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Bioelectrical Impedance Analysis

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The most value in providing BIA services and individual interpretations may be in the trending of body compartments. Why and how body compartment volumes move can tell you a great deal about the physiologic processes that may be occurring. Table 9 shows different profiles of body compartment change according to conditions that may affect nutritional stores.

Table 9. Categories of Body Compartment Change

Category	Weight	Body Cell Mass	Extracellular Mass	Fat
Optimal Profile	Reference range	Reference range	Reference range	Reference range
Athletic	Reference range or increased	Increased	Adequate	Adequate or decreased
Starvation	Decreased	Decreased	Decreased	Decreased
Infection/Injury (Stress)	Reference range or decreased	Decreased	Increased	Eventually decreased
Obesity	Increased	Increased	Increased	Increased
Sarcopenic Obesity	Increased	Decreased	Increased	Increased
Athletic Obesity	Increased	Increased	Increased	Increased

Calorie deprivation can cause a decrease in all compartments. Generally speaking, fat will comprise about 60% of this type of weight loss.[85] Injury or infection may or may not yield a weight loss, but can change body composition dramatically. The hallmark change in stress responses is the increase in extracellular mass. If weight is lost during a rousing stress response, it is likely to be less than 10-20% fat tissues. Once starvation or stress is resolved, you will be looking for normalization of the body compartments. If this does not happen, especially if body cell mass continues to be compromised while weight gain is primarily fat, then you may suspect some type of metabolic adaptation or dysfunction that prevents normalization.

Obesity as a function of caloric excess shows much the opposite of starvation: all compartments should increase. Remember that BCM increases are expected because of the additional muscle it takes to carry additional weight around. If reduced mobility follows, or if there is a metabolic alteration that prevents maintenance of this added body cell mass, sarcopenic obesity may result. The characteristics of sarcopenic obesity differ from “normal” obesity when the individual has less than expected levels of body cell mass. On the opposite hand, we might evaluate an athletic-type who is considered obese by weight, but are certainly a lower health risk by body composition evaluation. This person may have more than expected lean tissues and varying amounts of fat mass.

In trending body composition by BIA, it is important to know the conditions that change weight and its three compartments. A summary of this information is shown in Table 10.

Table 10. Summary of Physiologic Basis for Body Compartment Changes

Body Compartment Changes	Examples of Etiologies for Change
Weight: Increased	Calories: refeeding or overfeeding Recovery from stress
Weight: Decreased	Calories: starvation (imbalance through reduced intake or absorption, or increased utilization) Stress (especially when inadequate calories are consumed)
BCM: Increased	Appropriate response to refeeding, overfeeding Appropriate response to recovery from stress Exercise Anabolic medications (such as testosterone and derivatives and growth hormone)
BCM: Decreased	Calories: starvation Stress response: catabolism of skeletal muscle Metabolic alteration: altered hormonal balances or sensitivity to endogenous anabolic hormones
ECT: Increased	Increased weight Stress response Rehydration Chronic adaptation to stress response
ECT: Decreased	Decreased weight Stress response resolve Dehydration Anabolic therapies (if responding normally)
Fat: Increased	Refeeding or overfeeding Reduced activity/mobility Chronic adaptation or metabolic non-response
Fat: Decreased	Starvation Exercise Continued stress response Some anabolic therapies (particularly when combined with exercise)

That's it! You are ready to do some case interpretations! Let’s try this out on a few, neatly fitting profiles. The following cases are meant to illustrate the process of BIA interpretation utilizing different scenarios.

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Reference:

[85] Pritchard JE, Nowson CA, Wark JD. A worksite program for overweight middle-aged men achieves lesser weight loss with exercise than with dietary change. J Amer Diet Assoc. 1997;97(1):37-42.

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