30 DS and weight?

I'm trying to do more exercise, so figured that something like 30 day shred would be a good idea to start building up my strength and fitness. Just from looking on here I've seen some people say that it's slowed their weight loss, does anyone have any experience of this? Just because I can't quite understand why, I'm still at a calorie deficit and I'm definately feeling it from the cardio (I am MAJORLY out of shape!)

I know fitness is important, but I'm no expert, and I thought a load of you will know a ton more than me, so please tell me! And don't be mean, I know the whole calories in calories out, can't build muscle on a deficit stuff, I'm just asking from stuff I've read on here to be informed :smile: