Impedance scales: how they work and how reliable they are

How an impedance scale works

Kyle, Bosaeus, De Lorenzo, Deurenberg, Elia and colleagues (Clinical Nutrition, 2004, part I) describe bio-impedance as an estimate, not a direct measurement of each tissue. At 50 kHz, a current passes between electrodes. This frequency does not isolate total water: it mixes extracellular and intracellular water. Lean mass and total water are then deduced from an equation.

The same review says there is no single standard method, and no common quality control. The equation must match age, sex and population, and hydration must not be markedly disturbed. Outside this framework, the review does not recommend routine use.

Path on a scale with hand and foot electrodes: hands, arms, trunk, legs, feet. A scale with electrodes under the feet only (foot-to-foot set-up, described in the same review) keeps the current mostly in the legs.

Four electrodes or eight

Vita has eight electrodes, four under the feet and four in contact with the hands, and four weight sensors. The path can therefore include the trunk, which a foot-to-foot set-up does not. Eight electrodes are not proof of accuracy. No proprietary clinical study of Vita has been published. The general literature on bio-impedance is not a validation of this device.

Weight accuracy stated in the catalogue: ±0.05 kg. This is not an independent validation of fat mass. Price: £199 (local VAT and duties may apply on delivery), one-off payment.

Reliability compared with DEXA

DEXA and the four-compartment model are reference methods used to build equations, for example in Gallagher et al. (American Journal of Clinical Nutrition, 2000). Bio-impedance, by contrast, estimates. This page does not publish a numerical gap between Vita and a DEXA, because that gap has not been measured here.

Kyle and colleagues (part I) limit the estimation of lean mass and total water to people without a major abnormality of fluids and electrolytes, with a suitable equation. If hydration is markedly altered, single-frequency measurement is not valid. Vita is for tracking a trend under stable conditions. It does not replace a DEXA or a diagnosis.

Weighing under comparable conditions

Part II of the same review (2004) notes that a meal or a drink can lower impedance by 4 to 15 ohms over 2 to 4 hours, for an error of less than 3%. Just after exercise, resistance and reactance fall, then the measurement moves closer to the starting value when repeated an hour later.

Hence the simple protocol: same time of day, fasted if possible, after going to the toilet, dry feet, not just after sport. Compare weeks, not two mornings.

Contraindications: pacemaker and pregnancy

The Vita instructions forbid the bio-impedance function for people with a pacemaker or another implanted electronic medical device. The ESPEN position (Kyle, part II, 2004) reports no known incident with a pacemaker or a defibrillator, but it does not rule out interference and calls for monitoring of cardiac activity. On this device, the rule is that of the instructions: do not start bio-impedance.

Pregnant women: simple weighing only, and advice from the doctor or midwife before any composition tracking. The measuring current does not replace this advice.

Medical review in progress. This information does not replace the advice of a health professional.

Body composition estimates (bio-impedance) are not a medical diagnosis and do not replace professional advice. Values vary with hydration, meals, recent exercise and the time of weighing. Vita is not a DEXA or a medical device. Contraindication: pacemaker / implantable stimulator.

Consumer scale and professional measurement

In clinical practice, the ESPEN review calls for an equation validated on a similar population and a fixed procedure. A retail scale applies its manufacturer's equation. Both remain estimates. Neither is a DEXA.

Vita can estimate: weight, BMI, body fat, visceral fat, muscle mass, body water, bone mass, protein, metabolism/BMR, metabolic age, lean mass, calories.

Searches for “Decathlon”, “Lidl” or “Tanita” compare brands. This page does not rank these scales, does not give their prices and does not name a winner.

Summary: 8 electrodes and limits

Eight electrodes (feet and hands) open a path that also passes through the trunk. Four electrodes under the feet keep the current mostly in the legs. This does not give a numerical gap compared with DEXA. Hydration, meals, sport and time of day change the reading.

Confirmed metrics only: see the exact list on this page and on /produits/vita/.

What Vita does, and what it does not do

Vita does

• Estimates weight and body composition (fat mass, muscle, water, visceral fat) by bio-impedance.
• Automatically syncs weigh-ins over Wi-Fi to the Chutex app (up to 8 profiles).
• Manages weight goals, calories and macros with Aria AI and reviews over 6, 12 and 24 months.
• Works with the Elio band in the same app to cross-reference composition and wrist signals.
• With Elio + Vita correlated in the CHUTEX app: a non-invasive indicative estimate of blood glucose trends (not a glucose meter, not a blood measurement, not a diagnosis of diabetes).
• With an eligible Chutex subscription (France only): access to health professionals, including teleconsultation with GPs, included, by phone, in France only, with no guaranteed response time (prescription only if medically appropriate, no sick note or fitness certificate); other professionals depending on availability.
• Allows controlled sharing with a loved one, coach or professional (PDF export).
• Stores data in France with Free Pro, HDS-certified, with CHUTEX as data controller.

Vita does not

• Make a medical diagnosis (diabetes, osteoporosis, pathological obesity, etc.).
• Guarantee DEXA-type clinical accuracy or a hospital examination.
• Work as a glucose meter: Vita alone or Elio alone is not enough; an indicative estimate is given only when Elio and Vita are correlated in the CHUTEX app.
• Exist as a Vita Ring / connected ring: Vita is only a scale.
• Replace a dietitian, a doctor or medical advice.
• Work for people with a pacemaker or cardiac stimulator (BIA contraindication).
• Promise guaranteed weight loss.

Connected wellness device. Bio-impedance estimates are indicative and sensitive to hydration, meals, recent exercise and the time of weighing. Consult a health professional if you have any symptoms.

Sources

• Kyle UG et al., Bioelectrical impedance analysis, part I: principles and methods (Clinical Nutrition, 2004)
• Kyle UG et al., Bioelectrical impedance analysis, part II: utilization in clinical practice (Clinical Nutrition, 2004)
• WHO, Obesity and overweight (key points, limits of BMI)

How to get comparable measurements

• Weigh in the morning, fasted, after bathroom, dry feet.
• Same time daily when possible.
• Avoid immediately after exercise or a large meal.
• Flat, hard, stable surface.
• 12 measurement families, 50+ data points and trends per weigh-in.

Services by country

Vita services by market

The Vita bio-impedance scale is sold across Europe as a one-time purchase. Aria AI coach and the Chutex app are included. Chutex Care is available in France only; medical teleconsultation is currently available in France.

teleconsultation included, by phone, in France only, with no guaranteed response time and HDS hosting apply to eligible accounts in France only. Outside France, use local care pathways and emergency numbers (911 / 999 / 112). Vita is a wellness scale, not a medical diagnostic device.

Vita is a wellness connected scale for body composition monitoring. It is not a medical diagnostic device and does not replace NHS or private medical advice. Bio-impedance readings are indicative. Contraindicated for pacemaker wearers. teleconsultation included, by phone, in France only, with no guaranteed response time is currently available in France; Chutex Care is available in France only.

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