I've been a personal trainer for over 20 years. What I've learned, more times than not, the same mentality comes about with clients and the scale. Yes, depending on your current health and fitness condition weight loss, is of course, a good thing. It's more specific then just the numbers dropping on that balance, spring, or digital scale you're stepping on. Let's dive into this.
The body is extremely smart. When you first start your weight loss journey, and you don't get the correct caloric intake, your body will get its energy from somewhere. Usually this energy comes from stored fat. That's awesome right? I mean, that's the whole goal is to burn fat. Let's dive deeper. Yes, stored fat is being burned, but initially it's also fluid (water weight), lean tissue, and fat. Your body is being shocked because of the changes whether it be the exercising, change in diet, change in fluid intake, etc. Moving forward what's important is to make sure that the weight loss is consistent, yet very small. When you lose huge amounts of weight week after week you are losing something that is needed to be maintained....muscle!! I feel that your weight loss should be .5lbs-2.0lbs per week at the most. Any more than that you are sacrificing much more than fat. You can never trick the body. Let's put it this way, if you eat a total of 800 calories in a day then you go to the gym; do some weight training; a little cardio and burn 900 calories, theoretically there is a caloric deficient right? If you do that consistently you should be losing a lot of weight, right? In the beginning yes (both muscle and fat), but eventually your body will go into survival mode. The body will stop losing that stored fat we talked about earlier and keep it because your caloric intake is so low. The body will get to the point where it doesn't know the next time you will feed it, so it will withhold the fat. What little muscle you do have will be burning away, because muscle requires more calories then fat to sustain itself. What is my point? You have to eat to lose correctly. You have to eat to have your body trust you, so you can and will lose weight while maintaining your muscle. I might have forgotten to state this point, muscle is important because the more muscle you have the quicker your metabolism will be. Plus, you will look leaner, be stronger and all that other cool stuff!
Also, when you lose weight too fast your vital organs (brain, heart, kidney, and liver) will metabolize muscle, so they can continue to function. You cannot trick the body! It's true what they say, "You have to eat to lose correctly." Do not worry about the scale. You can gain 10lbs of fat, and lose 10lbs of muscle, or you can gain 10lbs of muscle and lose 10lbs of fat but the scale will show no progress. That's why, with my clients, we use body-fat calibers (to measure lean body tissue) and we use measuring tap (to measure inches gained or loss). Those 2 items, in my professional opinion, will tell the true story of your fitness journey.
Losing weight too fast will not benefit your psyche or you physically. Eat a macro-nutrient specific meal plan that will allow you to burn fat while maintaining muscle. Getting leaner and dropping your body-fat percentage is more important. Please don't dwell on the scale (see how that rhymed).