There are many classifications that are used to distinguish if one is “healthy.” Weight is often used but it’s a very arbitrary measurement. Judging someone by their weight is kind of like looking at a car and claiming, based solely on appearance, if the car is in tip-top shape. Just because someone weighs a lot doesn’t mean their unhealthy; conversely, just because someone is “skinny” or underweight does not justify that they are fit. Remember the car example; you fall in love with a shiny exterior only to find that the lemon shifts like garbage and leaks oil like a waterfall.
Your best bet for determining if someone is healthy is by measuring body fat. It’s the crème of the crop when it comes to determining body composition because it gets into the nitty gritty caveats of your body. I’ve seen women who are 160 pounds with only 12% body fat; on the flip side, I’ve come across women who weigh 130 pounds at 30% bodyfat. The keyword here is body composition: we’re basically doing a visual dissection to see how much of your body is muscle, bone, and organ with the rest of it being bodyfat. Thus is someone has a high body fat, they’re prone to cardiovascular disease, insulin issues, metabolic syndrome, and premature death. Muscle is the lively tissue and its party responsible for our metabolic rate, movement, and longevity.
Furthermore, body fat is ideal for anyone serious about getting in shape. Stepping on the scale is pretty meaningless if you have no idea what the scale is telling you. If you’re measuring your body fat regularly then you can tell if you’re building muscle (which is always a good thing regardless of age or gender) and how much actual fat you’re losing. You’ll also be able to measure directly where the fat is being lost from: are you losing measurements on your triceps, thighs, or both? It’s an honest, outcome based approach to your training and that’s how things should always be.
Depending on who gives you the numbers on what a healthy body fat should be, you need to consider the source. The wide variances in opinion will cause some head scratching, but someone’s background will give you a little insight as to what supports their opinion. Medical professionals will cite you the highest body fat possible that is considered “healthy” and may prevent the onset of disease; that’s great but doctors are not concerned with performance enhancement. Nor do they have the knowledge for it. In fact, most won’t even measure body fat and will rely on the totally unreliable and archaic B.M I.
Men need to have their body fat in single digits. Anything above that is going to throw your hormones out of whack. For females, under 15% is a great long term goal and consider that dipping below 11% for too long would be considered counter-productive and unhealthy.