So confused, could someone please explain...

You can do both if you're a beginner and/or very overweight. Or if you don't mind doing it very, very slowly.

But even if you don't fit in those categories, it's still important to avoid losing the muscles you do have - your body is perfectly happy to use them for energy, especially since they're metabolically expensive to carry around, so it's kind of killing two birds with one stone. You need to tell it that no, you're still using those, burn something else. And weight training has a whole bunch of other benefits, like increasing bone density.

So mostly - to look good and be healthy, same as why you do any exercise.

Building muscle means increasing the number of muscle fibers in any given muscle. to grow new muscle you need to stress your existing muscles and then provide enough nutrition to allow for repair and building new muscle. This requires adequate protein and calories on a regular basis.
When you eat at a deficit you will lose weight by losing fat but you will also lose muscle mass as well. However if you are stressing your muscles and providing adequate protein intake you can preserve more of your muscle mass than if you just eat at a deficit. The more muscle you maintain the higher your resting calorie burn will be.

One thing to be aware of that while you may not be able to increase the amount/number of muscle fibers you have while eating at a deficit and lifting heavy you will be able to increase the strength of the ones that you do have. Strength and muscle tone help improve your shape and general feeling of wellness and energy - all good reasons to do heavy lifting even when at a caloric deficit.

This is an interesting read along those lines.

http://liftstuff.blogspot.ca/2012/10/the-skinny-fat-annihilation-protocol.html

Bump

to keep the muscle you have... eat lots of protein and weight train and you will probably only lose fat.

So I read a lot on these boards. There is so much good information. The problem is, now I'm more confused than ever. It seems that the general consensus is to figure out your calorie needs(eat at a deficit) and do a combo of cardio and strength training. Well then I read that you can't build muscle if you are eating at a deficit, which makes total sense to me. The problem is, if you can't build muscle eating at a deficit, but you need to eat at a deficit to lose fat, why would you weight train? Could someone please break this down Barney style for me... lol. Thanks in advance

There's also a lot of junk. So let's keep this basic:
-Resistance training > cardio. Cardio isn't necessary if you train and eat properly. And there's 100 more reasons to weight train over a treadmill.
-Hypercaloric eating (surplus) = weight gain, hypocaloric (deficit) = weight loss. Basic human physiology: calories in vs calories out. Now, where it comes from depends on what you're eating.

For someone who has never truly weight trained before and has a higher BF%, there is a possibility to burn fat while building muscle naturally because of the stored energy already there. I call this "recomposition." Once again requiring weight training for numerous reasons where cardio is insufficient.

Any dietician that says you can build muscle on 60g a day needs their license revoked. The human body requires 0.8-1.0g/lbs bodyweight to carry out basic life functions on a daily basis which means you weigh a maximum of 75lbs (60/0.8). Now in order to build lean mass you need a surplus equating anywhere from 1.2-1.75 depending how active you are.

This really was an informative post. I feel better for having read it. Thanks for the info!

Bump!