DETERMINING YOUR IDEAL BODY WEIGHT

If the government, doctors or a calorie calculator tell you how many calories to eat in order to maintain an “ideal” body weight then how do we determine what that “ideal” body weight is? How do we know how much we should weigh and what percentage of our body should be made up of fat? How much body fat is unhealthy? Is the fat on certain parts of the body more of a health risk than on other locations? In this article, I will answer those questions and discuss the tools that can be used to determine an “ideal” weight and a healthy amount of body fat…or at least where to start.

 

IDEAL WEIGHT FACTORS

Key factors that help to determine an ideal weight include age, muscle-fat ratio, height, sex, and bone density. The ideal human weight is all about how much (or little) body fat we carry around as part of it. There are several methods commonly used to determine the healthy weight (and body fat) of an individual. The two recognized methods by the National Institutes of Health are the Body Mass Index (BMI) and waist circumference measurements. These are two of the most common and universally accepted methods that provide a generally accurate assessment of body fat and healthy weight levels. (1)

 

BODY MASS INDEX (BMI)

BMI is recommended as a practical approach for assessing body fat in the clinical setting and is more accurate than just body weight alone. BMI is a person’s weight in pounds multiplied by 703 and then divided by the square of height in meters. Below is an example using this mathematical formula to determine that the BMI of a person that is 65 inches tall and weighs 180 pounds is 29.9

While BMI does not measure body fat directly, it does moderately correlate with more direct measures of body fat measurements. These more direct measurements include underwater weighing, skinfold thickness measurements, and bioelectrical impedance. Additionally, BMI appears to be as strongly correlated with various metabolic and disease outcomes as are these more direct measures of body fatness. It is an easy and inexpensive method for screening to determine general weight categories and higher risk individuals. (2)

A healthy weight for adults is usually when your BMI is between 18.5 and 24.9, indicated as “normal” in Table 1 below. An ideal BMI reflects your ideal percentage of body fat for your specific height. Table 1 contains all 6 weight categories as it applies to BMI ranging from underweight to three different classes of obesity. 

Table 1 (1)

 

Standard weight status categories associated with BMI ranges are used for all adults over the age of 20 as shown on The Body Mass Index Table (Table 2) below.  This table is simply doing the BMI mathematical formula shown previously for you. These calculated weights for adults based on height are not age or sex-specific. You can use Table 2 to determine your approximate BMI based upon your height and weight. Are you outside of the normal range (18.5-24.9)? Although calculated mathematically the same way for children and adolescents, their BMI are age and sex-specific. Clinical growth charts are used for infants, children and adolescents (up to the age of 20) using different body measurements and age correlations to determine BMI expressed as percentiles. (3)

If you are an adult over the age of 20, you can use Table 2 below to find your height and weight to determine your approximate BMI.

 

Table 2 (4)

 

BMI LIMITATIONS

Although BMI is generally a useful tool to determine ideal body weight it certainly does have some limitations. This method does not take into account a person’s waist, chest, or hip measurements, as well as, bone density. It is often criticized for underestimating the amount of body fat in overweight/obese people and overestimating it in muscular or lean individuals. It does not take age and gender into account ignoring the fact that women naturally have more body fat than men of equal BMI and older people tend to have more body fat than younger people with the same BMI. There is also recent research that suggests ethnicity may affect the relationship between BMI and actual body fat. For example, this would perhaps explain why Asians have higher weight-related disease risks at lower BMIs. Despite these limitations, BMI is still considered a generally effective screening tool to identify high risk and healthy individuals. If your BMI score is outside of the healthy range, you are highly encouraged to seek medical advice and change your lifestyle in order to improve your overall health, reduce body fat and limit your risk of disease. (5,6)

 

WAIST CIRCUMFERENCE MEASUREMENTS

The second globally recognized method of determining healthy body fat is done by measuring the waist circumference. Graphic 1 below describes how to properly perform a waist circumference measurement. The key benefit of this method is that it directly measures fat within the abdominal region which is considered to be associated with a greater health risk than peripheral fat. It is also the most practical tool a clinician can use to evaluate a person’s abdominal fat before and during weight loss treatment.

Graphic 1 (1)

Even more so than BMI, waist circumference measurements can provide a more direct and accurate correlation to increased risk of type 2 diabetes and heart disease. Numerous studies have proven that individuals with central obesity result in a greater total mortality rate regardless of their BMI. Although both of these measurements are interrelated, waist circumference provides an independent prediction of risk over and above that of BMI. Reference Table 1 above again to see a further break down of the correlation between BMI and waist circumference and their association with disease risk. The waist circumference measurement is very useful in patients who are categorized as normal or overweight in terms of BMI (between 25 and 34.9). For these individuals an excessive waist circumference significantly increases the risk for disease more so than just BMI would suggest. Overall, men are at an increased risk if they have a waist circumference greater than 40 inches (102 cm) and women who measure greater than 35 inches (88 cm). (1,7)

 

RIPD RANGER INSIGHT

My body fat has fluctuated between 10 and 25 percent throughout my adult life. Despite being muscular, my BMI still provides a generally accurate screening assessment of my ideal weight but there have been some discrepancies. In January 2017, I weighed 180 pounds. According to the Body Mass Index displayed in Table 2, I had a BMI of 25.1 (71 inches, 180 pounds) which is considered “overweight”. According to a BOD POD result, which is an extremely accurate device comparable to underwater weighing, that same month my body fat percentage was 12.7 %. This 12.7 % measurement would suggest I was lean and well within normal measurements for body fat. Since January, I have lost weight and as a result my BMI has shifted into the “normal” category. My personal results prove BMI may not always be an accurate assessment of your actual body fat, however, it is a useful tool for most people. For all my athletic men and women readers do not be overly concerned if your BMI is higher than you want it to be if you are muscular. Use a more accurate body fat measurement to ensure you are in the healthy range and on the right path to achieving your goals.  The BOD POD is a great device to use that is highly accurate but it may be hard to find so check out local fitness centers for other accurate devices and techniques. For most readers, using BMI and waist circumference measurements is a good tool to help determine your healthy weight. However, they may not provide an accurate body fat assessment in all circumstances especially those that are muscular, very athletic and the elderly.

 

RESOURCES:

  1. The Practical Guide – Identification, Evaluation, and Treatment of Overweight and Obesity in Adults, National Institutes of Health, 2000, https://www.nhlbi.nih.gov/files/docs/guidelines/prctgd_c.pdf
  2. About Adult BMI, Centers for Disease Control and Prevention, 2017, https://www.cdc.gov/healthyweight/assessing/bmi/adult_bmi/index.html
  3. About Child & Teen BMI, Centers for Disease Control and Prevention, 2015, www.cdc.gov/healthyweight/assessing/bmi/childrens_bmi/about_childrens_bmi.html
  4. Body Mass Index Table, www.nhibi.nih.gov/health/education/lose_wt/BMI/bmi_tbl.pdf
  5. The Limitations and Inaccuracies of BMI, Medical News Today, 2016,https://www.medicalnewstoday.com/info/obesity/bmi-limitations.php
  6. Ethnic Differences in BMI and Disease Risk, Obesity Prevention Source, Harvard School of Public Health, https://www.hsph.harvard.edu/obesity-prevention-source/ethnic-difference-in-bmi-and-disease-risk/
  7. Sahakyan, et al, Normal-Weight Central Obesity: Implications for Total and Cardiovascular Mortality, Annals of Internal Medicine, 2015.

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