What is TDEE and how many calories do you need?

Your body uses energy all day, even when you sleep. TDEE adds it all up for 24 hours. It has two main parts:

• BMR (basal metabolic rate). The energy your body uses at rest to breathe, pump blood, keep warm and run your organs. For most people, this is the largest part.
• Activity. Everything you do on top of resting: walking to the LRT, carrying groceries, playing badminton or going to the gym.

Experts from FAO, WHO and UNU describe daily energy needs the same way. They divide total energy expenditure by BMR and call the result the physical activity level. Read the FAO report.

When you eat about the same number of calories as your TDEE, your weight stays roughly the same. Eat less and you lose weight over time. Eat more and you gain.

Most calorie calculators, and the Nibbs app, use the Mifflin-St Jeor equation. It comes from a 1990 study of 498 healthy adults aged 19 to 78, whose resting energy use was measured in a lab. The study gives a simple version for men and women:

The same study found that the older Harris-Benedict equations from 1919 overestimated measured resting energy use by 5%.

You multiply your BMR by an activity factor. The more you move, the bigger the factor. These are the factors the Nibbs app uses when it sets up your plan:

Be honest about your level. Count your usual week, not your best week. A desk job with two badminton sessions a week is lightly active, not very active.

Here are two worked examples with the formulas above. The numbers are rounded to the nearest 10 at the end.

The woman in this example needs about 1,770 kcal a day to keep her weight steady. For comparison, one plate of nasi lemak has 500 kcal, so a day of eating out can reach her TDEE quickly.

To lose weight, you need to use more energy than you take in. This is called a calorie deficit. The NHS suggests aiming to cut around 600 kcal a day from what you usually eat.

Nibbs offers three paces. It takes 250, 500 or 750 kcal a day off your TDEE, and it does not set a target below 1,200 kcal a day. It estimates the weekly change with the common figure of 7,700 kcal for each kg of body weight. By that estimate, a 500 kcal daily deficit is about 3,500 kcal a week, or a little under half a kilo.

A deficit is easier to picture in food. Each of these cuts a few hundred calories from a day:

• One plate of nasi lemak at 500 kcal.
• A Milo ais and a plain roti canai at supper: 530 kcal.
• Swapping char kway teow (740 kcal) for Penang assam laksa (380 kcal) saves 360 kcal.

Our guide on how to lose weight eating Malaysian food has more swaps and a sample day.

Here is one way the woman in the example could eat well below her TDEE of about 1,770 kcal, with plain drinks such as kopi O kosong or water.

An equation predicts the average for people of your size, age and sex. In the Mifflin-St Jeor study, weight, height, age and sex explained about 71% of the differences in resting energy use between people. The rest came from other things, so your real number can be higher or lower.

Activity is even harder to pin down. Two people who both work out three times a week can move very differently for the rest of the day.

Nibbs works out your personal calorie and macro targets from your TDEE when you set up the app. Then you log your meals by photo, by typing a description, by scanning a barcode or a nutrition label, or from your saved foods.

Log your weigh-ins to see your progress chart, so you can tell whether your target is working. To get your own target, set up your plan in Nibbs. To check your BMI, use the BMI calculator.