Saturday night, a friend's birthday, three glasses of wine, bed late. On Sunday morning the scale reads more than a kilo (2.2 lb) above Friday, and you know you did not eat enough to build a kilo of body fat.
The short answer: a jump the morning after drinking is mostly water, gut contents and the food from the night before, not new fat. It usually fades within a few days. Whether alcohol changes your weight over weeks is something only the trend can show, not a single morning.
Why the scale jumps after a night out
A night of drinking changes several things at once, and each one moves the number on the scale.
Water. Alcohol makes you urinate more. Some people weigh less the next morning because they lost fluid. When the body makes up for it over the following days, it holds on to water and the number climbs. Both directions happen, and neither has anything to do with body fat.
Salt and carbohydrates. Chips, pizza, fries or bread tend to come with the evening. Salt binds water, and carbohydrates are stored together with water. The effect comes from the food that goes with alcohol and from the food it prompts: after a few drinks, people eat later and more.
Digestion. A large dinner and a late snack are still in your gut in the morning. That weight is real but temporary. Why your weight fluctuates daily covers this in more detail.
Alcohol also supplies energy of its own. One evening hardly matters. If you drink several times a week, the amount adds up over weeks and can visibly slow your trend.
What a night of drinking looks like in the data
The scale gives you the daily value, and it contains everything: fat, muscle, water, gut contents. A night of drinking changes almost only the short-lived parts. That is why the daily value reacts strongly and the smoothed trend barely moves.
An example with made-up numbers. Your trend weight on Friday is 80.2 kg (176.8 lb), and the daily values that follow are:
| Day | Daily value | Trend (default smoothing) |
|---|---|---|
| Saturday (night out) | 80.2 kg (176.8 lb) | 80.2 kg |
| Sunday | 81.3 kg (179.2 lb) | 80.3 kg |
| Monday | 80.9 kg (178.3 lb) | 80.4 kg |
| Tuesday | 80.4 kg (177.2 lb) | 80.4 kg |
| Wednesday | 80.3 kg (177.0 lb) | 80.4 kg |
The daily value jumps by 1.1 kg (2.4 lb), the trend by 0.1 to 0.2 kg (0.2 to 0.4 lb). By Wednesday the daily value is nearly back, and the trend shows what stayed. If you read Sunday's daily value, you see a kilo of setback. If you read the trend, you see a small step that, after a single evening, usually disappears again.
How strongly your body reacts depends on the amount, the food, the salt and your sleep. There is no fixed figure for "one glass equals so many grams", so distrust anyone who gives you one. Your own history is the more reliable source.
Marking drinking days in Trendcurve
So that you do not have to guess later which spikes came from alcohol, record the drinking days. In Trendcurve you do this under "Settings & more" → "Experiments and markers":
- Choose the type Alcohol.
- Enter a label or take one of the suggestions.
- Set the start day. For a single evening, create a marker without an end.
- For a longer period, such as a holiday with drinks or a month without, choose a duration of 2, 4 or 8 weeks or your own end date.
- Add a note if you like.
Markers without an end appear in the chart as a line, experiments with a duration as a tinted band. Creating and marking is free. The evaluation is Pro.
Comparing before and after
The evaluation in Trendcurve (Pro) compares your weekly rate in the 28 days before the start with the rate during the run. For a marker without an end, it looks at up to 28 days afterwards. Each section needs at least 7 days and 4 weigh-in days. If something is missing, the card tells you how much.
A second example. For four weeks you drink every weekend. Before that period your trend ran at minus 0.4 kg (0.9 lb) per week, during the four weeks with alcohol at minus 0.1 kg (0.2 lb) per week. Something has changed, and it is worth asking what: the drinks themselves, the late food, or the Sunday workout that did not happen.
The card always carries the note "correlation, not causation". That is not a formality. If you had a stressful month, went on holiday or shifted your meals in the same period, you would see the same curve. The comparison gives you a lead, not proof.
The weekday pattern under "Patterns" (Pro) completes the picture. It shows the average deviation of your daily value from the trend for each weekday over 13 weeks. If your Monday regularly sits above the trend, that is a weekend effect.
What to do after a night of drinking
Nothing special. Weigh yourself in the following days as you normally do, ideally at your usual time. Going hungry or cutting fluids the next day changes the daily value, not your body fat.
Two things help your curve more:
- Log it, do not skip it. If you skip the scale after a night out, you get a gap exactly where the curve could explain something.
- Leave the outlier in. A high reading after alcohol is a real measurement. You can set it to "ignored" in Trendcurve, but that makes sense only if the scale itself was wrong, for example because it was not standing flat. It then stays visible and does not feed into the trend.
If you drink heavily on a regular basis or find you can no longer control how much you drink, talk to a doctor about it. Your weight is not the measure for that.
A rule of thumb for Monday
If you see a high reading the morning after a night out, set a marker and read the number in the curve three days later. If the trend is back on its line, it was water. If it sits one step higher and stays there, look at what else changed in the week before.