The Double Burden of Malnutrition According to WHO
Malnutrition, as defined by the World Health Organization (WHO), refers to deficiencies, excesses, or imbalances in a person's intake of energy and/or nutrients. This definition recognizes the "double burden of malnutrition," where undernutrition and overweight/obesity coexist within the same population, and even within the same household. The WHO’s comprehensive classification system is used globally to assess nutritional status and includes a range of anthropometric indicators for different age groups. These indicators are crucial for identifying specific forms of malnutrition and guiding appropriate interventions.
The Pillars of Undernutrition: Wasting, Stunting, and Underweight
The WHO’s classification of undernutrition relies on three key anthropometric measurements, each providing unique insights into a child’s nutritional history. These measurements are standardized against the WHO Child Growth Standards, and the results are expressed as Z-scores.
- Wasting: Defined as low weight-for-height, wasting is a marker of acute or recent and severe weight loss, often due to insufficient food intake or illness. Moderate or severe wasting in children increases the risk of mortality.
- Stunting: Characterized by low height-for-age, stunting indicates chronic or recurrent undernutrition. It is a long-term issue linked to factors like poverty and repeated infections, potentially hindering physical and cognitive development.
- Underweight: This refers to low weight-for-age, which may indicate a child is stunted, wasted, or both. It's a general measure of nutritional status.
Overweight and Obesity Classification (BMI)
Excess energy intake leading to overweight and obesity is classified by the WHO using Body Mass Index (BMI) for adults and age-dependent BMI-for-age Z-scores for children.
- For Adults: Overweight is a BMI of 25 kg/m² or higher, and obesity is a BMI of 30 kg/m² or higher, with further classifications based on BMI ranges.
- For Children (under 5 years): Overweight is a weight-for-length/height Z-score above +2 SD; obesity is a Z-score greater than +3 SD.
- For Children and Adolescents (5-19 years): Overweight is a BMI-for-age Z-score above +1 SD; obesity is a Z-score above +2 SD.
The Who Classification of Malnutrition Table: A Comparative Look
The following table summarizes key anthropometric criteria used by the WHO to classify different forms of malnutrition, particularly for children under five, using Z-scores relative to the median of the Child Growth Standards.
| Indicator | Nutritional Status | Z-score / MUAC Cut-off | Definition | Time Frame Reflected |
|---|---|---|---|---|
| Weight-for-Height/Length | Severe Wasting | < -3 SD | Very low weight for a child's length or height. | Short-term/Acute |
| Moderate Wasting | ≥ -3 SD and ≤ -2 SD | Low weight for a child's length or height. | Short-term/Acute | |
| Overweight | > +2 SD and ≤ +3 SD | Excessive weight for a child's length or height. | Excess Intake | |
| Obesity | > +3 SD | Excessive weight for a child's length or height, indicating significant fat accumulation. | Excess Intake | |
| Length/Height-for-Age | Severe Stunting | < -3 SD | Very low length or height for a child's age. | Long-term/Chronic |
| Moderate Stunting | ≥ -3 SD and ≤ -2 SD | Low length or height for a child's age. | Long-term/Chronic | |
| Weight-for-Age | Severely Underweight | < -3 SD | Very low weight for a child's age. | Composite (Acute & Chronic) |
| Moderately Underweight | ≥ -3 SD and ≤ -2 SD | Low weight for a child's age. | Composite (Acute & Chronic) | |
| Mid-Upper Arm Circumference (MUAC) | Severe Acute Malnutrition | < 115 mm (6–60 months) | Critical, high-risk indicator for severe acute malnutrition. | Acute |
Micronutrient-Related Malnutrition and the Role of Diet
The WHO also addresses micronutrient deficiencies, which are less apparent than anthropometric classifications. Deficiencies in essential vitamins and minerals like iron, iodine, and vitamin A are significant global public health issues, particularly in low-income settings. A balanced diet, along with fortification and supplementation, is crucial for prevention. The WHO promotes optimizing nutrition early in life and advocating for healthy, diverse diets to combat these deficiencies.
How WHO Standards Inform Clinical Practice and Public Health
The WHO's standardized classification system is vital for accurate data collection and informing global health policies. Tools like MUAC tapes help community health workers screen for severe acute malnutrition (SAM). Children with SAM are referred for specialized care and therapeutic feeding, often using Ready-to-Use Therapeutic Foods (RUTFs), based on criteria like severe wasting or oedema. Further resources on global nutrition are available on the WHO website.
Conclusion
The WHO classification of malnutrition provides a comprehensive framework for addressing nutritional health globally. By categorizing malnutrition using specific indicators and Z-scores, it allows for effective diagnosis, treatment, and monitoring. This system is crucial for developing targeted interventions, evaluating program success, and working towards eliminating all forms of malnutrition.
