Defining Clinical Nutrition BIA for Practice To begin to understand the concept of bioimpedance, the differences in systems are outlined Most exercise physiology and nutrition textbooks lump all BIA systems together without differentiating their equations or their use in health care but only as a measure of body fat. There are two ways that bioimpedance information is used in Canada. Two numbers (resistance and reactance) are obtained from a small device. They are then entered into equations along with height, weight, sex and age. These equations have been developed and researched since the early 1980’s. There are two types of systems on the market that are now easy to acquire and use. One is far more advanced and the RD is the ideal professional to interpret results, apply nutrition intervention and monitor results with a Clinical Nutrition BIA in practice. 1. Body Composition BIA systems are used in gyms and by some RD’s. They measure two basic body compartments: fat mass and fat free mass. The system may be a ‘stand on scale’ or ‘hand held’ device or a ‘4‐electrode method’ with the client lying down. They may or may not have a printout or desktop software. The newer segmental BIA is taken standing on a scale and holding part of the device in your hands. The segmental is not as widely researched as the 4‐ electrode methods but is promising. 2. The Clinical Nutrition BIA systems used in medical nutrition therapy and sports nutrition are usually systems using 4‐ electrodes on a supine patient. The electrodes are attached to alligator clips and a cable is attached to a small ohm meter. The software has many more parameters than the Body Composition Systems and was only used for research 15 years ago. In Canada, Europe and Australia a Clinical Nutrition BIA systems software includes the same measures of body composition and a measure of hydration both intracellular and extracellular water, a measure of muscle mass, BMR, BMI and a unique score called the phase angle indicating nutritional status. I have used this system in practice for 15 years and found it so amazing that I have offered workshops to other RD’s and wrote the section on BIA for the 2000 International Diet Manual. Phase angle has been used widely to assess nutritional status in many undernourished populations. This score can help identify undernutrition earlier than laboratory tests. There is so much literature now that a practitioner can search BIA phase angle and her specialty to find relevant articles suggesting different equations used for calculation, cut‐off point for healthy patients and pitfalls for certain population groups (1, 2,4, 5, 6).
BIA has been studied extensively around the world and Vivian Hayward’s text (3) outlines in detail all the body composition systems to estimate body fat. Most attention goes to correct hydration to measurement of body fat and not the nutritional status information available in a clinical system. Percent body fat and the issues around it are often irrelevant in clinical practice. For example poor hydration can be detected or overtraining in athletes is seen when intracellular water is low and phase angle is low. If underhydrated, patients will have a lower muscle mass and higher body fat than when well hydrated. RD’s should have training in the use and interpretation of advice to facilitate effective practice. There are now cut‐off points for many conditions and many of the indicators. The phase angle is the most important measure of nutritional status. In clinical practice we take an initial measure on a client (almost like using a stethoscope) and test again later to see if that individual has changed. The phase angle will be low in undernutrition and in athletes who are overtraining. Please take time to go through this article attached where RD’s compare phase angle with subjective global assessment in colon cancer patients (1). It summarizes the important literature in this area. I regularly see clients with phase angles well below the ones in this article (athletes, vegetarians, underweight or even obese patients) indicating its applications in primary care. 1. Gupta, D., Christopher, G.L. et al. The relationship between bioelectrical impedance phase angle and subjective global assessment in advanced colorectal cancer. Nutrition Journal 7:19doi:10.1186/1475‐2891‐7‐19, 2008. 2. Susanne Hengstermann, Andreas Fischer, MD, Elisabeth Steinhagen‐Thiessen, MD, PhD and Ralf‐ Joachim Schulz, MD, PhD, Nutrition Status and Pressure Ulcer: What We Need for Nutrition Screening. Journal of Parenteral and Enteral Nutrition, Vol. 31, No. 4, 288‐294 (2007) 3. Heyward, V., and Wagner, D. Applied Body Composition Assessment, Second Edition, Human Kinetics, Champaign IL, 2004. 4. Kyle, U.G., Bosaeus, I. Et al. ESPEN Guidelines 2004, Bioelectrical Impedance Analysis Part 1: review of principles and methods. Clinical Nutrition 23, 1226‐1243, 2004. 5. Kyle, U.G., Bosaeus, I. Et al. ESPEN Guidelines 2004, Bioelectrical Impedance Analysis Part 2: utilization in clinical practice. Clinical Nutrition 23, 1430‐1453, 2004. 6. Barbosa‐Silva, M.C.G., Barros, A.J.D. et al. Bioelectrical Impedance Analysis: population reference values for phase angle by age and sex. American Journal of Clinical Nutrition, 82;49‐ 52, 2005.