One think the gym has highlighted is body dysmorphia. Overall the gym absolutely massively improves my mental health and self confidence/positivity.
However It does still lead to those moments of thinking I'm still stick thin (I was always really skinny as a kid) or have gotten a little tubby.
In reality I'm neither, am getting to a point where I'm having to go up sizes in clothes and can see and feel real growth in muscle and strength. Just isn't always enough to keep those voices at bay.