Exploring family health
Exploring family health

This free course is available to start right now. Review the full course description and key learning outcomes and create an account and enrol if you want a free statement of participation.

Free course

Exploring family health

The body mass index

The body mass index (BMI) links weight and height to determine whether someone is an ideal weight, overweight or obese. This measurement is now used by the World Health Organization to make global comparisons about levels of over- and under-nutrition for people in different countries (Webb, 2008). The table below shows how different BMI scores relate to weight classifications, and you will see that the distinction between ‘overweight’ and ‘obese’ is actually a very precise difference in the BMI. ‘Overweight’ is classified in cases where the BMI is in the range 25—30, and ‘obese’ is classified for BMIs above 30. Obesity becomes ‘severe’ at a BMI above 40.

World Health Organization BMI classifications

BMI value: weight (kg)/height (m2) Classification
Under 18.5 Underweight
18.5–25 Ideal range
25–30 Overweight
Over 30 Obese
Over 40 Severely obese

BMI measurements need to be applied carefully, however. The same volume of muscle tissue is heavier than that of fat, so an athlete with well-developed muscles and little excess body fat is likely to be heavier than someone of the same size who has more fat and less muscle. The BMI measurement for the athlete is therefore likely to be abnormally high and would not provide a good guide to their possible health risks.

Y032_1

Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has over 40 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to university level study, find out more about the types of qualifications we offer, including our entry level Access courses and Certificates.

Not ready for University study then browse over 900 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus