Not eating all of my calories

Occasionally not eating enough won't hurt you. Most likely you will have other days when you eat too much. As long as they balance out then all is well.

Ok, so if this level of activity is new, it makes sense to be tired.

Keep in mind that as your power ratio changes (while you do lose both fat and lean mass at this point you're losing proportionately way more fat than lean mass plus as the weight is coming off you still have the power needed to haul around your former weight) you should be feeling more strong and energetic; not less.

If you start feeling less energetic I would definitely look to your minimal calories.

1600 is already low unless you're logging very loosely.

As an example after being stupid before finding MFP, I lost most of my weight on MFP averaging more than 2500 Cal eaten (even in the very beginning​ total eaten was in the 2300 range) by keeping my fitbit tdee, till very recently, at well over 3000.

Note that Fitbit's numbers are not "exercise". They are their estimate of your TDEE, i.e. what you spent in a day.

Look,

There IS such a thing as losing too fast.

There IS such a thing as a learning curve on learning how you have to eat and move for the rest of your life.

There IS such a thing as figuring out how you can handle family celebrations and dinners, friends, business dinners, Christmas, family emergencies, work and life stress, vacations and all you can eats or drinks from now on.

While you're geared to losing weight you can go through this learning curve and figure a few things out.

You may lose a little slower because of the explorations and lessons, but because you are geared towards a deficit it is less likely that you will have a period of intense weight gain while focused on losing.

You are short circuiting all that learning in multiple ways.

Nutrisystem for the food. Low low calories for faster weight loss.

So let's pretend that you now get to 160lbs? 170lbs? in a year or year and a half instead of the two, three, or more years it would take you to get there at a slower pace while learning things about yourself.

Let's assume you avoid gallstones and the cholecystectomy that follows (hey no guarantee that anyone losing lots of weight avoids them but you increase your chance of surgery exponentially by losing fast)

Let's assume that you don't lose more lean mass than you could have and are all happy with where you're at when you're done!

At some point of time, I assume, you will move beyond Nutrisystem... right?

What often happens then is that the hyperfocus breaks.

Plus you're proud of what the you've accomplished and you deserve some reward.

And you eat some of all the things you haven't been eating without having a good year or more of practice under your belt of eating and moving the way you will have to continue to move and eat for the rest of your life.

And your weight shoots up 5lbs after pizza and beer and wings with friends on the weekend.

And you're an all or nothing guy. So that's a bit disappointing.

So you will go all in next week and lose it and correct this increase.

BUT, this "all in" business has exhausted your will by that point. It has only been a couple of weeks since you were done dieting after all, so maybe you will maintain this week and tackle all this next week.

And your body and hormones are all primed to convince you... to sit in the couch and have another beer and wings. (Because you ARE primed to do so and to store most of the surplus calories as fat first)

So next week you're looking at another 3lbs increase after you went to your company conference.

Which you will kill in no time once you go all in with Nutrisystem on Monday.

But again this level of change so soon lacks appeal...

Your body will stop sabotaging you after a period of regain (quite often to above starting weight)

So, what's the difference with the "other method" that i am advocating?

The difference with the "other method" is that you are learning and exploring new ways to eat and move FOR EVER.

You will NOT be looking for a goal and time frame to finish and be done with your diet because you are not on a frigging diet.

You are changing the way you relate to food, movement, and exercise.

Yes. You are managing your weight manually because without that level of awareness your built in feedback loops haven't been working to stop you from overeating.

So you have to supervise yourself and make sure you're keeping to a plan which is where MFP comes in.

But the rest of it is finding the changes you're willing to make long term.

Whether this is eating more McDonald's and less Chinese food like I did, or whether it is eating more fish and chicken breasts like some of my MFPeops do.

Whether this is walking four to five times more than I used to in a day, or taking up crossfit or cycling like some of my MFPeops have.

The benefit of small permanent (or at least very long term changes) is the small buy in to a correction when things go wrong (which they always do)

First of all you don't go hog wild when you're done because there is no end date and a long term acceptable level of hog wildness is already included.

And you don't have to "change everything" to lose again because you have discovered that all you have to do is adjust by half a candy bar. Or a banana. And you will eventually get back on track.

Anyway. These are my thoughts on this. Don't know if I am right or wrong, will tell to you in five years, and even if I am right for me, each person views life differently.

But you may want to give these concepts some consideration.

And use trendweight together with Fitbit! Will help your sanity especially if you're scale oriented.