Bioelectrical Impedance Analysis (BIA)

Updated: 2024 March 17

Bioelectrical impedance analysis (BIA) is a safe, quick, non-invasive and painless assessment that can be used to measure and calculate a variety of anthropometric (body composition) parameters (e.g., body-fat percentage).

Body composition is assessed by the passing of a mild (painless) electrical current between two sets of electrodes, placed at your hands and feet. Measurement of the body’s “resistance” (the opposition encountered to the flow of an alternating electrical current – a value inversely related to the water and electrolyte content of the tissue) and “reactance” (a measure related to the ability of the of cell membranes to store the charge – variations occurring depending on its integrity, function, and composition) to this current, combined with information on your height, weight and sex can be used to determine information concerning body-fat levels, hydration status, cellular health, etc.

Information gleaned by BIA can be used to track progress towards health goals, including evaluating effectiveness of “detoxification” and weight management protocols; hydration status; and general health improvement in longevity and health span programs.

Although analysis of persons at anthropometric extremes (e.g., obese, very tall) is susceptible to a greater degree of error, it is not a specific reading, but the trend in readings over time that is of interest (i.e., is body-fat mass decreasing with dietary change).

Contraindications

• Having an implanted medical device (e.g., pacemaker, hip prosthesis)

Patient Preparation

Before BIA, patients should:

• Fast for at least 4 hours prior to analysis
• Drink at least one liter of water prior to analysis (over the course of that day)
• Avoid exercise for 2 to 12 hours
• Avoid caffeine for 2 to 12 hours
• Avoid sauna for 12 hours
• Avoid alcohol consumption for 12 to 24 hours
• Not be diaphoretic (i.e., “sweaty”)
• Urinate (if necessary)
• Lie at rest for 3 to 8 minutes

Interpreting Your BIA Results

Fat Mass (FM):

Fat mass is the total amount of stored lipids (fat) in the body, including subcutaneous fat (located directly beneath the skin and used as an energy reserve and as insulation against outside cold) and visceral fat (located at the organs and used as an energy reserve and as a cushion between organs).

Although some BIA devices offer visceral fat measurements, BIA is not a particularly reliable tool for visceral fat measurement. Visceral fat may be estimated to be 10 percent of FM.

FM is reported in pounds or kilograms, and as a percentage of body composition.

Healthy FM percentage varies according to sex and age.

Women:

• Age 18 = 17-31%
• Age 19 = 19-32%
• Age 20-29 = 21-33%
• Age 30-39 = 21-33%
• Age 40-49 = 23-34%
• Age 50-59 = 23-34%
• Age 60-69 = 24-36%
• Age 70-79 = 24-36%

Men:

• Age 18 = 10-20%
• Age 19 = 9-20%
• Age 20-29 = 8-20%
• Age 30-39 = 8-20%
• Age 40-49 = 11-22%
• Age 50-59 = 11-22%
• Age 60-69 = 13-22%
• Age 70-79 = 13-22%

Active Tissue Mass (ATM):

Active tissue mass (sometimes described as “basal cell mass”) refers to the metabolically active segment of the body (i.e., muscle, organs, blood cells and immune cells).

ATM can be calculated as:

• Women = 52.9 percent of fat-free mass (up to 57 percent in athletic women)
• Men = 58.4 percent of fat-free mass (up to 62.5 percent in athletic men)

A general guideline for target ATM values is:

• Women = equal or greater than fat mass (i.e., ATM = FM)
• Men = equal or greater than double fat mass (i.e., ATM = 2FM)

Total Body Water (TBW):

Total body water is the percentage of your body-weight that is accounted for by water.

Normal TBW values are 50-60%.

Intracellular (within cell) Water (ICW):

Intracellular water is the percentage of your body-weight that is accounted for by water that is found within your cells (as opposed to in tissue, plasma, etc.).

Desired ICW values are approximately 50-60% of total body water.

Phase Angle (Ph):

Although the biological meaning of phase angle is not completely understood, it is considered a non-specific indicator of general health. For example, it has been confirmed as a prognostic tool for survival in patients with HIV- positive AIDS (patients with a phase angle measurement of less than 5.3° had significantly shorter survival times than those with higher measures) and other critical illness (e.g., patients in sepsis had low phase angle measurements, on average, 4.2°.).