I can make any cardio machine at the gym tell me I've burned far, far more than this.
> f you are making an effort to count calories, you will notice if you're eating an extra 200 calories of food.
The person I was replying to mentioned in another reply that they managed to lose 170 lbs which is a huge achievement. Someone with that kind of weight to lose has been overeating for a long time. Dropping calories to the point that they will just maintain there weight may feel very restrictive. I'm not surprised someone in this situation might underestimate their intake. It also doesn't take much to eat an extra 200 calories. Thats less than 2 tbsp of butter or oil. Pour too much salad dressing on your kale and now you're a couple hundred calories over what you thought.
> And after a month, even if they were at a ~200 calorie deficit, they should have still noticed clear fat loss.
The usual numbers you hear for weight loss are 3500 cals per lb of fat. A month at a 200 calorie deficit would give you 6000 calories. To make this easy let's say this leads to a 2 lb loss of fat, muscle, etc. I'd argue that when undertaking a lifestyle change a 2 lb change in weight could be hidden by other factors like hydration, more/less food in your digestive tract, etc.
But that's one of the few numbers you can predict with pretty good accuracy.
Figuring out diet, exercise, and BMR is the hard part. Expecting a pound of fat to go away per 3000 calories is the easy part.
Well, here you've moved from "estimated deficit per day" to "exact total deficit". Sure, thermodynamics tells you with absolute certainty that if you've lost 1 pound of fat in 1 week, you've overall had 3000 Cal deficit in that month.
But that doesn't mean you can say "if you know your BMR at time t, eat exactly this much and exercise exactly this much, you will definitely have a 3000 Cal deficit over 1 week". This would assume already that BMR doesn't vary with exercise and diet. It also assumes that food digestion doesn't vary with exercise and diet. Both of these are assumptions that we don't really know. And even if they are true for 1 week, they are almost certainly not true for 1 year.
The fact that you think that there is a number like this shows you are using extremely old thinking about how even the CICO model works. There is no way to predict weight/gain loss amount based on calories across individuals.
Also, even if there is some error in BMR, calorie burn rate, calorie intake, I very much doubt it was `-1000 calories +- 1000 calories`. Exercising is at most 2-300 calories per day. If you are making an effort to count calories, you will notice if you're eating an extra 200 calories of food. So let's say from these that they were at 1000 +- 200. Unless they got their BMR extremely wrong, then something else was happening. And after a month, even if they were at a ~200 calorie deficit, they should have still noticed clear fat loss.