Renee J. Rogers, Ph.D. |
Recently, the U.S. Department of Health and Human Services published a National Health Statistics Report updating the trends in body weight, height, waist circumference and body mass index (BMI) in the U.S. population. This update uses data from the National Health and Nutrition Examination Survey (NHANES) and primarily focuses on trends from 1999-2000 through 2015-2016.
If you are not familiar with NHANES, it is a program of studies that examines the health and nutrition status of adults and children. NHANES actually began in the 1960s and, since 1999, has collected data every year through interviews and physical assessments with a nationally representative sample of ~5,000 adults.
This report examined the trends in ~45,000 adults over 20 years of age from measures of weight, waist circumference, height and BMI computed as weight (kg) / height2 (m).
There was a significant and linear increase in body weight over time, which means that there has been a steady increase in body weight over the measured years. In general, this pattern was seen in both men and women, for each race and for those of Hispanic origin, and across age subgroups. Overall, men had a body weight in 1999-2000 of 85.9 kg (189.4 lb) and it increased to 89.8 kg (197.9 lb) in 2015-2016. Women had a similar pattern going from 74.3 kg (163.8 lb) to 77.4 kg (170.6 lb).
Summary: Americans gained seven to eight pounds, which is approximately a five percent increase in body weight, over 18 years.
Waist Circumference and BMI:
There were similar patterns for waist circumference and BMI increases just like with weight. The increases were also linear with men increasing their waist circumference from 99.1 cm (39.0 in) in 1999-2000 to 102.2 cm (40.2 in) in 2015-2016. At the same time points, women went from 92.2 cm (36.3 in) to 98.0 cm (38.6 in). The average BMI remains in the overweight category (25.0 to <30.0 kg/m2), but still increased from 27.8 and 28.2 kg/m2 to 29.1 and 29.6 kg/m2 in men and women; respectively.
Summary: Just like body weight, there has been an upward trend in waist circumference and BMI without any major change in body height over time. When you look at waist circumference and BMI together, the risk of type 2 diabetes, hypertension, and cardiovascular disease is “high” when someone classified as overweight also has a waist circumference greater than 102 cm (40 in) for men and greater than 88 cm (35 in) for women.
What does this mean when we think about prescribing exercise and physical activity?
Being active is a key lifestyle behavior recommended for health and wellness and as a part of comprehensive treatment for weight management in conjunction with diet and behavior therapy. We know this. However, we must not overlook the fact that carrying excess body weight has been associated with other co-conditions such as low back pain, chronic pain, decreased health-related quality of life, lower physical function, balance and mobility issues, depression, body dissatisfaction, obstructive sleep apnea and knee osteoarthritis. The impact (literally) of carrying extra body weight can potentially hinder exercise participation, as every one pound of extra body weight can feel like four extra pounds on the knees (those seven to eight pounds gained can feel like 28-32 pounds). These are important considerations when we think about providing successful, safe and sustainable programs, while ensuring positive experiences for our participants.
It is easy to grab ahold of a position stand or a fitness trend and want to apply that guideline or mode to help a physically inactive participant - but it does not always work seamlessly. For example, the 2009 ACSM Position Stand on Physical Activity Strategies for Weight Loss and Prevention of Weight Gain recommends 150-250 minutes per week of moderate physical activity to prevent weight gain and produce modest weight loss, and greater than 250 minutes per week to achieve clinically significant (5%) weight loss. If you recall, the increase of seven to eight pounds in the U.S. population since 1999 is approaching an increase in weight of almost five percent.
Imagine what would happen if you initially recommended this high volume of activity early with your participants. What would their experience be like and how would they feel? Think about how those co-conditions could interfere and whether or not they are prepared for this volume of activity. In our weight management research programs centered around lifestyle with an emphasis on physical activity, we strategically work with our participants to “ramp up” to the high volumes of physical activity – this can take anywhere from 12-24 weeks, sometimes increasing time by 25 minutes every four weeks, to get to the 250-minute threshold. This strategy allows for eventual achievement of the recommendations of our ACSM Position Stand so we are still following evidence-based guidelines, but also considers the specific needs of the participant carrying extra body weight.
Let’s take a moment to pull an example from the newest Top 20 Fitness Trends in relation to the population carrying more body weight. I personally loved seeing yoga on this list (#7) and recently engaged in designing a research intervention that used yoga within a weight management program. Early on, we heard concerns related to the co-conditions mentioned above. More specifically, the participants reported not being able to balance in poses or transition into poses as quickly as it would be done in a typical class, and not having the strength to hold poses or lift the weight of their body in and out of poses. So while we were able to successfully engage our participants in a yoga practice over time, it was modified in a way that considered their excess body weight and was likely very different from the general drop-in Yoga studio class. A typical Vinyasa flow class may not have been an option early on for many of our participants.
In summary, the population continues to gain weight and being physically active may be more important than ever. However, let’s be cautious about recommending that participants engage in modalities of fitness that may be popular or beneficial without considering the impact that extra body weight may have on their ability to engage physically, confidently and, hopefully, for the rest of their lives.
Renee J. Rogers, Ph.D., is an Assistant Professor in the Department of Health and Physical Activity and the Director, Health and Wellness Programming and Moving Health with Media Core in the Healthy Lifestyle Institute at the University of Pittsburgh.