I believe a very close friend of mine is (at least moderately) underweight, but he does not fully agree. He's 19, and about 5'10 and about 61kg (134 lbs). He plays a good deal of sports, mostly soccer and running, and eats mostly right (as far as I'm aware, I've known him for a while), and he's slightly muscular. It is very unlikely that he has got any major health issues, because we both had our physical exams some months back and he was mostly fine. I would appreciate some opinions on whether he is underweight, which myself and many others believe he is.

Update: thanks for all the answers. I suppose that does help to discredit my belief, and I'm glad he's alright in terms of weight. Also I can't really estimate his body fat because I've had no past experience in doing so.

2 Answers 2


You can very generally tell a person is at a healthy weight by combining the Body Mass Index with the Body Fat Percentage.

Here is a study published by the National Institutes of Health indicating that BMI and body fat percentage together are a better measurement of healthy weight.

Your friend's BMI is 19.2, in the normal range, and you indicated he is lean, so his Body Fat Percentage is not an issue. Thus, he is considered at a normal weight.

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    I would recommend you to find references for your claim that it is completely normal to be skinny when young, which would greatly improve your answer. Currently, I fail to see how this is any different than a copied answer.
    – Narusan
    Commented Jun 8, 2017 at 21:24
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    Well, I did bring in the additional info that adding body fat % to BMI is a better heuristic for evaluating healthy weight. I'll edit to hopefully make my answer better. I'm new. Commented Jun 8, 2017 at 21:36

I used the BMI calculator from the National Institutes of Health to calculate your friend's Body Mass Index. It came out at 19.2, which is in the normal range. So he is not underweight. (Even if he was, that's between him and his doctor, and a gaggle of friends announcing their medical opinions that he weighs too little is probably not helpful.)

  • Just to add to this excellent answer, that friend's BMI is 11.17% of the range from minimum to max for normal.
    – BillDOe
    Commented Jun 9, 2017 at 0:27

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