Did your doctor tell you to lose weight? It may be good advice. Then again, he may have based it on bad science — the outdated Body Mass Index (BMI). Calculated from height and weight, it can be grossly misleading. For example, according to the BMI, Arnold Schwarzenegger in his prime — at 6’2″ and 257 pounds — was obese.

The problem with the BMI is that it doesn’t distinguish between fat and lean body mass. And muscle weighs more than fat. Ideally, a man should have between 10 and 14 percent body fat. A woman should have between 16 and 20 percent.

Here are two ways to determine how much body fat you have:

1. The skin-fold test, which is done with a caliper. It’s not only accurate, but is the simplest way to measure body-fat percentage. You can purchase a caliper at exercise-equipment stores.

2. A tape measure can give you a rough but useful approximation. Simply measure the circumference of your waist at your navel. Record the number in inches. Then measure the circumference of your hips at their widest point. Divide your waist measurement by your hip measurement to get your waist-to-hip ratio. For men, the ratio should be no more than .90. For women, it should be no more than .80.

Your fitness goal should focus on increasing lean body mass and reducing body-fat mass. Keep track of your progress. In most cases, measuring your body fat once a month is plenty.

[Ed. Note: Mark Morgan Ford was the creator of Early To Rise. In 2011, Mark retired from ETR and now writes the Palm Beach Letter. His advice, in our opinion, continues to get better and better with every essay, particularly in the controversial ones we have shared today. We encourage you to read everything you can that has been written by Mark.]

Mark Morgan Ford

Mark Morgan Ford was the creator of Early To Rise. In 2011, Mark retired from ETR and now writes the Wealth Builders Club. His advice, in our opinion, continues to get better and better with every essay, particularly in the controversial ones we have shared today. We encourage you to read everything you can that has been written by Mark.