I am not a big advocate of severely restrictive diets. However, many people (including some clients) place themselves on one. They initially see a weight loss, but ultimately they gain it back. This is because their bodies have several biological mechanisms that kick in when energy intake drops, such as: lean mass catabolism (break down), diminished metabolic rate, lethargy, and increased hunger. Ultimately, these are powerful enough to get them to increase their energy intake.
Sometimes it is possible to manage these biological mechanisms and maintain a low energy intake for a couple months or more. Most people would be very happy about this, but there are consequences to being on a very low-calorie diet indefinitely. As one of my clients found out, her hair started thinning and falling out! To add to her stress, her hair dresser told her that it was because she was eating too much protein; and someone else told her her kidneys were having problems! Note: don't take nutrition advice from your hair girl.
Now, if my client is having kidney problems, I would refer her to her physician. But, I think the issue is more straight forward. While her diet is relatively high in protein (as a percent of total calories) it is chronically low in energy. When this is the case, protein is used as energy, and is no longer available to be used to repair the body, including hair. Essentially, a low-energy diet is very malnurishing and can create nutrient deficiencies.
A better approach would be to cycle your fat loss efforts. There are many ways to do this. The Food Rules encourage cheat meals every tenth meal. Alternatively, you can limit your restrictive fat loss efforts to short, four-week cycles. Afterwhich, you go off for a week or two, then repeat. The bottom line is that you can't be on a low-calorie diet (even if it high in protein) indefinitely. It is malnurishing. Additionally, it is helpful knowing that you are restricting for only a finite period of time.