I thought this study was interesting. Here's the full info:
The effect of rate of weight loss on long‐term weight regain in adults with overweight and obesity
Roel G. Vink Nadia J. T. Roumans Laura A. J. Arkenbosch Edwin C. M. Mariman Marleen A. van Baak
First published: 27 January 2016
https://doi.org/10.1002/oby.21346
https://onlinelibrary.wiley.com/doi/...1002/oby.21346
Some main findings/points:
The study wanted to look at whether losing weight very quickly on a very low calorie diet (VLCD) vs losing weight slower on a low calorie diet (LCD) had any effect on whether someone regained weight, and how much they regained.
They had both groups lose the same amount of weight (VLCD had 500 calories for 5 weeks; LCD had 1250 for 12 weeks).
They found that both methods of weight loss showed statistically the same amount of regain (they did a 1 year maintenance diet and then a 1 year followup). This suggests that losing weight quickly or not quickly doesn't influence whether someone regains weight.
The VLCD group lost more fat free mass (FFM), but they still didn't regain more than the LCD group. However, the difference was small.
They looked at 'weight cycling' (losing and regaining cycles) and found that that didn't correlate with weight regain after the study either. That suggests that weight yoyoing doesn't make it harder to keep the weight off OR make you regain more than you lost (it DOES increase risk of heart problems, though).
They did a questionnaire about physical activity (PA), and reduced PA after the study DID correlated with weight regain. This suggests exercise is one important factor to maintain weight loss. Or at least lack of it is related to weight regain.