BMI, in the sense I mean, stands for Body Mass Index. It's a number that is increasingly being used to classify individuals as healthy, overweight, or obese. It's the number that some parts of government, as well as the weight-cycling industry, use to tell you that there's something wrong with you.
In my book, it's a fraud. According to the official BMI tables, LeBron James is "overweight." So is Kobe Bryant. So are 97 percent of the players in the National Football League, except for those who are officially "obese."
Some other "overweight" celebrities: Tom Cruise. Pierce Brosnan. President George W. Bush.
It should be obvious that it's arbitrary. The government can, and did, change the standards with the stroke of a pen. One night in 1998, 35 million Americans went to bed "healthy" and woke up "overweight" because a government panel had changed the definitions.
Eight of the nine members of that panel had ties to the weight-loss (really, weight-cycling) industry, either as consultants to pharmaceutical companies, recipients of research money from them, or advisers to for-profit groups such as Weight Watchers.
What's fundamentally wrong with the BMI is that it considers only height and weight, not body composition:
BMI makes no allowance for the relative proportions of bone, muscle, and fat in the body. Since muscle weighs more than fat and since bone is denser than muscle and twice as dense as fat, a person with strong bones, good muscle tone, and low fat may have a high BMI. Thus, athletes and fit, health-conscious individuals may be classified as "overweight" or even "obese".
Furthermore, it doesn't correlate with health:
Researchers from the Mayo Clinic College of Medicine, Rochester, Minnesota, found that patients with a low BMI had a higher risk of death from heart disease than those with normal BMI.
At the same time overweight patients had better survival rates and fewer heart problems than those with a normal BMI.
This apparently perverse result, drawn from data from 40 studies covering 250,000 people with heart disease, did not suggest that obesity was not a health threat but rather that the 100-year-old BMI test was too blunt an instrument to be trusted.
What does make sense is to measure the percentage of body fat. There are several ways to do this. Underwater weighing is considered the most accurate, but is also the most unwieldy and inconvenient. It's certainly not readily available to most of us.
Monitors that use electrical impedance are much easier to find. All they require is contact with your bare feet or hands, or both. Some gyms and health clubs have them, and there are home models that are reasonably accurate. Many are incorporated into digital scales--I like this one.
The average percentage of body fat among American men is 17%. Among midlife men, the average is 20%. Strangely, no government panel seems to be setting standards for this, but it seems that a figure of 10 to 14 percent is probably healthy for a man who is not an athlete.
Disclosure: my BMI is higher than the maximum the government table considers "healthy." Since I had access to a body-fat monitor, I did some math. The official table says that, to be at the maximum BMI number it considers healthy, I should weigh 173 pounds.
According to the body-fat monitor, my "lean body weight" today is 173 pounds.
So, to have the maximum "healthy" BMI, I would have to have 0% (yes, zero percent) body fat. That is not healthful. In fact, it's incompatible with life--think of the young anorexics who die of starvation.