Welcome back: let's talk about energy
In Level 1 we worked out who you can trust: the NHS, the British Dietetic Association and the Scientific Advisory Committee on Nutrition (SACN). Today we're using that on a word you see everywhere, which is calories.
First, a quick reminder. This course is general education. It isn't medical or dietetic advice. If you have a health condition, or you're unsure about your own needs, your GP or a registered dietitian is the right person to ask.
Right. Let's take some of the stress out of calories.
So what is a calorie, really?
Here's the simple answer. A calorie is a unit of energy. That's it. The NHS puts it plainly: the amount of energy in food or drink is measured in calories.
Think of it like miles on a road sign. A mile measures distance. A calorie measures energy. It doesn't tell you if a food is "good" or "bad", just as a mile doesn't tell you if the road is pretty.
On UK labels you'll usually see two numbers. kcal is short for kilocalories, and that's what people mean when they say "calories". kJ is short for kilojoules, a metric unit for the same thing. One kcal is about 4.2 kJ. That's why the kJ number is always the bigger one. Don't panic, it's the same energy in a different unit.
Where does the energy in food come from?
Food gets its energy from a few main parts. Carbohydrate and protein each give about 4 kcal per gram. Fat gives about 9 kcal per gram, a bit more than twice as much. Alcohol gives about 7 kcal per gram.
Does that make fat "bad"? Not at all. It just means fat is energy-dense. A small amount packs a lot of fuel. We'll look at each of these properly in later levels, so for now just hold on to the idea that different parts of food carry different amounts of energy.
Where does your body's energy go?
Here's a question for you. If you lay on the sofa all day without moving, would you use any energy?
Yes, and quite a lot! Your body uses energy just to keep you alive. Your heart beats, you breathe, your brain thinks, you stay warm, and your cells repair themselves. This resting energy use is called your basal metabolic rate, and for most people it's the biggest share of the energy they use each day.
On top of that, you use energy when you move. That means planned exercise, but also walking to the shop, climbing stairs, gardening and even fidgeting. The NHS gives a nice example: fast walking uses more energy than walking at a moderate pace.
And you even use a little energy to digest your food.
So your body is more like a house with the heating on all the time than a car parked in a garage. It's always using energy, even when you're resting.
Energy balance, explained calmly
Now for the big idea: energy balance.
The NHS explains it like this. To stay at about the same weight, the energy you use should roughly match the energy you take in from food and drink. Take in more than you use over time and you tend to gain weight. Take in less and you tend to lose weight.
You may have heard the guide figures: about 2,000 kcal a day for an average woman and 2,500 kcal a day for an average man. But notice the word "average". The NHS says your needs depend on things like your age, height, weight and how active you are. These are rough guides used on food labels. They aren't a personal target you have to hit.
Here's the part that matters most. Energy balance works over weeks and months, not over one meal.
Think of a bank account. One big spend doesn't make you broke, and one payday doesn't make you rich. What counts is the pattern over time. A slice of birthday cake, a big Sunday lunch or a day when you're extra hungry won't decide your health. Your body copes with ups and downs very well.
So if you've ever felt guilty after one meal, you can let that go. That's not how the science works.
Why not just count everything?
You might be wondering whether counting every calorie is the "proper" way to do this.
Some people find tracking useful for a while. But label and app numbers are estimates, and your body's needs change from day to day. Counting can also make food feel stressful for some people.
There's a gentler tool you already have, and that's your hunger and fullness cues. Hunger might feel like a rumbling tummy, low energy or finding it hard to focus. Comfortable fullness feels satisfied, not stuffed.
If thoughts about food, calories or your body ever feel overwhelming, please talk to your GP. The UK eating disorder charity Beat offers support too. Asking for help is a strong thing to do.
Your one-week experiment
Here's your change to try for a week. Before each meal, pause and ask yourself: how hungry am I right now? Then halfway through, check in again: am I still hungry, or comfortably satisfied?
There's no right answer. You're just noticing.
How to check it: each evening, write a short note of two or three lines. For example: "Lunch: very hungry before, comfortable after. Ate a snack when I was bored, not hungry." At the end of the week, read your notes back. Do you spot any patterns, like long gaps that leave you ravenous, or eating on autopilot?
Whatever you find is useful. There's nothing to pass or fail here.
Key takeaways
- A calorie is a unit of energy. On labels, kcal and kJ measure the same thing, and 1 kcal is about 4.2 kJ.
- Fat gives about 9 kcal per gram, carbohydrate and protein about 4, and alcohol about 7.
- Your body uses energy all the time: to keep you alive at rest (the biggest share), to move and to digest food.
- Energy balance works over weeks and months. One meal or one day doesn't decide your health.
- 2,000 kcal and 2,500 kcal are average guides, not personal targets.
- Noticing your hunger and fullness can be a calmer tool than counting everything.