I think a healthy BMI is a very poor goal for someone to shoot for if they are trying to lose weight. The BMI is a notoriously inaccurate determinant of health as it does not take into account the composition of the persons weight (fat vs. muscle).

If you've ever wanted to lose weight and heard about the infamous BMI make sure that you understand what the BMI really is and what it was designed for. Once you do you'll probably ignore it.

Personally, I pay no attention to it and I never will. Once you understand how your BMI is truly calculated I think you'll see what it's the false prophet of weight loss.

Calculating Your BMI

The Body Mass Index is simply a calculation of your body weight and height. Here is the exact formula they use (I'll plug in my own numbers as an example. I'm 6'1" and weigh 178 pounds)

Formula: weight (lb) / [height (in)]² x 703

Calculate BMI by dividing weight in pounds (lbs) by height in inches (in) squared and multiplying by a conversion factor of 703.

Example: Weight = 178 lbs, Height = 6'1" (73")
Calculation: [178 ÷ (73)²] x 703 = 23.48

Then you can reference it with the following chart:

So, according to the calculations I'm at high normal.  I also hover around 12% body fat.  Ideally, I would like to get up to 185 to 190 pounds at 10% bod fat.  This just feels like a little better number based on my frame.  Plus, I could stand to gain a few more pounds of muscle.  But, if I did that and got to 190 pounds I'd then fall into the overweight category. 

Now, let's use another example to show you where this formula fails.

I have a friend who, back in his day, was a nationally ranked drug free power lifter.  Over the years he began to put on weight but still worked out.  After ballooning to over 250 pounds he finally came around to my way of eating and watched his weight literally fall off in around two months.  While continuing to work out he settled in at around 214 pounds.  He is 6' tall.

Now, after working his numbers into the formula above his number would be 29.02. 

According to his BMI he is not just overweight, he is borderline obese.

Now, here is something else I can tell you about this guy.  After shedding the weight you can nearly see all his abs.  Just from experience I can assume that he is approaching 10% body fat.  He also has a significantly broader bone frame and is designed to carry more weight. 

So, if it was up to a doctor simply basing his decision on a BMI he would have a healthy man who is 88% to 90% muscle start a diet because he is worried about him being obese?

I could give you other examples.  But the point is this:  the BMI has one huge fault and that is it fails to take into account your actual amount of fat and muscle in the calculation.

References are careful to point out these kind of discrepancies but in the same breath paint the BMI as "a reliable indicator of body fatness for people".  How can it if it doesn't actually take body fat into account?

If you want to use the BMI as a red flag that is one thing.  Because there certainly are cases of it being a reliable indicator.  But my point is that it is simply too vague of a measurement and that you have to take into account your own individual situation including actual body fat measurements and other measurements of fitness.