People who try to lose weight often get the advice to "always measure their weight at the same time". The reason for this is that body weight varies a lot during the day. So measuring at lunch on day 1, and in the evening the next day might give weird results.

However, the scientist in me was curious about how high the variation actually was. That couldn't be hard to measure myself, right?

‍

Testing "method"

‍

Having called myself a scientist, I needed to live up to the expectations. I had to come up with a real scientific method to conduct my research. After careful consideration of the options, I decided to use my bathroom scale.

To make the results as consistent as possible, my colleagues were nice enough to design a professional "weighing station", made out of a reversed IKEA table:

I decided to measure every 15 minutes, and keep track of what clothes I'm wearing.

‍

Weighing results

‍

In total, I weighed myself 61 times over the course of 17 hours. Let's take a look at that visually:

‍

‍

The maximum weight is 65.00, the minimum 62.95. That is a 2.05 kg (4.52 lb.) difference between these two extreme points! Surprisingly, the minimum weight was not when I woke up (63.85 kg), but just before lunch at 12h31. The maximum was at 21h56, just when I finished the last chocolate as dessert.

But why does the graph above shows Measured Weight and Body weight? I had to account for the clothes that I'm wearing.

‍

Clothing weight

‍

I didn't want to spend the day naked at the office (not even taking my colleagues into account). So I tracked which clothes I was wearing when and also noted down their weight.

I subtracted the clothing weight from my measured weight to get a more accurate measurement of my actual body weight. The clothing variation looks like this:

‍

Inputs & outputs

‍

Most variations in my body weight can be explained by inputs and outputs.

The most common inputs are food and drink. I had three meals, and drank a lot of water during the day. At 06h35, I took a shower, making me "gain" 300 grams of weight. At 10h37, I drank 0.75 liters of water.

Outputs are mostly toilet visits. I'll leave it up to the reader to investigate at what times this occurred. Sweat also accounts for a lot of the weight loss. Sadly, I did not do intensive sporting this day, apart from some yoga in the morning. So there is no large weight drop in the data visible because of sweating. A few years ago though, I measured a weight difference of 1 kg (2.2 lb) after a long run on a hot day.

Someone on Reddit also suggested exhaling as a possible cause of weight loss. Indeed, for each extra CO2 molecule that we exhale, we added a carbon atom to the O2. According to research, this amounts to 200 grams of weight loss for an average person per day.

I annotated some of the inputs and outputs on the plot below (click Expand to view full screen):

‍

‍

Bonus: heart rate

‍

I also kept track of my heart rate. The lowest measurement was 52 bpm (just after waking up), highest 102 (just after starting the yoga session).

These are relatively low values. While running intensively, I have observed a heart rate of 196 in the past.

‍

Thanks for reading! If you want to react to this story, feel free to drop a comment on Reddit.