By Dr. Mercola
In 1832, a Belgian mathematician named Adolphe Quetelet developed what is today known as the body mass index (BMI).1 The formula divides a person's weight by the square of his height, and is one of the most commonly used measures of excess weight, obesity, and overall health.
Initially, BMI was primarily a tool used by insurance companies to set premiums (people with BMIs in the "obese" category may pay 22 percent more for their insurance compared to those in the "normal" category2).
Today, however, BMI is an accepted tool used in medical research and in clinical practice. When you have your height and weight recorded at your doctor's office, it will give him or her an automatic calculation of your BMI, classifying you as underweight if your BMI is below 18.5, normal if it's 18.5-24.9, overweight if it's 25-29.9, and obese if it's 30 or over.
Your doctor may use this number to advise you on your weight, as well as your risk of related conditions like heart disease, high blood pressure, and type 2 diabetes. Unfortunately, BMI is an incredibly flawed tool, and a high BMI doesn't automatically mean you're unhealthy, the way many physicians and health insurance companies imply that it does.
The Obesity Paradox: Sometimes Higher BMI Is Healthier
Research involving data from nearly 3 million adults suggests that a having an overweight BMI may be linked to a longer life than one that puts you within a "normal" weight range.
The research, which analyzed 97 studies in all, found that people with BMIs under 30 but above normal (the overweight range) had a 6 percent lower risk of dying from all causes than those who were normal weight, while those whose BMIs fell into the obese range were 18 percent more likely to die of any cause.3
Separate research published in the Journal of the American College of Cardiology, also found that a high BMI was associated with a lower risk of death, a phenomenon known as the "obesity paradox."4
Indeed, it is quite possible to be overweight and healthy, just as it's possible to be normal weight and unhealthy. And in some cases, it may, in fact, be healthier to carry a few extra pounds. In a Journal of the American Medical Association (JAMA) editorial, Steven Heymsfield, M.D. and William Cefalu, M.D. explained:5
"The presence of a wasting disease, heart disease, diabetes, renal dialysis, or older age are all associated with an inverse relationship between BMI and mortality rate, an observation termed the obesity paradox or reverse epidemiology.
The optimal BMI linked with lowest mortality in patients with chronic disease may be within the overweight and obesity range.
Even in the absence of chronic disease, small excess amounts of adipose tissue may provide needed energy reserves during acute catabolic illnesses, have beneficial mechanical effects with some types of traumatic injuries, and convey other salutary effects that need to be investigated in light of the studies…"
However, for the vast majority of those who carry around extra pounds, health problems will often result. So why would these studies suggest otherwise? They are likely examples of why BMI is such a flawed tool for measuring your health.
Makers of Weight Loss Drugs Altered BMI Categories, Making 29 Million Americans 'Overweight'
BMI is used as the measure of national obesity rates, which currently stand at close to 35 percent for adults and 18 percent for kids. However, the cut-off for classifying a person as normal or overweight seems to be quite arbitrary – and at one point was significantly modified by a task force funded, primarily, by companies making weight loss drugs. Mother Jones reported:6
"In 1998, the National Institutes of Health lowered the overweight threshold from 27.8 to 25—branding roughly 29 million Americans as fat overnight—to match international guidelines.
But critics noted that those guidelines were drafted in part by the International Obesity Task Force, whose two principal funders were companies making weight loss drugs.
In his recent book 'Fat Politics: The Real Story Behind America's Obesity Epidemic,' political scientist Eric Oliver reports that the chairman of the NIH committee that made the decision, Columbia University professor of medicine Xavier Pi-Sunyer, was consulting for several diet drug manufacturers and Weight Watchers International."
BMI Uses Weight, Not Body Fat, to Measure Risk
Branding yourself as unhealthy or overweight simply based on your BMI is not recommended (unfortunately, your insurance company probably won't see it this way). On the other hand, assuming you're healthy just because your BMI is normal isn't advised either.
Research suggests BMI may underestimate obesity rates and misclassify up to one-quarter of men and nearly half of women.7 According to researcher Dr. Eric Braverman, president of the nonprofit Path Foundation in New York City:8
"Based on BMI, about one-third of Americans are considered obese, but when other methods of measuring obesity are used, that number may be closer to 60%."
