These are the best ways to measure your body fat

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, on the basis of my BMI, to eat more butter and doughnuts. 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. So what should we be using instead? 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.

First, let’s talk about fat—the most demonized of all body components. Fat is stored in adipose tissue, which has some really important functions. It stores energy, keeps us warm, and provides protective cushioning for our organs. It also produces a whole host of important substances, from hormones that control our appetite to chemicals that influence the way our immune systems work.

Not all fat is equal, either. Our bodies contain white fat, brown fat, and beige fat. While white fat stores energy, brown fat helps burn calories. Beige fat tissue contains a mixture of the two. And white fat can also be broken down into two additional categories: the type under your skin is different from that which covers your internal organs.

It’s the visceral fat—the type surrounding your organs—that is thought to be more harmful to your health, if there’s too much of it. Having more visceral fat has been linked to an increased risk of diabetes and cardiovascular disease. (That relationship isn’t straightforward either, though; studies have shown that removing this “excess” fat doesn’t improve metabolic health.)

Either way, having a good idea of how much fat is in your body, and where it is, would be valuable. It might at least give us some idea of our risk of metabolic disorders. There are quite a few different ways of measuring this.

BMI is the most widely adopted. It’s the official measure the World Health Organization uses to define overweight and obesity. On the plus side, it’s very easy to calculate your BMI. Unfortunately, it doesn’t tell you very much about the fat in your body or how it corresponds to your health. After all, your body weight includes your bones, muscles, blood, and everything else, not just your fat. (And as we’ve seen, it can lead well-meaning health practitioners to recommend weight loss or weight gain when it’s really not appropriate.)