A story you might recognise
Sofia eats what most people would call "healthy". Porridge for breakfast. A salad at lunch. Salmon for dinner. She has not touched a chocolate bar in three weeks. And yet the scales had not moved.
The problem is not her food choices. The problem is that Sofia is eating roughly 400 kcal more than her body needs every single day. The extra drizzle of olive oil here, the generous handful of nuts there, the oat milk latte she does not count. None of it feels like indulgence. All of it counts.
Once Sofia really understood energy balance, she stopped blaming herself and started adjusting the right things. Within eight weeks she lost 4 kg without changing a single food she enjoyed.
Calories are your energy currency
Think of your body as a bank account measured in kilocalories. Every food and drink you consume makes a deposit. Every heartbeat, breath, step and thought makes a withdrawal. The balance at the end of each day determines whether you gain, lose, or maintain weight.
Calories in < out
Running a daily deficit
Body burns stored fat
Calories in = out
Perfectly balanced
Weight stays stable
Calories in > out
Running a daily surplus
Excess stored as fat
This is not a diet trend. It is the first law of thermodynamics applied to human metabolism, and it underpins every credible nutrition framework ever published.
What is your TDEE?
TDEE stands for Total Daily Energy Expenditure: the total number of calories your body burns in a day. It is made up of four components:
Basal Metabolic Rate
Energy burned at complete rest: keeping your heart beating, lungs breathing, cells repairing. This alone accounts for 60-70% of TDEE.
Non-Exercise Activity Thermogenesis
All movement that is NOT deliberate exercise: walking to the car, fidgeting, doing the washing up. Surprisingly large impact.
Exercise Activity Thermogenesis
Planned workouts: gym sessions, runs, yoga classes. Typically 5-15% of TDEE for moderately active people.
Thermic Effect of Food
Energy used to digest, absorb and process the food you eat. Protein costs the most (20-30%); fat costs the least (0-3%).
Approximate TDEE ranges by activity level (average woman, 65 kg):
| Activity level | Multiplier | Approx. TDEE |
|---|---|---|
| Sedentary (desk job, little movement) | ×1.2 | 1,560-1,700 kcal |
| Lightly active (1-3 workouts/week) | ×1.375 | 1,790-1,950 kcal |
| Moderately active (3-5 workouts/week) | ×1.55 | 2,010-2,200 kcal |
| Very active (6-7 hard sessions/week) | ×1.725 | 2,240-2,450 kcal |
Your personalised TDEE was calculated and sent to your email before you started this programme.
The pizza that explains everything
Pizza is not the enemy. But the difference between a takeaway pizza and a home-made pizza illustrates why calorie awareness changes everything.
Takeaway thick-crust (whole)
~2,400 kcal
- • Roughly a full day’s TDEE in one meal
- • High in refined carbs, saturated fat
- • Low protein relative to total calories
- • Engineered oil blends that are hard to track
Home-made thin-crust (whole)
~900 kcal
- • Fits comfortably in most daily targets
- • Control over ingredients and portions
- • Add extra protein toppings easily
- • Tastes just as satisfying
The lesson is not "never eat out"
If you did a long run this morning and burned an extra 600 kcal, even a 1,200 kcal post-run pizza fits your day. The same food, in the same quantity, is either a problem or perfectly fine, depending on the context of your total day. That is CICO in real life.
What CICO does not mean
"Calories in, calories out" does not mean all calories are equal or that food quality is irrelevant. Far from it. Within your calorie target, what you eat determines everything else:
Hunger
Protein and fibre keep you full for hours. The same calorie total in refined carbs leaves you ravenous two hours later.
Energy
Whole foods stabilise blood sugar. Ultra-processed foods cause the energy crashes that trigger afternoon snacking.
Hormones
Adequate protein and fat support oestrogen, thyroid, and cortisol, the hormones that directly influence fat storage and mood.
Sustainability
A diet of 80% whole foods with 20% flexibility is far easier to maintain than any rigid "clean eating" approach.
Small daily imbalances, big yearly results
Energy balance compounds over time. Here is what the maths looks like:
500 kcal above TDEE every day
~0.45 kg gained per week ? ~23 kg per year
250 kcal above TDEE every day
~0.23 kg gained per week ? ~12 kg per year
Exactly at TDEE every day
Weight stays stable: maintenance achieved
300 kcal below TDEE every day
~0.27 kg lost per week ? ~14 kg per year
The 500 kcal limit
A deficit larger than 500 kcal/day is counterproductive: it triggers muscle breakdown and metabolic adaptation. Sustainable fat loss sits between 250 and 500 kcal below TDEE.
Awareness alone causes change
A fascinating pattern emerges in nutrition research: people who simply start tracking what they eat, without changing anything deliberately, consume fewer calories within the first week. The act of noticing is itself an intervention.
You are not going to count calories forever. But doing it accurately for even five days builds an internal map of portion sizes and calorie density that stays with you for life. If you want to try it, here is how to get started.
Using a food tracker
The easiest way to track calories is with a free app. One of the most popular options is MyFitnessPal. Here is how to get started:
- 1Download the free MyFitnessPal app from the App Store or Google Play, then create a free account.
- 2Tap Diary at the bottom of the screen and select the correct meal (Breakfast, Lunch, Dinner, or Snacks).
- 3Tap Add Food. You can search by name, scan a barcode, or type a description.
- 4Adjust the quantity to match your actual portion. Weigh or measure where possible, especially for oils, nuts, and grains.
- 5Tap the tick / checkmark to save the entry. Repeat for every food and drink throughout the day, including cooking oils and sauces.
- 6At the end of the day, check your total calories against the diary summary and compare it with your TDEE.
Prefer a different tracker? That is fine.
- -Apple Health (iPhone)
- -Fitbit app
- -Samsung Health
- -Cronometer: free, accurate
- -Nutracheck: popular in the UK
- -Written diary: pen and paper works perfectly