Everyone has probably at one point in his/her life assessed his/her weight using the Body Mass Index (BMI) to calculate if he/she is healthy or not. Even now, many doctors still use the BMI as a sole determinant of our health status. However, doing so is very wrong for many reasons and can undoubtedly lead to detrimental effects for an individual’s physical and mental health.

Why is the BMI flawed?

Using a person’s BMI as an indicator of health has indeed been heavily criticized, with much of the criticism coming from how it was created in the first place. Its creator was a Belgian astronomer and statistician named Adolph Quetelet. The latter was neither a physician nor did he even study medicine.

Furthermore, he warned that the BMI was not to be used for individual diagnosis, treatment or assessment as it was simply created to predict the average size of a population. Also, this calculation could only really be used for male white Western Europeans, as it was solely based on their measurements. The World Health Organizatin (WHO) still decided to use this imperfect measurement and it was embodied into a public policy anyway.

Even though BMI is used as a means to determine the risk for individuals’ health problems, the calculation does not take into account many factors that affect disease risk. For instance, we cannot simply assess if a person is healthy or not just based on his/her weight for his/her height. It has indeed been proven that behaviors for a healthy lifestyle (healthy eating, regular exercise, good management of stress, etc.) are more accurate indicators of the health status of an individual. And weight is simply NOT a behavior.

In fact, a person’s weight could be in the normal BMI range but the latter could engage in unhealthy restrictive eating behaviours and excessive physical activity leading to nutrient deficiencies and the loss of menstruation. Undoubtedly, that person would be wrongly diagnosed as being healthy if we just relied on the BMI to assess her health status.

The opposite is also true for individuals who might be wrongly categorized as overweight or obese according to the BMI. Those people can be healthy as they lead healthy lifestyle and have normal bloodwork regardless of their weight.

Also weight is influenced by many factors which the BMI does not take into account. For instance, BMI does not take into account muscle mass, bone mass, genetics, ethnicity, gender, age, medication, past diet history, pregnancy, etc.

And many of these factors that influence our weight are out of our control. Indeed, it has been proven that genetics can determine up to 70% of our weight!

What is the set point theory?

On the other hand, the set point theory is a refreshing new concept based on scientific research that demonstrates that our bodies have a set point weight that is encoded into our DNA. This weight is one which we can maintain relatively easily without restricting ourselves in our food choices nor having to engage in excessive physical activity. It’s a weight where we feel energetic and in good health by listening to our body, without having to exert any control over it.

How do you know if you are at your natural weight?

Unlike BMI, there is no formula that we can use to calculate our natural weight. However, there are many factors that can help you achieve it. This includes being in tune with your body’s hunger and fullness signals, eating for pleasure and finding foods that truly satisfy you, accepting and respecting your body shape and size, moving regularly for physical and mental well-being and taking care of your body.

Since your body is genetically made to stay around a certain weight, it will do what it can to stay there. This is why it can be so difficult for people to maintain the weight lost through restrictive diets.

What happens to your body when you go on restrictive diets?

In fact, when you go on restrictive diets, your metabolism naturally decreases. This is because your body will go into starvation mode and start burning less energy to compensate for the low food intake.

In addition, since your body will not be getting the energy needed from food to meet its needs, your hunger hormones (called Ghrelin) will increase, making you more hungry than usual. Therefore, you might end up eating more and regaining all the weight lost and even more sometimes.

Another physiological change that contributes to weight regain is a decrease in satiety hormones. Therefore, it takes more food to give you that feeling of fullness and again, you might end up eating more and more as your body fights to go back to its natural weight.

One of the last major changes that contributes to this regain of weight is an increase in stress hormones. When you severely restrict your calories or exercise in an excessive manner, cortisol (the stress hormone) is often released. Increased cortisol can slow down your metabolism and therefore it becomes harder to maintain the weight lost.

Trusting your body

Letting go of all food rules and control over the weight might be hard especially if you have been exposed to diet culture for a long time. It is therefore important to give yourself time and self-compassion to heal your relationship with your body and food. However, trying to trust your body as it knows what your natural weight is, can definitely help you to ditch diets, stop obsessing about food and be more in tune with your body’s cues.