Weight vs. Sleep

I decided to keep track of my weight for a month, as a 30 day trial. I weighed myself first thing every morning on a cheap digital scale.

The result is the blue line in the chart below.

I knew there’d be some variation, but I wanted to figure out what is causing that. My attention was drawn to the sharp peak (73.0) at June 19th and so I looked back into my calendar to see what I was doing around that day.

Turns out, I woke up really early for some reason (might have been related to drinking a glass of alcohol the night before, but I haven’t kept track of that). So I looked at another peak on June 2nd. Turned out I had a doctor’s appointment early that morning.

I work from home and keep track of my working hours. I usually start work about 30 after I wake up, so these hours a pretty good indicator of wake up time.

I decided to plot wake up times that I could reliably reconstruct from my calendar. The result is the red line.

The earliest was 6:30 am, my usual and preferred time is 8:30 am and the latest recorded time was 10:30 am. I got up even later on some non-working days, but did not record them. I sleep about 9.5 hours a night on average and I almost always go to bed between 23:30 and 00:30.

Without doing any proper statistical analyses I think it’s safe to say that wake up time and weight are negatively correlated for me. My guess is that this is just water balance. I do drink a bit of water during the night, but not anywhere near as much as I drink during the day.

So here’s a trick. If you want to convince yourself that you are losing weight, simply get up 3 minutes earlier every day. Translated to a get-rich-quick-scheme: write a diet book that provides the reader with an excuse to get up earlier every day. Guaranteed result.

Is there anything useful that can be derived from this data? It tells me something about how my water balance changes between about 6:30 and 10:30. Any relevant parameters that can be derived from that knowledge?

Edit 3-7-2009 14:20: Here’s a scatter plot of wake up time versus weight. Google Spreadsheet finds a correlation of -0.6. It also finds a slope of -0.28 liters / hour.

Edit 3-7-2009 15:40: Armed with this knowledge I corrected my weight measurements for wake up time. The blue line shows the original measurements. The red line shows what they (probably) would have been at 8:30 in the morning. This leads to a reduced spread in daily weights, but it’s clear there are other factors involved here. I suspect bed time, temperature and daily water and food consumption play an important role too. I can’t be bothered to monitor all of those.

The worrying bit is that this plot has a positive slope of 0.65 kg / month (0.77 without time correction), which is about the opposite of what I have in mind… That said, if all goes according to plan, I’ll be upgrading from an average of 10 minutes of exercise a day in June to about 30 from August onwards. That should do the trick (I’ll be cycling at 25-30 km/h though, not walking 6 km/h). There’s plenty of room for diet improvements (-250 kcal / day) and experiments too and lower temperatures are also great for burning calories. Finally, weight is not a very good metric of health in the first place.


  1. The peak would suggest you did drink some alcohol, you were a bit dehydrated in the morning and drank fluids to correct this.
    Have you considered peeing, taking a dump and eating? The weather? Physical/mental activity, they both burn sugars, but with physical work longer than 30 minutes you also burn some fat and sweat more.

    1. I’m not sure if that peak was due to (that one glass of) alcohol. I measure first thing in the morning, before I start re-hydrating. Then again, I may have drunk a bit more water in the evening. I may also have woken up more often during the night, thus drinking more water.
      But this is the only night in this data set that I drank alcohol *and* still know at what time I woke up. So there has to be more too it.

  2. About your water balance between 06:30 and 10:30, I know that my body, when in a steady day/night rhythm, starts producing pee/poo a bit before I wake up zo I can dump it al in the morning. Perhaps this works the same with others of my species.

  3. I was thinking about your water consumption, how much do you actually drink in 24 hours?
    I’m asking this because drinking to much water makes you pee out minerals your body needs. So drinking alot of water in this weather can actually have a negative effect.

  4. That theory comes from what we have seen in people (often athletes) that thought they were rehydrating properly but used overly pure water. The biggest problem then lies with the depletion/dilution of your Na, Ca and K electrolytes; it is why IV’s have isotonic saline in them, not water.
    So when drinking a lot of water, you should watch your sodium intake as well.

  5. It’s not only about the salt; in a normal western diet I’d say no, do not add more, provided you’re not drinking water to excess. But salt (NaCl) is in no way the only electrolyte that can be imbalanced. Potassium is something to keep an eye on, as are magnesium and calcium.

    1. Here’s a list:
      Potassium (=Kalium?): there’s no daily target listed, so I guess the only way to know is to watch for signs of trouble:
      “a potassium deficiency will produce great fatigue and muscle weakness”. Not a very useful indicator.
      It continues to say that it’s especially important for “elderly, athletes, and people with high blood pressure”, which I’m not.
      Magnesium: if I look at http://www.healthandfood.be/html/nl/micro/micro74_magnesium_functies.htm
      it seems pretty hard to reach the daily target: I’d have to eat a kilo of broccoli or 24 slices of wholewheat bread per day.
      Lot’s of bad stuff seems to happen when you don’t get enough magnesium, but nothing very specific.
      Wouldn’t it be wonderful if the skin color
      of a particular finger would change to indicate a shortage….
      I don’t think I can be bothered to count every single food item and look for potential shortages that way.
      What I could do is – keeping most other things constant – try some supplements for a month and see if anything interesting happens.
      However, the only “interesting” effect I’d like to see is somehow needing less sleep. That’s probably achieved with more exercise, which I will automatically get once I stop working from home.

  6. Magnesium is so important because it is the functional group in a LOT of our enzymes and proteins, so if you’re really far away from the recommended dose supplements might be a good idea.
    As for potassium: it is important for everybody, but the groups and people on that site are specifically mentioned because they are at a much higher risk of ending up with a skewed level due to their circumstances; if you were to go out and bike for an hour in this weather and rehydrate with pure water, adding a banana as a snack might be a good idea.
    Though really, don’t become obsessed. Just pay a little extra attention when the weather is warm and you’re sweating.
    If you find this really interesting you’re welcome to come borrow some of my medical textbooks if you’d like.

    1. If for whatever mysterious reason, I were to go cycling for an hour in this heat, I’d probably drink lots of tap water during the ride, rehydrate with a Banana Milkshake and get a triple cheeseburger for the extra salt 🙂
      Do you have any medical text books that are well written and not too long?
      I find this sort of stuff interesting, but I’m not generally worried about it.

  7. Good, worrying is bad for you ^^
    “Human Physiology\ by Silverthorn is very understandable; it is long, but then you just pick the chapter you’re interested in. The other ones I have a dreadful to read :p
    (also, what kind of captcha is 26-year-old oregano??)

    1. Ben je vanavond op Biton toevallig?
      I’m using http://recaptcha.net/ ; the captchas help them to scan books. One of the words is known, which use to verify that you are a human. The other one is unknown and they use your input to decipher it.
      Since they can’t filter unknown words, it might explain the weird words you and Erik noticed.

  8. Ik ga niet naar Biton, ik moet nog een portfolio project afmaken voor de universiteit (klote ding).

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