The Odd Mystery of Maintenance (for me, at least!)

If you are still losing, all it means is that you are still in a deficit. So it's not really strange or odd. It's possible your logging is more accurate the second time around or your TDEE has increased in some fashion due to more movement. Rather than over complicate things, just continue to add 50-100 calories until you no longer are losing.

I have had this same problem for the past few months. I was actually worried I was sick, like I had cancer or something. No, I'm fine but I'm moving more and standing more than I was before. I've been to the grocery store and mall more than normal. Lots of walking that isn't normally considered exercise. I've also been bouncing around and shivering more when I'm outside. It's been pretty cold lately. That can really increase my TDEE. I'm keeping an eye on the scale but enjoying the extra calories and opportunities to eat out with friends. When I slow down I'll likely have to eat fewer calories but for now I'm thankful that I can fully enjoy the holiday season.

You can do the math yourself if you collected more precise records, but just doing a rough estimate: if you lost 16 pounds in 3 months while eating 1400 calories, then your loss rate was about 1.23 per week (16 pounds/ 13 weeks = 1.23 lbs per week). 1.23 pounds x 3500 calories per pound = a 4307 deficit each week. 4307 deficit per week / 7 days = 615 calorie deficit you were running each day. 1400 calorie goal + 615 deficit = 2015 calories for maintenance. Yes, this TDEE estimate is the average over your whole weight loss and so the current number will be on the low side of that average unless your activity level has increased during your weight loss as some people have mentioned.

My guess is that you'll have to get up to 1900ish before the weight loss stops. You can hone in more carefully on that number by doing what I just did using very current data (like from the last 6-8 weeks) and of course by adding calories slowly and watching the results. I also think that clearly you could have lost on 1600 at the beginning of your diet but you got a little impatient and worried that it wasn't working when your body kept holding on as you say it does. By the time you gave up on 1600 and dropped to 1400, your body was (by coincidence) ready for a "whoosh" so you thought that was what caused it. But really it was working all along. Just my guess.

As for why your body stalls at first, who knows exactly? I've heard of many people having that. Didn't happen to me, but I did stall occasionally for month-long periods every few months during my 100 pound loss even though I was still eating at a deficit. As long as I stayed the course I ended up having a huge loss within a few weeks that made up for the plateau. My hypothesis is/was that I was continually losing fat during that stalled period but some other thing that affected my weight (water retention, muscle, hormones, fiber intake, carb intake, sodium intake) was going up at the same time and obscuring the loss. Usually the stalls came when I made changes to my diet or exercise routine. For example, when transitioning my diet to vegan (my fiber intake was increased and I think my intestines were "gaining weight" due to the extra fiber and water), and while ramping up my exercise to run a 10k (I was maybe retaining water for muscle repairs and also from eating more calories due to increased TDEE even though net calories stayed the same). Maybe something like this happens with you? Maybe you don't just reduce your calories at the start of a diet while living exactly the same otherwise? But instead also change many other things that can cause temporary water weight spikes, such as more fiber or water or carbs or workouts or whatever? Maybe some hormone goes wacky for a while? Once your fat loss gets big enough that it is greater than the water gain (and/or your body lets go of the water), the fat loss starts to show up on the scale.