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Classification Under-weight
BMI

Your result:

BMI Classification Table
BMI Classification
Under 18.5 Underweight
18.5 - 24.9 Normal Weight
25-29.9 Overweight
30-34.9 Obesity Class I
35-39.9 Obesity Class II
Over 40 Obesity Class III

*This BMI calculator is for adults 20 years or older. Talk to your doctor about your BMI if you're under the age of 20.

What does this mean for you?

A BMI of 18.5 or less falls below the normal range and means you’re underweight. You may not have the same health risks as people living with obesity, but being underweight could be putting you in other risk categories. Contact your healthcare provider for an evaluation or help getting your nutrition on track.

Frequently asked Questions

Why is BMI important to know?

While underweight individuals may not face the same health risks as those living with obesity, it's important to acknowledge that there are still significant health concerns associated with being underweight. BMI is a good way to check your risks of health conditions related to being underweight. In general, the lower the BMI the greater the likelihood of developing health complications such as:

  • Osteoporosis
  •  Infertility
  • Impaired immunocompetence

Ask your doctor for more information about any of these conditions and how they relate to your BMI.

What are the limits of BMI?

BMI is a simple and objective measurement, but it can be misleading in certain cases and for some groups of people. Research has shown that BMI is less accurate in predicting the risk of disease in people who are older, athletes, those who are tall or short, and those with more muscular body types. For example, elite athletes or bodybuilders have more muscle and weigh more, which makes their BMI higher.

BMI also doesn't take into account:

  • Hereditary risk factors associated with obesity-related diseases, such as metabolic syndrome
  • Environmental and lifestyle factors that can contribute to your risk of developing chronic disease
  • How body fat is distributed in individuals

It's important to remember that living with obesity doesn't necessarily mean you're unhealthy, just as being at a ‘normal’ weight doesn't mean you're healthy. Your BMI doesn't define you, but knowing and understanding your BMI can be a powerful tool for taking charge of your own health.

References
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  2. Yumuk, V et al, “European Guidelines for Obesity Management in Adults” Obes Facts. 2015 Dec; 8(6): 402–424. Published online 2015 Dec 5. doi: 10.1159/000442721.
  3. Garvey, W T et al, “American Association of Clinical Endocrinologists and American College of Endocrinology comprehensive clinical practice guidelines for medical care of patients with obesity.” Endocrine Practice 2016;22:1–203. DOI:https://doi.org/10.4158/EP161365.GL
  4. Guh, D P et al, “The incidence of co-morbidities related to obesity and overweight: A systematic review and meta-analysis,” BMC Public Health, vol. 9, no. 1, p. 88, 2009, doi: 10.1186/1471-2458-9-88.
  5. Prospective Studies Collaboration, “Body-mass index and cause-specific mortality in 900000 adults: collaborative analyses of 57 prospective studies,” Lancet, vol. 373, no. 9669, pp. 1083–1096, Mar. 2009, doi: 10.1016/S0140-6736(09)60318-4.
  6. “Obesity Screening – Medline Plus, U.S. National Library of Medicine” Available: https://medlineplus.gov/lab-tests/obesity-screening/.
  7. “Assessing Your Weight and Health Risk – National Heart, Lung, and Blood Association – U.S. Department of Health & Human Services” Available: https://www.nhlbi.nih.gov/health/educational/lose_wt/risk.htm.
  8. Hussain, A et al, “Type 2 Diabetes and obesity: A review” Journal of Diabetology, June 2010; 2:1.
  9. Katzmarzyk, P T et al, “Body mass index and risk of cardiovascular disease, cancer and all-cause mortality” Can. J. Public Health, vol. 103, no. 2, pp. 147–151, 2012, doi: 10.1007/BF03404221.
  10. Kurth, T et al, “Prospective Study of Body Mass Index and Risk of Stroke in Apparently Healthy Women,” Circulation, vol. 111, no. 15, pp. 1992–1998, Apr. 2005, doi: 10.1161/01.CIR.0000161822.83163.B6.
  11. Landi, F et al, “Body Mass Index is Strongly Associated with Hypertension: Results from the Longevity Check-Up 7+ Study” Nutrients. 2018 Dec; 10(12): 1976. Published online 2018 Dec 13. doi: 10.3390/nu10121976.
  12. Dağ, Z Ö et al, “Impact of obesity on infertility in women,” J. Turkish Ger. Gynecol. Assoc., vol. 16, no. 2, pp. 111–117, Jun. 2015, doi: 10.5152/jtgga.2015.15232.
  13. Moussa, O M et al, “Effect of body mass index on depression in a UK cohort of 363037 obese patients: A longitudinal analysis of transition,” Clin. Obes., vol. 9, no. 3, p. e12305, Jun. 2019, doi: https://doi.org/10.1111/cob.12305.
  14. Zhao, G et al, “Depression and anxiety among US adults: associations with body mass index,” Int. J. Obes., vol. 33, no. 2, pp. 257–266, 2009, doi: 10.1038/ijo.2008.268.
  15. Lamon-Fava, S et al, “Impact of Body Mass Index on Coronary Heart Disease Risk Factors in Men and Women,” Arterioscler. Thromb. Vasc. Biol., vol. 16, no. 12, pp. 1509–1515, Dec. 1996, doi: 10.1161/01.ATV.16.12.1509.
  16. Van Hemelrijck, M et al, “Longitudinal study of body mass index, dyslipidemia, hyperglycemia, and hypertension in 60,000 men and women in Sweden and Austria” Published: June 13, 2018https://doi.org/10.1371/journal.pone.0197830.
  17. Loomis, A K et al, “Body Mass Index and Risk of Nonalcoholic Fatty Liver Disease: Two Electronic Health Record Prospective Studies,” J. Clin. Endocrinol. Metab., vol. 101, no. 3, pp. 945–952, Mar. 2016, doi: 10.1210/jc.2015-3444.
  18. Zafar, S et al, “Correlation of gastroesophageal reflux disease symptoms with body mass index,” Saudi J. Gastroenterol., vol. 14, no. 2, pp. 53–57, Apr. 2008, doi: 10.4103/1319-3767.39618.
  19. Han, T S et al, “A clinical perspective of obesity, metabolic syndrome and cardiovascular disease,” JRSM Cardiovasc. Dis., vol. 5, pp. 2048004016633371–2048004016633371, Feb. 2016, doi: 10.1177/2048004016633371.
  20. Health risks of obesity – Medline Plus, U.S: National Library of Medicine.” Available: https://medlineplus.gov/ency/patientinstructions/000348.htm.
  21. Canadian Adult Obesity Clinical Practice Guidelines. Available:  https://obesitycanada.ca/guidelines/ 
  22. Canadian Guidelines for Body Weight Classification in Adults - ONPP. Available: https://publications.gc.ca/collections/Collection/H49-179-2003E.pdf
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