Calorie deficit explained – how does your body actually lose weight?

There are many misunderstandings and misconceptions surrounding weight loss: miracle berries, the “don’t eat after 6pm” rule, crash diets, detox waters… and the list just keeps growing. The reality is much simpler than that. Your body is a biological machine that uses energy for every movement, thought, and breath – and this is called “calories”. And the basis of weight loss is only one law: without a calorie deficit, there is no sustainable fat loss.

What is a calorie deficit?

A calorie deficit occurs when you consume less energy through food than your body uses during the day. This can be from exercise, walking, housework, or even just your heart beating and breathing – this is called your basal metabolic rate.

If you need 2,500 calories a day but only eat 2,000, you are in a 500 calorie deficit per day. At this point, your body will make up the difference from fat stores, meaning real fat loss occurs.

Why don't "fasting" diets work?

If you suddenly eat too little (e.g. 600–800 kcal), your body goes into emergency mode. It slows down your metabolism, reduces hormone production, and starts breaking down muscle tissue to save energy. In this case, the weight loss may seem fast, but it's mostly muscle loss - not much fat. And as soon as you start eating properly again, everything comes back.

A sustainable deficit is 300–600 calories per day. This can help you lose 0.5–1 kg of fat per week without feeling hungry or weak.

How do you maintain the deficit?

– Eat more protein: this reduces appetite and increases satiety.
– Drink enough, because thirst is often mistaken for hunger.
– Walk more: a simple but extremely effective fat burning tool.
– Prepare meals in advance so you won’t be tempted.
– Don’t calculate too strictly; stay flexible.

So weight loss is math, not magic. When you understand deficit, your body finally does what you want it to do.