What Is a Calorie?

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iStock

The word calorie carries a lot of weight. We know we're supposed to avoid too many of them, but things get more complicated after that. What, exactly, are calories, and how do I burn them?

THE SCIENCE OF THE CALORIE

A calorie is a unit of heat energy that fuels your body, making it possible to move, breathe, think, sleep—and even digest food to make more energy.

While there is some disagreement about who first coined the term calorie, we know the French chemist Antoine Lavoisier used it in experiments he conducted during the winter of 1782–1783. He used a device called a calorimeter to measure how much ice melted in a metal container due to the heat emitted by guinea pigs housed inside it. Over time, that measurement was refined by other scientists to mean the amount of energy needed to raise the temperature of a kilogram of water by 1°C—what's known as a kilocalorie.

The food calorie and a kilocalorie (kcal) are technically the same thing, but we use the term calorie rather than kilocalorie because of an American chemist named Wilbur Olin Atwater. In the late 1880s, Atwater traveled to Germany to study at physiologist Carl Voit's laboratory, where Voit was researching the nutritional value of food and animal feed. Inspired by that research, Atwater took measurements of different foods with a bomb calorimeter—a device that essentially measures the heat in food when burned—by having study participants eat, and then measuring and subtracting [PDF] the amount of heat leaving their bodies through respiration and waste. He used a respiration calorimeter to measure their breath and a bomb calorimeter to burn their poop, and from that calculated just how many calories were left in their bodies to be used. When writing about his research, Atwater used the word calorie (kcal wouldn't be used in America until 1894, when it was published in a physiology textbook).

Based on his experiments, Atwater created a system for calculating the calories that human bodies can get from our food. There are three types of food nutrients that deliver caloric energy—fats, proteins, and carbohydrates—and Atwater arrived at a caloric measurement of each: A fat gram has nine calories, while a gram of protein and a gram of carbohydrates each have four. That system was modified [PDF] by USDA scientists in 1973, but it's otherwise still the basis for how calories are calculated today.

WHAT HAPPENS TO A CALORIE IN YOUR BODY

When you eat, enzymes in the mouth, stomach, and intestine break down nutrients by turning fats into fatty acids, sugars into simple sugars, and proteins into amino acids. Then, using oxygen cells throughout your body, these components are broken down into energy—a process known as metabolism.

Most of the calories we burn each and every day are used just to keep our body functioning, with about half going toward powering our major organs—the brain, liver, kidneys, and heart. We use the rest for physical activity and the process of converting food to energy. Anything not used by the body is then stored, first in the liver and eventually as fat cells.

Some foods, like honey (carbohydrates), are easily digestible, whereas nuts (a mix of carbohydrates, fat, and protein) can't actually be fully digested at all. There are also digestibility differences within the same type of food. For example, in plants, older leaves tend to be sturdier (and therefore harder to digest) and less caloric than younger ones. Most significantly, especially in terms of human evolution, whenever we cook or process food, the body can get more calories as compared to that same food eaten raw. All of this has an impact on the amount of calories we can actually use.

There's no food you can eat to speed up the rate at which you burn calories (changes from foods like spicy peppers are fleeting), but factors like age and rapid, drastic weight loss can slow it down.

Building more muscle can increase your metabolic rate (although how much is debatable), since muscle requires more energy to function than fat does. And while cardiovascular exercise might not permanently boost your metabolism, it does burn calories; just how much depends on your weight and how vigorously you exercise.

Examples of higher calorie burning exercises include cycling and running, but almost every activity burns something, so you could potentially burn more calories throughout the day by consistently doing low-energy activities like gardening or pacing during a conference call than you would during 30 minutes of fast cycling.

CALORIES: A SCIENCE IN FLUX

We still use the Atwater system for calculating food calories, but it's far from perfect. For one thing, a USDA study found that people absorbed fewer calories from nuts than had been estimated under Atwater's system—a serving of almonds, for example, provided not 170 calories, but 129. There's some evidence that people tend to digest food at all sorts of different rates too, depending on the individual makeup of our gut bacteria, meaning that the absorption of calories may differ from person to person.

Scientists now believe the numbers on food labels are more of an estimate than a precise measurement. While companies are required to provide caloric information on food labels, the FDA doesn't specify exactly how those calories should be calculated. Some companies, like McDonald's, send their food to a lab for measurement, while others estimate the total by adding up the calorie count for each food component from the USDA's massive food composition database. As scientists continue to refine how we calculate calories, we'll come to have a better idea of the energy we can actually get from these different foods.

10 Wireless Chargers Designed to Make Life Easier

La Lucia/Moshi
La Lucia/Moshi

While our smart devices and gadgets are necessary in our everyday life, the worst part is the clumsy collection of cords and chargers that go along with them. Thankfully, there are more streamlined ways to keep your phone, AirPods, Apple Watch, and other electronics powered-up. Check out these 10 wireless chargers that are designed to make your life convenient and connected.

1. Otto Q Wireless Fast Charging Pad; $40

Otto Q Wireless Fast Charging Pad
Moshi

Touted as one of the world's fastest chargers, this wireless model from Moshi is ideal for anyone looking to power-up their phone or AirPods in a hurry. It sports a soft, cushioned design and features a proprietary Q-coil module that allows it to charge through a case as thick as 5mm.

Buy it: Mental Floss Shop

2. Gotek Wireless Charging Music Station; $57

Gotek Wireless Charging Music Station
Rego Tech

Consolidate your bedside table with this clock, Bluetooth 5.0 speaker, and wireless charger, all in one. It comes with a built-in radio and glossy LED display with three levels of brightness to suit your style.

