A calorie is a unit of measurement for energy. When it comes to nutrition, it helps to measure the amount of energy that food and drinks provide to the body. It also helps us measure how much energy is needed for the body to function in basic tasks like walking and breathing, while keeping up the functions of all of our organs. 

Here is everything you need to know about how they work, why they matter, and the differences between them.
 

What Is a Calorie?

Scientifically, a calorie is defined as the energy required to raise the temperature of 1 gram of water by 1 degree Celsius. When we look at food labels, we are actually looking at kilocalories (kcal), or 1000 calories. These calories come from three main macronutrients found in our diets, and each macronutrient provides a different amount of corresponding calories. 

• Carbohydrates: 4 calories per gram

• Protein: 4 calories per gram

• Fats: 9 calories per gram

The Energy Balance Equation

Your body weight is a balancing act between the calories you take in and the calories you burn. This is the reason that fitness trainers all expound on the idea of calories in and calories out. 

• Calorie Deficit: When you consume fewer calories than your body burns, it uses stored fat (and sometimes muscle) for fuel, leading to weight loss. This is the main driving factor of weight loss. Muscle loss can be minimized if you pair your caloric deficit with strength training to retain muscle. 

• Calorie Surplus: When you consume more calories than you burn, your body stores the excess energy as fat, leading to weight gain. This also provides you with additional energy necessary to get bigger, through bulking. In order for you to gain more muscle mass, our body needs larger storages of energy to repair and build muscle fibres, without just burning protein that we ingest for just energy. 

• Maintenance: When calories consumed equal calories burned, your weight remains stable. This state is where you want to be once you have reached your ideal weight. This phase is very important for the longevity of your desired weight, as maintaining your caloric balance can help to balance out other aspects of your body, like your metabolism and hormones, to keep you from just gaining (or losing) all your progress. 

How Many Do You Need?

Your daily caloric needs are highly individual. They depend on your age, sex, current weight, and physical activity levels. General recommendations suggest that adult women typically need between 1,600 and 2,400 calories per day, while men usually require 2,000 to 3,000. Very active individuals, such as athletes, will burn significantly more calories and would need to eat more to be able to continue fueling their activity. A general guide for how much more would be about 100 calories more per day for every 10 minutes of physical activity. Endurance athletes who train all day can need as much as 3000+ more calories than normal!

Why "Not All Calories Are Created Equal"

While a calorie is a strict unit of measurement from a physics standpoint, how your body processes those calories depends entirely on the food source. This means that we can’t just eat junk food and expect our bodies to function the same as if we were eating whole foods. Here are some of the reasons why calories can differ:

1. The Thermic Effect of Food : Your body takes energy to burn energy. The energy goes into digesting and absorbing food that we eat. Depending on what we eat, different energy is required. More specifically, processing protein requires more energy (about 25% of the total calories) than processing fats or carbohydrates.

2. Nutrient Density: Not all food provides the same benefits. 100 calories of broccoli provide fiber, vitamins, and minerals, which keep you full longer and provide you with the essential nutrients needed for our bodies to function. 100 calories of sugary soda on the other hand, offers quick energy with no nutritional value.

3. Biochemical Pathways: Different foods can also affect our hormones, like leptin , ghrelin, and insulin. Highly processed foods can trigger different hormonal responses, sometimes causing you to feel hungrier (ghrelin) or store fat more easily (insulin) than if you ate whole, unprocessed foods.

Finding a Healthy Approach

While tracking calories is a popular and useful short-term tool to build awareness of portion sizes, relying entirely on it can be exhausting. For long-term health, nutritionists generally recommend focusing on the quality of the food matrix, prioritizing whole, fiber-rich, and protein-dense foods.