I get lots of messages from people with a sizable amount of weight to lose who are having trouble losing when they otherwise wouldn't be for mainly one simple reason--too much exercise. It is important to remember that if you have more than 50 lbs to drop, your dieting needs are different from these casual weight-losers on MFP who just want to carve off something like 5 or 25 lbs from their midsection.
The truth about exercise is that when you are big, you release the stress hormone called cortisol much easier with the same amount of exercise that a smaller person would have little or no trouble doing. Look at how much easier a smaller person can run upstairs compared to a bigger person, or how much further a smaller man or woman can run than a bigger person. Because of this strain on your body, a body can go into shock. Bodies react differently. Not all exercise is the same, but this is due to your body's inability to handle the stress more than anything else. What is good for one person can be bad for another, and what saves one life can end another.
Don't worry about exercise. You can switch over to a higher calorie, more intense exercise program once you get closer to your goal weight. Ideally, once you get within 20 or 40 lbs of your goal weight, you should up your calories to just under maintenance level and drastically pick up the calorie expenses. But when you have lots of weight to lose, your biggest priority should be to get that excess weight off, which means it is best to put a halt on most exercise routines and just stay mobile and lightly active all throughout your day.
Why is this the case? Because, as stated, being big has you taxing your body severely at a calorie deficit. It is already hard enough on your body as you maneuver your weight around. This produces stress, which impedes weight-loss, and in fact, puts your body into fat-building mode since it starts to "freak out" and seek ways to store fat for hard times ahead.
Get into a deep deficit with OMAD and stay the course--it sounds simple, and yet this is the single biggest thing people seem not to be able to do. The messages keep filling my inbox and even after I warn them, they get feisty and overstimulated by a new gym membership or the purchase of some new piece of workout equipment and go crazy. Then, they observe their progress being undone as the scale numbers go up.
This does not mean that by working out that you cannot ever lose weight. It does mean, however, that 1) you will gain weight initially and 2) that your losses will be slow even when you do begin to lose and that you will feel drained and somewhat cloudy (and if your deficit is too low for too long, you can even become anemic). Follow the example of the bear and let your body feast off of your reserves without interruption. Take it easy. Do housework, office work, travel, swim, walk, and at most, do bodyweight exercises (pushups, chin-ups, sit-ups, etc). When done moderately, these are light activities that won't jack your heart rate up through the roof and disrupt your daily rhythm. This is your heart we are talking about here!
And let's not forget the fact that your body must keep storing water to heal those microscopic tissue tears you keep sustaining in hard workouts...which, by the way, is another reason of why people complain of not dropping the big pounds. Your body responds to exercise as a catabolic (tearing down) process, which is the opposite of the anabolic (building up) process. That just means that your body wants to keep reserves of water/nutrients/stored energy around your limbs and midsection to ward off any future tearing down you do as you continue to work out--hence, the weight gain is intended to literally stop your progress. Take a hint! lol
Don't listen to these 5K runners and their ilk, not if you have more than a little to lose. You have to be in a deep, sustained caloric deficit for a while to break past your first set point (mine was 326-313 coming down from 363, and it took a while). Your body has gotten used to your staying big for a while, so it has become comfortable there. You must reset your system, which means you must keep to bigger deficits. Otherwise, your progress will take 3 or 4 years for what could just take a year, and you will mostly keep losing the same few lbs and it will just be water weight and the glycogen reserves you keep burning.
Think about it: this is why there is a fat-burning setting on a treadmill where it recommends to keep your heart rate lower at a certain level since you want fat-burning instead of glycogen reserve burning for harder exercising. Once you remember this, it should be very easy to see that the rest of this makes perfect sense.
If you must lift weights, limit any weight-lifting to one or two sets at a maximum about twice a week. Do what you must, but don't feel like you aren't doing enough and then start assaulting your body with wild attempts at shocking yourself into losing. It doesn't work that way. The key is consistency and not quitting.