3500 calories is how much energy is IN one pound of body fat—yes. But it takes so much more than 3500 calories to actually gain a pound of body fat. A lot of it goes towards maintaining lean tissue.
This is why I stopped believing in the calories in calories out model for weight loss. It’s not a direct exchange system.
First, you don’t absorb all the calories that you consume. Second, the energy you consume gets used in order to aide in the digestion process and other processes. So you end up storing soooo much less energy than you consume. A lot of the energy you consume goes to repairing your body.. muscle tissue.. etc.
So don’t worry about the 3500 calorie rule! It’s meaningless.
Any weight gain/loss is just fluctuations depending on water retention, food mass, and waste mass. You gained food mass from eating a bulk of food more than usual, you gained weight from extra waste in your body that hasn’t been eliminated, you gained water weight because water is a huge byproduct of digestion and chemical reactions that happen in your body, you retained water weight because for every gram of carbs you eat you gain x amount of water, the waste you have requires water to pass through, etc. If you worked out (by walking 6 miles), there is some muscle damage so water/fluids rush to the damaged muscle tissue in order to repair it.
The only real weight loss/weight gain happens extremely gradually and can’t be measured on a day-to-day basis. But rather as an OVERALL TREND LINE. Remember that and don’t be so stressed out about scale fluctuations. :) And I hope you enjoyed every second of that weekend!