Normal Weight Obesity Part II

Thanks to all of my readers who provided feedback, comments, and questions regarding last week's blog on Normal Weight Obesity. The questions generated were important, and I'd like to share some of these key issues with you this week!

One of my readers enquired as to whether everyone in the normal BMI range (18.5-25) is at risk of Normal Weight Obesity (NWO). The answer is that the higher your BMI is within the normal range, the higher the risk of NWO. In other words, an individual with a BMI of 19 is extremely unlikely to have NWO, whereas an individual with a BMI of 24 has a higher likelihood of NWO. (Stay tuned for a little more detail on this one - I've just submitted a research article for publication along with my colleague Dr. Arne Astrup in Copenhagen, looking at our own DEXA scan data and BMI misclassification rates.) Women are also at higher risk of NWO than men.

Another important issue to point out is that the opposite classification problem can occur as well: that is, that some people are classified as being overweight by BMI, but do not have excess body fat. Men are at higher risk of this type of misclassification than women (though it can happen in women as well). Picture, for example, a male hockey player with lots of lean muscle mass, and a BMI of 27. This individual is overweight by BMI criteria, but his fat mass may be only15%, well under the 25% fat mass cutoff that defines excess body fat in men. It would be entirely inappropriate to recommend to this hockey player to lose weight!

This example highlights the importance of having other estimates of body fat than just BMI. Waist circumference can be helpful as well: you could imagine that the ultra-fit hockey player would have a trim waist, whereas a sedentary man with a BMI of 27 may be collecting a little extra around his midline. Our ideal upper limits for waist circumference are:

• Caucasian, Middle Eastern, Africans: men 94cm, women 80 cm
• South Asians, First Nations, Chinese, and Japanese: men 90 cm, women 80 cm

This discussion also highlights another important issue with regards to weight struggles, and that is to remember to take pride in a change in body composition that you might be making by stepping up your exercise routine, even if you are not seeing a change in weight. Building muscle in place of fat is beneficial in terms of decreasing your risk of complications of excess body fat (cardiovascular disease, high blood pressure, and many others), and will likely also provide you with an improved sense of general well being and overall health. Changing your body composition in favor of less body fat is a victory in itself!

Dr. Sue © 2010 www.drsue.ca drsuetalks@gmail.com