Firstly, diet doesn't mean 'going on a diet.' That's probably one of the worst things you can do. Starving oneself by eating far less than is needed to sustain health results in the body overcompensating by storing fat the moment you come off the diet. The message to the body being 'this might happen again, I'd better store up for the upcoming emergency.'
If you must shed weight (never say, 'lose weight.' When we lose something we subconsciously always want it back again) make it a long-term project. And I mean long term! Easy does it.
Diet, in the sense I'm talking about it means a good balance of fruit, vegetables and protein. Most people eat far too much meat compared with their input of fruit and vegetables. We need fats and oils. Take 'em in moderation. Though olive oil is fine, apparently, has a lot of marvelous health qualities.
The big one! Don't eat too much. Eat when hungry, not for the sake of eating.
Exercise IS important. You weren't given the biggest muscles in your body to rest them all the time in an armchair. I'm talking legs and backside in particular. However, all your muscles need a regular workshop. And don't forget the stretches. Yoga is excellent.
But from what I'm learning of late, the biggest drawback to diet health is SUGAR. Most people consume too much of it. In a recent TV program it was mentioned that a century ago people consumed about four pounds of sugar in a full year, now it's a hundred pounds in a year - 25 times as much!
I'm not saying to go back to four pounds of sugar a year. You couldn't do that anyway. Sugar is in just about every product. But drop the routine of soft drinks every day. They're just about all sugar. A can of Coke every week or so is fine. Even one a day and you're asking for trouble if you don't exercise much. More than that you're almost certainly going to get health troubles in the form of diabetes or some-such down the track.