One of the rules often stated to achieve weight loss is to put your body in a calorie deficit in order to force it to draw on its reserves. What does that mean ? How to achieve this? Is it really effective? The answers from Raphaël Gruman, dietitian and nutritionist in Paris.
Definition: What is a calorie deficit?
Every day, and at every moment, our body burns calories to provide the energy necessary for its various vital functions (breathing, blood circulation, digestion, regulation of body temperature, etc.) and for its daily physical and sporting activities.
To meet these energy costs and stay healthy, it needs calories that we provide it through food. “We speak of a calorie deficit when the body expends more calories than it absorbs. The energy input/output balance is therefore unbalanced, which theoretically forces our body to draw the energy it lacks from our body fat reserves. The key: weight loss” summarizes Raphaël Gruman.
Calculation: How to be or create a calorie deficit?
To be able to create a calorie deficit, you must first estimate your calorie expenditure. “A person's calorie expenditure depends on several factors: their weight, age, height, gender and level of physical activity.” indicates the dietitian.
They are divided between:
- Basal metabolic rate (BMR) : which corresponds to the number of calories burned by the body which fulfills its basic (basal) functions of maintaining life;
- Expenses related to daily activities : professional, family, sporting activities…
There are several calculation formulas to estimate your BMR, and the best known is the Harris-Benedict formula, which is as follows:
- For a woman : (9,740 x Weight in kg) + (172.9 x Height in meters) – (4,737 x age in years) + 667,051
- For a man : (13,707 x Weight in kg) + (492.3 x Height in meters) – (6,673 x age in years) + 77,607
This calculated basic metabolism must then be multiplied by a coefficient based on the person's level of physical activity (PAL), in order to obtain the daily calorie expenditure.
The NAP varies depending on its weekly activity:
- 1,2 for people who have a sedentary job, are very little active otherwise,
1,4 for people whose work is sedentary but who are rather active: one hour of walking or equivalent per day,
1,6 for active people, who walk for example one hour a day and do one hour of sport (running, basketball, cycling, etc.) 3 times a week
1,8 for very active people, who combine a physical job and daily sporting activity.
Calculating total calorie expenditure is BMR multiplied by NAP. Example for a 45 year old woman, 60 kilos, 1m73 and active:
- Calculation of MBR = 1338 calories
- NAP = 1,6
- Total energy expenditure: 1.6 x 1338 = 2140 calories per day.
Once this daily energy expenditure is estimated, there are three ways to create a calorie deficit in order to force the body to draw on fat reserves and cause weight loss:
- Reduce only your caloric intake and therefore your diet;
- Only increase your calorie expenditure linked to sport or lifestyle;
- Or combine a slight reduction in your contributions and a slight increase in your expenses.
The best way to put yourself in a calorie deficit to lose weight and maintain this weight loss is to combine a moderate reduction in calorie intake and a reasonable increase in expenditure, through physical activity. “Maintaining good muscle mass is in fact essential to maintaining a stable weight, because muscle is a large consumer of calories: the more muscular you are, the more calories you burn, even when resting or sleeping!” recalls our expert.
Weight loss and diet: What is the optimal calorie deficit to lose 1 kg per week?
“First of all, I prefer to remind you that a loss of one kilo per week is important, and that I recommend losing more gradually to facilitate stabilization and limit the yo-yo effect.” underlines Raphaël Gruman.
To lose around a kilo per week, the calorie deficit must be at least 20%, which is important! “A person who burns 2000 calories should therefore reduce their caloric intake by 400 calories each day, the equivalent of a small meal: that's a lot!” explains the nutritionist. The best in this specific case is to reduce your caloric intake by 200 calories per day and increase your expenditure by 200 calories as well.
Is a deficit of 500 calories per day enough to lose weight?
A deficit of 500 calories does not have the same impact depending on the person's profile. For example, it is enormous for a sedentary and elderly person, who only burns 1600 calories per day, but it is relatively little for a young and very active and sporty man who burns 3500 calories per day.
However, from the moment we burn more than we consume, the body will have to draw on its energy reserves, and therefore lose weight in the more or less long term.
“But it's worth remembering that going into a calorie deficit is not the only way to lose weight, nor is it necessarily the most effective.” underlines Raphaël Gruman.
Does going into a calorie deficit to lose weight always work?
If putting yourself in a calorie deficit to lose weight is ultimately the principle of low-calorie diets. Although this is a fairly effective method on paper, it does not take into account certain essential factors:
- This technique is relatively bindingit forces you to weigh and calculate everything, which can tire you and push you to abandon everything;
- The calorie deficit we impose on ourselves is often too greatwhich risks causing hunger and frustration, “two enemies of lasting weight loss!” explains the nutritionist;
- By putting yourself in a calorie deficit for several weeks, the body will naturally get used to it and reduce your energy expenditure in order to adapt to your intake. “The problem is that the basal metabolism adapts and gradually lowers to align with intake, and weight loss is therefore less and less over time. And as soon as you stop dieting, the body stores calories and you gain weight back much more quickly.” details Raphaël Gruman;
- Finally, the calorie deficit method does not take into account the fact that not all calories are equaland that certain nutrients are metabolized and therefore stored more easily than others:
- “Carbohydrates, even more so when they have a high GI, are the nutrients most easily stored in the form of fat: you can lose weight by significantly reducing carbohydrates but with very little caloric deficit. Conversely, you can gain weight despite a calorie deficit if you mainly eat foods rich in fast sugars.” sums up the dietician;
- Protein is the most difficult nutrient to store as fat. “You can therefore greatly increase the proportion of proteins in your diet to the detriment of sugars and lose weight, without reducing your caloric intake and therefore without starving yourself: this is the principle of the Keto diet.” concludes Raphaël Gruman.
