Note: if you arrived looking for phase angle in electricity, waves or mechanical vibration, this article covers body phase angle in bioimpedance and clinical nutrition, a related but different concept.
What phase angle is
When a bioimpedance device passes a gentle alternating current through your body it measures two things: resistance, the opposition to current passing through body fluids, and reactance, the delay produced by cell membranes behaving as small capacitors.
Phase angle is the relationship between the two, expressed in degrees. Put plainly: the more intact and numerous your cell membranes, the greater the reactance and the greater the angle.
What it actually measures
It is not a measure of fat or muscle. It is an indicator of cellular integrity and mass. It reflects two things simultaneously: how many functional cells you have and what state their membranes are in.
That makes it different from the rest of the report. Skeletal muscle mass tells you how much tissue you have; phase angle tells you how well that tissue is. It is possible to have acceptable muscle mass with a low phase angle, and that indicates a problem no other parameter would have shown.
It has another important advantage: it is a directly measured parameter, not calculated with prediction equations. The fat mass and muscle mass in your report are estimates based on population algorithms. Phase angle is direct arithmetic on what the device measured.
Which values are normal
Ranges depend on age and sex, and the device should compare you against its reference population. As general orientation in healthy adults, values usually sit between 5 and 8 degrees, higher in men than women and declining progressively with age.
A value below 5 degrees in a young adult deserves attention. Values below 4 are consistently associated with worse prognosis across clinical situations.
A necessary caution: algorithms differ between manufacturers. Do not compare a phase angle from a seca with one from an InBody. For follow-up, always measure on the same device.
What raises and lowers it
Lowered by: malnutrition, chronic inflammation, muscle mass loss, dehydration, acute illness and ageing. Any process damaging cell membranes or reducing active cell mass.
Raised by: strength training, adequate protein intake, nutritional recovery after a deficit period, correction of inflammation and resolution of underlying disease.
It moves slowly. Do not expect change in two weeks: it is a trend parameter rather than a daily fluctuation, and that is precisely its usefulness.
What it is used for in practice
- During weight loss. If it falls while you slim, the deficit is too aggressive or protein intake insufficient. An early warning signal before muscle mass drops visibly. Especially relevant in GLP-1 drug treatment.
- In chronic disease. In inflammatory bowel disease, coeliac disease or short bowel syndrome it functions as a global nutritional status indicator and responds before other markers.
- In sarcopenia follow-up. Alongside skeletal muscle mass and grip strength, it completes the picture of tissue health.
How to improve it
- Regular strength training. The most powerful stimulus available.
- Enough protein, distributed. 1.4 to 2.0 g per kilo daily depending on your situation.
- Correct underlying inflammation. Treat the disease if there is one, and sustain an anti-inflammatory dietary pattern.
- Adequate hydration. It affects both the measurement and the real state.
- Avoid aggressive, prolonged calorie deficits.
If you want to know your phase angle, it is included in the body composition assessment along with the rest of the seca mBCA Alpha parameters and their interpretation.