30 frequently asked questions about body mass index (BMI)

30 of the most frecuently asked questions about body mass index (BMI)


1. What is BMI?

BMI or body mass index is a measure relating weight and height to determine if a person's weight is healthy.


2. How do you calculate BMI? 

BMI is calculated by dividing weight (in kg) by the square of height (in meters). BMI can also be calculated by entering weight and height into a BMI calculator.


3. What are the standard BMI ranges?

The standard BMI ranges are:

- 18.5 to 24.9: Normal weight

- 25 to 29.9: Overweight 

- 30 or more: Obesity


4. Is BMI calculation the same for men and women?

Yes, BMI is calculated and classified in the same way for both men and women. 


5. From what age can BMI be calculated?

BMI can be calculated from age 2 onwards. For children under 2, specific BMI-for-age charts are used.


6. What are the limitations of BMI? 

BMI only considers weight and height. It does not distinguish between fat and muscle mass, or fat distribution.


7. Is it better to have low or high BMI?

The healthy recommended BMI range is 18.5 to 24.9. Below or above this range increases health risks.


8. How can I lower my BMI?

To lower BMI, it's advisable to reduce calorie intake, especially sugars and fats, and increase regular physical activity.


9. Is increasing BMI bad? 

When BMI increase is due to extra muscle mass from exercise, it can be beneficial. But if it reflects excess body fat, it increases disease risks.


10. Does BMI determine if someone is off the ideal weight?  

Not necessarily. BMI doesn't account for body composition, so muscular people can have a high BMI without excessive fat.


11. What health risks does very low BMI have?

A BMI below 18.5 can indicate malnutrition or eating disorders, leading to osteoporosis, anemia, immunodeficiency, among others.


12. What diseases are linked to high BMI?

Obesity associated with very high BMI is linked to heart disease, hypertension, type 2 diabetes, fatty liver disease and even some cancers.


13. Is someone with BMI of 30 considered obese?

Yes, a BMI of 30 or above indicates obesity. But there are degrees, from mild (BMI 30-34.9) to morbid obesity (BMI 40 or over).


14. Is it possible to be overweight and healthy?

Yes, mild overweight (BMI 25-29.9) is considered relatively healthy, especially when fat is carried around the hips and thighs. 


15. How does genetics influence BMI?

Some genetic variations may predispose people to accumulate more fat, but genetics does not make obesity inevitable.  


16. Is calculating children’s BMI recommended?

 Specific weight-to-age charts are used.


17. How often should I calculate my BMI? 

It's advisable to calculate BMI at least once a year to monitor weight changes, although frequency may vary per medical advice.


18. Does BMI work for pregnant women?

No, during pregnancy BMI is not considered valid due to weight gain from the fetus, amniotic fluid, placenta and other tissues.


19. Does ethnicity affect BMI calculation?

The BMI categories are the same across all ethnicities. However, some research suggests certain ethnic groups may have higher obesity risk.


20. Where can I find a reliable BMI calculator?

You can calculate your BMI for free using our reliable online BMI calculator tool by entering your weight and height.


21. What are the problems associated with high BMI?

A very high BMI can increase the risk of cardiovascular disease, high blood pressure, type 2 diabetes, respiratory issues, and certain cancers.


22. Is BMI an accurate indicator of body fat?

BMI is a screening tool and may not correspond to the same degree of fat in different individuals with the same BMI. Other measures like waist circumference are used.


23. What are healthy strategies to lower BMI?

Healthy strategies to lower BMI include exercising more, reducing processed and high-calorie foods, eating more vegetables and whole grains, and maintaining a consistent routine.


24. Why is BMI categorized differently for children? 

Children's BMI is plotted on growth charts specific to age because the amount of body fat changes with age and the amount considered healthy is different from that of adults.


25. Does BMI change with age?

BMI typically peaks around ages 40 to 50 and declines with age after that. Loss of muscle mass as we age shifts BMI distribution toward the obese range in older adults.


26. Does BMI measure body fat accurately?

BMI is a screening tool that gives a general indication if weight may be unhealthy, but other methods like skinfold thickness, waist circumference and DEXA scans measure body fat more accurately.


27. What are the health risks of having low BMI?

Very low BMI can potentially lead to malnutrition, osteoporosis, anemia, decreased immune function, and complications in surgery or childbirth.


28. Can you be overweight according to BMI but have normal body fat? 

Yes, athletes and very muscular people may have a high BMI but normal or low body fat percentage. BMI has limitations in extremely fit individuals.


29. Does BMI change during pregnancy?

BMI normally increases during pregnancy and is not used as an accurate indicator of body fatness. Specific pregnancy BMI charts are used instead to monitor weight gain.


30. How often should I measure BMI during weight loss?

It's recommendable to measure BMI once a week when actively losing weight to monitor progress, but not to obsess over normal fluctuations. Aim for consistency.