From "Malnutrition" to "Undernutrition": What the ICD-11 Change Means, and What It Doesn't

A quiet but meaningful change is coming to how clinicians document one of the most common conditions they treat. Beginning in 2027, the World Health Organization's ICD-11 will, for the first time, include a formal code for undernutrition in adults in clinical settings, and with it, a deliberate shift in language from "malnutrition" to "undernutrition."

For dietitians and the teams they work alongside, it's worth understanding why the change was needed, what it changes, and, just as importantly, what it does not.

Why the change was needed

Under ICD-10, malnutrition was framed narrowly, essentially as a deficiency of energy and protein. When ICD-11 was introduced, the situation in adult clinical practice remained incomplete: the only readily applicable adult primary code was "underweight in adults," defined as a body mass index below 18.5. In contrast, most of the remaining nutrition codes were oriented toward children.

That left a significant gap.

Many adults become undernourished in the context of acute or chronic disease, and a great number of them do not have a low BMI. Without a relevant, standardized code that reflected this reality, undernutrition in adults was documented inconsistently and, too often, went unrecognized altogether, despite being a condition that lengthens hospital stays, raises complication and readmission rates, slows recovery, and increases costs. Our understanding of the condition has also matured, particularly the central role of inflammation in disease-related undernutrition. The new code was created to close that gap and reflect that science.

Why "undernutrition" instead of "malnutrition"

The terminology shift is not cosmetic; it's a correction toward precision. "Malnutrition" is technically an umbrella term. It spans the full spectrum of poor nutrition, from undernutrition at one end to overweight, obesity, and nutrient excess at the other. Using "malnutrition" to mean only the state of deficit has always been imprecise.

The WHO adopts "undernutrition" to name exactly what clinicians usually mean: a loss of mass, weight, BMI, or muscle mass, occurring in the context of disease, inflammation, or starvation.

One nuance deserves emphasis, because it is easy to get wrong. The undernutrition code does not exclude patients living with overweight or obesity. A patient of any body size can meet it, provided there is weight or muscle loss accompanied by a disease, inflammatory condition, or starvation. Undernutrition is about depletion and its drivers, not the number on the scale.

What the new malnutrition criteria mean for practice

The most tangible effect is on documentation. Medical record templates, intake forms, and reports will need to reflect the term "undernutrition," and documentation should map to the diagnostic framework specified by the code: one etiologic criterion, what is causing the undernutrition, paired with one phenotypic criterion, how it shows up in the body. Beyond the individual chart, a standardized, globally consistent code carries real weight for coding, reimbursement, and research, and, over time, should help combat the chronic under-recognition that has long undercut nutrition care.

What the change does not mean

This is the part that matters most, and it's the part most at risk of being misread. The change does not alter the clinical work of identifying and treating undernutrition.

The existing, validated tools remain valid. The Subjective Global Assessment (SGA), the Academy of Nutrition and Dietetics/ASPEN Indicators (AAIM), the Mini Nutritional Assessment (MNA), and the Global Leadership Initiative on Malnutrition (GLIM) criteria, the standard screening and diagnostic tools clinicians use, all already capture the etiologic factors (inadequate intake, disease burden) and phenotypic findings (unintentional weight loss, low muscle mass) that the new code requires. Screening, assessment, and the nutrition-focused physical exam are unchanged. Similarly, the interventions, individualized plans, oral nutrition supplements, feeding support, and interdisciplinary coordination remain the same.

In other words, the change is in what we call the condition and how we document it, not in what we do about it. The clinical rigor stays exactly where it is.

Why does the precision matter anyway

If the clinical work doesn't change, it's fair to ask why the terminology should. The answer is that language shapes recognition. A clearer, standardized term and code make undernutrition more visible in the chart, in aggregate data, and in the decisions that follow from data, including how resources are allocated.

When clinicians, hospitals, researchers, insurers, and public health systems all identify the same condition the same way, the condition finally counts the way it should.

That alignment is deliberate. Ahead of the 2027 rollout, the major nutrition societies, ASPEN, the Academy of Nutrition and Dietetics, and the American Society for Nutrition, published joint guidance across their journals to help the field implement the code consistently.

What to do now

There is a runway before 2027, and it's best used deliberately. Now is the time to:

• Update record templates and documentation workflows,
• Align teams on the one-etiologic-plus-one-phenotypic framework,
• Educate staff.

That way, when the code takes effect, the transition registers as a change in vocabulary rather than a disruption in care.

Dietitians are already the clinicians who screen for, identify, and diagnose this condition. They are the natural leaders of this transition, the ones best positioned to ensure that a more precise name is matched by the same rigorous, consistent care patients have always needed.

FAQ

What is ICD-11? It's the World Health Organization's 11th revision of the International Classification of Diseases, the coding system clinicians and healthcare organizations use to document diagnoses in medical records worldwide.

How is ICD-11 different from ICD-10? For malnutrition specifically, the key difference is a formal code for undernutrition in adults, something ICD-10 never had. Beginning in 2027, that gap closes.

When does the ICD-11 code take effect? Beginning in 2027, per WHO's approval. In the U.S., adoption may lag behind that date, pending an ICD-11 clinical modification.