3,500 is the number of calories in one-pound of fat.
Think about that for a second.
How many calories do you eat everyday in total? 1,000? 2,000? 3,000+? Now, realize that there's something called basal metabolic rate (BMR), which in short, is the energy (calories) your body requires to wake up and simply survive the day. Meaning, if you woke up and didn't even move an inch for an entire day, your body would be burning calories just sustaining basic function. I'm not lying to you, but it's probably obvious this doesn't account for much of your total daily energy expenditure. Don' try that.
Back to my point... SO, when you weight yourself every day or multiple times per day, you will almost certainly drive yourself crazy. Unless you consume 3,500 calories of energy MORE or LESS (aka, a crap-ton of exercise) than your caloric baseline over the course of a single day, then any number differences on the scale is from fluid shift (retained or lost) from the body.
Activity/exercise, what you eat and drink, and a number of other daily doings affect this. For example: you wake up, you run out the door for work, not even eating breakfast because you're new to IlluminActive... it's a scorcher, your car's dashboard reading 90 degrees. You're wearing nice clothes, but they're not breathable, so you're sweating. Now, your body is doing it's best to maintain homeostasis by retaining water [weight gain]. The situation is compounded by compounded the 16 ounce slushy containing 80 grams of sugar you grab from the local quickie-mart before getting on the freeway [entirely hypothetical, but again, weight gained]. You have a busy morning at work and don't even think to drink a bottle of water, even after I, your trainer, told you to set a case next to your desk so you can't possibly forget. Lunch comes and you're ravenous because you skipped breakfast and subconsciously dehydrated... you're stressed and nutrition is the last thing on your mind is tracking macros so you grab two slices of pepperoni pizza. You don't know this, but the pizza contains the amount of sodium that you should consume in an entire day –given that you're drinking water, which you aren't. You finally remember to get a quick sip of water before running back upstairs for the afternoon. Unfortunately, it's only 4 ounces worth, less than you sweat out walking from the parking garage to the office that morning.
Nothing noteworthy happens in the afternoon, though, you're even more stressed because a project is due and you know you have a workout appointment with me, your trainer, right after work.
^ Stress = ^ Cortisol = ^ Sodium Retention = ^ Water Retention = Weight Gain
You arrive at the gym on time... whew! First thing you do before you hop on the treadmill to warmup is hop on the scale in the locker room. You always hesitate, but c'mon, it's staring at you every time you walk in. You're also thinking to yourself, "I did pretty good with calories today. I didn't eat breakfast, so that's no calories. I had that slushy, but it was small and it was a fruit slushy... fruit is healthy. And then I did have two pieces of pizza, but that's it, and it's 6:00. When I get home, I'll have a protein shake and be under calories for the day!". You step on.
Your jaw drops when it's two pounds HEAVIER than it was the day before. All the sudden, the workout you were psyched up for seems pointless... you even think about leaving before I, your trainer, walks out and finds you. Your mind is now becoming your worst enemy... you're thinking you had such a good week since last weight in three days ago. You didn't miss a workout and you've been under calorie goal. "I should stay... I've payed for it", you think to yourself. But with that line of thinking, how good/productive is your workout going to be?
Exit –to real life.
Hopefully this story makes sense. It may eerily resonate with some of you as the situation I described is super common... not necessarily all the little details, but the fact that normal daily habits DO and WILL mess with your body weight.
For this reason, I have my clients weight in once per week -at most- under very controlled conditions and I still encourage they be emotionally removed from the reading. Leave the science and the adjustments up to your health professional.
To have success with weight loss or any fitness goal, focus on the controllable and only use things like the scale and measurements to help assess rate of progress.
Take home: Stop Freaking. Just Be Consistent.