You count calories accurately by doing four things: weigh your food (at least at the start), use the per-100 g values from the label or a reference database, log right after eating, and never skip oil, sauces or drinks. Everything else is fine-tuning worth a few dozen calories, not a few hundred.
What does counting calories actually mean?
Counting calories means writing down what you eat and how much, then adding up the energy in each food. The goal is not a perfect number but an estimate good enough to show the trend: whether your weight holds, rises or falls at a given intake.
A food calorie (kcal) is the energy your body gets from protein, carbohydrate, fat, fibre and alcohol. Your body does not count perfectly, and neither will you. What matters is being wrong in the same way every day, so one week can be compared with the next.
How are the calories in a food calculated?
Calories are calculated from the amount of each macronutrient, multiplied by conversion factors set in law. In the European Union the factors are listed in Annex XIV of Regulation (EU) No 1169/2011, and manufacturers use them for the values on the label.
| Component | Energy per gram |
|---|---|
| Fat | 9 kcal |
| Alcohol (ethanol) | 7 kcal |
| Protein | 4 kcal |
| Carbohydrate (excluding polyols) | 4 kcal |
| Polyols (sweeteners such as sorbitol, maltitol) | 2.4 kcal |
| Dietary fibre | 2 kcal |
| Erythritol | 0 kcal |
Example: 100 g of plain yoghurt with 3.96 g protein, 2.65 g carbohydrate and 1.5 g fat (Ciqual values) gives 3.96 × 4 + 2.65 × 4 + 1.5 × 9 ≈ 40 kcal, plus a little from other components; Ciqual lists it at 45.5 kcal. You never need to do this sum yourself, but it explains why fatty foods carry far more calories at the same weight.
Why do we get calorie counts wrong?
We get them wrong mostly because we underestimate portions and forget what we ate between meals. In a 1992 study in the New England Journal of Medicine, people who said they could not lose weight despite eating little under-reported their intake by 47% on average and over-reported their physical activity by 51%. Their energy expenditure was normal.
Professionals are not immune. In a 2002 study, dietitians under-reported their intake by about 223 kcal a day and people without nutrition training by about 429 kcal a day. Practice and the habit of keeping a diary reduce the error; they do not remove it.
| Source of error | Typical size per day | How to reduce it |
|---|---|---|
| Cooking oil poured by eye | 100–250 kcal | Measure with a spoon or weigh the bottle before and after |
| Portions estimated without a scale | 10–30% of the meal | Weigh for 2–3 weeks, then spot-check |
| Forgotten snacks and bites | 100–300 kcal | Log on the spot, not in the evening |
| Drinks (soft drinks, milky coffee, alcohol) | 100–400 kcal | Log them like any food |
| Wrong database entry (raw instead of cooked) | up to double or half | Pick the exact form you weighed |
The figures in this table are orders of magnitude worked out from common portions (a tablespoon of oil is about 13–14 g, so roughly 120 kcal), not results from a single study.
Should you weigh food raw or cooked?
Weigh it raw whenever you can, because label values refer to the product as you buy it. Rice, pasta and pulses absorb water when cooked, while meat loses water, so the same energy ends up at a different weight.
| Food (Ciqual) | Raw, per 100 g | Cooked, per 100 g |
|---|---|---|
| White rice | 352 kcal | 145 kcal (boiled) |
| Wheat pasta | 336 kcal | 126 kcal (boiled) |
| Skinless chicken breast | 110 kcal | 141 kcal (pan-fried) |
| Lentils | 331 kcal (dry) | 104 kcal (boiled) |
If you weighed it cooked, choose the cooked entry. The classic mistake is weighing 200 g of cooked rice and logging 200 g of raw rice: 704 kcal instead of 290.
How do you log oil, sauces and drinks?
Log them separately, as ingredients, at the moment you use them. Oil has about 900 kcal per 100 g (Ciqual sunflower oil: 901 kcal), so every tablespoon counts as much as a slice of bread.
- Frying oil: weigh the bottle before and after, or measure with a spoon. If oil is left in the pan, subtract roughly what you did not eat.
- Sauces and dressings: a tablespoon of mayonnaise, sour cream or pesto has more calories than a bowl of green salad.
- Drinks: sugary soft drinks and fruit juices have about 40–45 kcal per 100 ml (Ciqual cola with sugar: 41.8 kcal), so a 250 ml glass has roughly 100–115 kcal.
- Alcohol: 7 kcal per gram, and sweet drinks add sugar on top.
How accurate are food labels?
They are accurate enough for counting at home. A study of 24 popular packaged snacks found that lab-measured calories were a median 4.3% higher than the label. Restaurant food varies more: in a study of 269 dishes, 19% had at least 100 kcal per portion more than stated.
In practice: for packaged food, the label is a good source. For meals out, log a generous estimate and do not chase precision that does not exist.
What about home-cooked meals?
For home cooking, log the recipe once and then divide by portions:
- Weigh and log each raw ingredient, including the oil.
- Weigh the empty pot once (and remember it), then the pot with the finished dish.
- Divide the total calories by the weight of the finished dish to get calories per 100 g.
- At each meal, weigh only what is on your plate.
For soups, stews and casseroles this is far more accurate than any “average” value from a table, because every household uses different amounts of oil and meat. A nutrition app does the arithmetic for you: in Rod, the nutrition app we are building, you save the recipe once and then add it by portion weight.
How long does it take, and is it worth it?
At first it takes around 20 minutes a day, and much less after a few months. In a study of an online food diary, participants spent an average of 23.2 minutes a day logging in the first month and 14.6 minutes in the sixth. Those who lost at least 5% of their weight opened the diary more often: 2.4 times a day versus 1.6 times.
A 2011 systematic review found a consistent link between self-monitoring (of diet, weight or activity) and weight loss. It is not magic: it shows you where the calories go and gives you concrete data to discuss with a professional.
What does a method that works look like?
A method that works is simple, repeatable and takes little time after the first few weeks:
- Use a digital kitchen scale (1 g precision).
- Take values from the label or a reference database (Ciqual, label-based databases).
- Log right after each meal, not from memory in the evening.
- Weigh raw, or pick the right cooked entry.
- Log oil, sauces, drinks and snacks separately.
- Look at the 7-day average, not at each single day.
- After 2–3 weeks, compare average intake with your weight trend and adjust.
If you have a history of eating disorders, or counting calories makes you anxious, talk to a doctor or a registered dietitian first. For many people other methods, such as hand-sized portions or the divided plate, work better.
