Training & Nutrition - sudden weight gain

I have been riding very regularly and have slowly increased the distance I ride from 13miles to 50miles. Simultaneously, I have cut down my food portions and also completely stayed away from unhealthy and fatty foods. I have seen the results, total of 23 lbs lost in 75 days and feel great about it. This last weekend I did my first 50 mile ride and just had regular recovery food (milk, fruits, protein whey powder, bagel, chicken salad etc.) after the ride and had a healthy meal in moderate quantity for dinner. Since then, my weight has shot up by 5 lbs. I am not convinced that my food intake contributed to this sudden weight gain as I haven't eaten anything out of ordinary.

What should I make of this? Water weight? Muscle gain weight? or fat gain weight?

Obviously water. It's possible you were dehydrated for the past week. Are you sleeping enough? Do you crave salty foods for days after you ride? Do you feel bloated? What is your calorie in/out differential a day?

Hmmm! I have been sleeping something like 8 hours a day, although the day of that 50 mile ride, I did not get to take a nap in the afternoon and also did not sleep well in the night. But other than that I have gotten 8 hours every night which has been sufficient for me generally.

As for calories, I tend to stay under 1700kcal intake per day, except on long ride days when it can go upto 2500 kcal, but then the ride alone burns around 2000 kcal on such days. I have been trying to keep my in/out deficit around 500kcal.

I haven't felt bloated and haven't craved salty foods, but then again I regularly eat spicy/salty foods so I may not have noticed the craving.

Not sleeping well at night indicates poor recovery food to me. But then your main focus is losing weight so it's a fine balance. Just give your body a few more days to even itself out. I did a 24 hour MTB race this weekend and gained 4 pounds in the following 2 days. It'll fall off eventually but my body is still working out the pain. Maybe you're in the same sort of boat. Give it time and focus more on the lost 23 pounds than the gained 5.

Today is Tuesday. 5lbs in three days must be water, unless you ate 15,000 calories above and beyond of course. You know you could be sleepwalking. :)