T Nation

Scale Weight: AM vs PM

Lately I’ve been wondering why is it that I can go to bed at a certain weight and wake up 4 pounds lighter?

I don’t recall waking up in the middle of the night to take a piss on these nights and even if I did - 4 pounds of urine?!?! I don’t see how its possible.

Can anybody explain this phenomenon to me?

[quote]chrismcl wrote:
Lately I’ve been wondering why is it that I can go to bed at a certain weight and wake up 4 pounds lighter?

I don’t recall waking up in the middle of the night to take a piss on these nights and even if I did - 4 pounds of urine?!?! I don’t see how its possible.

Can anybody explain this phenomenon to me?[/quote]

Breathing, sweating, evaporation, and heat expenditure. It also depends on what you ate before bed because I rarely wake up that much lighter. Scale weight usually fluctuates about 3-4lbs daily and even though you aren’t exercising at night, your muscles still generate a lot of heat and are using the most calories during sleep. The more muscle you carry, the more calories burned during sleep. Water can also be lost by the methods mentioned at the top of this.

You might start noticing what foods you eat in relation to which days you lose that much weight e.g. if I eat wheat I’ll gain 2-4 lbs and lose it all overnight.

Glycogen depletion is a huge factor. The average person also has a ‘set’ bodyweight. Your body will do everything possible to maintain that weight, no matter how much it has to burn off. The only way to beat this is through constant overfeeding and forcing a new maintenance level to create a new set bodyweight.

Another anomaly I’ve noticed with my BMI scale is that it always shows my bodyfat 2% higher first thing in the morning, no matter what. It actually goes down after eating breakfast. I’m interested in the reasoning behind that. I’m guessing it also has to do with glycogen depletion…possibly the scale is counting the glycogen as lean body mass?

Hmmmm, thanks for the input guys.

Try measure your weight after a nice full dinner and being fully hydrated. I weighed 13 stone 12 pounds one day, I then weighed again in the morning and was 13 stone 4/1 Thats 8 pounds swing!

[quote]highersights wrote:
Glycogen depletion is a huge factor. The average person also has a ‘set’ bodyweight. Your body will do everything possible to maintain that weight, no matter how much it has to burn off. The only way to beat this is through constant overfeeding and forcing a new maintenance level to create a new set bodyweight.

Another anomaly I’ve noticed with my BMI scale is that it always shows my bodyfat 2% higher first thing in the morning, no matter what. It actually goes down after eating breakfast. I’m interested in the reasoning behind that. I’m guessing it also has to do with glycogen depletion…possibly the scale is counting the glycogen as lean body mass?[/quote]

Those scales only note differences in body water (and the resistance to an electrical current)…which is why I believe they are so off for larger bodybuilders. Muscle is largely water as well with only about 22% making up the dry weight as protein. Your level of hydration would change the reading which is why most recommend you take the reading at the same time of day. I don’t consider those accurate at all.

[quote]chrismcl wrote:
Lately I’ve been wondering why is it that I can go to bed at a certain weight and wake up 4 pounds lighter?

I don’t recall waking up in the middle of the night to take a piss on these nights and even if I did - 4 pounds of urine?!?! I don’t see how its possible.

Can anybody explain this phenomenon to me?[/quote]

I agree with the breathing/loss of fluid, and heat expenditure.
I am the same way too. 179 at night, 175 in the morning.

Someone mentioned gyclogen depletion. It makes sense that this is number one reason people see a sharp loss in weight when they start dieting and/or working out. I was losing weight and got down to 171, while doing ~16hrs/week on my bike. I took a rest week and my weight went up 4lbs. I didn’t get any “fatter”.

If I go out and do a 6hr ride, i come back and I’m 5lbs less than before the ride. After rehydrating completely I’m still ~3 lbs under. I probally burned 4500 calories (1.3 lbs), and the remainder of weight loss is gyclogen depletion.

[quote]KiloSprinter wrote:
If I go out and do a 6hr ride, i come back and I’m 5lbs less than before the ride. After rehydrating completely I’m still ~3 lbs under. I probally burned 4500 calories (1.3 lbs), and the remainder of weight loss is gyclogen depletion.[/quote]

The same happens to me on muy motorcycle so yes, it is mostly due to loss of water. If I ride for up to 3 hours, I can come back and weigh up to 5lbs less with no real energy expenditure aside from maneuvering the road. It can be chalked up to sweating and the thermal changes my body goes through being exposed to open air at high speeds.