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Weighing less than is normal, healthy, or required.
Insufficiency of weight.


Etymology: AS, under + wiht
1 a body mass index of less than 18.5. See also body mass index.
2 less than normal in body weight after adjustment for height, body build, and age.

Obesity Task Force classification

Bariatric medicine A weight classification based on the body-mass index–BMI, per intl consensus. See Obesity.
Weight type–OTF classification  
Underweight  BMI ≤ 18.5
Normal  BMI 18.5–24.9
Overweight  BMI 25–29.9
Obese  BMI 25–29.9
 Class I   BMI 30–34.9
 Class II   BMI 35–39.9
 Class III   BMI ≥ 40


A ratio of height-to-waist circumference that is below an acceptable range for healthy people.

Patient discussion about underweight

Q. I need food guide for underweight. This is Liam. I had three kids and all are underweight? I don’t know how to make them healthy. I need food guide for underweight. They refuse to have healthy food. How can I get him to eat more and eat healthy, without having to force them?

A. Liam, do not give them too much of juice as it often contain more sugar and less vitamins than fresh or frozen fruits. After a period, give them healthy drink (like milk) instead of juice. If your child is more active than the food they had, then the child will surely be termed as an underweight. So make sure to give, more energizing foods like carbohydrates for an over active kid.

Q. How to loss weight like a diet with tea,pills or other kind of healthy thing.

A. drink 8 oz of warm water with 1 tablespoon of lemon... first thing in the morning

More discussions about underweight
References in periodicals archive ?
Median marks (IQR) in the admission test for obese, overweight, normal, underweight and severely underweight children were 76.
Being underweight was defined as having a Body Mass Index (BMI) of less than 18.
Nevertheless, the large number of moderately or severely underweight children and adolescents in 2016 (75 million girls and 117 million boys) still represents a major public health challenge, especially in the poorest parts of the world.
Among housing conditions, ventilation, indoor air pollution, type of fuel used for cooking, source of drinking water, method of waste disposal and practice of open air defecation were found to be significantly associated with underweight among pre-schoolchildren whereas type of house, overcrowding and presence of breeding site had no significant association with underweight among pre-schoolchildren.
Caption: Women of childbearing age in rural China are at risk of being both overweight or obese and underweight, which could complicate pregnancy, according to a new AJPH study.
Comparison of normal continuous data between underweight, normal weight, and overweight groups was carried out with one-way "ANOVA" test.
The babies of obese mums also face a risk of being premature and underweight, giving them a poor start in life.
and Eurozone equities remained unchanged in October, net 7% underweight and net 5% overweight, respectively.
Among the respondents that had no serving per day of fatty food, 44 (44%) were normal, 7 (7%) were overweight, 3 (3%) were obese and 3 (3%) were underweight.
A spokesman for the charity said: "Upon collecting the dog it became evident that it was in a poor state, underweight and that the dog had an injury to his shoulder.
The world's obese population already outnumbers people who are underweight, the study pointed out.
Conclusion: Mothers from all educational and social backgrounds believe that their children are underweight for age and use force-feeding and appetite stimulants to improve their feeding.