost instantly, leaving little work for your body to do. Fats, meanwhile, are efficient fuel—great for long-term energy, but easy to store if you don’t use them.
Even more bizarre, some foods can trigger extra calorie burning through something known as the thermic effect of food (TEF). Spicy meals, for example, can slightly raise your metabolic rate because of compounds like capsaicin. Green tea and coffee also stimulate temporary increases in calorie expenditure by activating thermogenic processes.
Then there’s fiber, which throws an even bigger wrench into the system. High-fiber foods like beans and whole grains technically contain lots of calories, but your body can’t absorb them all because much of the fiber passes through undigested. That’s why 200 calories of lentils will leave you far fuller—and ultimately leaner—than 200 calories of candy.
So, while the laws of thermodynamics say that “a calorie is a calorie,” your body’s biology disagrees. It’s not just about how many calories you eat—it’s about what kind of calories they are, how fast they’re absorbed, and what your body has to do to use them. In short, not all calories are created equal, and some work a lot harder for you than others.[9]
1 Modern Calorie Counts Are Based on a 19th-Century Mistake
Here’s the strangest fact of all: the calorie system that dominates modern dieting—those numbers we obsessively count, label, and track—is based on an outdated experiment from the late 1800s that was never meant to guide human nutrition in the first place.
The man behind it was Wilbur Olin Atwater, an American chemist who wanted to understand how much “usable energy” people could get from food. He used a contraption called a bomb calorimeter—essentially a sealed metal chamber where food was burned to measure the heat it produced. From there, Atwater calculated that every gram of protein and carbohydrate released about 4 calories, and every gram of fat released about 9.
The problem? Humans are not furnaces. When food burns in a calorimeter, everything combusts perfectly, releasing all its potential energy. But our digestive systems don’t do that. We lose energy through undigested fiber, inefficient absorption, and metabolic processes that a machine can’t replicate. Atwater knew this, so he introduced rough “correction factors” based on the limited science of his time. Those rough estimates—4, 4, and 9—are still used on food labels more than 120 years later.
Modern research shows these values are often inaccurate by 10–25%, depending on the food. Protein, for example, varies by source; plant-based proteins may yield fewer usable calories than meat. Nuts, seeds, and fibrous foods are also undercounted because their calories aren’t fully absorbed. Yet the Atwater system remains the global standard for calorie calculation.
Even more astonishing, no major overhaul has ever been implemented despite scientists’ awareness of these flaws. The calorie counts on modern packaging are essentially educated guesses based on experiments done before the invention of the airplane.
In short, every “calorie” you’ve ever counted is part of a century-old mathematical compromise. It works well enough for general estimates, but it’s far from scientific precision. The fact that the entire world still measures diet and nutrition by this Victorian-era mistake is perhaps the most bizarre calorie fact of all.[10]