3. Understanding Body Mass Index
The concept of Body Mass Index (BMI) was developed during research in the 1960s-1970s, trying to correlate easily procured body measurements with more precise--but technically more difficult-- methods to quantify relative body fat composition. This was closely associated with research attempting to better understand increasing rates of mortality then occurring in the USA from cardiovascular diseases. Both in the USA and other industrialized societies, there appeared to be a strong association of CV disease with increased levels of (cholesterol and tri-glyceride) fat in the blood, which appeared to be closely associated with body mass that was disproportionately high in adipose (fat) tissue.
BMI is a mathematical calculation comparing basic anthropomorphic measurements of a person's body-- mass (in kilograms, or pounds)--divided by height (in meters, or inches), that produces a numerical result that implies a certain degree of healthfulness, similar to what blood pressure and blood sugar measurements do. This relatively simple relationship of body weight compared to vertical height results in a two-digit number that can describe the "shape" of that body. In American English jargon, being "in good shape" generally describes someone who actively exercises (see also Blog 2: Exercise). Participation in regular and serious exercise will typically result in strength, speed, and/or endurance reflected in muscle mass, while body fat will generally decline, and will usually result in a BMI of 22-28.
A minor criticism of BMI is that it does not necessarily correlate with functionality (see Blog 2: Exercise). Many younger people who go to work every day, sit at desks for 7-10 hours a day, practice no exercise regimen whatsoever, and are not (yet) obviously overweight, have BMIs = 25-26. However, this BMI also describes the physique, strength, and stamina typical of (professional american) football defensive backs. So, this same BMI applies to two groups of people who have very different functional (fitness) profiles...
Depending on the sport and on the position played, there are different physical challenges that demand more muscle mass. Such is the case in american football, where offensive and defensive linemen--a group of large, powerful, (and very functional) athletes--typically have BMIs in the 35-40 range. However, this same BMI range is what we in the medical field see routinely in sedentary, not very functional 35-45 year olds, who are having to be treated for the serious condition of Adult-onset Diabetes Mellitus.
Over the last half century, there has been a progressive (in some nations, exponential) increase in the number of people with BMIs in the 30-40 range. In medical-speak, BMI > 35 is one major and basic criteria defining morbid obesity because most "regular folks" who have such a BMI are at a very high risk of developing debilitating and life-threatening conditions (high blood pressure, clotting disorders, problems with sugar metabolism, severe osteoarthritis), leading to severe health consequences and /or early death.
So, if you are relatively young (less than 40 y/o) and have a BMI of 27 or greater, and you do not have a regular exercise regimen, my message to you is that you are at a very high risk for progressing to BMI > 35 in the next 10-15 years. If only for your own sake, but also for the ones you love or who may be dependent on you, you need to pay attention to your nutrition and to your activity level and do the work that it takes to maintain a BMI < 27 (where you are also more likely to have a higher "quality of life").
S. Leifheit, DO
early March 2017