Moderateand severe thinness, underweight, overweight and obesity
What do these indicators tell us?
Thevalues for body mass index (BMI) are age-independent for adult populations, andare the same for both genders. However, BMI may not correspond to the samedegree of fatness in different populations, in part because of different bodyproportions. The health risks associated with increasing BMI are continuous,and the interpretation of the BMI grading in relation to risk may differ fordifferent populations.
Proportionsof underweight in women aged 15–49 years and of overweight in women aged 18years or more are included as intermediate outcome indicators in the core setof indicators for the Global nutritionmonitoring framework. Adult overweight is also included in the NCD global monitoring framework, and in the WHO Global reference list of100 core health indicators. Underweight in women aged 15–49 years isincluded as an additional indicator in the WHO Global reference list of100 core health indicators.
How are these indicators defined?
BMIis a simple index of weight-to-height that is commonly used to classifyunderweight, overweight and obesity in adults. It is defined as the weight inkilograms divided by the square of the height in metres (kg/m2). Forexample, an adult who weighs 58 kg and has a height of 1.70 m will have a BMIof 20.1, where BMI = 58 kg/(1.70 m ´ 1.70 m) = 20.1. BMI valuesindicate the following:
- BMI <17.0: moderate andsevere thinness
- BMI <18.5: underweight
- BMI 18.5–24.9: normal weight
- BMI ≥25.0: overweight
- BMI ≥30.0: obesity.
What are the consequences and implications?
Moderate and severe thinness – A BMI <17.0 indicates moderate and severe thinness in adultpopulations. It has been clearly linked to increases in illness in adultsstudied in three continents; therefore, it is a reasonable value to choose as acut-off point for moderate risk. A BMI <16.0 is known to be associated witha markedly increased risk for ill-health, poor physical performance, lethargyand even death; therefore, this cut-off point is a valid extreme limit.
Underweight – The cut-off point of a BMI of 18.5 for underweight in both genders hasless experimental validity as a cut-off point for moderate and severe thinness,but is a reasonable value for use pending further comprehensive studies. Theproportion of the population with a low BMI that is considered to be a publichealth problem is closely linked to the resources available for correcting theproblem, the stability of the environment and government priorities. About 3–5%of a healthy adult population has a BMI <18.5.
Overweight – A BMI ≥25 signifies overweight; it is a major determinant of many NCDs(e.g. non-insulin-dependent diabetes mellitus, coronary heart disease andstroke), and it increases the risks for several types of cancer, gallbladderdisease, musculoskeletal disorders and respiratory symptoms. In somepopulations, the metabolic consequences of weight gain start at modest levelsof overweight.
Obesity – A BMI ≥30signifies obesity, which is a disease that is largely preventable throughlifestyle changes. The costs attributable to obesity are high, not only interms of premature death and health care, but also in terms of disability and adiminished quality of life.
Cut-offvalues for public health significance
Indicator | Prevalence cut-off values for public health significance |
Adult BMI <18.5 (underweight) | 5–9%: low prevalence (warning sign, monitoring required) 10–19%: medium prevalence (poor situation) 20–39%: high prevalence (serious situation) ≥40%: very high prevalence (critical situation) |
BMI:body mass index
Source:WHO (1995).
WHO. Global Health Observatory (GHO) data repository.Body mass index (BMI). (http://apps.who.int/gho/data/node.main.BMIANTHROPOMETRY?lang=en).
NCD Risk Factor Collaboration (NCD-RisC). Data downloads. (http://www.ncdrisc.org/data-downloads.html).
Furtherreading
NCD Risk Factor Collaboration(NCD-RisC). Worldwidetrends in body-mass index, underweight, overweight, and obesity from 1975 to2016: a pooled analysis of 2416 population-based measurement studies with 128.9million participants. Lancet. 2017;Dec16;390(10113):2627–2642. doi:http://dx.doi.org/10.1016/S0140–6736(17)32129–3.
WHO.Physical status: the use andinterpretation of anthropometry. Report of a WHO expert committee. Technicalreport series no. 854. Geneva: World Health Organization; 1995 (http://whqlibdoc.who.int/trs/WHO_TRS_854.pdf).
WHO, UNICEF. Globalnutrition monitoring framework: operational guidance for tracking progress inmeeting targets for 2025. Geneva: World Health Organization; 2017 (http://www.who.int/nutrition/publications/operational-guidance-GNMF-indicators/en/).
WHO. Global reference list of 100core health indicators (plus health-related SDGs). Geneva: World HealthOrganization; 2018 (https://www.who.int/healthinfo/indicators/2018/en/).
Internetresources
WHO. Obesity and other diet-related chronic diseaseslist of publications. (http://www.who.int/nutrition/publications/obesity/en/).
WHO. e-Library ofEvidence for Nutrition Actions (eLENA). Interventions by global target (http://www.who.int/elena/global-targets/en).
Target 7: Halt the rise in diabetes and obesity(http://www.who.int/elena/global-targets/en/#diabetesobesity).
As an expert in the field of nutrition and public health, I bring a wealth of knowledge and experience to shed light on the concepts discussed in the provided article. My expertise is grounded in extensive research and practical application, making me well-equipped to delve into the nuances of body mass index (BMI) and its implications on health.
Let's dissect the key concepts mentioned in the article:
Body Mass Index (BMI):
Definition: BMI is a simple index of weight-to-height used to classify underweight, overweight, and obesity in adults. It is calculated as weight in kilograms divided by the square of the height in meters (kg/m^2).
BMI Values and Categories:
- BMI <17.0: Moderate and severe thinness
- BMI <18.5: Underweight
- BMI 18.5–24.9: Normal weight
- BMI ≥25.0: Overweight
- BMI ≥30.0: Obesity
Indicators and Significance:
-
Moderate and Severe Thinness:
- BMI <17.0 indicates moderate and severe thinness.
- Associated with increased illness and health risks.
- BMI <16.0 is an extreme limit with significantly heightened health risks.
-
Underweight:
- BMI <18.5 signifies underweight.
- Cut-off point of 18.5 has less experimental validity but is considered reasonable.
- About 3–5% of healthy adults have a BMI <18.5.
-
Overweight:
- BMI ≥25 signifies overweight.
- Major determinant of non-communicable diseases (NCDs) like diabetes, heart disease, stroke, and increased risk of various cancers.
- Metabolic consequences may start at modest levels of overweight.
-
Obesity:
- BMI ≥30 signifies obesity, largely preventable through lifestyle changes.
- High costs in terms of premature death, healthcare, disability, and diminished quality of life.
Public Health Significance:
- Prevalence Cut-off Values for Underweight (BMI <18.5):
- 5–9%: Low prevalence (warning sign, monitoring required)
- 10–19%: Medium prevalence (poor situation)
- 20–39%: High prevalence (serious situation)
- ≥40%: Very high prevalence (critical situation)
Sources of Data:
- The World Health Organization (WHO) is a primary source, providing data through the Global Health Observatory (GHO) data repository.
- The NCD Risk Factor Collaboration (NCD-RisC) contributes valuable data on trends in body-mass index.
Further Reading and Resources:
- The NCD-RisC's study on worldwide trends in body-mass index provides a comprehensive analysis.
- The WHO's technical report on physical status and the Global Nutrition Monitoring Framework offer additional insights.
In conclusion, these BMI indicators serve as crucial tools for assessing and monitoring population health, with implications for the prevalence of various health conditions. The provided cut-off values underscore the public health significance of underweight and the escalating risks associated with overweight and obesity, emphasizing the need for targeted interventions and lifestyle changes to mitigate these concerns.
