DAY 15 — 48 Hour Fast Results: New Series Low and Highest HRV of the Experiment
Day fifteen. The halfway point. The 48 hour fast results are visible across every device today, and the most interesting number is not the one on the scales. Heart rate variability on the Hume Band came in at 88.5 ms this afternoon — the highest reading of the entire experiment, beating the previous best of 76.1 ms set on Day 6. Weight is also at a new series low, blood pressure has swung from last Monday’s 139/92 to an essentially optimal 105/78, and a gym session happened before sunrise. The data today is telling a coherent and positive story. Here is all of it.
Day 15 Data Summary
Understanding the 48 Hour Fast Results
| Metric | Morning | Afternoon | Source |
|---|---|---|---|
| Weight | 99.35 kg | 99.05 kg | Eufy |
| Hume Pod weight | — | 99.1 kg | Hume Pod |
| Metabolic Age | — | 52 yrs | Hume Pod |
| BMI | 27.7 | 27.7 | Eufy |
| Body fat % | 30.2% | 30.1% | Eufy |
| Body fat mass | 29.90 kg | 29.70 kg | Eufy |
| Lean body mass | 69.50 kg | 69.40 kg | Eufy |
| Visceral fat | 15 | 15 | Eufy |
| Water % | 49.7% | 49.8% | Eufy |
| Protein | 12.5% | 12.5% | Eufy |
| Subcutaneous fat | 26.6% | 26.5% | Eufy |
| BMR | 1,719 kcal | 1,714 kcal | Eufy |
| HRV | — | 88.5 ms | Hume Band |
| Stress | — | 17.6 | Hume Band |
| SpO₂ | — | 95–98% | Hume Band |
| Body temperature | — | 35.6–37.1°C | Hume Band |
| Heart rate | — | 55 bpm | Hume Band |
| Metabolic Momentum | — | 7 (→) | Hume Band |
| Metabolic Capacity | — | 67 | Hume Band |
| Strain | — | 70 | Hume Band |
| Recovery | — | 64 | Hume Band |
| Hume Band sleep | — | 6h 55m | Hume Band |
| CPAP usage | 08:03 | — | CPAP App |
| Fitbit sleep | 6h 23m | — | Fitbit |
| Sleep timeline | 21:29–05:47 | — | Fitbit |
| Blood pressure (avg) | 105/78 / Pulse 96 | — | BP Monitor |
| Steps | — | 5,166 | Hume Band |
| Hume Health Score | 635/900 — Above Average | — | Hume Pod |
| Biological Age | 31 years | — | Hume Pod |
| Gym | Cross trainer + leg press + leg curl, ~20 min | — | — |
HRV: A New Series High
88.5 ms. That is the number that deserves the most attention today, and it arrives from the Hume Band’s afternoon sync. To put it in context: the previous series high was 76.1 ms on Day 6 — the morning after the experiment’s first perfect CPAP score of 100/100 and 8h 29m of usage. Today’s 88.5 ms represents a meaningful step beyond that. The upward trend on the HRV chart across the past week is visible and consistent — not a single-day spike but a sustained climb.
What is driving it? The most likely combination: the CPAP compliance arc maintaining good overnight oxygenation across multiple consecutive nights, the extended fast reducing systemic inflammation and metabolic load, the early bedtime of 9:30pm giving the nervous system adequate recovery time, and the relatively low-intensity gym session providing stimulus without excessive physiological stress. The resting heart rate of 55 bpm is also the lowest recorded in this series and is directly connected — a lower resting rate and higher HRV both reflect a well-recovered autonomic nervous system.
Stress at 17.6 is low and consistent with recent days. Recovery at 64 is solid. The Strain reading of 70 is the highest of the series and reflects the gym session load on a fasted body — the Band is reading that the body worked hard relative to its current baseline today, even in a short session.
The Weight: A New Series Low, Twice
The morning Eufy reading of 99.35 kg was already the lowest figure of the experiment, edging below the 99.4 kg from Day 7. The afternoon reading at 15:01 shows 99.05 kg, with the Hume Pod independently confirming 99.1 kg at 15:05.
Both scales agree on the direction. The Eufy and Hume Pod readings are as close as they have been at any point in this series — 0.05 kg apart — which provides some confidence that the absolute figure is reliable. Body fat mass at 29.70 kg in the afternoon reading is the lowest of the series, as is the BMR at 1,714 kcal, reflecting the fasted metabolic state.
