It is often mentioned in the lay press and amongst healthcare professionals that "the faster you lose weight, the quicker you regain it", yet there is little evidence to support this assumption and in fact the opposite may be true. Post hoc analyses of weight loss intervention studies show that a greater initial weight loss, usually achieved in the first 2-4 weeks of treatment, is associated with a better long-term outcome, i.e. a sustained weight loss 1-5 years later1.
VLED vs Non-VLED weight losses1

A recent study by Purcell et al. randomised 200 participants to either a 36-week gradual weight loss group or a 12-week rapid weight loss group using a VLED. Participants that lost 12.5% of their initial weight loss from both groups were then placed onto a 144-week weight maintenance group. What they found was the amount of weight regain was similar in both groups. The author concluded that the rate of weight loss does not affect the proportion of weight regained with 144 weeks2.
References
1. Delbridge, E. and J. Proietto, State of the science: VLED (very Low Energy Diet) for obesity. Asia Pacific Journal Clinical Nutrition, 2006. 15 (Suppl): p. 49-54.
2. Purcell, K., et al., The effect of rate of weight loss on long-term weight management: a randomised controlled trial. The Lancet Diabetes & Endocrinology, 2014. 2(12): p. 954-962.