Is Lower Always Better?

Printed with permission from the Cooper Institute.

unhealthy bmi

Healthy body weight is the new skinny. Seriously! For example, as of January 2013, Israel banned male and female models with documented body mass indexes (BMIs) below 18.5 (underweight classification) from media, catwalks, and Israeli websites in an attempt to encourage healthy eating behaviors/habits (1). In addition United States companies have begun utilizing images of “real women” such as Dove whose recent advertising shows women confidently posing to show “real; beautiful; soft; skin.” These are just a few examples of the influential changes that are occurring to promote healthy body weight.

BMI is calculated by taking weight (in kilograms) divided by height squared (in meters). This calculation serves as a screening tool to identify potential weight problems. Classification categories for adults are as follows:

  • Underweight, <18.5 kg/m2
  • Healthy Weight, 18.5-24.9 kg/m2
  • Overweight, >25-29.9 kg/m2 and
  • Obese >30 kg/m2

(Not good with math? If you want to use a calculator to calculate your BMI, create a free account on, click on Tools and use the “Weigh Your Risk” tool.)

Similar to categories overweight and obese, underweight has been recognized as a weight problem that should be addressed due to its many adverse effects on overall health (2-5). Individuals who practice unhealthy dieting and exercise behaviors that lead to a low BMI put themselves at increased risk for unfavorable health results. Influential industries are now heeding the message; hence, the increased interest in encouraging images of healthy weight models. Let’s compare and contrast the benefits of the healthy weight and underweight categories. We will explore 3 topics below:

1) Diabetes

A multi-ethnic study by Maskarinec et. al. showed that the prevalence of diabetes tended to be high or higher for underweight participants in comparison to normal weight. However, BMIs exceeding the normal category had 2-3 times higher prevalence of being diagnosed with diabetes in men and women. This trend was seen among Caucasians, African Americans, Native Hawaiians, Japanese, and Latinos and further suggests “healthy weight” is optimal (4).

2) Bone Mineral Density

In regards to bone mineral density, low body weight and low BMI have been found to increase the likelihood of osteoporosis-related fractures in younger women (3,6). This trend has been found in  older populations as well (2). In the Study of Osteoporosis Fractures (SOF), as a participant’s BMI decreased, risk of hip fracture increased so much so that participants 65 and older who fell in the lowest BMI groups had twice the hip fracture occurrence (3,6).

3) Hospital Stay

Hsu et. al investigated the influence of underweight BMI classification on patients with cardiovascular disease and found that underweight patients receiving an implantable cardioverter-defibrillator had increased complications and prolonged hospital stays compared with normal weight patients.

So the key message: Lower is not always better. In terms of weight, optimal (healthy weight) is best. While our society tends to be weight-focused, enhancing health should always be the primary goal, with losing weight secondary. This year I challenge you to let any weight loss resolutions center around pursuing health, instead of solely focusing on the number on that scale.

Reference List

1. Judy Siegel-Itzkovich. Law against anorexic models goes into effect. The Jerusalem Post 2013 [cited 2013 Jan 4];Available from: URL:

2.  Cummings SR, et al. Risk factors for hip fracture in white women. Study of Osteoporotic Fractures Research Group. N Engl J Med 1995 Mar 23;332(12):767-773.

3.  De Laet C, et al. Body mass index as a predictor of fracture risk: a meta-analysis. Osteoporos Int 2005 Nov;16(11):1330-1338.

4.  Maskarinec G, et al. Diabetes prevalence and body mass index differ by ethnicity: the Multiethnic Cohort. Ethn Dis 2009;19(1):49-55.

5.  Tremblay A, Bandi V. Impact of body mass index on outcomes following critical care. Chest 2003 Apr;123(4):1202-1207.

6.  Morin S, Tsang JF, Leslie WD. Weight and body mass index predict bone mineral density and fractures in women aged 40 to 59 years. Osteoporos Int 2009 Mar;20(3):363-370.

7.  Hsu JC, et al. Low body mass index but not obesity is associated with in-hospital adverse events and mortality among implantable cardioverter-defibrillator recipients: insights from the national cardiovascular data registry. J Am Heart Assoc 2012 Dec;1(6):e003863

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