How to weigh yourself so the number means something

The trial curves were built from weights taken at scheduled visits on calibrated clinic scales, in light clothing, at roughly the same time of day. Your bathroom scale can produce numbers of similar quality if you control the same things.

The method

1. One scale. Scales disagree with each other by more than a week's loss. Pick one and stay on it. Put it on a hard floor, not carpet.
2. One time. First thing in the morning, after the bathroom, before food or drink, in the same amount of clothing or none.
3. One day, or every day averaged. Either weigh once a week on the same weekday, or weigh daily and write down the seven-day average as that week's number. The average is better; it soaks up the day-to-day swing.
4. Write it down with the date and the week on therapy, counted from your first injection. A note of anything unusual (illness, travel, a missed dose, a period) next to the number will save you guessing later.
5. Convert to percent of your starting weight when you want to compare with anything published. The plateau checker does this for you.

Why the swing is not loss or gain

Body water is several tens of litres and moves by a litre or more between mornings with salt intake, carbohydrate intake (glycogen is stored with water), alcohol, the menstrual cycle, a hard training session, illness and bowel transit. On a GLP-1, slower gastric emptying and changes in bowel habit add to this. None of it is fat. A single reading a kilogram up or down from last week is inside that band. Four readings in a row that all sit above the previous four is a trend.

The checker uses a least-squares slope across your last four weekly readings, rather than the difference between two readings, for exactly this reason. It also refuses to give a verdict on fewer than four.

When the scale is the wrong instrument

• You have started or increased resistance training. Muscle gain can offset fat loss on the scale for weeks. Measure your waist monthly at one landmark (see body composition measures) and log a few lifts.
• You are unwell or dehydrated. Weigh, note it, and do not read anything into that week.
• You are constipated. A common effect of GLP-1 therapy; see hydration and fibre. Bowel contents weigh something.
• The number is affecting how you eat. If weighing pushes you towards skipping meals or protein, weigh less often and tell your prescriber. On a GLP-1 the failure mode is eating too little, not too much.

What a good log looks like

Illustrative numbers. Paste the weight column into the checker with the starting week and it does the rest. Take the log to every prescriber visit; it is more useful to them than any single clinic weight.