Body Mass Index

The Healthiest Weight Is Not What You Think


These machines were once ubiquitous, costing only a penny, but offering mostly non-medical fates. However attempts to predict health from body weight go back at least 150 years to the Body Mass Index or BMI.

There are innumerable (and identical) BMI calculators to be found on the Internet, and by entering your height, weight and sometimes your sex and age, they will duly compute a number, your BMI, and will often sort you into a thin, normal, overweight, obese, or really obese category. Normal is 18-25, overweight is 25-30, and so on.

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Now as measures go, BMI is a really lousy one. What’s a lot more important is the percentage of that weight that is muscle, and (not unrelated) your waist measurement. But lousy or not, a huge amount of medical advice is dispensed based on BMI, and a surprisingly high amount of medical research has been done connecting it with expected mortality.

The Healthiest Weight Is Not What You Think

Now here’s where it gets really interesting, or maybe ‘odd’ is the right word. Virtually all the medical authorities say that the ideal, healthiest BMI is the ‘normal’ range, 18-25. However, virtually all the medical research says the healthiest BMI is ‘overweight’. For men the best BMI number is around 27 and for women around 30. This is well into the ‘overweight’ range. There is a 15-40 pound difference between ‘normal’ and the ideal ‘overweight’.

Overweight is best? Surely this is a joke. But it’s not. It’s (another) case of doctors appearing to ignore their own research. What is going on here? The doctors are advising a BMI 15 to 40 pounds lower than their own researched optimum. That many pounds is quite a lot, as anyone who has ever tried to lose it can attest. Why the disconnect? Here are some possible reasons:

  • Doctors watch too much TV. We learn from TV that one notch up from emaciated is ideal.
  • The published advice is lagging behind the research. Could be, but some of this BMI research is 15 years old.
  • Moral hazard. A medical profession favorite. As soon as the public learns overweight is best, they are going to pig-out and end up very obese. Well maybe there is a risk here, but after all we are grown-up’s…

Does this mean you should plump up? Not really. The overweight health advantage, though real, is quite slight. There are many other factors that make huge health differences. The real message is that quite a broad range of weights are healthy. For a 5’ 10” male 130 to 210 pounds is likely OK , for a 5’ 6” woman, a weight of 115 to 185 is in the ‘don’t worry about it’ zone. If your weight is changing rapidly for no reason, up or down, worry about that.

So what is important weight-wise? It’s simple enough. Belly fat is bad. Other fat is not bad. Muscle is good. Don’t worry about fat for now. Figure out which weight is best for you. Your healthiest weight can be measured, but not with a scale, with a blood test. If your sugar and lipid numbers are in good stead, especially your glucose, insulin, and triglycerides, your weight, whatever it is, is healthy.

We will have quite a lot more to say about this topic. Stay tuned.

  3 comments for “Body Mass Index

  1. Sri
    February 9, 2015 at 8:18 pm

    Excellent Post Doc, thanks

  2. Lora
    February 13, 2015 at 4:33 am

    ty Info

  3. Rod Griffiths
    October 31, 2015 at 12:03 pm

    Just look at BMI for professional athletes. The supposed correlation to overall health is just junk science.

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