Hi ,
This week I want to talk properly about calories.
You’ve probably heard both of these:
“It’s simple – calories in, calories out.”
“It’s not that simple, hormones and metabolism matter more.”
The truth, as usual, sits somewhere in the middle. The physics is simple. Real life… isn’t always.
What is a calorie, really?
A calorie isn’t “good” or “bad”. It’s just a unit of energy. Like centimetres for distance, or degrees for temperature.
On food labels we actually use kilocalories (kcal), but everyone just calls them “calories”. When you see 200 kcal on a packet, that’s basically “this food contains 200 units of usable energy”.
In the lab, it’s measured in a very un-foodie way. Scientists dry the food, seal it in a metal container, and literally burn it in pure oxygen. The container sits in water. As the food burns, the water warms up. By seeing how much the water temperature rises, they can work out how much energy was inside the food.
We obviously don’t burn our food like that inside our bodies (hopefully), so we use standard values instead:
Protein and carbs give roughly 4 kcal per gram
Fat gives roughly 9 kcal per gram
Alcohol sits in the middle at about 7 kcal per gram
Food labels are based on these averages. They aren’t perfect for every single person in every situation, but they’re accurate enough to be useful.
Calories in vs calories out – the simple bit
If you zoom out, the basic rule still holds:
Over time, if you consistently take in more energy than you use, you gain weight.
Over time, if you consistently use more energy than you take in, you lose weight.
Your daily “calories out” comes from three main things:
Keeping you alive at rest (heart beating, brain working, keeping you warm)
Moving around (steps, training, cleaning, fidgeting, all of it)
Digesting food (your body uses some energy to process what you eat)
That side of the equation is real, but it’s not a fixed number. It changes as your body and habits change. That’s where people get tripped up.
How a calorie deficit works (and why it slows down)
If, over time, you eat less than your body uses, your body has to dip into its energy stores. First it leans on carbohydrate stored in your muscles and liver (glycogen), then more and more on body fat. If protein is low and the deficit is very aggressive, your body can also break down a bit of muscle, which we don’t want.
This is why, when people ask me about fat loss, I usually come back to:
A moderate calorie deficit
Enough protein
Some form of resistance training
That combination makes it easier to lose fat while keeping as much muscle as you reasonably can.
Here’s the frustrating bit: as you lose weight, your body quietly adapts. A lighter body simply uses less energy to exist and move. Many people also start moving a little less without noticing – fewer steps, less fidgeting, more collapsing on the sofa when they’re tired. Hunger hormones can shift too, so you feel hungrier.
So the deficit you had at the start often shrinks over time, even if you’re eating “the same”. You haven’t “broken” your metabolism, but your body has adjusted to a new situation. That’s one reason weight loss often slows down or plateaus.
How a calorie surplus works
On the other side, a small surplus – just a bit more food than you need – doesn’t feel like much in a single day. But over weeks and months, it quietly adds up.
Extra energy can be stored as:
More body fat
Some muscle, if you’re lifting weights and getting enough protein
Two people can eat apparently similar diets and gain at different rates because their “calories out” differs. One person naturally moves more, fidgets more, or has a more active job. The other sits more without really thinking about it. Same input, different output.
Again, the basic physics still applies – it’s just happening in a moving target, not a fixed machine.
How to use this without going crazy
I don’t think most people need to count every calorie forever. For some, tracking for a short period can be eye-opening. For others it becomes stressful very quickly.
A few ideas that sit in the middle:
Use calories as information, not judgement.
Get a rough sense of where your “heavier” calories are coming from – drinks, oils, ultra-processed snacks, big portions of energy-dense foods.
Instead of obsessing over every number, build structure:
Protein at each meal
Vegetables taking up space on the plate
If your goal is fat loss and the scale hasn’t moved for a few weeks, rather than assuming something is wrong with you, first ask:
Have my portions crept up a bit?
Am I moving less because I’m more tired or my routine changed?
Do I need a small adjustment, not a drastic overhaul?
Think of it like steering a ship, not flipping a switch. Small course corrections over time matter more than one “perfect” week followed by giving up.
Got questions about tracking, plateaus, or how calories fit alongside hormones and hunger cues?
Reply to this email – I read every message personally.
See you next week,
Gabriel, Nutrition Hacks | gbMeals