The link between weight and health: what to think about it?


Based on a healthy weight, is this the solution?

We hesitated for a long time to broach the topic today. Indeed, the link between body weight and health is a thorny subject, often tinged with fatphobia, even among many health professionals (who can, like all humans, have biased comments). However, we believe in the relevance of looking into the question and separating the true from the false, based on the most objective data possible. We will begin the two-article series on this topic by discussing the concept of healthy weights.

Part 1 – What is healthy weight?

We often hear about the importance of maintaining a healthy weight, which for many people is automatically associated with being thin.

For the majority, these terms are implicitly linked to the body mass index (BMI): a quick calculation consisting of the ratio of the weight (in kg) to the height of a person (in m) squared. This formula makes it possible to classify the weight in categories:

  • Insufficient weight,
  • Normal weight,
  • Overweight (or overweight),
  • Class 1 obesity,
  • Class 2 obesity
  • Class 3 obesity.

The category with the lowest risk of developing health problems would be the normal weight category.

Despite the fact that BMI has been widely questioned in recent years, many health professionals have used BMI as a reference for a long time, without even worrying about its origin.

The history of BMI and its impact on healthy weight

The BMI (originally called the Quetelet Index) was created in the 1830s by an astronomer and statistician named Adolphe Quetelet, who sought to determine the characteristics of the average man and show the distribution of these characteristics in the population he was studying: young adult European males.

The BMI was therefore established solely for statistical purposes for a given population and not for the purpose of determining a healthy weight for each individual. Initially, even once popularized, this formula was deemed inadequate for individual assessment. It is as a result that not only its classification was modified (you now had to have a lower weight to be in the normal weight category!), but also its function.

BMI limits

Despite its popularity, BMI has several limitations. It ignores several important data in the analysis of the risk of developing diseases:

– The gender of the person

The same formula is used for all while body composition and genetics (among other things) are different.

– Age

The body changes as you age, but the BMI categories do not.

– Ethnicity

Genetics and ethnicity influence weight, height, body composition and susceptibility to certain health problems. They should be taken into account.

– Body composition

BMI does not differentiate between the amount of fat tissue and the amount of muscle tissue. So someone with a low body fat percentage could theoretically fall into the same category as someone with less muscle but a high body fat percentage.

– Body fat location

The adipose tissue located at the abdominal level (especially that around the internal organs) would be associated with a higher risk of suffering from diseases than that located at the level of the lower body (hips, buttocks, thighs). However, BMI does not provide this information.

These limitations make BMI an inaccurate tool for predicting the risk of suffering from diseases. On the other hand, it has been widely used in scientific studies to classify weight; that is why we will have to continue talking about BMI categories to report the results in this article.

What the research says about BMI

According to several scientific studies, it is not necessarily the BMI category of normal weight that would be associated with the lowest risk of mortality, nor even the only category that would present a low risk. Indeed, having a BMI in the overweight category would (depending on the study) either be associated with the lowest mortality risk of all categories, or be associated with a relatively low mortality risk.

A study questioning the effect that BMI would make it possible to determine cardiometabolic health (based on the blood tests of 40,420 participants), showed that 70% of people in the normal weight category; almost 50% in the overweight category; 29% in the class 1 obesity category; and 16% in the obesity class 2 and 3 categories, were in good cardiometabolic health!

Certainly, the number of people with metabolic problems increases with BMI, while in each category there are significant chances of being wrong if only this indicator is used.

There are other indicators for weight and health

This means once again that BMI is not an adequate predictor of health, but also that the link between weight and health is more complex than it seems. Regardless of the degree of influence of the figure on the scale, more reliable indicators exist to establish individual consistency between the weight and the health of each, such as the blood test.

In the next article, we will look at the impacts of the weight-centric approach as well as the limitations of the research that seems to prove that weight influences health.
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Maude Martinez, Nutritionist, Dt.P
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