In one sentence
Three small logs with large explanatory power: what you drank, in milliliters; what you drank with alcohol in it, in standard drinks; and whether today was a deliberate break from your plan.
Hydration
Each drink as it happens, with its time; the log shows the day's total, the number of drinks and the first and last. It explains the scale: a liter of water is a kilogram on the morning scale and a point of body fat on a bioimpedance reading, and it explains a hot training day's readings. Nothing scores it.
Alcohol
Logged in standard drinks of 10 grams of alcohol each, the New Zealand standard, with half drinks allowed. It is the single most useful confounder in the record, because it moves almost everything else. Overnight, an evening of heavy drinking raised heart rate by about 6 percent and lowered HRV by about 12 percent across 9 million readings (Altini 2021); it shortens the time to fall asleep and breaks up the second half of the night at every dose, delays and reduces REM (Ebrahim 2013); it cuts the liver's new-glucose production by about half for several hours (Siler 1998), so a night's glucose runs lower; and it sheds water and then holds it, so the morning scale moves. Logged, each of those becomes an explanation; unlogged, each looks like a change in you. VT reads the amount: Symptom Radar gives that night's readings less weight in proportion to how much you drank, the TDEE engine down-weights the day, and the last seven days of alcohol are 30 percent of the lifestyle area of the Vitality Score.
The diet break
A yes on the day marks a deliberate overshoot, a refeed or a break from the plan, so that the TDEE engine reads it as intended rather than as a lapse in logging or a change in what you burn, and so that a planned break does not trigger a change point. The idea has evidence of its own: in the MATADOR trial, 51 men with obesity were randomized to 16 weeks of continuous restriction or to the same restriction in two-week blocks alternating with two-week blocks at maintenance; the intermittent group lost more weight (14.1 against 9.1 kg) and more fat, and their resting expenditure fell less once body composition was accounted for (Byrne 2018). The Weight Loss Plan can schedule breaks on that basis; whether to take them is yours.
How to log well
Alcohol on the day it was drunk, before bed if you can, in standard drinks rather than glasses (a large glass of wine is close to two). Water as you go, each drink with its time. The diet break on the day it applies to, in that day's evening entry.
How Vitality Tracker uses it
Alcohol: a confounder in Symptom Radar (scaled) and the TDEE engine, and a Vitality Score lifestyle input. Hydration: drawn on your glucose line; nothing scores it. Diet break: a flag the TDEE engine and the Weight Loss Plan read.
How far to trust the number
Self-reported; the standard-drink conversion is the main source of error, and a consistent one.
Sources
- Altini M, Plews D. What is behind changes in resting heart rate and heart rate variability? Sensors 2021;21:7932. doi:10.3390/s21237932
- Ebrahim IO, Shapiro CM, Williams AJ, Fenwick PB. Alcohol and sleep I: effects on normal sleep. Alcohol Clin Exp Res 2013;37:539–49. doi:10.1111/acer.12006
- Siler SQ, Neese RA, Christiansen MP, Hellerstein MK. The inhibition of gluconeogenesis following alcohol in humans. Am J Physiol 1998;275:E897–907. doi:10.1152/ajpendo.1998.275.5.E897
- Byrne NM, Sainsbury A, King NA, Hills AP, Wood RE. Intermittent energy restriction improves weight loss efficiency in obese men: the MATADOR study. Int J Obes 2018;42:129–38. doi:10.1038/ijo.2017.206
- Vitality Tracker, What VT measures (catalogue of 15 October 2026).