Ever lost weight quickly? It's OK if you've been
a) really ill or
b) been on a proper binge -> your body is bloated due to excess fluids -> you're losing the excess fluids fast.
Any other occasion (like a fad diet)? This is where it gets scary - because it will never work in the long term.
If you lose a lot of weight initially, you must ensure your lifestyle habits are radically changed directly following the rapid initial weight loss.
See, that's what it is - weight loss - not fat loss. And there's a massive difference.
Rapid weight loss 95% of the time results in you ending up heavier than you ever were before. And this is due to the muscle mass lost in the progress (meaning slower metabolism). Anyone saying you can lose a lot of fat and not muscle tissue in a short space of time is bullshitting you. This is a scientific fact.
There was a woman who came to me at the gym the other day asking about personal training and bragging that she can lose up to a stone in a week, easy (my reaction certainly wasn't WOW). I then asked if she's prepared to change her eating and drinking habits for good with a bit of help, and the answer was negative (all the regular excused; "I can't [you can] because my social life depends on getting drunk twice a week"/"I don't have time to cook [yes you do]"/"I can't cook [yes you can]"/"I don't like cooking or preparing meals [that's just being lazy and a big part of the problem]"/"My husband eats takeaways every night so I must as well [no you don't/how about the healthier options and smaller portions?]"/"I have to eat chocolate and cake every night" [unnecessary emotional eating] and other invalid reasons).
It was desperately obvious she wasn't ready for a real change - and consequently because of that I wasn't interested in training her as a private client. It's also obvious she'll continue yo-yo dieting = getting bigger every year. I truly hope she doesn't keep going like that forever, because it is frustrating seeing people voluntarily (yes, voluntarily) suffer with their weight.
There's one important message everyone seeking a positive long term change in their body composition must internalise:
Personal training doesn't give you motivation. You must have it first. Don't even think about radically changing your body composition for good if
1) you can't see beyond tomorrow (unless you're seriously ill or significantly change your everyday activity levels) or
2) are not ready to change.
Personal training can "only" give you the tools to change your life. For good. But you must want it first.
P.s. I do personal training differently from many others - I sell results, not exercise sessions. Not all PTs will provide you with anything but exercise - and that's fine - but not my cup of tea :-)