You see the word calories everywhere: on food labels, diet plans, gym equipment, etc. But what does it mean?

A calorie is a unit of energy. It’s the energy needed to raise the temperature of 1 gram of water by 1 degree Celsius. Sounds super scientific, right? 

But in everyday life, when we say “calorie,” we’re talking about how much energy your body gets from food.

When you eat food, your body digests it and extracts energy. That energy fuels everything you do. And when we say “everything,” it means everything, including walking, talking, exercising and even the stuff you don’t even think about, like your heart beating, lungs breathing, and brain thinking.

Now, why do calories matter? And why do you need to know about them? Well, keep reading to see all you need to know and why you need to know about calories. 

Why Do Calories Matter?

They matter because they’re essential for survival! 

Without enough calories, your body wouldn’t have the energy to function. And on the flip side, too many, especially without enough physical activity, can lead to weight gain and other health problems like high blood pressure, diabetes, and heart disease.

So it’s not about whether they are good or bad; it’s about balance. The goal isn’t to fear them or avoid them entirely. It’s to understand how much your body needs and make sure you’re getting them from nourishing, nutrient-dense foods.

In simpler terms, as fuel is to the car, so are calories to the body. You don’t get it?

Okay, here’s what we mean: your body is like a car, and calories are the fuel. If you don’t put in enough, you’ll stall. Put in too much without driving around? You’ll end up with excess fuel (aka stored fat) by sitting around.

How Calories Work in the Body

Calories don’t just enter your body and magically disappear. There’s a whole process going on behind the scenes! Let’s walk you through that process.

Calories In vs. Calories Out

This is a simplified way of saying: The calories you consume (food and drink) vs. the calories your body burns (through daily activities and bodily functions)

If you eat more calories than you burn, your body will most likely store the extra energy as body fat. If you eat fewer of them than you burn, your body taps into stored fat (or sometimes muscle) to get the energy it needs.

This balance between your calorie intake and output determines whether you maintain your weight, lose it, or gain it. 

The Journey of a Calorie

Once you eat food, digestion kicks in. Your body breaks that food down into smaller molecules, which are mainly glucose (from carbs), amino acids (from protein), and fatty acids (from fat). These molecules enter your bloodstream and are either used right away for energy (especially glucose) or stored in muscles, liver, or fat cells for later use

So, let’s say you eat a bowl of oatmeal. Your body breaks it down into glucose, sends it into your blood, and your cells use it to give you energy. If you don’t need all that energy immediately, some of it gets stored, just in case you skip your next meal or need a burst of energy later.

Basal Metabolic Rate (BMR): Calories You Burn at Rest

Did you know that you burn calories even when you’re doing absolutely nothing? Your Basal Metabolic Rate (BMR) is the number of calories your body uses just to keep you alive. That includes:

• Breathing
• Circulating blood
• Regulating body temperature
• Maintaining organ function
• Repairing cells

BMR accounts for about 60–75% of your total daily calorie burn. Yes, that much! 

Your BMR depends on several factors, such as

• Age (it tends to slow down as you get older)
• Sex (men typically have a higher BMR than women)
• Muscle mass (more muscle = higher BMR)
• Genetics (some people naturally burn more calories)
• Physical Activity and Thermogenesis

Total Daily Energy Expenditure (TDEE)

Total Daily Energy Expenditure (TDEE) is simply a fancy term for how many calories you burn in a day. Beyond your BMR, you  also burn calories through:

• Physical Activity: Any movement counts: walking, working out, climbing stairs, or dancing in your room.
• Thermic Effect of Food (TEF): Believe it or not, your body burns calories just to digest and absorb food. Protein requires more energy to process than carbs or fats.
• Non-Exercise Activity Thermogenesis (NEAT): These are the calories you burn doing stuff like fidgeting, typing, or doing chores.

Conclusion

Calories are a crucial part of how your body survives and thrives. Every bite of food provides energy that fuels your cells, keeps your organs running, and gives you the power to move, think, and grow.

So, instead of counting them out of fear or guilt, start thinking about them as the power source behind your amazing body. 
You can check out Calorie 102 to see how to know if you’re taking enough calories, how to track them, and much more!