You won’t necessarily lose weight with any form of exercise, so don’t start doing it with that expectation. If you’re already doing 5:2 then taking up any extra exercise along with it may have an effect on your weight loss. It might be a positive effect but it might also be negative so just be ready for that and do whatever you feel will help your body get into better condition. You might like cycling, if so, do that and incorporate some HIT into it. You might be more interested in weights, if so, do the same there. Or you might be very overweight and better off starting small with walking everywhere you possibly can and taking the stairs instead of lifts and escalators whenever possible. Up to you what you do, but do it for fitness and conditioning, not weight loss per se.