One of the primary reasons why BMI is such a flawed measurement tool is that it uses weight as a measure of risk, when it is actually a high percentage of body fat that increases your disease risk. Your weight varies according to the density of your bone structure, for instance, so a big-boned person may weigh more, but that certainly doesn't mean they have more body fat or make them more prone to heart disease, for example.
Athletes and completely out-of-shape people can also have similar BMI scores, or a very muscular person could be classified as "obese" using BMI, when in reality it is mostly lean muscle accounting for their higher-than-average weight. BMI also tells you nothing about where fat is located in your body, and it appears that the location of the fat, particularly if it's around your stomach, is more important than the absolute amount of fat when it comes to measuring certain health risks, especially heart disease.
Waist-to-Hip Measurement Is Superior to BMI, But Only 10 Percent of Physicians Use It
Your waist-to-hip ratio is a more reliable indicator of your future disease risk because a higher ratio suggests you have more visceral fat. Excess visceral fat—the fat that accumulates around your internal organs — is far more hazardous to your health than subcutaneous fat (the more noticeable fat found just under your skin) – a measure that BMI tells you nothing about. The danger of visceral fat is related to the release of proteins and hormones that can cause inflammation, which in turn can damage arteries and enter your liver, and affect how your body breaks down sugars and fats.
Unfortunately, according to Donna Ryan, a physician who has trained thousands of primary-care doctors in obesity screening, only about 10 percent use waist circumference as a health indicator. She told Mother Jones:9 "Doctors are so pressed for time… And it's intrusive. You have to put your arms around the patient." To determine your waist-to-hip ratio, get a tape measure and record your waist and hip circumference. Then divide your waist circumference by your hip circumference. For a more thorough demonstration, please review the video above.
Waist to Hip Ratio Men Women Ideal 0.8 0.7 Low Risk <0.95 <0.8 Moderate Risk 0.96-0.99 0.81 - 0.84 High Risk >1.0 >0.85
How Much You Exercise Also Predicts Your Disease Risk
Your fitness level is also a far better predictor of mortality than your BMI. One study found that people who rarely exercised had a 70 percent higher risk of premature death than those who exercised regularly, independent of their BMI.10 If you want a simple test to gauge your fitness level, try the abdominal plank test (for a demonstration of how to do a plank, see the video below. If you can hold an abdominal plank position for at least two minutes, you're off to a good start. If you cannot, you're likely lacking in core strength, which is important for overall movement stability and strength.
A strong core will also help prevent back pain. Being unable to hold a plank for two minutes may also indicate that you're carrying too much weight and would benefit from shedding a few pounds. Unfortunately, over 50 percent of American men, and 60 percent of American women, never engage in any vigorous physical activity lasting more than 10 minutes per week.11 This despite a growing body of research clearly showing that "exercise deficiency" threatens your overall health and mental well-being, and shortens your lifespan.
In fact, according to research published in the American Journal of Physiology, the best way to stay young is to simply start exercising, as it triggers mitochondrial biogenesis, a decline of which is common in aging.12 Researchers have also suggested that exercise is "the best preventive drug" for many common ailments, from psychiatric disorders to heart disease, diabetes, and cancer.13 According to Jordan Metzl, a sports-medicine physician at New York City's Hospital for Special Surgery and author of The Exercise Cure: "Exercise is the best preventive drug we have, and everybody needs to take that medicine."
So rather than stressing over an arbitrary number like your BMI, you'd be better served by coming up with a comprehensive fitness plan. I recommend incorporating high-intensity interval training (HIIT), strength training (including super slow), core exercises, stretching, and non-exercise activity into your routine. The key is to simply get moving, and work at a high enough intensity with enough variance to keep your muscles adequately challenged.
Every person is different, so there's not just one "correct" way to exercise. Equally, if not more, important is incorporating regular intermittent movement into your day, as this will help to counteract some of the effects excess sitting has on your body. If you exercise correctly and keep moving throughout your day, and combine it with a healthy eating program, you will optimize your body-fat percentage naturally, and with it gain a predisposition for optimal health.