Calories and calories out
At first glance, calculating weight loss seems very easy. Simply take the number of calories you burn, subtract the number of calories you take in from food, and you have a calorie deficit. Your body will have to cover this deficit by burning its fat reserves, which means you can estimate the weight that will be lost.
We can look at a hypothetical example of this calorie math. Your caloric expenditure consists of 3 main parts:
- resting metabolic rate (BMR) – The number of calories your body burns just to stay alive, such as breathing, pumping blood, etc.
- Thermic effect of food The calories your body uses to digest, absorb and metabolize food.
- The thermal effect of activity – The calories you use during exercise and non-sport activities such as gardening, cleaning the house or fidgeting.
Let’s say you’re a man with a BMR of 1,800 calories. Normally the thermic effect of food is about 10% of your BMR, so that would be 180kcal. You have a sedentary job but you go cycling every day. The thermic effect of activity may amount to about 700 calories. This means that your total daily caloric expenditure is 2,680 calories.
If you decide to take in 2,130 calories from food, you’ll be left with a 550-calorie deficit. To lose 1 kilogram of body fat, you must burn approximately 7,700 calories. At a rate of 550 calories per day, it can take about 2 weeks to lose 1 kg of body fat and about 1 month to lose 2 kg. Losing 2kg in January with a very modest calorie deficit of 500 calories sounds amazing. Unfortunately, the math is not that simple.
It is difficult to estimate weight loss
The first problem is that measuring calories is not easy. You can get away with hundreds of calories even if you try really hard. Check out our series on calorie counting if you want to know all the potential issues.
On top of counting calories, there are other factors that influence how you lose weight. Below are the main ones.
- Gender – Men tend to lose weight a little faster than women, on average.
- Age – It gets more difficult to lose weight as we get older.
- Initial weight – an obese person can lose much more weight per month than someone who carries a few extra kilos.
- Sleep – People with poor sleep have a hard time losing weight.
- Medications and medical conditions – eg, antidepressants can stop weight loss and even promote weight gain.
- Frequent Dieting – People who go through the phases of yo-yo dieting lose and gain significant weight and have difficulty losing weight with each attempt.
Losing weight too quickly is unhealthy
Almost everyone who wants to lose weight prefers to do it quickly. Unfortunately, rapid weight loss carries some serious risks. Here are the most common side effects of losing weight that happen too quickly.
- muscle loss
- Dehydration and malnutrition
- Headache, irritability and fatigue
- hair loss
- Menstrual disorders
Aim to gain 1% of your body weight per month
So, what is a safe rate of weight loss? It depends on where you are currently in your weight loss journey. Weight loss usually occurs faster in the first few weeks and then slows down. In general, there is a safe range for weight loss somewhere in between 0.5 – 1.4 kg or about 1% of body weight per week.
Before you start comparing your numbers to this range, keep in mind that weight loss is not a linear process. A successful weight loss journey consists of weeks when you don’t lose weight and weeks when you lose more than you thought. This is completely healthy and should be expected. Research shows that people who keep a food diary and weigh themselves regularly are more likely to stay on track and achieve their goal.