Calories Explained Simply: The Beginner's Guide

0 to Elite course · Lesson 32 of 100 · Level 2: Beginner Training & Nutrition

Calories sound complicated, but the idea behind them is simple. In this lesson you will learn what a calorie is, what maintenance, deficit and surplus mean, and how to find a sensible starting point without obsessing over numbers.

What is a calorie?

A calorie is a unit of energy. Food contains energy, and your body uses energy to stay alive, move and train. When people talk about calories in food, they mean kilocalories, written as kcal on UK food labels. You will also see kilojoules (kJ), which is the same energy in a different unit. Just use the kcal number.

You do not need to count calories forever. Learning roughly what is in your usual foods, even for a few weeks, teaches you portion sizes for life. Many people find that is the most useful thing counting ever gives them.

Calories come from three main nutrients, which you will meet properly in lesson 33 on macronutrients:

• Protein: about 4 kcal per gram.
• Carbohydrate: about 4 kcal per gram.
• Fat: about 9 kcal per gram.

Alcohol also contains calories, about 7 kcal per gram, but no useful nutrients. We cover it in lesson 41.

Energy balance: maintenance, deficit and surplus

In lesson 6 you learned the basic rule of body weight. Here it is with names attached:

• Maintenance: you eat roughly what you burn. Your weight stays about the same.
• Calorie deficit: you eat less than you burn. Your body makes up the gap from stored energy, including body fat, so you lose weight over time.
• Calorie surplus: you eat more than you burn. You gain weight. With strength training and enough protein, some of that can be muscle.

Your daily burn is made of your resting metabolism, digestion, exercise and everyday movement. That last part, NEAT, was the subject of lesson 31, and it is why two people of the same weight can need quite different amounts of food.

How many calories do you need?

The NHS uses reference intakes of about 2,000 kcal a day for women and 2,500 kcal for men. These are general guides for food labels, not personal targets. Your real needs depend on your size, age, sex, muscle mass and how active you are.

The easiest way to get a starting number is our free calorie and macro calculator. Treat whatever it gives you as an estimate. Then test it: eat at that level for two to three weeks, weigh yourself several times a week, and look at the trend. If your weight is steady, you have found roughly your maintenance.

For fat loss, a modest deficit works best. A safe rate for most people is about 0.5 to 1kg a week. Do not go below about 1,200 kcal a day without medical supervision. Our full guide to the calorie deficit explains how to set one, and how many calories are in 1kg of fat shows the maths behind it.

How to read a UK food label

Most UK packaging shows energy and nutrients per 100g and often per portion. Check what the portion size actually is: a “serving” of cereal or crisps is often smaller than what most people pour. Many front labels also use traffic light colours for fat, saturates, sugar and salt, which are a quick guide to how often to eat something.

Do calories matter more than food quality?

Calories decide whether your weight goes up or down. Food quality decides how full you feel, how well you recover and how healthy you are. You need both. A diet built mostly on lean protein, vegetables, fruit, whole grains and some healthy fats makes it much easier to hit your calorie target without feeling starving.

Safety: if you have diabetes, a medical condition, are pregnant or breastfeeding, or have a history of disordered eating, speak to your GP or a registered dietitian before counting calories or changing your diet.

Your action steps

1. Use the calculator to get an estimated maintenance number and write it down.
2. Read the labels on five foods you eat often. Note the kcal per portion and check if your real portion matches.
3. Log everything you eat for three normal days, including drinks and snacks, without changing anything.
4. Weigh yourself first thing in the morning three times a week and record it in the training log you started in lesson 28.

Frequently asked questions

What is the difference between a calorie and a kcal?

In everyday food talk they mean the same thing. UK labels show kcal, which is what people call calories, alongside kJ, which is the same energy in a different unit.

How many calories should I eat a day UK?

The NHS reference intakes are about 2,000 kcal for women and 2,500 kcal for men, but your needs depend on your size and activity. Use a calculator for an estimate, then adjust based on your weight trend.

Is a calorie deficit the only way to lose fat?

Yes, to lose body fat you need to use more energy than you take in over time. You can create that deficit by eating a little less, moving more, or ideally both.

Keep going

Previous: Lesson 31: What Is NEAT? The Calories You Burn Without Exercise

Next: Lesson 33: Macronutrients Explained: Protein, Carbs and Fat

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