Key takeaways
- Being overweight or obese is a risk factor for 12 different cancers
- BMI is a measure of whether you are healthy for your weight, and is used by doctors to screen people for future obesity-related health issues
- BMI doesn’t take into account variations in age, sex, ethnicity and muscle mass, so can give a misleading picture of someone’s health
- Nevertheless, maintaining a healthy weight is important, and the best way to do this is by staying active and eating a balanced diet.
According to the World Cancer Research Fund (WCRF), there is strong evidence that being overweight or obese throughout adulthood increases the risk of at least 12 different cancers. Body Mass Index (or BMI) is a reasonably accurate way of measuring whether someone is overweight or obese, and can therefore help doctors screen patients for potential weight-related health problems, including cancer. However, because BMI doesn’t tell us anything about muscle mass, it can also give a misleading picture of someone’s health. In this article, Perci professionals help you understand your BMI, and why it doesn’t necessarily mean you are overweight.
What is BMI and what does it mean?
BMI is a measure of whether you’re a healthy weight for your height. You can use the NHS BMI healthy weight calculator to find out your BMI.
For most adults, if your BMI is:
Below 18.5 – you’re in the underweight range
18.5 to 24.9 – you’re in the healthy weight range
25 to 29.9 – you’re in the overweight range
30 to 39.9 – you’re in the obese range
40 or above – you’re in the severely obese range
If you have an Asian, Chinese, Middle Eastern, Black African or African-Caribbean family background if your BMI is:
23 to 27.4 – you’re in the overweight range
27.5 or above – you’re in the obese range
Why do doctors use BMI?
BMI is a simple, inexpensive way to get a reasonably accurate idea of how much body fat a person has. Research has shown that individuals with a higher BMI are more likely to experience obesity-related health problems and are at a higher risk of morbidity and death. Therefore, BMI helps doctors to screen patients for obesity and its health risks.
However, BMI can be considered most useful at a population level. Because it has been used for so long, it can help researchers track population data and help public health professionals to see trends and explore large-scale interventions.
The problems with BMI
BMI has some limitations because it actually measures whether a person is carrying too much weight, rather than too much fat. For example, people who are very muscular, like professional sportspeople, can have a high BMI without much fat. Also, BMI does not distinguish between excess fat, muscle or bone mass, nor does it provide any indication of fat distribution.
Measuring BMI can also be problematic because it doesn’t take into account factors that influence body fat, such as age, sex and ethnicity. For example, an older adult will tend to have more body fat than a younger adult with the same BMI and a woman will have more body fat than a man with the same BMI. Individuals whose backgrounds are Asian, Chinese, Middle Eastern, Black African or African-Caribbean tend to have higher weight-related disease risks at lower BMIs.
How to maintain a healthy weight
While the usefulness of BMI at an individual level is often called into question, there is no doubt about the fact that maintaining a healthy weight reduces your cancer risk and improves your overall health. The best way to do this is to eat a healthy balanced diet and have an active lifestyle.
Making lifestyle changes can be challenging. Our Cancer Nurse Specialists can talk you through cancer risk factors, as well as refer you to other Perci professionals, like registered dietitians and clinical exercise specialists, who can offer support.
While we have ensured that every article is medically reviewed and approved, information presented here is not intended to be a substitute for professional medical advice, diagnosis, or treatment. If you have any questions or concerns, please talk to one of our healthcare professionals or your primary healthcare team.
References:
‘Body Mass Index: Considerations for Practitioners,’ CDC, accessed April 2024, https://www.cdc.gov/obesity/downloads/bmiforpactitioners.pdf
‘Overview: Obesity,’ NHS, February 2023, https://www.nhs.uk/conditions/obesity/