Calorie Deficit

A week isn't long enough to worry about.

Number 1, if your tracking is accurate, don't eat that little or try to lose that fast. Extremely fast weight loss increases health risks, some of which can be major; and it's hard to stick with long enough to lose a meaningful total amount of weight. At your current weight, 2 pounds a week would be fine for a while, maybe the next 40-ish pounds.

It's normal to have short stalls of scale weight while losing. It's extra likely when starting a truly extreme calorie deficit like you're doing.

In the early weeks of weight loss, even at a sensibly moderate rate, part of the loss is reduced water retention.

Another part of the loss is less food waste in our digestive tract on the way to the exit, because we're eating less food. In your case, that second part - waste - is likely to be larger than average because you're following such an aggressively extreme diet.

Also in your case, after you've been at it for a while, there's IMO a higher than average chance of increased water retention beyond what would be seen for someone losing at a sensibly moderate rate. That's because extreme loss is a physical stress, stress can increase the hormone cortisol in our bodies, and in extreme cases that can increase water retention.

So: You've lost quite a lot of fat so far, in all probability. You've also lost some water weight, in the early weeks, and some amount of weight from less food waste on its way through your system. High odds that now the stall you're seeing is your body re-adjusting and rebalancing its water retention, masking continuing fat loss on the scale. You're losing fat, it's just hidden by the added water.

Shifts in water retention are part of what keeps a healthy body healthy. They know what they're doing. We don't want to try to mess with this. The right thing is to try to understand and accept that scale ups and downs will be normal through the weight loss process, but while fat is being lost, the overall trend of scale weight will be a downhill slope. There are just some up and down bumps on that slope.

If I can be frank, I think you're at a truly crucial moment here and now.

A common thing we see here is people who freak out at a brief scale stall, and cut calories more deeply, maybe start adding exercise that they're not getting enough calories to fuel. Their stress ramps up, their self-blame ramps up.

Those people are over-reacting, and it's usually not going to end well: They will give up because it's just too hard, or they'll have some significant health consequence from the extremes, they may begin to develop an eating disorder . . . lots of bad options, few good ones. Honestly, the best case among those is that first one, giving up, because the other possibilities are worse. But no one needs any of those outcomes, right?

Better idea: Think about a calorie level that can be sustained for many months, and help learn new, positive habits that will not just lead to goal weight, but make it easy to stay there long term, ideally permanently. Learn how the body responds to weight loss, and why the scale fluctuates. This thread, especially the article linked in the first post, would be a good start in that learning:

https://community.myfitnesspal.com/en/discussion/10683010/the-weird-and-highly-annoying-world-of-scale-fluctuations/p1

Super common advice here: Any time you change your diet/activity regimen, give the new plan a 4-6 week trial period, or at least one full menstrual period for women who have those (to compare body weight at the same relative point in at least two different cycles). The result of that new regimen is the average of weight change over the whole time.

Short of that amount of time, any weight change is more influenced by water/waste fluctuations than fat loss, potentially even in cases of extreme loss like yours.

In your case specifically, you lost 18 pounds in 5 weeks, 3.6 pounds per week on average. That's your result, not the one week stall. The one-week stall is meaningless in the big picture.

Losing 3.6 pounds per week, your average calorie deficit has been roughly 1800 calories per day. In other words, whatever the average amount you've eating per day is, your current weight maintenance calories would be that daily average amount of calories, plus about 1800. (Calculation: Roughly 3500 calories in a pound of fat, times 3.6 pounds per week lost, divided by 7 to get a daily deficit estimate = estimated daily 1800 calories eaten below current weight-maintenance calories.)

Just as an example, since you can figure out your daily average calories eaten, but I can only approximate: If you've averaged eating 1000 calories your maintenance calories would be around 2800. Any time you ate under 2800, you'd expect to lose fat. If you want to lose 2 pounds a week - more sensible IMO than 3.6 pounds - you'd expect to accomplish that eating 1800 calories daily on average.

I'm not telling you to eat 1800. I don't have the data to do a better calculation, but I described how to do it above, so you can do the calculation if you wish.

I'm not in charge of your weight loss rate, that's your call how extreme you want to be, but I'd strongly advise you to slow down . . . partly based on negative experiences of my own when I accidentally lost too fast at first. If a person weighed maybe 125-150 pounds more than you do now, 3.6 pounds per week might keep health risk in a reasonable range, but I'd still be urging the person to get regular blood tests and other medical attention to monitor for deficiencies or complications. There's no way to get adequate nutrition on too-few calories, among other possible problems.

For sure, a one week scale stall, in the overall situation you've described to us, does NOT mean you've stopped losing fat. There is definitely no reason to cut calories further or add exercise to "get things going again". The scale will move again, with patience and persistence. You're seeing a water retention effect, and it will settle out over the next few weeks.

Best wishes: Please stay healthy as you succeed with your weight-loss goals!