This is today's edition of The Download, our weekday newsletter that provides a daily dose of what's going on in the world of technology.

We all know that being overweight is not great for your health -- it's linked to metabolic diseases like diabetes and cardiovascular problems. But weighing yourself won't tell you all you need to know about your disease risk.

A friend of mine is a super-fit marathon runner. She's all lean muscle. And yet according to her body mass index (BMI), which is a measure of weight relative to height, she's overweight. Which is frankly ridiculous.

I, on the other hand, have never been all that muscular. I like to think I'm a healthy weight -- but nurses in the past have advised me to eat more butter and doughnuts based on my BMI. This is advice I never expected to receive from a health professional. (I should add here that my friend and I are roughly the same height and wear the same size in clothes.)

The BMI is flawed. Luckily, there are several high-tech alternatives, but a simple measure that involves lying on your back could also tell you about how your body size might influence your health. Read the full story.

This story is from The Checkup, our weekly newsletter giving you the inside track on all things biotech and health. Sign up to receive it in your inbox every Thursday.