The Paper of the Month for October is ‘Challenges in identifying malnutrition in obesity; An overview of the state of the art and directions for future research‘. The blog is written by authors Natasha N. Mwala, Jos W. Borkent, Barbara S. van der Meij and Marian A.E de van der Schueren. The paper is published in the Nutrition Research Reviews and is free to access.

When we think of malnutrition, we often picture individuals who are underweight or experiencing hunger, struggling with inadequate levels of essential nutrients. However, malnutrition can also exist in individuals with obesity. Many people in this population may have a relatively low intake of essential nutrients, especially during illness, leading to physiological changes often overlooked in clinical assessments. Identifying protein-energy malnutrition in individuals with obesity is challenging due to distinctive physical and physiological characteristics, including increased body weight, adipose tissue dysfunction and metabolic dysregulation presented as systemic inflammation.

Our research was inspired by the prevalence of malnutrition in healthcare settings and its association with longer hospitalisation, increased care burden, slower recovery, and reduced quality of life. The COVID-19 pandemic further highlighted the risks for individuals with obesity, who experienced more severe symptoms and longer recovery times. This situation revealed how the failure to properly identify malnutrition in this population—due to the lack of suitable screening tools—may have worsened health outcomes.

In our review, we explore the challenges of diagnosing malnutrition in obesity, particularly distinguishing it from sarcopenic obesity, which combines obesity with reduced muscle function. While both conditions share risk factors such as high-fat mass, reduced muscle mass and function, and systemic inflammation, recognising their differences is essential for accurate diagnosis. A key distinction lies in the emphasis on muscle function; sarcopenic obesity prioritises muscle function over muscle mass, meaning individuals may have reduced strength or function without exhibiting classic signs of malnutrition.

Unfortunately, the absence of screening tools specifically designed for individuals with obesity complicates the identification of malnutrition. Most existing tools rely heavily on anthropometric measurements—such as weight and Body Mass Index (BMI)—while often neglecting crucial factors like nutrient intake. For instance, to be considered significant, weight loss in individuals with obesity must be substantial due to their higher initial weight, making it inappropriate to compare this loss with that of normal-weight individuals. Similarly, defining underweight as a BMI<18.5 kg/m² is unsuitable for identifying malnutrition in this group, as overweight and obesity are classified as BMI >25.0 kg/m². Assessing muscle mass in individuals with obesity is essential but challenging. A higher BMI can overestimate muscle mass due to fat distortion in measurements like upper arm or calf circumference, potentially leading to an underdiagnosis of malnutrition.

Additionally, the Global Leadership Initiative on Malnutrition (GLIM) criteria, widely used for diagnosing malnutrition, are difficult to apply to individuals with obesity because their cut-off values for all five criteria (unintentional weight loss, low BMI, low muscle mass, reduced food intake and disease burden/inflammation) were designed for those with a normal weight.

In conclusion, effectively identifying malnutrition in individuals with obesity requires modifying existing screening tools and diagnostic criteria to account for their unique physical and physiological complexities. Collaborative efforts among experts in malnutrition and obesity are crucial for developing context-specific assessment parameters and methods. By improving early detection and intervention, healthcare practitioners can greatly enhance health outcomes and overall well-being for this at-risk population.

Each month a paper is selected by one of the Editors of the six Nutrition Society Publications (British Journal of Nutrition, Public Health Nutrition, Nutrition Research Reviews, Proceedings of the Nutrition Society, Journal of Nutritional Science and Gut Microbiome). Take a look at the entire Nutrition Society Paper of the Month Collection.