What is considered skinny or underweight when it comes to body mass index?
Take a look at this chart. The information is from two big health institutions—the World Health Organization (WHO) and the US Centers for Disease Control and Prevention (CDC).
Let’s take the average male height at 5’8 or 176cm.
- Clinically underweight or dangerously skinny:
- BMI of 15, 16, 17, or 18
- 100–120 pounds (46–55kg)
Here’s the thing, though. In 2010, a study from the National Institutes of Health found that people were still getting negative health effects from being underweight even in the 18 and 19 BMI “normal” bodyweight category.
That means, people were still getting negative side effects from being skinny, even if they had a “normal” BMI.
So if you’re trying to avoid the health effects of being underweight, you ought to aim for getting a BMI of at least 20.
The BMI measurement isn’t perfect
It’s good to remember that the BMI measurement isn’t perfect. It has problems with shorter and taller people. And it doesn’t distinguish between muscle and fat.
For example, an elite athlete might be considered “overweight” in terms of BMI just because they carry a lot of muscle. They might otherwise have a perfect bill of health because they’re active, muscular, and put a high priority on health like eating well.
Saying goodbye to being skinny
My personal opinion: it’s worth fixing a skinny body
If you are skinny, I’d highly recommend working on fixing it. This isn’t coming from a place of condemnation or judgement but rather encouragement. I was dangerously skinny at one point in my life. I was 6.0 tall (183cm) at 130 pounds (59kg), making me clinically underweight, or dangerously skinny. Once I rapidly added over 30 pounds in one month in an experiment my roommate and I dubbed “Muscle May,” many of my health problems were erased (alopecia, tendonitis, feeling weak, etc.)
Moving from a Skinny BMI to a Normal BMI
If you’re skinny, ideally, that extra weight wouldn’t come from more fat, but from more muscle. Muscle is incredibly healthy as it plays a central role in metabolism and prevents a number of common diseases. (review)
Now, this may seem unbelievable at first, but skinny guys and gals can build muscle so fast, that it’s almost on a steroid-like level — the reason why is because they are very far from their genetic potential in terms of muscle mass. Their body is practically begging to build muscle, and just need the right stimulus (resistance training), the right nutrition (such as lots of protein), and the right amount of quality sleep. If you want to learn more about this phenomenon, check out this nerdy article on the science of “newbie gains.“
If you’re a skinny woman who wants to improve their BMI through muscle, check out Bony to Bombshell (full disclosure, I co-founded it.)
If you’re a skinny man who wants to improve their BMI through muscle, check out Bony to Beastly (co-founded).
If you’re either a skinny-fat guy or an extremely sedentary skinny guy, check out our brand new True Gains program. It’s designed for guys to build rapid amounts of muscle without getting fatter. It’s designed for those who sit a lot, such as desk workers or those who commute a lot.