with zone 2 training. For me that's a heart rate of maybe 130, and a pace that feels like a little bit of work, but I can hold a conversation or watch a show pretty easily while riding at that pace. One reason it's so good for losing weight is that you burn a ton of calories without a ton of fatigue, so I can hold that level of exercise for a long time, but also repeat it the next day. As you are burning fat stores rather than glycogen, you don't have to eat that much while actually exercising.

That'll burn around 800-900 calories in an hour for me. You'd probably want to add some weights if you want to keep muscle mass. You'll probably want to add some intensity if you want to gain fitness.

Not sure how much of a deficit is healthy, but I usually only aim for a 500-800 calorie deficit each day, when I'm trying to lose weight. That will help me lose a lb or two in a week.

Not a nutritionist, but the above has helped me.