Calorie deficit

A calorie deficit occurs when you take in less energy over the day than your body uses – it then draws on its reserves, mainly body fat. This is the mechanism behind every successful weight loss, whether it's called low-carb, intermittent fasting or simply “fewer sweets”. The method is a matter of taste; the deficit is the physics behind it.

How big should it be? The rule of thumb: 300 to 500 kcal below your total daily energy expenditure. Since a kilogram of body fat stores around 7,000 kcal, that's equivalent to roughly 0.3 to 0.5 kg a week. The guideline of the German Obesity Society sets a framework of a deficit of around 500 kcal a day and a maximum of 0.5 to 1 kg a week – the slower pace is easier for most people to stick with. Larger deficits bring faster results at first, but they cost muscle, mood and staying power and make energy expenditure drop more sharply. Eating below your basal metabolic rate for a long time is not a good idea.

Important: the 7,000 kcal calculation only holds true at the beginning. With every kilo you lose, your total energy expenditure falls by roughly 20 to 30 kcal a day, and your metabolism also adapts slightly. That's why the second half of a weight loss almost always takes longer than the first – that's normal and no sign that you're doing anything wrong. Recalculate your deficit every few kilos.

The deficit doesn't have to come from your plate alone: eating 200 kcal less and moving 200 kcal more usually feels easier than eating 400 kcal less. Filling foods with plenty of protein, fibre and water help to ensure that a deficit is barely noticeable as hunger.

A calorie deficit is not for children and teenagers who are still growing – for them, the goal is to keep their weight stable while they grow into it, with support from their paediatrician. In cases of underweight, during pregnancy and breastfeeding or after an eating disorder, weight loss should also be medically supervised. If you notice that food and weight are dominating your thoughts, you can get anonymous help from the eating disorders helpline of the German Federal Institute for Public Health (BIÖG, formerly BZgA) on 0221 892031 – and you can raise the subject with your doctor at any time.