Gaining

Without a truly dedicated effort nothing changes.
Everyone is different so expecting concrete numbers or at what point something will happen is an un answerable question,

Do you mean at what point does weight gain affect your metabolism? For example if you stop gaining, your metabolism should burn off the fat without effort. So at what Point does your metabolism not burn off the extra fat and you have to put a lot of effort at losing the weight?

At your height, I’d say the irreversible point would be 200. You’d likely look marvelous as well :-)

It is fairly uncommon for people to lose more than 10% of body weight and to then keep that off in the long run. So it depends a bit on what you consider 'fat' to look like, but that plus a bit more than 10% would probably mean that you won't ever not look fat for too long. (for my my rule of thumb is that most people look solidly fat by a BMI of about 35, but that is just to my eye, and other beholders would have different numbers)

But others are entirely correct, the real turning point is when your mentality has changed to regard being fat as normal, and the way that you used to live your life as alien and undesirable.

Similar to what Edxl said:

Long term weight loss studies suggest that people who intentionally try to lose weight do not do so in the long term--the vast majority of people regain lost weight, and most go on to gain more.

Put another way, any stable gain is permanent. For example, if someone overeats a lot to gain quickly, and then changes their eating habits to eat comfortably instead of overeating, they may lose a *little* weight, but any weight that doesn't come off quickly is likely permanent, in the long run.

This is related to the idea of "set point theory" (probably more properly "hypothesis" )--it seems to be that our bodies establish preferred weights that they try to maintain, which is related to plateus both for dieters and gainers.

Ah yes, the Point of No Return. I don't think that's based on absolute weight so much as 1) your own metabolism 2) your eating habits 3) how much you like gaining 4) how much you like being bigger.

I chatted with one woman who wanted to go from 130 to 180 pounds. She was having trouble gaining, so she finally started stuffing herself to the point she couldn't take a deep breath. Every day! At that point she started gaining and got up to 180 in a few months. She quit stuffing herself like that then but her appetite had gotten so good she kept gaining without trying to. When I chatted with her she weighed 300 pounds and was still gaining. She couldn't stop.

So she probably reached the Point of No Return before she was even fat!

Another woman planned to gain 25 pounds and stop there. So she did gain 25 pounds, and maybe could have stopped there, but found that she LOVED it. She didn't want to stop, and decided to simply let herself go, figuring that limits didn't work for her.

Of course, some people gain and do lose it, or at least find a final weight they're comfortable with.

In short, once you decide to gain on purpose and start doing it, it's very hard to predict where you're going to end up. Just accept that there's a chance you'll get bigger than you want (of course that can happen even if you never gain on purpose!). If you're worried but still want to do it, just take it slow. You can stuff yourself on junk food now and then--I mean, that's probably part of the fun, right? But eat healthy the rest of the time.

Obviously everyone is different and there are always exceptions but if you are 150 I think a gain of 40 pounds would be almost impossible to reverse completely and even 30 would be very hard