Why do hydration and nutrition affect BIA body composition results?

Overview

BIA measures the speed of an electrical current through the body. Because that current travels through water, anything that changes the body's water content — hydration, food intake, or exercise — can significantly affect results. Standardized testing conditions are essential for accurate and comparable readings over time.

How Hydration and Glycogen Affect Results

For every 1 gram of glycogen (stored glucose in muscle and liver), the body retains approximately 3 grams of water. Changes in glycogen stores therefore directly affect body water levels, which in turn affect BIA measurements.

Condition | Effect on Body Water | BIA Result

Increased hydration / high glycogen | More water in tissues | **Overestimates** body fat mass; **underestimates** fat-free mass

Decreased hydration / low glycogen | Less water in tissues | **Underestimates** body fat mass; **overestimates** fat-free mass

Practical Example

Measuring a client immediately after exercise will typically show a falsely lower body fat percentage because exercise depletes glycogen and causes fluid loss — both of which reduce tissue water content and alter the electrical signal.

Steps / Details: Recommended Testing Controls

To ensure reliable and consistent BIA results, clients should follow these conditions before every assessment:

1. No exercise for at least 12 hours prior to testing.
2. No eating or drinking for at least 4 hours prior to testing.
3. No alcohol for at least 24 hours prior to testing.
4. Normal hydration — avoid excessive fluid intake immediately before testing.
5. Test at the same time of day for each follow-up measurement.
6. Use the same device and protocol across all sessions.

These controls should be communicated clearly to clients before their appointment.

Notes

• Results from assessments conducted under different conditions are not directly comparable and may show changes that reflect hydration shifts rather than true body composition changes.
• Professionals are strongly encouraged to enforce these controls consistently, especially when tracking progress over time.

If this resolves your issue, no further action is needed.

If the problem persists, contact support and include: notes on testing conditions at the time of the scan and the client's reported activity and nutrition status.

Applies to: All Styku configurations using BIA integration