What is a calorie deficit and how will it help me lose weight?

Our body needs energy not only for exercise, but also for everyday work, recovery, and for running and maintaining its physiological functions and metabolic processes.

We get energy by eating food and drinking beverages of varying energy value, which we measure in kilocalories (kcal) or kilojoules (kJ).

Fats are the most energy-dense; 1 g of fat gives the body 37 kJ of energy. While 1 g of protein and 1 g of carbohydrates each provide around 17 kJ, fibre is the least energy-dense, at just 8 kJ per gram.

For our body to work properly, energy intake and energy expenditure need to be in balance. The amount of energy we take in from food should equal what we burn through movement, exercise or other physical work.

If we take in more energy than we use, we end up with an energy surplus. With excess protein intake, however, the body does not build fat stores; instead, the unused amino acids are oxidised and excreted in urine as urea.

Read also: Exercising without changing your diet is like taking one step forward and two steps back

But if we overdo it with fats or carbohydrates (sugars), the excess energy is stored in the body as fat. Later on, this leads to various negative health consequences in the form of lifestyle diseases.

How it works

Conversely, when energy intake is insufficient, an energy or calorie deficit occurs. In this case, the body looks for a way to make up the missing energy and draws on its own reserves.

It burns sugars, or carbohydrates, first, because they are an immediate source of energy. The body does not hold much of them, though, since they are stored only as glycogen. Next, fats and proteins are burned, which is what brings body weight down. Be careful, though, because a calorie deficit can also lead to the breakdown of muscle mass.

That is why you need to make sure you get enough protein during a calorie deficit. It has been shown that slower weight loss (when the calorie deficit is not too large) protects muscle mass better. A high protein intake during a calorie deficit also leads to greater muscle gains and greater loss of body fat.

This is down to the high thermic effect of protein, which determines how much energy is used up digesting it. For protein it is 20 – 30 % of the energy, carbohydrates use up 15 %, and for fats it is only 2 – 3 %.

In short: fats give you the most energy per gram, but digesting them costs you nowhere near as much energy as digesting protein, for example.

The numbers matter

Almost all diets are based on a calorie deficit. If you want to lose weight this way, it is best for your calorie deficit to be no more than 30 % of your energy needs. For example, if your energy metabolism is 1,500 kcal, you still need to take in at least 1,050 kcal.

Make sure you get enough protein, roughly 1.6 – 1.8 g/kg of body weight. The International Society of Sports Nutrition, for example, recommends as much as 2.3 g of protein per kg of body weight during a calorie deficit.

The simplest way to cut the energy value of your diet is to significantly limit fats (Low Fat Diet), because they have the highest energy value. This was confirmed by experiments manipulating the nutrients in the diet, where an energy-dense, high-fat diet led to greater weight gain, and vice versa.

You can also manipulate the energy value by cutting carbohydrates (Low Carbohydrate Diet), where carbohydrates make up less than 40 % of the energy intake from food. On a Very Low Carb Diet, carbohydrates make up only 10 % of energy intake.

In all of these cases, we lower the energy value of food and the thermic effect of food goes up.

Even in a calorie deficit, keep the nutrients in balance (protein, carbohydrates, fats and, above all, fibre). With a well-balanced diet, even an energy-“poor” diet contains everything you need.

Do not forget your micronutrients either, such as vitamins, minerals and omega-3 fatty acids. The last of these are easy to get into your body: just take a spoonful of fish oil, ground flaxseed or chia seeds.

Beware of extremes

When we go from a calorie deficit back to a diet where we eat energy-dense food, we end up in a calorie surplus again, we gain weight, and that well-known, dreaded effect named after a children's toy sets in.

A large calorie deficit and a high-protein diet are not something you can sustain long term. If you see results after 8 – 12 weeks, you can slowly increase your calorie intake, but take care to keep the right protein ratio and do not stop going to training.

Definitely combine a calorie deficit with training, because training burns additional energy, which lets you burn fat faster. On top of that, exercise has many other positive effects on the body. But never forget quality nutritional supplements and joint support when you train!

Read also: How exercise relieves stress

With too severe a calorie deficit, low protein intake and insufficient physical activity, so-called adaptive thermogenesis sets in: the body reduces its energy expenditure and slows down its metabolism, which slows weight loss or stops it altogether. It is a natural evolutionary defence mechanism that helps the body survive periods of food scarcity.

Research has shown, however, that even with a severe calorie deficit, as long as protein intake is sufficient and strength training is in place, neither adaptive thermogenesis nor muscle loss occurred.

What is the optimal ratio of protein, carbohydrates and fats in a calorie deficit? In a calorie deficit, most of your energy should come from protein (roughly 40 – 50 %), and fats and carbohydrates should be in an amount and ratio that gets you to the desired reduction in the energy value of your food.

Simply put: add protein and cut back on fats and carbohydrates.

Calorie tables?

If a coach or nutrition adviser is putting together your meal plan, it makes no sense for them to say: “Have 50 g of oats in the morning, wash it down with a protein shake, have an apple as a mid-morning snack, salmon with rice for lunch, a banana with an apple and a protein shake in the afternoon, and bread with mozzarella for dinner.” And if you then ask how many nutrients and kJ you are taking in that way and they tell you they do not know, run away from that person.

A good nutrition adviser definitely works with calorie tables or similar programs and will first work out your basal metabolic rate in detail, go by the numbers, and not just fire off meals off the top of their head.