The fast ends at dinner this evening. Tomorrow’s morning reading will be the more structurally meaningful data point — the weight after refeeding, rehydration, and the return to the 16:8 pattern. Today’s readings capture the furthest point of the fast’s effect. Both are valid data, and both are recorded here as exactly that.
Sleep: Three Devices, One Story
Three devices recorded last night’s sleep and they tell a consistent story. The CPAP logged 8 hours 3 minutes of usage — a strong night, third in the series behind April 5th and April 8th. The Fitbit recorded 6 hours 23 minutes of sleep on a timeline of 21:29 to 05:47, reflecting time-asleep only as established throughout this series. The Hume Band, now synced for today, records 6 hours 55 minutes — sitting between the other two figures and representing the Band’s own interpretation of session duration including lighter sleep stages.
All three are consistent with the same underlying night: bed at 9:30pm, mask on immediately, a mid-night swap from full face mask to nasal pillows after approximately 70 minutes, and a 5:47am alarm. The earliest bedtime of the experiment produced one of its strongest CPAP nights.
Blood Pressure: From 139 to 105 in 48 Hours
Three readings between 07:59 and 08:09, all green:
- 07:59 — 105 / 77 / Pulse 96 — OK / OK
- 08:07 — 112 / 80 / Pulse 97 — OK / OK
- 08:09 — 98 / 76 / Pulse 94 — OK / OK
Daily average: 105 / 78 / Pulse 96.
The trend chart visible in the BP app shows the systolic line running from 143 on Day 13 — the alarming post-weekend reading — down through 118 on Day 14 and now to 105 this morning. Two days of better sleep, no alcohol, fasting, and a return to movement have reversed the social weekend’s cardiovascular signature completely. The diastolic has followed the same arc from 92 to 78. Both values are now in the green across all three readings for the first time since blood pressure monitoring was introduced to this series.
5:47am at the Gym
Bed at 9:30pm. Up at 5:47am. Cross trainer, leg press, leg curl — approximately twenty minutes, fasted. The left knee cooperated. The Strain reading of 70 on the Hume Band confirms the session registered as meaningful physiological load even at short duration. The Metabolic Momentum at 7 — up from the 6 of recent days — reflects the cumulative positive trajectory the Band has been tracking across this week.
CPAP: The Full Face Mask Question
The familiar pattern on night fifteen: full face mask on at 9:30pm, strong therapy for approximately 70 minutes, then pressure and seal issues requiring a swap to nasal pillows. The nasal pillows carried the remainder of the night well. The full face mask settings — specifically the ramp time and pressure ceiling — need a conversation with the CPAP supplier this week. Two consecutive nights of the same failure mode at the same point in the sleep cycle is a settings issue, not a fit issue.
Hume Health Score: 635 and Biological Age 31
The Hume Health Score of 635/900 rated Above Average, with a biological age of 31 against a chronological age of 55, covers the week of 6–12 April. Cardiovascular Health grades A with an upward arrow — consistent with the HRV trend this afternoon. Activity grades C- with a downward arrow. Body Composition grades F with an upward arrow showing improvement in progress.
The biological age figure reflects the cardiovascular and autonomic markers that today’s HRV of 88.5 ms exemplifies. Both tell the same story: the heart and nervous system are performing well; the body composition and activity patterns are the remaining work.
The Fast Ends Tonight
A couple of hours from now, dinner closes out approximately 48 hours of fasting. The data captured today is the fullest single-day picture of the experiment so far — two Eufy readings, Hume Pod confirmation, a complete Hume Band sync, blood pressure, CPAP, Fitbit, and Strava all contributing to a coherent picture. Tomorrow the series resumes its regular morning rhythm, with food, rehydration, and a deliberate focus on the protein intake that has been flagged as Low throughout.
Data captured Wednesday 15 April 2026. Morning Eufy reading: 15/04/2026 at 08:13. Afternoon Eufy reading: 15/04/2026 at 15:01. Hume Pod afternoon reading: 15:05. Hume Band synced 15:05 — all readings confirmed for 15/Apr/26. Blood pressure taken 07:59–08:09. CPAP covered the night of 14–15 April, usage 08:03. Fitbit sleep timeline 21:29–05:47, 6h 23m. Gym session approximately 05:47am. 48-hour fast commenced Monday 13 April at dinner; ending Wednesday 15 April at approximately 19:00.
— Day 15 of 30
