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What are calories?


what are calories walking

We all know calories are key to losing and gaining weight, but what exactly are calories and how do they work? Here’s everything you need to know about calories.


What exactly are calories? 

You’ve probably heard people say calories are a unit of energy. And that’s correct – when food is measured in calories, it means that’s the amount of energy in the food. But that still doesn’t really explain what a calorie is.


In scientific terms, one calorie is the amount of energy needed to raise 1 kilogram of water by 1 degree Celsius. So now you know!


Is kcal the same as calories?


Calories are sometimes listed on food labels and on diet plans as kcal. This is just a short way of writing kilocalories, which is another word for calories. Whether you see kcal, cals, or calories, it’s all the same thing. 100 kcal is 100 calories.


How are calories measured?


Ever wondered how the people who write food labels actually measure the number of calories in the food? It’s a good question. These days, it’s done by adding up the calories per gram in the food’s protein, carbohydrates, and fats (minus the fibre component of the carbs). (1)



What happens to calories in the body?


As we know, calories are a unit of energy. So when you eat or drink, the calories are released as energy during the digestion process. Your body uses all the energy it needs, and stores the rest for later. Excess calories are stored as glycogen (sugars) and body fat.


Calories from carbohydrates tend to be converted into glycogen and stored in your muscles and liver cells. Every 1g of carbs needs 3g of water to be stored. According to scientists, the average healthy human body can store about 500g of carbohydrates in this way (that’s about 2000 kcal of energy). (2) Once your glycogen stores are filled up, your body will store any extra calories as body fat.

What are calories running

What happens when calories are burned?


Ready to understand how your body actually burns calories? This complex process – known simply as your metabolism – combines the calories in food and drink with oxygen to release energy. Remember, your body doesn’t just need energy for energetic stuff like training. You are constantly using calories for invisible functions like cell repair, hormones, blood circulation, and breathing.


Can calories make you fat?


Calories are at the root of weight gain and fat gain. It’s pretty simple – if you consume more calories than your body needs, you will eventually gain weight. Some of this weight will be from the water needed to store the carbohydrate calories. And some will be body fat, as your fat cells fill up with stored energy.


The best way to avoid getting fat from calories is to make sure you balance your calories in (from food and drink) with your calories out (from your BMR, daily activity, and training).


Does drinking calories make you gain weight?


It’s really common to gain weight from calories in drinks, but this isn’t because those liquid calories are any more calorific than others. The reason some people gain weight from drinking calories is that it’s much harder to know how many calories you’re drinking.


Think how easy it is to drink a 500 kcal hot chocolate, fancy coffee, or cocktail. It just doesn’t fill you up, does it? But if you ate 500 kcal from lean protein and vegetables, you’d feel pretty full. That’s why calories from drinks are sometimes called “empty calories”.


If you don’t want to gain weight, make sure you understand how many calories are in your drinks and keep a note of your calorie intake.

what are calories walking

What do 2000 calories look like?


Counting calories helps you see all the ways you could eat 2000 kcal. For example, you could splurge 2000 kcals on a cooked breakfast, large latte, and burger meal with chips. Or you could spread out those calories and fit in a smoked salmon bagel, chicken sandwich, rice and chilli dish with a side salad, and still have room for a PhD Smart Bar. Eye-opening!


What is my maintenance calories?


Wouldn’t you love to know how to maintain a healthy weight? The truth is, it’s not a secret. Your body holds the key, and it’s called your TDEE. TDEE is the total daily energy expenditure. This is the total amount of calories per day your body needs for its BMR (basal metabolic rate), your NEAT (non-exercise activity thermogenesis), and any physical activity.


If that sounds complicated, just remember that the number of calories you need every day will be different to anyone else. Your height, weight, muscle mass, age, and activity level creates your personal magic number. And your maintenance calories will change over time, too, especially after weight loss.


Use this website to get a decent estimate of your current TDEE maintenance calories, but remember to review it any time your lifestyle or body changes and seek medical advice if you need help. (3)


Don’t forget to fuel yourself Pre, Intra and Post-workout – You can grab yourself all your workout must-haves here.  Make sure to let us know how you get on with your training program and tag us in your workouts on InstagramFacebook, and Twitter – @phdnutrition.

We love seeing your workouts, recipes, and having you as part of our community. If you want to make sure to check out more of our amazing blogs here or grab yourself some of our other Smart Whey Protein to fuel your workouts even further.










Nicola is a specialist freelance copywriter for the fitness industry @thefitwriter