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Determining a Healthy Body Weight

Robyn Kievit is a family nurse practitioner and registered dietitian in the Boston area. E-mail your nutrition and weight loss questions to robyn@robynkievit.com or visit her website at www.robynkievit.com. On Facebook and Twitter, search for nutritionmentor.

How can we accurately determine a healthy weight for our patients? Identifying ideal body weight can be challenging, but it is essential to weight loss and maintenance. From a healthcare provider's standpoint, identification of a healthy body weight can help us monitor and improve health status. The use of several tools can help you and your patient determine a realistic and healthy weight goal.

Body Mass Index
Body mass index (BMI) is the most recognized screening tool to assess body weight and classify level of obesity. According to population-based studies, BMI assesses weight relative to height and gives a fairly acceptable approximation of total body fat. BMI is an indirect measurement of body fat and is only moderately correlated with body fat percentage.

The calculation of BMI is simple: weight in kg/height in meters squared. Interactive BMI tables are widely available (http://www.nhlbisupport.com/bmi/). For patients who are athletes, a miscorrelation exists among BMI, body fat and where their weight falls on the rating scale for obesity. Overweight is present at a BMI between 25 and 29.9, and obesity is present at a BMI above 30.1

The National Heart, Lung, and Blood Institute (NHLBI) has developed clinical guidelines for the treatment of overweight in adults. The most recent version was published 1988, and it will be updated in 2011. The NHLBI states that BMI has limitations, and it recommends acting on that score in combination with NHLBI's Obesity Education Initiative.2

Waist-to-Hip Ratio
Waist-hip ratio or measurement of weight circumference is another way to determine the presence of overweight. This value represents body fat pattern or the ratio of abdominal to gluteal-femoral body fat.2 A ratio of more than 0.90 for men and more than 0.80 for women indicates risk for overweight. Waist measurements alone are also considered predictive of risk. In men, risk increases at any waist circumference greater than 40 inches (102 cm). In women, risk increases at 35 inches (88 cm). These measurements are listed in NHLBI and WHO standards for the prediction of cardiovascular disease.3

Waist-hip ratio is more time consuming and cumbersome to perform in the office than calculating BMI. However, growing evidence suggests that healthcare providers use a combination of BMI, waist circumference and risk factors for disease to evaluate the need for weight loss.3

BMI Scrutiny
Although BMI may be the easiest way to estimate ideal body weight in the office setting, it has come under recent scrutiny. Author and body image blogger Kate Harding started the "BMI Project," which displays photos of people of normal-appearing weight who fall into the obese and overweight categories of the BMI. Such information is out there for our patients to view and can be hard to address in an office visit, but BMI and waist circumference should still be used to classify obesity and overweight in the primary care setting. Use of these tools represents evidenced-based practice.

Setting Weight Loss Goals
Individualizing weight loss goals is the key to successfully working with patients who want to reduce their body weight. Building personal relationships can greatly aid weight loss.4

Consider Mary, a 38-year-old mother of three who works full time and has been your patient for 5 years. She is 5 feet, 4 inches tall and weighs 150 pounds. Her last pregnancy was at age 33. Before Mary's first pregnancy, during her 20s, Mary's weight was consistent at 128 pounds. She followed a healthy diet and got regular exercise consisting of five or six sessions of cardiovascular activity per week with some weight training. At this point, Mary's BMI was 22.0 and within normal limits.
Today, Mary's BMI is 25.7. This puts her in the overweight category. Mary has told you that she is attending two 60-minute boot camp exercise classes per week, and her food record shows she is taking in about 200 extra calories per day in a late night snack before bed. Mary's complete blood count, comprehensive metabolic panel and lipid profile are all normal for her age, and she has no other significant health risk factors. Her family history includes cardiac disease on her paternal side, but she has an otherwise healthy family medical history. The best recommendations for Mary would be as follows:

  1. A personalized ideal body weight range of 140 pounds, based on normal BMI and her own weight history after children.
  2. Eliminating the late night snack. The 200 added calories per day it represents equals about 20 pounds in a year.
  3. Committing to exercise three times per week for 60 minutes each time at the boot camp class she enjoys with her friends. This will aid in achieving weight loss (calories burned vs. calories taken in).

Asking Mary to reach the weight she did in her 20s is most likely not a goal she can achieve at her current age and in light of her work and parenting responsibilities. However, asking her to consistently exercise three times per week, to eliminate one food item, and to reach 140 pounds is quite realistic. This will decreases her health risks significantly.

Evidenced-based weight loss research tells us that individualized goals to reduce weight at a rate of 1 to 2 pounds per week are sound. If Mary reaches 140 pounds, she will achieve a weight loss of 7% from her starting weight of 150 pounds.
Please feel free to post a case study about one of your overweight patients. I'd be happy to make recommendations using the comment feature.


References
1. Sports Nutrition. A Practice Manual for Professionals. 4th ed. Chicago: American Dietetics Association; 2006.
2. Iwao S, et al. Effect of aging on the relationship between multiple risk factors and waist circumference. J Am Geriatr Soc. 2000;48:788-794.
3. National Heart, Lung and Blood Institute. Obesity Education Initiative. http://www.nhlbi.nih.gov/about/oei/index.htm. Accessed June 14, 2010.
4. American Dietetic Association. Evidenced Based Analysis Guidelines, Adult Weight Management Guideline. Executive Summary of Recommendations. http://www.adaevidencelibrary.com/topic.cfm?cat=2798. Accessed June 14, 2010.


Nutrition Now Archives
 

Good review. I would also add some weight lifting, as more muscle burns more calories throughout the day, and some behavior modification such as eating on smaller plates, putting eating utentil down between each bite, chewing and swallowing before picking up your eating utentil again, and drinking water with meals, taking a sip of water between each bit as well.
Mary Arthur

Mary Arthur,  Director, Health Center,  College HealthJuly 15, 2010
Carlisle, PA




     

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