How to Find Your Ideal Weight

Using Your Body Mass Index to Know How Much You Really Should Weigh

Nov 7, 2008
Adrienne Larocque

Your ideal weight is your healthy weight - photo by Serghei Starus

There are health risks associated with being overweight as well as being underweight. So how do you know whether you need to gain or lose some weight to be healthy?

In this day of super-thin supermodels, it’s easy for women to look at their own bodies and be dissatisfied. When Gisele Bunchen is held up as the ideal of feminine beauty, it’s natural for women to feel that they can’t measure up. But comparing yourself to models can be misleading, and even dangerous to your well-being.

Being underweight carries risks such as nutritional deficiencies. New guidelines are being put in place to ensure that models are not too thin to be healthy. But what, exactly, is too thin? Being overweight increases the probability of developing Type II diabetes, heart disease, cancer, and other diseases. When so many of the adults around you are overweight or obese, how can you know where you weigh in?

Body Mass Index

One way to determine your ideal weight is by calculating your Body Mass Index or BMI. The BMI is not a measure of fat, although it correlates well with direct measures of body fat. It is simply a number that relates your weight to your height:

BMI = Weight in kilograms/(Height in metres)2

(If you don’t have a calculator handy, there are several BMI calculators available online.)

BMI cutoffs according to the Standards Committee of American Society of Obesity Surgery (Obesity Surgery, 1997) for women are as follows: below 19.1 is underweight, 19.1 - 25.8 is ideal, 25.8 - 32.3 is overweight, and above 32.3 is obese. For men, BMI below 20.7 is underweight, 20.7 - 26.4 is ideal, 26.4 - 31.1 is overweight, and above 31.1 is obese.

The Singaporean government uses a single set of cutoffs for both women and men: below 18.4 is underweight, 18.5 - 22.9 is ideal, 23.0 - 27.4 is overweight, and above 27.5 is obese.

BMI cutoffs depend on factors like gender, age and ethnicity. According to the US Centers for Disease Control (CDC), at the same BMI, women generally have more body fat than men, and older people have more body fat than younger people. The BMI cutoffs used by the World Health Organization and the CDC are best suited to young adults of European ancestry.

Median BMIs for adult men and young adult women remain constant regardless of height, while those for older women decrease with increasing height. The BMI calculator developed by Steven B. Halls, M.D., takes this into account and allows you to calculate the medically-recommended weight range for your height, age and gender.

Health Risks

Regardless of the precise BMI values used, the categories correspond to different health risks. Obese people have the highest risk of developing weight-related diseases. Overweight individuals have a moderate risk. Those at their ideal weight have the lowest chance of becoming ill. Anyone in the underweight category may develop nutritional deficiencies or osteoporosis.

BMI numbers are a guide to determine healthy weight. However, just because you have a BMI in the ideal range doesn’t mean that you are healthy; it simply means that your risk of developing health problems because of having too much or too little fat is reduced.

The US National Heart, Lung, and Blood Institute recommends looking at two other predictors to assess an individual’s probability of developing overweight- or obesity-related diseases: waist circumference (since belly fat is a predictor of risk for these diseases), and other factors such as high blood pressure or physical inactivity.

BMI calculations are not useful for determining healthy weight for pregnant women. Because of physiological changes that occur during growth, interpretation of BMI numbers for children is complicated. Athletes and bodybuilders may not be able to use this approach because the calculation will yield a high BMI due to their increased muscularity.

Disclaimer: This information is for educational purposes only and should not be considered as medical advice. It does not replace the advice of the physician who cares for you. All medical advice and information should be considered as incomplete without a physical exam, which is not possible without a visit to your doctor.