So I heard this week if you lose weight, gain and go back to trying to lose weight it's quite difficult and your bodies metabolism slows down

I really need to sit and read up on this later but has anyone else heard of this and/or relate?

Ooooo not heard about this,
Sounds interesting.

Online FB friend has qualification in nutrition ... I'm going to look that up now before I get up again to clean kitchen!

From what I understand of the metabolism its just the basic amount of energy needed to keep your body processes working. One of the major factors is muscle mass. More muscle mass = more energy needed. So I guess if you crash diet or something to the point where your body starts destroying your muscles for energy then you regain the weight as fat that would fit. In theory though your body would adapt to the heavier weight by bulking up those support muscles that need it so your metabolism would increase again. Unless you became more sedentary to adapt.
I personally believe that lifestyle and exercise is more important than diet for weight loss. The last time I successfully lost several stone was when i jumped up and down on my modem one day and had to spend several weeks coping with real life stuff thankfully things haven't got desperate enough to do it again.

I think if you regularly exercise you can avoid that.

Mostly it would be mentally tough to go back to dieting after breaking out of it for a bit.