Wikipedia:Reference desk/Archives/Science/2018 December 11

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December 11

Is 90 pounds a healthy weight for a 9-year-old girl?

I apologize if this is an extremely random question, but is 90 pounds a healthy weight for a 9-year-old girl? Futurist110 (talk) 05:49, 11 December 2018 (UTC)

Read about children's BMI from the CDC; and consider using the child BMI calculator. Their warning, verbatim: Please keep in mind that this BMI calculator is not meant to serve as a source of clinical guidance and is not intended to be a substitute for professional medical advice.

Nimur (talk) 05:56, 11 December 2018 (UTC)

You need to measure the body fat percentage of that girl. Count Iblis (talk) 07:25, 11 December 2018 (UTC)

Body water percentage can also give an indication if someone is too fat: "The figure for water fraction by weight in this sample was found to be 58 ±8% water for males and 48 ±6% for females.[2] The body water constitutes as much as 93% of the body weight of a newborn infant, whereas some obese people are as little as 15% water by weight.[3] This is due to how fat tissue does not retain water as well as lean tissue." Count Iblis (talk) 07:29, 11 December 2018 (UTC)

A weight chart is more useful here perhaps. [1] indicates that weight would be 96th percentile for a boy or 94th for a girl. So quite high. Rmhermen (talk) 10:13, 11 December 2018 (UTC)

Indeed, but there's much more to health than simple weight. If she's taller than average or has exceptional amounts of muscle, that number on the scale becomes less useful. Hence the links above that shift the discussion to metrics more directly targeted to health. Matt Deres (talk) 13:11, 11 December 2018 (UTC)

90 pounds = 40.9 kg. Looking at [2] we see that at 108.5 months, 40.5 is just under 95th percentile, and at 119.5 months, it is below 90th percentile. What that means is quite another question, as is what you define as "healthy". Can 10% of the population genuinely be unhealthy? Wnt (talk) 02:33, 12 December 2018 (UTC)

20% are obese: "In the United States, the percentage of children and adolescents affected by obesity has more than tripled since the 1970s. Data from 2015-2016 show that nearly 1 in 5 school age children and young people (6 to 19 years) in the United States has obesity.". Count Iblis (talk) 03:11, 12 December 2018 (UTC)

I feel I should emphasise what Matt Deres and Nimur have indicated. All these percentile etc stuff are interesting, but without knowing the height it's very difficult to comment on health or obesity. While BMI is far from perfect probably even more so for children, it's much more meaningful than just commenting on weight at a certain age. A quick test suggests the girl would be underweight if her height was 5 feet 8 inches (~173cm) [3]. This may be an extreme height but is probably plausible. For example Zeng Jinlian was 1.56 m (5 feet 1.5 inches) 2.17 m (7 feet 1.5 inches) at 13. Anna Haining Bates was "5 feet 2 inches (157.48 centimetres)" at 6 and "6 feet 2 inches (188 cm)" and "197 pounds (89 kg)" at 11. To be fair, such heights as these people reached are not generally healthy as indicated by the ages at death her List of tallest people#Women. And I wouldn't be that surprised if being 173 cm at 9 probably suggests she will reach a height where it starts to become a problem. But still, the weight is only a small part of that and in particular, I'm not sure that keeping a low weight, especially being underweight is likely to improve health. More to the point being 4 feet 10 inches [4] means her weight falls just within the healthy weight range. Being ~147 cm at 9. According to [5] (dunno the quality) such a height is in the 98.3 percentile. I would expect that a girl 147 cm at 9 may still end up with a height that is within the 95th or probably even 85th percentile and where it's not a significant health problem. Nil Einne (talk) 10:39, 12 December 2018 (UTC)

Thank you very much for all of this information--especially the charts which talk about what BMI people with various heights and weights have. Indeed, I will check out all of your links here. Futurist110 (talk) 05:15, 16 December 2018 (UTC)