Every way of losing weight that works, works for the same reason: for a while, you burn more energy than you eat. That's a calorie deficit. Fad diets, fasting, low carb: when they work, it's because they created a deficit. The difference is how easy it is to keep that deficit without going hungry and without quitting.
The good news is that the math isn't a secret. It has three steps.
Step 1: what your body burns at rest
Resting energy is what your body uses just to exist: breathing, keeping warm, keeping your heart beating. The most widely used formula today to estimate it is Mifflin-St Jeor, published in 1990:
- Women: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
- Men: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
Example: a 32-year-old woman, 165 cm (5'5") and 82 kg (181 lb). The math is 820 + 1,031 − 160 − 161 = 1,530 kcal a day at rest.
Step 2: what you burn in your day
Nobody spends the day lying down. To get your total, multiply your resting energy by an activity factor:
| Routine | Factor |
|---|---|
| Sitting most of the day | 1.2 |
| Lightly active (walking, chores) | 1.375 |
| Moderately active (exercise 3 to 5 times a week) | 1.55 |
| Very active | 1.725 |
In the example, with a lightly active routine: 1,530 × 1.375 = about 2,100 kcal a day. That's what she burns.
Step 3: a deficit you can keep
Here's the most common mistake: cutting too much. Eating 1,000 kcal a day makes the scale drop fast in week one and makes people quit in week three. Hunger rises, sleep gets worse, mood crashes and the loss starts taking muscle with it.
A sustainable pace is usually around 0.5 kg (1 lb) a week. For that, a daily deficit of around 500 to 700 kcal is the most common starting point. In the example, the budget would be close to 1,400 kcal a day.
Why the math changes over time
As you lose weight, you burn less, because a smaller body uses less energy. A budget calculated on day one gets too generous as the weeks go by. That's why redoing the math every few kilos, or using something that redoes it for you, is part of the method and not a detail.
How not to go hungry in a deficit
- Protein at every meal. Eggs, chicken, fish, beans, yogurt. It keeps you full longer and helps preserve muscle.
- Volume with few calories. Salad, vegetables and fruit fill the plate and barely touch the budget.
- Watch what you drink. Soda, juice and alcohol add calories without killing hunger.
- Spread out your day. Saving everything for dinner usually ends in afternoon snacking.
The short way
If you don't want to do this by hand, Bora does it for you at sign-up: it asks your weight, height, age, sex and routine, calculates your energy use with the Mifflin-St Jeor formula, applies the deficit and respects the safety floor. Then, with weekly weigh-ins, it reviews your budget on its own and explains every change.
Sources
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. The American Journal of Clinical Nutrition. 1990;51(2):241-247.
- Hall KD, Sacks G, Chandramohan D, et al. Quantification of the effect of energy imbalance on bodyweight. The Lancet. 2011;378(9793):826-837.
This content is for information only and doesn't replace advice from a doctor or dietitian.
