Exercise is a good thing, and is something that I think more people should do, and is something that will probably improve your life in a lot of ways if it isn’t something that you are currently doing in one form or another.
Exercise is not mandatory for fat loss. Does it help? Absolutely. Does it speed things up and have really positive effects on body composition? Sure does. But you can get into better than average (remember that average is obese now, not fitness model) shape just by controlling the shit you put in your face.
If you eat less calories than you burn on a day to day or week to week basis, you will lose weight. And no matter what you may have heard, especially if you have a lot to lose, a good proportion of that will be fat mass, at least initially. That is why your body like to keep extra fat around – to help us survive when our food supply disappears.
The main advantages of adding exercise into your defattening plan are twofold: to maintain or even build muscle mass, and to increase caloric expenditure. Resistance training will at a minimum maintain muscle mass, and in most untrained individuals will actually increase muscle mass while you lose fat. This is considered the holy grail of body recomposition, and for good reasons – it is something that basically doesn’t happen outside of untrained or chemically enhanced people. The big difference between someone who is too skinny and looks like shit and someone who turns heads at the same bodyfat level is muscle mass. Want to look “toned”? That’s muscle mass doing that for you.
A side note for women who refuse to pick up anything heavier than a 5lb pink dumbell because they don’t want to look “bulky” like a female bodybuilder: unless you are taking massive amounts of anabolic steroids, are genetically gifted AND are dedicating your entire life to it, you will never look like that. Think about how many skinny guys you see in the gym, who have been going for years but still look like twigs. If it was possible to put on muscle mass that easily, every person who ever walked into a gym would look like Mr or Miss Universe. Last time I checked, most people don’t. Look at the women who compete at the Crossfit games and similar if you want a good example of what kind of physique you can get with proper resistance training. Not many people would call them too bulky or generally physically unattractive. Anyways, moving on.
Cardio is really good for increasing caloric expenditure. You can also just lift weights faster instead of getting on a treadmill or an exercise bike, but that carries some inherent risks if you don’t know what you are doing so if you want to go this route, shell out a couple of bucks for a session with a decent trainer first so you don’t kill yourself accidentally.
I personally lift weights to maintain my muscle mass, then spend a bunch of time on a bike. I prefer the bike to the treadmill because it is low impact and I like my joints. I can put in my headphones with some good drum and bass to set the tempo, put my e-reader on the console, and just zone out and read while I’m burning off a bunch of calories. It’s also a nice dedicated block of time that I can just read, which is something I just don’t get otherwise.
As a general rule, if you had to choose just one of the two, resistance training is probably preferable to straight cardio. Both would be ideal, but absolutely anything is better than nothing. If you currently aren’t exercising at all and going to the gym is something that is too scary/expensive/whatever for you, getting one of those newfangled fitness tracker things that are all the rage these days isn’t a bad idea. Doesn’t really matter which one you get.
Track your daily activity levels, and try to increase it by a measurable increment each week. If you are currently taking 2000 steps per day, try to make it 3000, then 4000, and so on. Every little bit helps, and small successes can really keep you motivated.
In summation: exercise good. Really good. Not necessary to lose fat. Do it anyways. Lift heavy things, then put them down. Wash, rinse, repeat.