Body composition & weight
The Body Mass Index, mostly known as BMI (body weight in kilogram divided by the square of height in meter; kg/m2), is a mathematically constructed score. Commonly used in research and clinical practice, this score is not always a good indicator. The current categories for classification of underweight (<18.5 kg/m2), normal weight (>18.5 and <25.0 kg/m2), overweight (>25 kg/m2) or obese (>30 kg/m2) do not take into consideration the differences in nutritional status, age, sex, lifestyle, physical activities, disease risks as well as genetic backgrounds (Müller et al. 2016). That’s why, for example regarding the ethnic background of people, lower cut-offs have been proposed for Asians as ‘normal’ values were designed for Caucasian, African and Hispanic populations.
In addition to this, a person can be considered as overweight regarding his BMI but his relative high weight can be due to high body fat or large muscle mass, which does not imply the same in terms of risks and management.
Because of these limits, body composition appears to be the key to be able to go further in the understanding of physiology and to be able to determine the risk factors associated with a weight or BMI “number”.
Interest
Losing weight strategies
When a patient follows a special diet to lose weight, unfortunately the weight loss is often accompanied by a loss in lean body mass, which can have problematic health implications for the subject. This can lead to the alteration of daily activities and fatigue, declined neuromuscular function, and an increased risk of injury (Willoughby, Hewlings, and Kalman 2018).
Furthermore, the loss of lean body mass influences the resting energy expenditure as this type of tissue consumes more energy than fat mass, so it is a double disadvantage for the patient! In addition to this, if the patient stops the diet and lives as before, this can result in a subsequent regain in fat mass.
For this reason, quantifying lean body mass may be especially helpful by guiding protein intake during patient care to adopt the patient’s food diet. You should know that lean body mass is the main body’s protein storage and its decrease is not recommended (Looijaard, Molinger, and Weijs 2018).
Programs that focus on weight loss should target the improvement in body composition (decrease fat mass and increase or maintain the lean mass) rather than target only the number on the scale.
Sarcopenia
Sarcopenia is defined as a low muscle mass, impaired muscle function, and is especially observed in vulnerable populations, such as postmenopausal women and older adults (Cava, Yeat, and Mittendorfer 2017).
That’s why the prevalence of obesity in elderly people raises concerns about sarcopenic obesity, because these patients need specific care. Important diet-induced weight loss can lead to an important muscle mass loss, which could increase the risk of sarcopenia. Sarcopenic obesity increases functional decline and is related to a higher risk of diseases and mortality (Kuriyan 2018). This risk needs to be assessed.
Infants and children
Body composition could also be used for infants as a marker of fetal adaptation and developmental programming of health and disease at a later age. In the context of the increase of pediatrician obesity, the assessment of body composition during childhood and adolescence is relevant to understand the physiology of the changes occurring in the patient’s body, in order to define the corresponding care. In addition, it is relevant to monitor body composition and the changes occurring with some specific diseases such as chronic inflammation, Crohn’s disease, and chronic kidney disease (which can affect growth and may lead to a deficit in lean body mass) (Weber, Leonard, and Zemel 2012).
Disease risk factor
The abdominal distribution of fat, and more specifically an increase in the amount of internal abdominal fat (visceral), is independently related to total corpulence, occurrence of metabolic complications (type 2 diabetes) and cardiovascular diseases (hypertension, ischemic events). A high waist circumference can be an alarm signal but to be able to measure the real visceral fat, tools such as DXA and MRI are needed.
Conclusion
In conclusion, monitoring body composition is relevant to prescribe the right medical and nutritional care. Valid and reliable tools must be chosen.
Hélène CHEVALLIER, Methodologist, Biofortis
References:
Cava, Edda, Nai Chien Yeat, and Bettina Mittendorfer. 2017. ‘Preserving Healthy Muscle during Weight Loss123’. Advances in Nutrition 8 (3): 511–19. https://doi.org/10.3945/an.116.014506.
Demerath, Ellen W., and David A. Fields. 2014. ‘Body Composition Assessment in the Infant’. American Journal of Human Biology : The Official Journal of the Human Biology Council 26 (3): 291–304. https://doi.org/10.1002/ajhb.22500.
Kuriyan, Rebecca. 2018. ‘Body Composition Techniques’. The Indian Journal of Medical Research 148 (5): 648–58. https://doi.org/10.4103/ijmr.IJMR_1777_18.
Lemos, Thaisa, and Dympna Gallagher. 2017. ‘Current Body Composition Measurement Techniques’. Current Opinion in Endocrinology, Diabetes, and Obesity 24 (5): 310–14. https://doi.org/10.1097/MED.0000000000000360.
Looijaard, Wilhelmus G.P.M., Jeroen Molinger, and Peter J.M. Weijs. 2018. ‘Measuring and Monitoring Lean Body Mass in Critical Illness’. Current Opinion in Critical Care 24 (4): 241–47. https://doi.org/10.1097/MCC.0000000000000511.
Müller, Manfred James, Wiebke Braun, Janna Enderle, and Anja Bosy-Westphal. 2016. ‘Beyond BMI: Conceptual Issues Related to Overweight and Obese Patients’. Obesity Facts 9 (3): 193–205. https://doi.org/10.1159/000445380.
Weber, David R., Mary B. Leonard, and Babette S. Zemel. 2012. ‘Body Composition Analysis in the Pediatric Population’. Pediatric Endocrinology Reviews : PER 10 (1): 130–39.
Willoughby, Darryn, Susan Hewlings, and Douglas Kalman. 2018. ‘Body Composition Changes in Weight Loss: Strategies and Supplementation for Maintaining Lean Body Mass, a Brief Review’. Nutrients 10 (12). https://doi.org/10.3390/nu10121876.