Buy it: Mental Floss Shop

3. BentoStack PowerHub 5000; $100 (37 percent off)

BentoStack PowerHub 5000
Function101

This compact Apple accessory organizer will wirelessly charge, port, and store your device accessories in one compact hub. It stacks to look neat and keep you from losing another small piece of equipment.

Buy it: Mental Floss Shop

4. Porto Q 5K Portable Battery with Built-in Wireless Charger; $85

Porto Q 5K Portable Battery with Built-in Wireless Charger
Moshi

This wireless charger doubles as a portable battery, so when your charge dies, the backup battery will double your device’s life. Your friends will love being able to borrow a charge, too, with the easy, non-slip hook-up.

Buy it: Mental Floss Shop

5. 4-in-1 Versatile Wireless Charger; $41 (31 percent off)

4-in-1 Versatile Wireless Charger
La Lucia

Put all of those tangled cords to rest with this single, temperature-controlled charging stand that can work on four devices at once. It even has a built-in safeguard to protect against overcharging.

Buy it: Mental Floss Shop

6. GRAVITIS™ Wireless Car Charger; $20 (31 percent off)

GRAVITIS™ Wireless Car Charger
Origaudio

If you need to charge your phone while also using it as a GPS, this wireless device hooks right into the car’s air vent for safe visibility. Your device will be fully charged within two to three hours, making it perfect for road trips.

Buy it: Mental Floss Shop

7. Futura X Wireless 15W Fast Charging Pad; $35 (30 percent off)

Futura X Wireless 15W Fast Charging Pad
Bezalel

This incredibly thin, tiny charger is designed for anyone looking to declutter their desk or nightstand. Using a USB-C cord for a power source, this wireless charger features a built-in cooling system and is simple to set up—once plugged in, you just have to rest your phone on top to get it working.

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8. Apple Watch Wireless Charger Keychain; $20 (59 percent off)

Apple Watch Wireless Charger Keychain
Go Gadgets

This Apple Watch charger is all about convenience on the go. Simply attach the charger to your keys or backpack and wrap your Apple Watch around its magnetic center ring. The whole thing is small enough to be easily carried with you wherever you're traveling, whether you're commuting or out on a day trip.

Buy it: Mental Floss Shop

9. Wireless Charger with 30W Power Delivery & 18W Fast Charger Ports; $55 (38 percent off)

Wireless Charger from TechSmarter
TechSmarter

Fuel up to three devices at once, including a laptop, with this single unit. It can wirelessly charge or hook up to USB and USB-C to consolidate your charging station.

Buy it: Mental Floss Shop

10. FurniQi Bamboo Wireless Charging Side Table; $150 (24 percent off)

FurniQi Bamboo Wireless Charging Side Table
FoneSalesman

This bamboo table is actually a wireless charger—all you have to do is set your device down on the designated charging spot and you're good to go. Easy to construct and completely discreet, this is a novel way to charge your device while entertaining guests or just enjoying your morning coffee.

Buy it: Mental Floss Shop

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It's Black Birders Week—Here's Why Celebrating Black Scientists and Naturalists Matters

Rawpixel/iStock via Getty Images
Rawpixel/iStock via Getty Images

BlackAFInSTEM, a community of Black scientists, kicked off the inaugural Black Birders Week from May 31 through June 5. What started as a group chat organized by birder Jason Ward evolved, in a matter of mere days, into a week-long celebration of Black naturalists. “It is a movement that was started out of pain, and its goal is not necessarily pleasure, but uplifting,” Alexander Grousis-Henderson, a zookeeper and member of BlackAFInSTEM, tells Mental Floss. “We want people, especially our community, to come out of this stronger and better.”

The movement started after a video of a white woman harassing and threatening Christian Cooper, a Black birder, went viral. As part of Black Birders Week, you can follow along as professional and amateur Black naturalists, scientists, and outdoor enthusiasts share their expertise and experiences and celebrate diversity in the outdoors. Throughout the week, members of BlackAFInSTEM are facilitating online events and conversations like #AskABlackBirder and #BlackWomenWhoBird.

Though Black Birders Week was created for Black nature enthusiasts, everyone is welcome to participate. Follow along the #BlackBirdersWeek hashtag, or check out the @BlackAFInSTEM Twitter account. Ask questions, engage with their posts, or simply retweet the scientists to help amplify their voices.

Scroll through the hashtags on Twitter and Instagram, and you’ll find a stream of Black naturalists honoring their love of the outdoors. “We want kids to see our faces and attach them to the outdoors, and we want our peers to recognize that we belong here too,” Grousis-Henderson tells Mental Floss.

Not only does Black Birders Week make space for Black birders to share their passion, it’s also a way for the community to raise awareness of their unique experiences and address systemic racism in nature and STEM (science, technology, engineering, and math). According to Grousis-Henderson, it’s an opportunity to foster a dialogue within the birding community; to prompt conversations about diversity within the outdoors.

“We wanted to draw on what we know about the diversity of biological systems and bring that perspective to social systems,” Grousis-Henderson says. “A diverse ecosystem can stand up to a lot of change, but a non-diverse ecosystem, one lacking biodiversity, is easy to topple.”

The movement goes beyond birding. Alongside Black Birders Week, Black outdoorspeople are sharing their experiences of what it’s like to be a Black person in nature—a space where they’re far too often made to feel unwelcome and unsafe. Organizations like Backyard Basecamp, Melanin Base Camp, and Outdoor Afro continue to foster the Black community's connection to nature.

"Black Birders Week is an opportunity to highlight joy and belonging, to showcase expertise, and to remind people that Black people have been inextricably connected to nature for generations," Yanira Castro, communications director for Outdoor Afro, tells Mental Floss in an email. "It is a celebration of that relationship."