L'body mass index (BMI) is often used as a reference when talking about weight and health.
But is it really a reliable indicator for assessing health risks and general well-being? This article explores the limitations and benefits of BMI, while proposing alternatives for better health assessment.
Understanding BMI and its categories
BMI is a health risk indicator (4). According to the WHO, BMI is a surrogate marker of adiposity (fat accumulation) (3).
It is calculated as follows (4) :
Weight (in kg) / height (in m) 2
It can be categorized into different groups (4):
Underweight
Normal weight
Overweight/overweight
Class I obesity
Class II obesity
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The impact of a high BMI on health
An above-normal BMI is often associated with a variety of health problems, including (1)(3)(4):
Type 2 diabetes
Hypertension
Lipid markers: elevated cholesterol and triglycerides
Cardiovascular diseases
Non-alcoholic hepatic steatosis (fatty liver)
Sleep apnea
However, it's important to point out that some individuals with a high BMI may be in perfect metabolic health, which calls into question the reliability of this indicator.
The limits of BMI: an imperfect tool
Although BMI is a widely used indicator, it has several limitations:
A tool for populations, not individuals
BMI can be a useful health indicator for populationsbut is less useful for individuals (2). At the individual level, BMI is just a part of an overall health assessment (2)(4).
Not a direct measure of fat mass
BMI does not take into account weight distribution in the body (2)(4). It does not differentiate between body fat and muscle mass (2).
For example, an athlete with a high muscle mass could be categorized as overweight according to BMI, despite having little body fat.
Tools for adults only
BMI cannot be used for people under 18 (4). Nor does it apply to pregnant or breast-feeding women (4). Classification nuances are often necessary for people from over 65 as well as ethnic and racial groups. (4)
Other health indicators
Knowing the limits of interpretation of BMI and weight, there are other markers that can be used to assess a person's health risks.
Waist circumference
Health risk indicator associated with excess abdominal fat (1)(2)(4)
According to several studies, waist circumference is more "reliable" as an indicator of health, since an accumulation of fat close to the organs (visceral) is more "harmful" to health (1).
Thresholds of 102 cm (40 in.) for men and 88 cm (35 in.) for women are associated with an increased risk of chronic disease (e.g. type 2 diabetes, hypertension (2)(4).
Blood and physical markers
Blood glucose, cholesterol, triglycerides, blood pressure. (1)(3)
All these markers are risk factors for certain diseases. They should therefore be considered as part of the overall picture of metabolic health.
Lifestyle habits
Nutrition, physical activity, sleep, stress management, smoking, alcohol (1)(3)
It is important to consider all lifestyle habits to assess a person's health risks. Limiting interpretation to weight and BMI is not adequate. Health is influenced by many factors!
We're also talking about natural weight or equilibrium weight for one person. This weight corresponds to that which the body reaches with the adoption of healthy, balanced lifestyle (1). It is not equivalent This is neither the "ideal" weight based on BMI, nor a weight achieved through excessive habits that cannot be maintained over time. It can also vary over time with age and hormonal changes such as the menopause.
To find out more about the effect of menopause on weight, read this blog article.
Conclusion: BMI, one tool among others
- L'BMI is just one indicator among many for assessing health.
- Focus on the big picture, taking into account the waist circumferenceand lifestyle habits and metabolic markers.
- Do not target weight loss based solely on BMI, but rather on weight loss targets. sustainable health andimproved quality of life.
- Visit natural weight or equilibrium weight is the weight that the body stabilizes after adopting healthy living (1). It is not equivalent to the "ideal" weight based on BMI.
- A nutritional support with a personalized nutritionist-dietitian will enable you to establish healthy lifestyle habits and not focus on a particular number or on losing weight at all costs!
References
(1) Obesity Canada (2020) Adult obesity: clinical practice guideline, guideline. https://www.cmaj.ca/content/cmaj/192/49/E1757.full.pdf
(2) ODNQ (2024) The state of the art in treatment approaches for weight loss in adults. https://odnq.org/nouvelles/letat-science-approches-traitements-visant-perte-poids-chez-ladulte/
(3) WHO (2024) Obesity and overweight. Page consulted online : https://www.who.int/fr/news-room/fact-sheets/detail/obesity-and-overweight#:~:text=Pour%20les%20adultes%2C%20l’OMS,%C3%A9gal%20ou%20sup%C3%A9rieur%20%C3%A0%2030
(4) Health Canada (2003) Canadian Guidelines for Body Weight Classification in Adults. https://www.canada.ca/fr/sante-canada/services/aliments-nutrition/saine-alimentation/poids-sante/lignes-directrices-classification-poids-chez-adultes/guide-reference-rapide-intention-professionnels.html
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